Corn: Chemistry and Technology (Third Edition) 9780128119716, 9780128118863, 3053053063, 0128119713

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Corn Chemistry and Technology

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Corn

Chemistry and Technology Third Edition

Edited by

Sergio O. Serna-Saldivar

An imprint of Elsevier

Woodhead Publishing is an imprint of Elsevier The Officers’ Mess Business Centre, Royston Road, Duxford, CB22 4QH, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, OX5 1GB, United Kingdom Copyright © 2019 AACCI. Published by Elsevier Inc. in cooperation with AACC International. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the Publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/ permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither AACCI nor the Publisher, nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-811971-6 (print) ISBN: 978-0-12-811886-3 (online) For information on all Woodhead publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Andre Gerhard Wolff Acquisition Editor: Megan R. Ball Editorial Project Manager: Barbara Makinster Production Project Manager: Denny Mansingh Cover Designer: Matthew Limbert Typeset by SPi Global, India

Contents Contributors Preface

xiii xv

1. Corn History and Culture Silverio Garcı´a-Lara and Sergio O. Serna-Saldivar Production and Importance Corn History and Culture Origin and Evolution Historical Perspective Growth and Development Germination Vegetative Development Pollination and Kernel Development Culture and Management Climatic Requirements Soil Management Water and Nutrient Management Pest Management Storage Management General Uses Conclusions References Further Reading

1 4 4 5 6 7 7 8 8 8 9 10 11 12 13 17 17 18

2. Breeding, Genetics and Seed Corn Production

Breeding Techniques for Selection of Improved Genotypes Mass Selection Random Selfed Lines S1 and S2 Line Selection Recurrent Selection Extraction of Inbred Lines from Populations Improved by Recurrent Selection Inbred Line Development From Recycling Existing Lines or From Inbred Line Families Evaluation of Experimental Material Kernel Modification Through Breeding Single-Mutant Endosperm Genes Altering Kernel Composition and Integrity by Selection Molecular Genetic Tools and Quantitative Traits Molecular Markers for Corn Research Genetic Maps for Corn Research Quantitative Trait Locus Analysis in Corn Seed Production Crossing Techniques Isolation Requirements Seed Conditioning Seed Classification Contract Production Conclusions References

25 25 25 25 26 28 29 29 30 30 31 32 32 33 34 36 36 37 37 38 38 39 39

3. Genetic Modifications of Corn

L.L. Darrah, M.D. McMullen and M.S. Zuber

Jos e Luis Cabrera-Ponce, Eliana Valencia-Lozano and Diana Lilia Trejo-Saavedra

Introduction 19 Reproduction of the Corn Plant 19 Kernel Structure 19 Endosperm-Dosage Effect 20 Endosperm Variation 21 Progress in Corn Improvement 23 Early Inbreeding and Hybridization Experiment 23 Use of Open-Pollinated Varieties, 1910–36 23 Introduction of Hybrids, 1937–65 23 Single-Cross and Modified Single-Cross Hybrids, 1966 to the Present 24 Host-Plant Resistance 25

Introduction Radiation Chemical Tilling Plant Tissue Culture as Tool in Mutagenesis Transposon-Based Tagging as Sources of Mutations Production of Double Haploids In vivo Production Via Genetic Methods Use of In Vitro Culture Techniques Genome Editing Oligonucleotide-Directed Mutagenesis

43 44 45 45 47 48 49 50 50 51 51 v

vi

Contents

Genome Editing With Engineered Nucleases Traits Altered by Genome Editing in Corn Gene Knockout: Waxy Example Gene Edit: Acetolactate Synthase Example Promoter Swap: ARGOS8 Gene Insertion: Complex Trait Locus Genetic Transformation Transgenic Plants (GMOs) Electroporation and Polyethylene Glycol Treatment: Protoplast Transformation Particle Bombardment Agrobacterium-Mediated Transformation Alternative Methods Other Considerations of Transformation Genetic Modification Through Biotechnology Input Traits Output Traits Regulatory Issues Concerns About Transgenic Corn Conclusions References Further Reading

51 55 55 55 55 55 57 57 60 60 62 63 64 64 65 70 72 72 76 76 85

4. Economics of Production, Marketing and Utilization Ernesto Lozano Martinez and Francisco Javier Belden Fernandez Introduction 87 Corn (Maize) as a Crop 87 Corn Demand 88 Worldwide Corn Utilization 88 Utilization per Country and per Capita 88 USA Corn Utilization 90 Breakfast Cereals 94 Corn Price and Trends 95 Corn Production 96 Global Production 96 Productivity, Key Elements for Competitiveness, and Production Costs 98 Corn Global Trade 100 Markets and Exchanges 102 Transport and Logistic 102 Conclusions 105 References 105 Further Reading 106

5. Harvesting and Postharvest Management Carl J. Bern, Graeme Quick and Floyd L. Herum Harvesting Systems Harvest Systems Defined by End Uses for Corn

109 109

Combine Harvesting Corn for Grain What Is Special About Corn Combines? Categories of Corn Combines Combine Performance Criteria Corn Heads or Platforms on Combines and Pickers Threshing Separating Cleaning Materials Transport Coordinated Functions Spreading Material Other Than Grain The Harvest and Kernel Quality Managing Field Operations Cleanout and Combine Hygiene, Fires Cost Management: Private Ownership Versus Contracting Control and Information Systems The Harvester as a Tool in Precision Farming Corn Preservation Moisture Content Drying Ear Corn in Cribs Forced-Air Corn Drying High-Moisture Corn Preservation Handling Systems Ear Handling Shelled Corn Handling Storage and Storage Management Ear Corn Storage References Further Reading

109 112 112 112 112 116 118 119 119 119 120 120 122 123 123 124 124 125 125 128 128 134 135 135 135 140 140 143 145

6. Development and Structure of the Corn Kernel Silverio Garcı´a-Lara, Cristina Chuck-Hernandez and Sergio O. Serna-Saldivar Botanical Classification Main Kernel Structure Physical Properties Hardness Density Kernel Weight Color Moisture Content Thermal Properties Kernel Development Pollination and Fertilization Endosperm Development Germ Development Pericarp Development Structure of the Mature Kernel Whole Kernel

147 147 149 149 151 151 152 152 152 152 152 153 155 156 156 156

Contents vii

Pericarp Endosperm Conclusions Acknowledgments References

156 157 161 162 162

203 203 204 205 211

8. Effect and Control of Insects, Molds and Rodents Affecting Corn Quality

7. Measurement and Maintenance of Corn Quality Marvin R. Paulsen, Mukti Singh and Vijay Singh Introduction U.S. Grades and Standards History, Classes, and U.S. Grades Importance of Grades in Corn Marketing Alternative Marketing Channels ISO 9000 Certification Grades and Standards of Other Countries History of Grades and Standards for Export Trade Corn-Grading Factors of Other Countries Sampling Accuracy of Sample/Grade Determinations Moisture Moisture Shrink Reference Moisture Methods Moisture Meters Individual Kernel Moisture Measurement Near-Infrared Spectroscopy Broken Corn, Foreign Material, and Dust Broken Corn, Foreign Material (BCFM) Dust Density True Density Bulk Density (Test Weight) Porosity Hardness Significance Measurements Other Physical Quality Tests Pericarp Damage Stress Cracks Breakage Susceptibility 1000-Kernel Weights Fungal Invasion Damage Grade Factor Role of Microorganisms in Quality Deterioration Quality in Corn Utilization Wet Milling Ethanol Processing Beverage Alcohol Dry Milling

Alkaline Processing Seed Corn Conclusions and Trends References Further Reading

Linda J. Mason 165 166 166 168 169 169 169 170 170 174 174 175 175 178 180 181 181 183 183 184 185 185 186 190 190 190 190 191 191 192 194 195 195 195 196 199 199 200 202 202

Introduction 213 Common Pest of Stored Corn 213 Important Insects Affecting Corn Quality 213 Important Fungi Affecting Corn Quality 216 Important Rodents Affecting Corn Quality 216 Development of Insects, Rodents, and Fungi in Stored Grain 217 Insect Developmental Stages 217 Sampling and Measurements of Pest Populations 219 Insects 219 Mycotoxins 221 Management of Insects, Mold, and Rodents in Stored Corn 221 Preventive Methods 221 Control Measures After Binning 223 Alternative Control Measures to Traditional Pesticides 226 Conclusions 228 References 228 Further Reading 234

9. Mycotoxins in Corn: Occurrence, Impacts, and Management Gary P. Munkvold, Silvina Arias, Ines Taschl and Christiane Gruber-Dorninger Introduction Toxigenic Fungi in Corn Fusarium Aspergillus Penicillium Stenocarpella Major Mycotoxins in Corn and Their Impacts Fumonisins Trichothecenes Zearalenone Other Fusarium Toxins Aflatoxins and Other Aspergillus Toxins Penicillium Toxins Occurrence of Mycotoxins in Corn and DDGS

235 239 239 240 240 241 241 241 244 247 248 249 252 252

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Contents

Global Mycotoxin Occurrence in Corn Mycotoxins in North American Corn Mycotoxins in Corn in Countries Outside USA Multi-Mycotoxin Analysis of North American Corn Samples Global Mycotoxin Occurrence in Corn DDGS Mycotoxins in North American Corn DDGS Occurrence of Mycotoxins in Corn-Based Food Mycotoxins in Corn Silage Mycotoxin Analysis General Procedures Conventional Methods: Chromatographic Analysis Rapid Methods for Mycotoxin Determination: Immunochemical Analysis Emerging Techniques Management of Mycotoxins in Corn Preharvest Harvest and Drying Postharvest Management Remediation and Detoxification Physical Methods Chemical Degradation Biological Degradation Conclusions Acknowledgment References

252 253 253 255 255 257 258 258 259 259 263 264 266 267 267 270 271 273 273 276 276 277 277 277

10. Specialty Corns Paul Scott, Richard C. Pratt, Nicholas Hoffman and Randall Montgomery Overview and Definition of Specialty Corn Food-Grade Corn Corn With Improved Nutritional Value Amino Acid Balance and Quality Protein Maize High Mineral Availability High-Oil Corn Popcorn Sweet Corn Silage Corn Silage Production and Its Importance Silage Quality Genetic Variation in Silage Quality and Yield Corn for Specialty Starch Production Organic and GMO-Free Corn Conclusions References Further Reading

11. Carbohydrates of the Kernel Bruce R. Hamaker, Yunus E. Tuncil and Xinyu Shen Introduction Corn Starch Structure and Function Starch Molecular Fine Structure Lamellae and Crystalline Regions of Amylopectin, and Starch Granule Structure Starch Functional Properties Gelatinization Retrogradation Gel Structure Genotypic and Environmental Effects on Corn Starch Structure and Function Variation of Corn Starch Structure and Function Within Kernel Variation Genotype and Environment Variation Nutritional Properties Nonstarch Polysaccharides Cellulose Hemicelluloses Arabinoxylans b-Glucan Lignin Biological Functions of Nonstarch Polysaccharides in Corn Cell Wall Nutritional Importance of Nonstarch Polysaccharides of Corn Conclusions References Further Reading

305 305 306 307 307 307 307 308 308 308 308 308 309 309 310 311 311 312 313 313 313 315 315 318

12. Proteins of the Kernel 289 289 291 291 292 292 293 295 296 296 296 298 299 299 300 300 303

Brian A. Larkins Introduction Traditional Approaches to Kernel Protein Extraction and Characterization Current Approaches to Corn Kernel Protein Identification Proteomics: An Integration of Techniques for Protein Identification Corn Kernel Proteins in Differentiated Cell Types Endosperm Storage Proteins: Zeins and Globulins Zein Protein Bodies Relationship Between Zein Proteins and Vitreous Endosperm Mutations Affecting Zein Synthesis Increasing the Nutritional Quality of Corn Kernel Proteins

319 320 321 321 322 325 325 327 328 330

Contents

Zein Structural Features and Utilities Utilization and Application of Corn Kernel Proteins Conclusions References Further Reading

330 331 331 332 336

13. Lipids of the Kernel Tong Wang and Pamela J. White Introduction Oil Content Factors Affecting Corn Oil Content Fatty Acid Composition Factors Affecting Fatty Acid Composition of Corn Oil Genetic Control of Fatty Acid Composition Corn Lipid Class Composition Triacylglycerols (TAG) Phospholipids Glycolipids Sphingolipids Phytosterols Hydrocarbons Polyisoprenoid Alcohols Waxes and Cutin Carotenoids Tocols Other Phenols Distribution of Lipids in the Corn Kernel Dissected Grain Corn Fiber Oil Starch Lipids Enzymatically Derived Lipids and Hormones Oil Obtained from Coproduct of Corn Dry-Grind Ethanol Fermentation Future Needs Conclusions References Further Reading

337 338 338 340 341 341 341 341 343 345 345 347 349 349 349 350 352 354 354 354 356 359 360 361 362 362 363 368

14. Minor Constituents and Phytochemicals of the Kernel Beatriz A. Acosta-Estrada, Janet A. Guti errez-Uribe and Sergio O. Serna-Saldivar Introduction Minerals Major Minerals Trace Minerals Vitamins Water-Soluble Vitamins Fat-Soluble Vitamins Phytochemicals

369 370 370 374 377 377 382 385

Phenolic Compounds Carotenes and Xanthophylls Phytosterols Phospholipids Policosanols Arabinoxylans Conclusions References Further Reading

ix

386 391 392 393 396 397 397 398 403

15. Corn Dry Milling: Processes, Products, and Applications Brian Anderson and Helbert Almeida History of Corn Dry-Milling Industry Overview Corn Grain Quality for Dry-Milling Dry-Milling Processes Full-Fat Milling Process Bolted Milling Process Tempering-Degerming Milling Process Beall Degerminating System Buhler Degerminating System Satake Degerminating System Other Degerminating Systems Dry-Milled Products Categories and Composition Dry-Milling Inferences for Selected Corn Food Categories RTE Breakfast Cereals Brewing Adjuncts Extruded and Sheeted Snacks Breadings, Batters, and Prepared Mixes Fortified Food Nonfood Applications Animal Feeds Gypsum-Board Starch Pregelatinized Binders Starch Conversions Future Trends and Developments Conclusions References Further Reading

405 406 408 409 409 411 412 414 416 417 418 419 419 422 422 423 424 425 426 428 428 428 428 429 429 430 431 433

16. Food Uses of Whole Corn and Dry-Milled Fractions Sergio O. Serna-Saldivar and Esther Perez Carrillo Introduction Human Consumption of Corn Specialty Corns Food-Grade White and Yellow Corns Popcorn Sweet Corn

435 435 436 436 436 439

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Quality Protein Maize Blue and Pigmented Corns Giant Cuzco Corn High Oil Corn Traditional Corn Food Corn on the Cob African and Asian Traditional Corn Food Latin America Traditional Corn Food North American Traditional Corn Food Food Uses of Whole Corn Processing of Popcorn Processing of Sweet and Immature Corn Hominy Baby Corn Whole Grain Products Gluten-Free Products Food Uses of Dry-Milled Fractions Dry-Milled Fractions Breakfast Cereals Extruded Snack Food Beer Alcoholic Beverages Nutritional Value of Corn Food Future of Corn Food Conclusions References

440 440 441 441 442 442 442 442 442 443 443 445 446 446 447 447 448 448 448 453 460 461 461 461 462 464

17. Food Uses of Lime-Cooked Corn With Emphasis in Tortillas and Snacks Sergio O. Serna-Saldivar and Cristina Chuck-Hernandez Introduction Basic Ingredients for Corn Tortilla Production Corn Quality for Lime-Cooking Lime Water Optional Ingredients for Table Tortillas Traditional Products Based on Nixtamalized Corn Industrial Manufacturing of Corn Tortillas Fresh Masa Industrial Manufacturing of Dry Masa Flour Novel Technologies for Production of Fresh Masa and Dry Masa Flours Basic Ingredients for Lime-Cooked Snacks Frying Oil Salt and Seasonings Antioxidants and Chelating Agents Industrial Manufacturing of Lime-Cooked Snacks Production of Alkaline-Cooked Parched Products

469 470 470 472 472 472 474 476 477 480 482 483 483 483 484 484 484

Production of Extruded Corn Chips Production of Tortilla Chips, Taco Shells, and Tostadas Low-Fat Tortilla Chips Quality Control for Tortillas and Related Snacks Nutritional Value of Lime-Cooked Corn Products Conclusions References Further Reading

485 486 488 489 496 497 498 500

18. Wet Milling: The Basis for Corn Biorefineries Kent D. Rausch, Dell Hummel, Lawrence A. Johnson and James B. May Introduction Current Wet Milling Practices Grain Drying, Storage, and Handling Cleaning Steeping Separation of Kernel Components Coproduct Processing Germ Processing Process Management Automation Utilities Wastewater Air Pollution Control Laboratory and Pilot Plant Simulation of Corn Wet Milling Laboratory Wet Milling Procedures Pilot Scale Wet Milling Procedures Corn Varieties Processed Commercially Normal Corn Identity-Preserved Corn Yields, Production, and Marketing of Products Alternative Corn Fractionation Processes Enzymatic Wet Milling Westfalia Process Steeping Grits Alternative Steeping Practices Intermittent Milling and Dynamic Steeping Process Alkali Wet Milling Sequential Extraction Processing Membrane Filtration Decolorized Corn Gluten Meal Corn Fiber Utilization Processing Transgenic Corn for Industrial Enzymes and Specialty Chemicals References Further Reading

501 503 503 505 506 507 514 515 516 516 516 517 517 518 518 520 521 521 521 525 526 526 527 527 528 528 528 529 529 529 529 530 531 535

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Contents

19. Corn Starch Modification James N. BeMiller Introduction Basic Natures of Corn Starch Granules and Molecules Chemical Modifications Objectives Reactions Physical Modifications Objectives Thermal Treatments Nonthermal Treatments References

537 537 539 539 539 545 545 546 547 548

20. Corn Sweeteners Scott Helstad Introduction Process Overview Corn Syrups Acid Conversion Acid/Enzyme Conversion Enzyme-Enzyme Conversion Enzymes Used in the Corn Sweetener Process Protein Removal Decolorizing/Carbon Treatment Decolorizing Resins/Demineralization/ Ion-Exchange Evaporation Maltodextrins Acid Hydrolysis Acid-Enzyme Hydrolysis Enzyme-Enzyme Dextrose High-Fructose Corn Syrups Liquid and Crystalline Fructose Storage and Handling of Corn Sweeteners Regulatory Definitions Glucose Syrup Maltodextrin High-Fructose Corn Syrup Crystalline Fructose Dextrose Monohydrate Dextrose Anhydrous Dried Glucose Syrup Total Sugars Important Properties and Measurements of Corn Sweeteners Carbohydrate Profile Dextrose Equivalents Solids Viscosity

551 552 553 553 554 556 558 559 559 561 561 561 562 562 562 562 564 565 565 567 567 567 567 567 567 567 567 567 568 568 568 568 572

Sweetness Color Fermentability Freezing-Point Depression Boiling Point Elevation Humectancy and Hygroscopicity Crystallization Water Activity Applications of Corn Sweeteners Baking Beverages Brewing Confections Ice Cream Carbohydrates and Health Conclusions Acknowledgments References Further Reading

574 575 576 577 577 577 578 579 580 580 580 587 588 588 589 589 590 590 591

21. Corn Oil: Composition, Processing, and Utilization Daniel Barrera-Arellano, Ana Paula Badan-Ribeiro and Sergio O. Serna-Saldivar Introduction Regular and High-Oil Corns Composition of Saponifiable and Unsaponifiable Fractions of Corn Oil Fatty Acid Composition Triacylglycerol Composition Minor Lipids Corn Oil Extraction Conventional Corn Germ Extraction Alternative Extraction Processes Pretreatment and Refining of Corn Oil Degumming Refining By-Products of Corn Oil Processing Modification Processes Blending Hydrogenation Interesterification Uses and Applications of Corn Oil Nonfood Uses of Corn Oil Quality Control Assays for Corn Oil Free Fatty Acids Peroxide Index (PV) Iodine Value Refractive Index Color—Lovibond Smoke Point Oxidative Stability Index (OSI) Cold Test

593 594 594 594 594 595 597 597 599 600 600 601 604 604 605 605 606 606 607 607 607 607 608 608 609 609 609 609

xii Contents

Solid Fat Content (SFC) Trans Fatty Acids Nutritional Aspects Conclusions References

609 609 609 610 610

22. Bioethanol Production From Corn Deepak Kumar and Vijay Singh Introduction Bioethanol Current Status of Bioethanol Industry Feedstocks for Bioethanol Production Corn Composition and Structure Biomass Composition and Structure Bioethanol Production Technologies Ethanol Production From Corn Ethanol Production From Corn Stover Technology Developments in Corn Ethanol Production Corn Fractionation Ethanol From Corn Fiber Decrease of Exogenous Enzyme Use High Solid Use Control of Process Conditions Conclusions References Further Reading

615 615 615 615 616 617 618 618 620 622 623 625 625 626 627 629 629 631

23. Nutritional Properties and Feeding Value of Corn and Its Coproducts D.D. Loy and E.L. Lundy Introduction Nutritional Value of Corn Starch Regular, Waxy, and High-Amylose Corns Starch Type

633 633 633 633

Nutritional Value of Corn Proteins Normal and High-Protein Corn High-Lysine Corn and Synthetic Lysine Nutritional Value of Corn Lipids Corn Oil Carotenoids Vitamins Minerals Antinutrients Feed Processing Particle Size Steam Flaking Popping and Micronization Reconstituted and High-Moisture Extrusion and Puffing Pelleting Corn Feed Coproducts From Food and Fuel Corn Wet-Milling Feed Products Corn Gluten Feed Corn Gluten Meal Condensed Fermented Corn Extractives (Steep Liquor) Corn Dry-Mill Feed Products Corn Distillers’ Dried Grains Wet and Modified Distillers Grains Distillers’ Solubles Changing Distillers Grains Corn Dry-Milling Process Hominy Feed Conclusions References

Index

634 634 635 636 636 636 637 639 639 640 640 641 641 641 641 641 641 642 642 646 646 647 649 650 651 651 651 651 652 654 654

661

Contributors Numbers in parentheses indicate the pages on which the authors’ contributions begin.

Beatriz A. Acosta-Estrada (369), Centro de Biotecnologı´a FEMSA, Escuela de Ingenierı´a y Ciencias, Tecnologico de Monterrey, Monterrey, Mexico Helbert Almeida (405), Bunge Milling, Inc., St Louis, MO, United States Brian Anderson (405), Bunge Milling, Inc., St Louis, MO, United States

Christiane Gruber-Dorninger (235), BIOMIN Holding GmbH, Getzersdorf, Austria Janet A. Gutierrez-Uribe (369), Centro de Biotecnologı´a FEMSA, Escuela de Ingenierı´a y Ciencias, Tecnologico de Monterrey, Monterrey; Tecnologico de Monterrey, School of Engineering and Science, Puebla, Mexico Bruce R. Hamaker (305), Whistler Center for Carbohydrate Research, Department of Food Science, Purdue University, West Lafayette, IN, United States

Silvina Arias (235), Department of Plant Pathology and Microbiology, Seed Science Center, Iowa State University, Ames, IA, United States

Scott Helstad (551), Cargill, Inc., Starches, Sweeteners and Texturizers North America, Dayton, OH, United States

Ana Paula Badan-Ribeiro (593), Fats and Oils Laboratory, School of Food Engineering, University of Campinas—UNICAMP, Campinas, Brazil

Floyd L. Herum (109), Department of Agricultural Engineering, Ohio Agricultural Research and Development Center, The Ohio State University, Columbus, OH, United States

Daniel Barrera-Arellano (593), Fats and Oils Laboratory, School of Food Engineering, University of Campinas— UNICAMP, Campinas, Brazil James N. BeMiller (537), Whistler Center for Carbohydrate Research, Purdue University, West Lafayette, IN, United States Carl J. Bern (109), Ag/Biosystems Engineering, Iowa State University, Ames, IA, United States Jose Luis Cabrera-Ponce (43), Centro de Investigacio´n y de Estudios Avanzados del IPN, Departamento de Ingenieria Genetica, Unidad Ira puato, Irapuato, Guanajuato, Mexico Cristina Chuck-Hernandez (147, 469), Centro de Biotecnologı´a FEMSA, Escuela de Ingenierı´a y Ciencias, Tecnologico de Monterrey, Monterrey, Mexico L.L. Darrah (19), Plant Genetics Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Geneva, NY; Department of Agronomy, University of Missouri, Columbia, MO, United States Francisco Javier Belden Fernandez (87), Director of Supply and Sales of Commodities, RAGASA Industrias, Monterrey, Mexico Silverio Garcı´a-Lara (1, 147), Centro de Biotecnologı´a FEMSA, Escuela de Ingenierı´a y Ciencias, Tecnologico de Monterrey, Monterrey, Mexico

Nicholas Hoffman (289), Iowa State University, Department of Agronomy, Ames, IA, United States Dell Hummel (501), Alfa Laval Oak Brook, Oak Brook, IL, United States Lawrence A. Johnson (501), Center for Crops Utilization Research, Iowa State University, Ames, IA, United States Deepak Kumar (615), Department of Agricultural and Biological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, United States Brian A. Larkins (319), University of Nebraska, Lincoln, NE, United States D.D. Loy (633), Department of Animal Science, Iowa State University, Ames, IA, United States E.L. Lundy (633), Iowa Beef Center, Iowa State University Extension and Outreach, Ames, IA, United States Ernesto Lozano Martinez (87), EGADE Business School, Tecnolo´gico de Monterrey, San Pedro Garza Garcı´a, Mexico Linda J. Mason (213), Department of Entomology, Purdue University, West Lafayette, IN, United States James B. May (501), A.E. Staley Manufacturing Co., Decatur, IL, United States xiii

xiv

M.D. McMullen (19), Plant Genetics Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Geneva, NY; Department of Agronomy, University of Missouri, Columbia, MO, United States Randall Montgomery (289), New Mexico State University, Department of Plant and Environmental Sciences, Las Cruces, NM, United States Gary P. Munkvold (235), Department of Plant Pathology and Microbiology, Seed Science Center, Iowa State University, Ames, IA, United States Marvin R. Paulsen (165), Department of Agricultural and Biological Engineering, University of Illinois, Urbana, IL, United States Esther Perez Carrillo (435), Centro de Biotecnologı´a FEMSA, Escuela de Ingenierı´a y Ciencias, Tecnologico de Monterrey, Monterrey, Mexico Richard C. Pratt (289), New Mexico State University, Department of Plant and Environmental Sciences, Las Cruces, NM, United States

Contributors

Xinyu Shen (305), Novozymes North America Inc., Franklinton, NC, United States Mukti Singh (165), Functional Foods Research Unit, USDA, Agricultural Research Service, National Center for Agricultural Utilization Research, Peoria, IL, United States Vijay Singh (165, 615), Department of Agricultural and Biological Engineering, University of Illinois, Urbana, IL, United States Ines Taschl (235), BIOMIN Holding GmbH, Getzersdorf, Austria Diana Lilia Trejo-Saavedra (43), Centro de Investigacio´n y de Estudios Avanzados del IPN, Departamento de Ingenieria Genetica, Unidad Ira puato, Irapuato, Guanajuato, Mexico Yunus E. Tuncil (305), Food Engineering Department, Ordu University, Ordu, Turkey

Graeme Quick (109), Ag/Biosystems Engineering, Iowa State University, Ames, IA, United States

Eliana Valencia-Lozano (43), Centro de Investigacio´n y de Estudios Avanzados del IPN, Departamento de Ingenieria Genetica, Unidad Ira puato, Irapuato, Guanajuato, Mexico

Kent D. Rausch (501), Agricultural and Biological Engineering Department, University of Illinois at UrbanaChampaign, Urbana, IL, United States

Tong Wang (337), Department of Food Science and Human Nutrition, Iowa State University, Ames, IA, United States

Paul Scott (289), USDA-ARS, Corn Insects and Crop Genetics Research Unit, Ames, IA, United States

Pamela J. White (337), Department of Food Science and Human Nutrition, Iowa State University, Ames, IA, United States

Sergio O. Serna-Saldivar (1, 147, 369, 435, 469, 593), Centro de Biotecnologı´a FEMSA, Escuela de Ingenierı´a y Ciencias, Tecnologico de Monterrey, Monterrey, Mexico

M.S. Zuber (19), Department of Agronomy, University of Missouri, Columbia, MO, United States

Preface Approximately 30 and 14 years have passed since the publication of the first and second editions of the classic book Corn: Chemistry and Technology, respectively, first edited by Drs. Stan Watson and Paul Ramstad and then by Drs. Pamela White and Lawrence Johnson. During these periods, the yearly worldwide production of this cereal grain has increased from 453 and 645 million tons, respectively, to more than one billion tons. Nowadays, corn is undoubtedly the most planted crop in the planet due to its wide adaptation capability to different ecosystems, high production capacity, and its use as direct food, feed, and other industrial processes. During this time span, worldwide population has grown from 5.0 and 6.4 billion to more than 7.7 billion people with per capita direct corn consumption increasing nearly 25%. The current value of the actual yearly production as a commodity exceeds the astonishing amount of 160 billion US dollars. More importantly, corn kernels are transformed into an array of value-added food, feeds, industrial products, and fuel bioethanol. The farming, storage, and transformation of this crucial cereal grain generate more value and countless jobs both in the primary and secondary sectors and is fundamental in terms of food security. Three important events have occurred since the release of the second edition of this book: the relevant breeding for production of new transgenic seeds using novel agrobiotechnology tools that have increased average yields nearly 20% during the past 10 years, the use of more than 120 million metric tons of corn per year for production of approximately 54 billion liters (14.3 billion gallons) of first-generation fuel ethanol, and the development of corn-based nutraceutical food that positively impact human health and life expectancy. In this third edition of the book, authors updated scientific and technical information generated during the past 15 years and three new chapters were incorporated. The extra chapters deal with the characteristics of regular and specialty corns, minor compounds and phytochemicals associated to different sorts of corn kernels, and nixtamalized or lime-cooked food and snacks. This new edition provides revised information about the importance, biology, traditional breeding, and use of genetic modification strategies to improve the productivity and resistance of the crop to different agroecosystems. Next, expert authors covered relevant topics related to agriculture economics, specialty corns, grain morphology, and anatomy, physical properties of different corns and the detailed chemistry of the kernel in terms of starch and other carbohydrates, proteins, lipids, and minor constituents such as vitamins, minerals, and phytochemicals. The next chapters focus on the pre- and postharvest managements, especially in terms of farming, grain storage, insect, and mold control. It is especially worrisome as regard the susceptibility of field and stored corn to mycotoxicogenic molds, which can cause in domestic animals and humans diseases, cancer, and even death. The FAO considers mycotoxins associated to corn and other grains as one of the most significant food security issues that faces humankind. The core of the book consists of chapters which cover industrial dry-milling, wet-milling, and lime-cooking or nixtamalization that supply important intermediate and value-added products for production of breakfast cereals, extruded snacks, table tortillas and tortilla chips, batters and breadings, sweeteners, baking items, and an array of traditional food still widely consumed especially in developing regions of Africa, Latin America, and Asia. The tortilla and related products chapter covers the two major milling processes used to obtain lime-cooked dough or masa that is the backbone for the fabrication of soft tortillas and snacks. These food industries are considered one of the fastest growing worldwide. Two chapters are devoted to the transformation of refined cornstarch into modified or functional starches and the array of syrups and sweeteners that compete with crystallized sugar extracted from sugarcane or sugar beet. Likewise, the corn oil chapter complements the lipids of the kernel chapter and comprises properties of corn oil in terms of fatty acid composition, phospholipids, tocopherols, and other compounds and focuses on the extraction of crude oil, physical and chemical refining, and modification of the physical, chemical, and functional properties of oils. The final two chapters deal with the utilization of corn for fuel bioethanol production and animal feeds. It is estimated that 70% of the current corn crop is channeled to these industries. Corn biorefineries currently utilize about 15% of the world corn in order to produce renewable fuels that partially substitute gasoline, especially in the USA market. This chapter

xv

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Preface

thoroughly describes conventional and emerging processes for the production of fuel ethanol from whole corn kernels, fractionated corn, and cornstarch. The last chapter deals with the relevance of whole corn and its by-products in animal nutrition which are converted by domestic animals into eggs, pork, poultry, beef, milk, and even for the formulation of aquaculture diets for fish and crustaceans. The feed industry is undoubtedly the major user of corn with more than 0.5 billion tons. I wish to acknowledge the time, effort, and kind contributions of contributing authors and the editorial project manager Barbara L. Makinster who have worked in this endeavor during the past two years and thank them for their tireless efforts through the completion of this volume. Lastly, I would like to dedicate this effort to Dr. Stanley A. Watson, who passed away in 2005 and was the first person who conceptualized this book; my mentor Dr. Lloyd W. Rooney, who taught, guided, and introduced me to the prodigious field of cereals; and countless deceased and retried corn scientists who devoted their lives to the fascinating fields of corn chemistry, breeding, production, and utilization. Their efforts have been translated into more food on the plate of the increasing world population, which is expected to exceed 9 billion people in year 2040, and have created the platform needed to increase and improve corn for generations to come. Sergio O. Serna Saldivar

Chapter 1

Corn History and Culture Silverio Garcı´a-Lara and Sergio O. Serna-Saldivar Centro de Biotecnologı´a FEMSA, Escuela de Ingenierı´a y Ciencias, Tecnologico de Monterrey, Monterrey, Mexico

PRODUCTION AND IMPORTANCE Cereals are the most important source of food, and cereal-based food are a major source of energy for the world population (Food and Agricultural Organization, 2018). Worldwide, the three cereal crops with the greatest production are corn, rice, and wheat; among other commodities such as vegetables, roots, and tubers (Fig. 1.1). These cereals are the most relevant grains in the human diet and are one of the main sources of nutrients in developing countries because of their availability and affordability. Of these cereals, the greatest land area by far is devoted to wheat, but because of its lower average yield per unit of land area, the total production of wheat is less than that of corn or rice. Of these main cereals, wheat and rice are primarily food crops, whereas corn is primarily used as feed (see Chapter 23) and fuel bioethanol crop (see Chapter 22). Corn (Zea mays L.) belongs to the grass family Poaceae (Gramineae), tribe Maydeae. Cultivated maize is a fully domesticated plant and is one of the most productive species of food-plant. It is a C4 plant with a high rate of photosynthetic activity, a multiplication ratio of 1:600–1:1000, and the highest potential for carbohydrate production per unit area per day. Corn originated in the tropics; however, it is grown in a wide diversity of environments located from 58°N in Canada to 40°S in Argentina (Paliwal et al., 2000). Today, corn is the most important cereal grain in terms of production. Corn became the world leader surpassing rice and wheat about 10 years ago due to the development of high-yielding regular and genetic-modified genotypes and its wider adaptation to different ecosystems. It is the top ranking cereal in grain yield per hectare. Corn has high value and economic importance worldwide not only as human food, but also as animal feed and as feedstock for a large quantity of industrial products and biofuels. In subsistence agriculture, corn is grown and used as a basic food crop, but in developed countries, with a concurrent increase in demand for wheat flour and animal-derived food, the primary use is as animal feed. As a result, in many developed countries, more than 85% of the corn produced or imported are used for animal feed (Food and Agricultural Organization, 2018). Maize is the most extensively cultivated and consumed cereal in the world, with a production of more than 1 billion of metric tons and an area harvested of almost 200 millions of hectares in 2016. World corn production has increased due to both increased land area devoted for its production and increased yield per unit of land. In 2016, approximately 70 and 63 millions of hectares were planted with corn in America and Asia, respectively (Fig. 1.2) (Food and Agricultural Organization, 2018). The American continent produces nearly 55% of the world’s total production, followed by Asia, Europe, and Oceania. The U.S. Com Belt produces 38% of the world’s total, followed by China (18%), Brazil (8%), Argentina (8%), Baltic States (9.5%), India (5%), and Mexico (3%). Corn is consumed across the world in a variety of whole and processed products that are described in Chapters 16, 17, and 20. Corn is consumed on the cob and suitable for the development of a variety of food such as popcorn, polenta, tortillas, mush, breakfast cereals, snack food, bakery items, and cornmeal among others. Nowadays, eating habits of people all over the world have changed from eating traditional to nontraditional corn food, such as fast food, breakfast cereals, and extruded and nixtamalized snacks. The refined cornstarch is transformed into an array of syrups and sweeteners that are strongly competing with the traditional crystallized sugar refined from sugarcane or beet (Serna-Saldivar, 2010a). Direct corn consumption is concentrated in America and Africa. Particularly in Mexico, the per capita food supply (included protein) for maize is higher than that for the rest of America and superior than the values for the world and the five continents. Mexico is one of the ten major consumers of maize with a per capita consumption of 34 kg/year (Fig. 1.3) (Food and Agricultural Organization, 2018).

Corn. https://doi.org/10.1016/B978-0-12-811971-6.00001-2 Copyright © 2019 AACCI. Published by Elsevier Inc. in cooperation with AACC International. All rights reserved.

1

2 Corn

3000

Production (millions tons)

2500

2000

1500

1000

500

0 Cereals, Sugar cane Coarse Total grain, Total

Vegetables Vegetables primary & melons

Maize

Roots and tubers

Rice, Paddy

Wheat

Commodities

FIG. 1.1 Most produced commodities in the world, 2016. (Source: Food and Agricultural Organization, 2018. FAOSTAT, FAO Statistical Databases. Available from: http://apps.fao.org/ (2 February 2018).)

200

1,200

Production (millions tons)

Area harvested (millions ha)

180 160 140 120 100 80 60 40

1,000 800 600 400 200

20 0

0 World

Africa America

Asia

Europe Oceania

World

Africa America

Region

Europe Oceania

Region 450

8

400 Production (millions tons)

9

7 Yield (ton/ha)

Asia

6 5 4 3 2

350 300 250 200 150 100 50

1 0

0 World

Africa America

Asia

Europe Oceania

USA

China

Brazil Argentina Ukraine India

Region Country FIG. 1.2 Worldwide corn production. (A) Maize area harvested by region, (B) maize production by region, (C) maize yield by region, and (D) Top 6 maize producers. (Source: Food and Agricultural Organization, 2018. FAOSTAT, FAO Statistical Databases. Available from: http://apps.fao.org/ (2 February 2018).)

Corn History and Culture Chapter

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3

350

Consumption (millions tons)

300 250 200 150 100 50

China

Brazil

Mexico Indonesia

(A)

India

Japan

Argentina

Egypt

Canada

Canada

United States

Ghana

0

Region 160

Consumption food (kg/capita)

140 120 100 80 60 40 20

(B)

30 Protein supply quantity (g/capita/day)

Food supply quantity (g/capita/day)

Ethiopia

Region

140 120 100 80 60 40 20 0

25 20 15 10 5 0

World

(C)

Egypt

Colombia

Mozambique

Tanzania

SouthAfrica

Zambia

Mexico

0

Africa Americas Asia

Region

Europe Oceania Mexico

World

(D)

Africa Americas Asia

Europe Oceania Mexico

Region

FIG. 1.3 Maize consumption worldwide. (A) Top 10 maize consumers based on average values from 2013 to 2015. (B) Top 10 maize consumers per capita based on average values from 2013 to 2015. (C) Per capita supply of maize available for human consumption as food and protein supply. (Source: Food and Agricultural Organization, 2018. FAOSTAT, FAO Statistical Databases. Available from: http://apps.fao.org/ (2 February 2018).)

4 Corn

Corn has a high yield potential in many environments. Very few crops average more than 3.5 metric tons per hectare (t/ha) on a worldwide basis; potatoes, corn, and rice are the primary exceptions. Not all corn-producing areas have corn yields that exceed 3.5 t/ha. In fact, the United States, Canada, China, Europe and the Baltic States, Argentina, and Oceania are the only areas to significantly yield more than this amount.

CORN HISTORY AND CULTURE Origin and Evolution Corn was originated in the highlands of Mexico between 7000 and 10,000 years ago. Archeological data has shown that corn was cultivated in the year 2000–2500 BCE. The oldest paleoetnobotanic evidence of its domestication is in an archeological site named “Nac Neish,” located in the southern part of the state of Tamaulipas, Mexico. It consists of three primitive caves presenting data between 6000 and 20,000 years BC. Other important archeological sites were located in the states of Puebla, Oaxaca, and Mexico. The oldest record for corn and teosinte (Zea mexicana and Zea perennis) dated 5000 years BC was found in the archeological sites named “La Playa” and “Nevada,” located in the Tehuacan valley. Two types of teosintles named Chalco and Balsas were found in western Mexico located at high and low altitudes, respectively. Three theories about the evolutive origin of corn have been postulated. The first one proposed that maize is the result of crossing teosinte by Tripsacum. The second is that it comes from a tunicated maize and that teosintle is the result of crossing Zea by Tripsacum. The third, and most recognized, is that corn evolved from teosinte (Table 1.1) (Galinat, 1988; CuevasSa´nchez, 2011; Serna-Saldivar, 2015). Mangelsdorf (1986) believed that corn evolved from extinct popping corns that contained glumes covering each kernel. Wilkes (1972) found that teosinte and Tripsacum could not cross in nature, nor in laboratory conditions, and the structure of the pollen of these two genus also confirmed that teosinte did not derive from their hybridation. In addition, Paulis and Wall (1977) determined that electrophoretic patterns of zeins and alcohol-soluble reduced glutelins of teosintes were similar to corn, but those of Tripsacum showed marked differences. Then, the most accepted theory of the origin of corn is that teosintle is the ancestor because (1) the free and frequent hybridation of teosintle and corn occurring in nature, (2) the same number of chromosomes (n ¼ 10) with an identical structure in both species, and (3) cultivars share several anatomical features including similar morphological pollen characteristics. According to Galinat (1988), the origin of corn occurred during the invention of the new world agriculture. The American Indians developed corn and were the first breeders because they transformed the tiny two-rowed ear of teosinte of about 3 cm long into the first tiny corn ear with its four ranks of paired female spikelets. This transformation likely took between 100 and 200 years. Evidence based on chromosomal studies and cob morphology indicates that at least two independent domestications from two teosintes gave origin to two different corns (classified as pyramidal or cylindrical corns). The pyramidals such as Palomero Toluquen˜o, Conico, and Chalquen˜o are distant descendants from Chalco Teosinte TABLE 1.1 Teozintle Diversity in Mexico Group

Cycle of Life

Specie (Location)

Luxurians

Annual

Zea luxurians Zea nicaraguensis Zea sp. (Oaxaca)

Perenne

Zea perennis (Jalisco, Colima) Zea diploperennis (Jalisco) Zea sp. (Nayarit, Michoacan)

Annual

Zea mays spp. huehuetenanguensis Zea mays ssp. mexicana Races: Nobogame (Chihuahua) Durango (Durango) Mesa Central (Guanajuato, Jalisco, Michoacan) Chalco (Estado de Mexico, Puebla, Tlaxcala) Zea mays spp. parviglumis (Nayarir, Jalisco, Michoaca´n, Guerreo, Oaxaca)

Zea

Source: Comisio´n Nacional para el Conocimiento y Uso de la Biodiversidad, 2011. Recopilacio´n, generacio´n, actualizacio´n y ana´lisis de informacio´n acerca de la diversidad genetica de maı´ces y sus parientes silvestres en Mexico. CONABIO. Mexico. Available from: http://www.biodiversidad.gob.mx/genes/ proyectoMaices.html (23 September 2017).

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5

(Z. mexicana) which still grows wild from Chihuahua (Mexico) to Guatemala. The cylindrical corns are most prevalent in modern corn and represent another group of races tracing back to Guerrero or Balsas Teosinte (Zea parviglumis). The oldest remains of 8-rowed corn from Tehuacan, Mexico, are 7200 years old. The 12-rowed ear of Chapalote with a higher cob diameter is about 3000 years old (Table 1.1). Apparently, the large kerneled eight-rowed maize (Cacahuacintle or Cuzco) arose independently from Balsas Teosinte about 2500 years ago. Parallelly, the Palomero Toluquen˜o indigenous Mexican race, characterized by elongated flint kernels that evolved from Chalco Teosinte, originated the 16-rowed Pepitilla corn. The cross of Cacahuacintle from Balsas and Pepetilla from Chalco teosintes originated the high-yielding 14-rowed dent corns generally planted in the Corn Belt today. The recurrent selection by many generations of humans has resulted in a magnificent kernel-bearing structure capable of carrying a high number of broad caryopses that would not shatter from the dry cob. The 10-chromosome races encoded precious genetic information that made corn the most adapted and productive crop in the world (Galinat, 1988).

Historical Perspective Corn is also known by various common names, being the most widely used maize. In Spanish, it is called “maiz,” in French “mais,” in Portuguese “milho,” and in India “makka.” Wellhausen et al. (1951) classified several races of corn; one group denominated “indigenous or ancient” dated at least 5000 years old that included: Nal Tel, Chapalote, Palomero Toluquen˜o, and Conico or Arrocillo amarillo. These produce small ears with vitreous kernels that are able to pop or revert. A second group of four distinctive races called “exotic precolombian” was probably introduced to Mexico from Central and/or South America: Cacahuaicintle, 8 rowed floury, oloton, and sweet corn. Cacahuacintle is characterized for producing large and floury kernels on a large ear. The cacahuacintle name derives from the Nahuatl cacahuacentli, meaning (centli) kernels that look alike cocoa beans (cacahuatl) (Table 1.2). Today in Latin America, there are recognized 220 races of corn, from which 64 races are associated to Mexico (Comisio´n Nacional para el Conocimiento y Uso de la Biodiversidad, 2011). Races of corn are a group of racial complexes which are associated to a defined climatic and geographic region. There are seven racial complexes defined as “Conicos,” “Sierra de Chihuahua,” “Ocho Hileras,” “Chapalote,” “Tropicales Precoces,” “Dentados Tropicales,” and “Maduracion

TABLE 1.2 Races of Corn in Mexico Indigenous or Ancient

Exotic or Pre-Columbian

Mestizas Prehistoric

Moderns Incipient

Not Defined

Palomero Toluquen˜o

Cacahuacintle

Co´nico

Chalquen˜o

Conejo

Arrocillo Amarillo

Harinoso de Ocho

Reventador

Celaya

Mushito

Chapalote

Oloto´n

Tabloncillo

Co´nico Norten˜o

Complejo Serrano de Jalisco

Nal-Tel

Maı´z Dulce

Tehua

Bolita

Zamorano Amarillo

Tepecintle

Blando de Sonora

Comiteco

Onaven˜o

Jala

Dulcillo del Noroeste

Zapalote Chico Zapalote Grande Pepitilla Olotillo Tuxpen˜o Vanden˜o Source: Wellhausen, E.J., Roberts, L.M., Herna´ndez, X.E., Mangelsdorf, P.C., 1951. Razas de maı´z en Mexico. Su origen, caracterı´sticas y distribucio´n. Oficina de Estudios Especiales-Secretarı´a de Agricultura y Ganaderı´a, Folleto tecnico No. 55, Mexico.

6 Corn

TABLE 1.3 Groups of Racial Complex of Corn Complex

Races

Conicos

Arrocillo, Cacahuacintle, Co´nico, Co´nico Norten˜o, Chalquen˜o, Dulce, Elotes Co´nicos, Mixteco, Mushito, Mushito de Michoaca´n, Negrito, Palomero de Jalisco, Palomero Toluquen˜o, and Uruapen˜o

Sierra de Chihuahua

Cristalino de Chihuahua, Gordo, Azul, Apachito, Complejo Serrano de Jalisco. Mountain Yellow

Ocho Hileras

Blando de Sonora, Onaven˜o, Harinoso de Ocho, Tabloncillo, Tabloncillo Perla, Bofo, Elotes Occidentales, Tablilla de Ocho, Jala, Zamorano Amarillo, Ancho, and Bolita

Chapalote

Chapalote, Reventador, Dulcillo del Noroeste, and Elotero de Sinaloa

Tropicales Precoces

Nal-Tel, Zapalote Chico, Conejo, and Rato´n

Dentados Tropicales

Tuxpen˜o, Vanden˜o, Tuxpen˜o Norten˜o, Tepecintle, Zapalote Grande y Celaya, Pepitilla, Nal-Tel, Choapaneco, Chiquito, and cubano amarillo

Maduracion tardia

Olotillo, Dzit-Bacal, Comiteco, Motozinteco, Tehua, Oloto´n, Coscomatepec, Dzit Bacal, Negro de Chimaltenango, Quichen˜o, and Serrano

Source: Comisio´n Nacional para el Conocimiento y Uso de la Biodiversidad, 2011. Recopilacio´n, generacio´n, actualizacio´n y ana´lisis de informacio´n acerca de la diversidad genetica de maı´ces y sus parientes silvestres en Mexico. CONABIO. Mexico. Available from: http://www.biodiversidad.gob.mx/genes/ proyectoMaices.html (23 September 2017).

tardia” or late maturing (Vielle-Calzada and Padilla, 2009; Comisio´n Nacional para el Conocimiento y Uso de la Biodiversidad, 2011; Sa´nchez, 2011). Each complex is represented by several local races distributed along Mexico and Latin America (Table 1.3). These races crossed with the ancient corn germplasm and produced the base of the races widely used to breed highyielding varieties and hybrids. In 1963, researchers at Purdue University stumbled across a naturally occurring corn mutant that contained about twice as much lysine and tryptophan than their regular counterparts (Mertz et al., 1964). The opaque-2 corn was rapidly transformed into varieties and planted throughout the world. Unfortunately, opaque-2 failed because of low yields and lack of resistance to pests. Researchers from International Maize and Wheat Improvement Center (CIMMYT) eventually developed improved forms, now named quality protein maize (QPM). Yellow and white QPM open-pollinated varieties and hybrids are being tested around the globe. In some countries such as South Africa, Brazil, China, Ghana, and Mexico, it is also being commercially grown. Corn was so important for the Mesoamerican cultures that they have named it differently: The mayans called it ixim, whereas the Aztecs denominated corn on the cob centli and kernels tlaolli. Tlaolli had many different varieties, distinguished by the color size and texture of the grains filling the cobs. White kernels were called iztactlolli, black (blue or purple) yahuitl, yellow xiuhtoctlulli, stained xuchicentlaulli, mixed colored cuappachcentlulli, and the early maturing tepitl (Serna-Saldivar, 2015). After the American continent was discovered, the corn crop eventually adapted to Spain and from there it was distributed to other parts of Europe. Corn was mainly planted on farmlands close to Portugal and soon disseminated to the neighboring country. During the middle of the XVI century, corn was established in Angola and it reached France, Italy, and Turkey until the middle of the XVIII century. From this last country, it rapidly spread to east Africa and all the way south to Madagascar. The Spaniards catalyzed the Asian connection because they traded goods from Acapulco, Mexico, to Manila, Philippines. This occurred as early as 1565, but corn became important in Asia after the XVII century (Serna-Saldivar, 2015). Today, corn is the most important cereal and productive crop in the world. The success is due to its adaptation to different ecosystems from coasts to mountains and the development of highly producing regular and biotechnological hybrids capable of yielding under commercial conditions up to 16 tons/Ha. Corn is a crop with a remarkable genetic variability; therefore, many specialty genotypes are available (see Chapter 10). The main specialty types are popcorn, waxy, high-amylose or amylomaize, sweet, blue, Cuzco, high-oil, and quality protein (QPM) (Hallauer, 2000).

GROWTH AND DEVELOPMENT Corn is classified based on the altitude and the environment in which it is grown into two main types: tropical corn and temperate corn. Tropical corn is grown in warmer conditions located between the equator and 30°N and 30°S, while

Corn History and Culture Chapter

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7

temperate corn is grown in cooler climates beyond 34°N and 34°S. An intermediate environment known as a subtropical considers corn grown between 30° and 34° latitudes (Dowswell et al., 1996). Normal corn plants grow and develop from a seed to a mature plant in a few months. Plant size, length of growth period, and yield potential vary importantly, depending on the production region. The corn plant is a tall leafy structure with a fibrous root system, supporting a single shoot with many leaves and one lateral branch terminated by a female inflorescence, which develops into an ear covered by husk leaves. In the upper part of the plant develops the male inflorescence known as tassel. Among commercial cereals, corn is the only one that has the male and female flowers separated. After pollination, the kernel or fruit, botanically named caryopsis, develops. The corn kernel consists of three major structures: pericarp, endosperm, and germ. The pericarp or fruit coat is a thin outer layer that protects the true seed consisting of germ and endosperm considered the first and second reserve tissues. The germ contains the embryonic axis and the scutellum, whereas the endosperm consists mainly of starch granules, which serves as the major energy source for the germination of the seed and small seedling and gluten proteins (Paliwal et al., 2000; Serna-Saldivar, 2010b). The structure, development, and description of these anatomical parts are described in Chapter 6.

Germination Under optimal conditions of temperature and humidity, corn seeds germinate between 6 and 15 days after planting. The real time varies significantly, depending on type, temperature, and moisture of the soil. The phytohormone gibberellin plays an important role in the physiology of germination because it promotes the synthesis of lipases, phytases, several cell wall degrading enzymes, endo and exoproteases, and a and b-amylases needed to generate the necessary energy and nutrients for germination (Serna-Saldivar, 2010b). The first structure to break through seed coat is the radicle, followed by the coleoptile (protective sheath covering the emerging shoot), and then the seminal roots. The growth and elongation of the coleoptile origin the plant that emerges from the soil. The elongation of the mesocotyl stops when the coleoptile reaches light, giving a place for splitting of the coleoptile tip and the emergence of first true leaf (Fig. 1.4).

Vegetative Development The vegetative development of the new plant continues with the growth of the seminal root system, which emanated from the seed, and continues with the nodal root system. The function of the seminal roots is primarily water absorption for the first weeks of life of the new plant. All nutrients that the young plant needs emanate from the endosperm, which stored food reserves during seed development. Additional nodal roots are developed and root system achieves its greatest depth at the Tassel floret Glume Anthers Tassel

Flag leaf

Silks Ear

Second leaf (V2 growth stage)

Leaf blade

First leaf

Leaf sheath Coleoptile Growing point Mesocotyl

Nodal roots Internode

Seminal roots Radicle FIG. 1.4 Corn seedling plant and mature corn plant. (Source: Based on Benson, G.O., Reetz, H.F., 1984. Corn Plant Growth-From Seed to Seedling. National Corn Handbook, Purdue Univ. Coop. Ext. Serv., West Lafayette, pp. 1–240.)

8 Corn

middle of the reproductive stage (approximately 3 months after emergence). Roots and new leaves develop from the apical meristem (growing point). As other organs in the plants, rooting depth varies greatly because of genotype and environment, but depths of 1–2 m are considered in a normal range (Benson and Reetz, 1984). All corn plants have the same development pattern. A corn develops in its lifetime close to 30 leaves, produces silk after around 2 months, and reaches physiological maturity after 3 months. Under optimal conditions and depending on the specific agroecology, a new leaf emerges every 3–4 days until the tassel emerges, indicating that the plant has achieved full height. Growth during the latter part of the vegetative stage shows very rapid leaf-area formation and reproductive development (Fig. 1.4). It is important to mention that the time between growth stages varies with plant maturity, planting date, location, and number of daylight hours or phytoperiod. (Ritchie and Hanway, 1997). A brief field guide for the identification of production problems in tropical and temperate corns throughout the vegetative development is presented by Lafitte (1994) and Troyer (2001), respectively.

Pollination and Kernel Development Corn is a monoecious plant, which means that staminate flowers are the tassel and the pistillate flowers are the ear shoots. This separation of male and female parts allows auto and cross pollination and is the key to the improvement of corn by maize breeders and geneticists. The emergence of the tassel from the whorl and of silks from the ear shoots indicates the beginning of the reproductive phase of the plant development. Anthers are in the individual stamens and at the anthesis time (period during which a flower is fully open and functional); anthers are expelled and the pollen escapes. The tassel is capable of producing between 2 and 5 million pollen grains per plant. In contrast, in the ear, each potential kernel (ovule) produces a fiber called a silk which is an elongation of the style, attached to an individual ovary. An ear may produce between 600 and 1000 silks. Pollen shed by tassels fall on these silks (Fig. 1.4). A single pollen grain germinates on each silk and produces a pollen tube that grows down the silk until the ovary is fertilized (Hoeft et al., 2000). Chapter 6 provides details of this process. The main function of the plant, after fertilization, is to develop the corn ears. Ear development or postsilking stages are identified as blister, milk, dough, dent, and physiological maturity. In general, it takes approximately up to 65 days to pass from silking to physiological maturity. Physiological maturity is reached when the kernels on the ear have reached maximum dry matter accumulation and an excellent visual indicator is known as a “black layer” or hilum (a dark closing layer develops between the basal endosperm and the vascular area in the pedicel) as well as the kernel “milk line” (a boundary between the solid and liquid phases of the maturing endosperm and visible on the side opposite to the germ). This line moves gradually from the crown to the tip of a kernel as maturity approaches. Milk line helps to estimate the time to maturity, whereas the black layer indicates strictly presence or absence of maturity (Farnham et al., 2003).

CULTURE AND MANAGEMENT Climatic Requirements Climate is fundamental in determining major production regions for corn cultivation. Although corn is grown over a wide range of agroclimatic conditions, specific weather factors greatly influence the production potential. In this sense, many management practices are determined by climate variability. Temperature and moisture are the key factors that determine if corn is adapted to a target area, but growing-season length and solar radiation are also limiting factors. Firstly, growing season is defined as the part of the year during which local weather conditions permit normal plant growth. Growing season varies over diverse areas of the world (from Northern hemisphere to tropical area, and southern hemisphere). In most regions of the world, the “rainy seasons” set limits to the length of the growing season. Secondly, temperature and moisture interact and influence directly the developmental aspects, and thus the physiological processes. For corn, Sanchez et al. (2014) defined temperature thresholds for the key physiological processes such as leaf initiation, shoot growth and root growth, and for the most susceptible phenological phases such as sowing to emergence, anthesis, and grain filling (Table 1.4). Corn responses to temperature in different ways to phenological phases and development stages. Temperature influences corn germination and emergence. For example, radicle and shoot elongation is better at about 30°C and almost nonexistent below 9°C and above 40°C. The influence of temperature for later vegetative stages is similar to that of early stages. The fastest rate of development is reached at temperatures of 21°C (daily minimum) and 32°C (daily maximum). However, during the reproductive stages, development is less temperature-sensitive compared to the vegetative stages. There is a curvilinear relationship between temperature (15–30°C) and the time from emergence to tassel initiation. Optimum temperatures to obtain maximum grain yields may not be optimum for accelerated

Corn History and Culture Chapter

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9

TABLE 1.4 Summary of Differential Temperatures for Relevant Processes and Development Phases in Corna n

Mean Temperature (°C) Processes

Tmin

Topt

Tmax

1.8  1.9

–

46.0  2.9

14

Developmental phases Lethal Leaf Initiation

7.3  3.0

31.1  1.7

41.3  1.9

24

Shoot growth

10.9  1.5

31.1  0.8

38.9  2.8

10

Root growth

12.6  1.5

26.3  1.8

40.1  3.6

11

10.0  2.2

29.3  2.5

40.2  2.1

7

Sowing to tassel initiation

9.3  2.7

28.3  3.8

39.2  0.6

27

Anthesis

7.7  0.5

30.5  2.5

37.3  1.3

10

Grain filling

8.0  2.0

26.4  2.1

36.0  1.4

11

Whole plant

6.2  1.1

30.8  1.6

42.0  3.3

29

Phenological phases Sowing to emergence

a

Temperatures: Tmin, base; Topt, optimum; Tmax, maximum; n, number of literature sources (modified from Sanchez et al. (2014)).

corn development. Maximum corn yields are related with maximum daytime temperatures (24–30°C) (Hoeft et al., 2000). Cool nights and sunny days with moderate temperatures are considered ideal. High-temperature stress during the pollination period can result in poor kernel establishment. The third factor is moisture, which is associated with soil water availability. Moisture accessibility to the corn plant contemplates the quantity of moisture in the soil, the soil texture, and the atmospheric demand for water. Atmospheric demand for water is a function of temperature, solar radiation, wind, and humidity of the air. The magnitude of plant stress depends on the relationship between soil moisture availability and atmospheric demand. In fact, stress occurs when evapotranspiration drops below potential transpiration. Based on that, the dimensions of yield loss vary depending on evapotranspiration, crop stage, and soil fertility. In most relevant corn-growing areas, a shortage of water, especially at critical stages of the growing cycle, is often a serious yield-limiting factor (Ribaut et al., 2009). The amount of moisture in the soil is also relevant. For example, optimal soils store more than 5 cm of plant-available moisture per 30 cm of soil depth, and during periods of peak demand, water use may exceed the amount of precipitation that is received. Water use by corn depends on crop stage and this period also coincides with flowering and pollination. Therefore, to reduce the potential stress, subsoil moisture reserves are crucial. However, excess of moisture also reduces corn yields where plants under flooding are damaged or killed; nevertheless, the main diminutions are due to saturated soil conditions (Farnham et al., 2003). Dowswell et al. (1996) describe the main corn-growing environments in more detail, indicating the mean, minimum, maximum, and optimal temperatures and moisture in a given season.

Soil Management Corn is grown in a multiple-cropping system. Such systems involve growing two or more crops on the same field in a year. Sequential cropping (growing one crop after another in the same year) and intercropping are types of multiple cropping and include numerous different systems. Sequential systems are most common where the growing season is long, and intercropping systems are most popular where labor is readily available and inexpensive. Various forms of multiple cropping include corn, especially in more tropical areas. Some of the more common crops grown in rotation with corn are oats, wheat, barley, soybean, sorghum, alfalfa, and numerous clovers and grasses (Farnham et al., 2003; Brummer, 2006). The greatest negative consequence of cropping systems involving mainly row crops is soil erosion. A term denominated soil-loss tolerance is defined as the maximum amount of soil erosion that will permit a high level of productivity to be sustained both indefinitely and economically. Then the excessive cultivation of soils that are row-cropped can create problems with soil structure. Techniques for conserving soil are numerous and include cover crops, strip cropping, contour strip cropping, wind breaks, grass waterways, terracing, choice of crops grown, and conservation tillage. It is important to

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understand that the main components of the soil environment include structure, texture, temperature, moisture, air, and nutrient availability and all of them need to be considered to maintain a proper soil structure (Carter, 1994). Rotations with forage legumes allow the equilibrium at a higher level of soil organic matter compared with nonleguminous row crops. Where corn yields are high and the crop residues are returned to the soil, the level of organic matter is also high. Cropping and tillage systems have major impacts on potential soil erosion. Less row cropping, delayed tillage, and greater crop residues on the soil surface all serve to reduce potential soil losses. Erosion can be reduced with the use of conservation tillage. Tillage includes benefits in terms of its soil-loosening, seedbed-preparation, and weed-control effects. The objective of a tillage system is to provide a good seedbed, help control weeds, and modify the soil environment to make it as favorable as possible for corn growth while minimizing soil erosion. There are two main types of tillage, conventional and conservation. Conventional tillage includes the most common and is based on a moldboard plow, chisel plow, disk plow, rotary tiller, or large disk harrow for primary tillage. Primary tillage generally would be followed by various operations involving the disk harrow, field cultivator, spring-tooth harrow, and spike-tooth harrow to further prepare the soil for planting (secondary tillage). In contrast, conservation tillage is related with any system that reduces loss of soil or water (Manning and Fenster, 1983). Such systems emphasize leaving varying amounts of crop residue on the soil surface. Conservation tillage has many forms, ranging from those in which only a small slit is opened in the soil ahead of the planter unit to full-width tillage that could even involve a modified moldboard plow. However, any definition of conservation tillage depends on what is considered to be conventional tillage for a given area (Carter, 1994). One of the major reasons conservation tillage methods are becoming so popular is that they allow increased intensity of row crop production, while keeping soil loss below established tolerance levels on soils where this would be impossible with conventional tillage methods. A recent review by Abdalla et al. (2013) showed that the adoption of conservation tillage practices reduced carbon dioxide emissions, while also contributed to increases in soil organic carbon and improvements in soil structure with a number of other advantages that justify its wider adoption.

Water and Nutrient Management Main crop management practices include proper irrigation and plant nutrition. The major factors affecting water availability is how much water the soil can store per unit of depth and to what depth the subsoil is favorable for water storage and root growth. It is important to remember that part of the rainfall is lost to runoff, drainage, and evaporation. Soil storage capability determines how much moisture can be in reserve to supplement crop-season rainfall. Strategies to decrease evaporation and runoff and to increase infiltration and storage capacity are desirable. In tillage systems, less water runs off. Excess water can be a problem with fine-textured soils to the extent that drainage becomes an important management input. Irrigation may also require certain drainage needs. Random systems are used to drain scattered wet spots, whereas regular systems feature uniformly spaced equipment to drain an entire area. Ditches are the main method of surface drainage, whereas tiles are the main method used in subsurface systems (Farnham et al., 2003). In term of essential nutrients for plant nutrition, it is necessary to recognize which ones are most likely to limit production. Essential elements are defined as those which plants acquire from the air and water like carbon (C), oxygen (O), and hydrogen (H). The other elements come from the soil. The six that are used in the greatest quantities are nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). These elements are referred to as macronutrients and are sometimes further subdivided into primary (N, P, and K) and secondary (Ca, Mg, and S). The nutrients iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), boron (B), molybdenum (Mo), and chlorine (CI) are required by plants in very small amounts and are called micronutrients, or sometimes trace or minor elements (Pingali, 2001). Nevertheless, soils vary in the availability of the various essential elements. A key practice is to identify which nutrients are needed and numerous laboratory soil tests exist, but correlation studies must be conducted to see how well the soil tests relate to actual nutrient availability to plants. Some tests for P, K, and lime requirements and bioavailability are quite good, but for most other nutrients, the reliability ranges from fair to poor (Hoeft et al., 2000). Plant analyses can also be useful in determining nutrient deficiencies; however, they are often not useful for correcting the problem in the year they are taken. The two most distinctive deficiency symptoms on corn are those for N and K. Severe N deficiency early in the growing season is typified by spindly pale green to yellow plants. As plants get larger, the lower leaves show a V-shaped yellowing from the leaf tips down the midrib, with the leaf margins remaining green the longest. This response is in contrast to K deficiency, in which yellowing and then dying of lower leaf margins occurs, leaving the midrib green. Fertilizer usage in the world has shown a tremendous increase since the green revolution. The principal factors affecting total commercial fertilizer use include cropland area, fertilizer price, commodity price and programs, soil characteristics, climate and weather conditions, and other practices such as crop rotation and nutrient applied technology. Nitrogen, P, K, and sometimes S are applied as fertilizers to the soil as manure and/or commercial fertilizers. Calcium and Mg are supplied

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Demand (millions tons)

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Nitrogen fertilizers (N total nutrients) Phosphate fertilizers (P205 total nutrients) Potash fertilizers (K20 total nutrients) Total

150

100

50

0 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Time (years) FIG. 1.5 Fertilizers consumption worldwide. (Source: Food and Agricultural Organization, 2018. FAOSTAT, FAO Statistical Databases. Available from: http://apps.fao.org/ (2 February 2018).)

as part of liming programs. Global fertilizer usage in 2018 is estimated to be more than 200 million tons, 25% higher than the amount recorded in 2008 (Fig. 1.5). Fertilizer use varies widely by geography, with sub-Saharan Africa posting robust demand for N and K. Asia as a whole is the largest consumer of fertilizer worldwide and relies on imports of all three major nutrients. Europe also offers a surplus of all three nutrients due to large positive balances in East Europe and Central Asia. Latin America and the Caribbean depend on imports of all three main nutrients. In 2018, it is predicted that Africa will demand 4.1 million tons, Europe 15.7 million tons, the Americas 23.5 million tons, and Asia 74.2 million tons (Food and Agricultural Organization, 2018).

Pest Management Under the concept of integrated pest management, pest control has the goal to achieve a crop production system in a way that optimizes the use of natural resources, protecting the environment and maximizing the output in a sustainable system. Control of pests assumes an important position, especially in developing countries where insect and disease pressures tend to be severe due to the subtropical and tropical climates found in these zones. Recently, pest control strategies emphasize the reduction and/or use of selective pesticides and include the use of natural, cultural, and biotechnological controls. Natural control involves the reduction of insect pest populations by the use of natural enemies, while cultural control consists of the deliberate alteration of the production system to reduce pest populations or avoid pest injury to crops. Conversely, biotechnology control includes the use of modified plants with a specific gene that imparts resistance against a particular pest, such as Bt genes, which controls the expression of the Bt toxin effective against lepidoptera (Garcı´a-Lara and Serna-Saldivar, 2016). In terms of chemical control, there are four types of chemical insecticides which protect against insect infestations: organophosphate, carbamates, organochlorine, and pyrethroid. Organophosphate and carbamate insecticides affect the insect nervous system by disrupting the enzyme that regulates acetylcholine, a neurotransmitter. These insecticides are not persistent in the environment. Parathyroids were developed as a synthetic version of the naturally occurring pesticide pyrethrin, which is found in chrysanthemums. Pyrethrin is the most popular botanical insecticide that acts by contact as a poison. Pyrethrins such as permetrin and bioresmetrin are popular insecticides due to its low toxicity to mammals and safe use. Pyrethrins are fast-acting insecticides and are particularly effective against adult insects. Insecticides have several advantages over fumigants: their effect is long lasting, they are easier to apply, are less dangerous, and can be applied both as preventive agents or to kill established insect populations (Garcı´a-Lara and Serna-Saldivar, 2016). There are other naturally occurring botanical insecticides which are available as an alternative to chemical control. More than 3500 compounds in approximately 400 plant families have been described to have toxic insect effects. Some botanical insecticides are not as efficient as synthetic ones, but they are similar in toxicity to humans. Citrus oils (limonene, linalool) which are extracted from citrus peels have been combined with soaps as contact poisons against aphids and mites. Nicotine derived from tobacco is a fast-acting contact killer for soft-bodied insects. Rotenone is derived from the roots of over 68 plant species. It is toxic to animals because direct contact may cause skin and mucous membrane irritation. It has a

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broad spectrum poison mainly used to control leaf-eating caterpillars and beetles. Neem (Azadirachta indica) extracts are derived from the tropical neem tree and are effective for the control of over 200 types of insects, mites, and nematodes. The solution is effective for only 8 h after mixing and has a low toxicity to mammals. Neem is most effective under humid conditions or when the insect and plants are damp. The use of beneficial insects, pheromones, and growth regulators has been studied as a possible alternative for biological insect control. Among the most promising biological control techniques are the use of predators and the release of sterile insects. Sterile insects treated with mutating agents can considerably lower grain infestations, especially when insects belong to the Lepidoptera order. The main disadvantage of the use of beneficial insects is that they leave behind body casts, exoskeletons, and other insect residues. Pheromones are chemical agents secreted by insects as sexual attractors. These chemicals are used to attract insects and predict populations. Pheromone traps are used to catch insects especially when the number of insects infesting is low, giving the opportunity to detect and control insect populations before they cause economic damage. The use of pheromones when insect populations are reduced also lowers their reproduction rate because these chemicals confuse insects. The use of growth agents and hormones that are essential for metamorphosis has potential in insect control programs, since these chemical compounds inhibit important physiological processes and have low toxicity for mammals (Garcı´a-Lara and Serna-Saldivar, 2016). Biotechnology has become a prominent player in pest management. Genetically engineered crops are capable of resisting insect and disease infestations as well as of exhibiting resistance to particular herbicides. Through the use of genetic engineering, scientists have been able to select a desirable gene from one species and insert it into another, resulting in a highly specific variety that expresses highly desirable attributes. There are several gene-insertion technologies, for example, a natural delivery system (Agrobacterium-mediated) or a physical delivery system (gene gun). Genetic engineering also has enabled the insertion of multiple resistance genes into corn hybrids, resulting in hybrids that may exhibit both herbicide and insect resistance. These types of hybrids are referred to as “stacked genes” hybrids and GE crops have generally had favorable economic outcomes for producers in early years of adoption, but enduring and widespread gains will depend on institutional support and access to profitable local and global markets, especially for resource-poor farmers (National Academies of Sciences, Engineering, and Medicine, 2016). The development and introduction of genetically engineered crops has proceeded under tremendous controversy. Specific concerns related to the use of these crops include human health (potential allergenicity introduced by the inserted gene), environment (damaging to nontarget organisms; development of resistant biotypes), and economic (added costs, which may not be recovered, to pay for the technology). In addition, international market acceptance of genetically engineered crops perhaps has been one of the greatest stumbling blocks to their widespread introduction and use. Today, genetically engineered crops continue growing in a sustainable way and several countries are using this technology. According to the annual report of International Service for the Acquisition of Agri-biotech Applications (2016), the percentage of adoption to genetically engineering corn hybrids in the world is 33% compared with the traditional ones (Fig. 1.6). Novel technologies are coming to enhance the adequate control and management of pest in corn and other crops. For example, the use of “gene editing” by the technology of CRISPR (clustered regularly interspaced short palindromic repeats)-associated RNA-guided endonuclease Cas9, which can be easily targeted to virtually any genomic location of choice by a short RNA guide (Hsu et al., 2014).

Storage Management The main purpose of grain storage is to equilibrate supply and demand and this postharvest operation is a key step in the complex logistics of moving grain from producers to processors and grain products from processors to consumers. Good storage practices are aimed to provide wholesome cereals, free of insect and mold damage, mycotoxins, pesticides, insect fragments, and rodent filth. The final target is to manage stored grain wisely with insignificant losses while maintaining its nutritional and functional qualities. Grains are preferably stored in weather- and pest-proof storage structures so that their viability, food energy, nutritional quality, and marketability can be assured. Grain elevators are centers where the grain is concentrated with the aim of preserving and improving the grain grade. Incoming lots of grains are, in most cases, sampled, analyzed (in order to assign class), graded (quality attributes), weighed, unloaded, cleaned, and stored. After sampling, most grain lots are inspected and graded by licensed inspectors or by experienced employees (Serna-Saldivar, 2010c). The main operation for storage management includes: grain analysis, weighing and unloading, dehydration, cleaning, rotation, and aeration. For analysis, the main grain quality factors are moisture, test weight, dockage, heat damage, insect damage, and mycotoxins. Grain shipments are usually weighed on platform scales and then dumped into underground bins via gravity. Grains are elevated or conveyed using screw conveyors or buckets. The aim of this operation is to lower the grain moisture content to levels adequate for storage to maintain grain viability and to keep minimum grain physical

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FIG. 1.6 Global adoption rate (%) for the principal biotechnological crops. (Source: International Service for the Acquisition of Agri-biotech Applications, 2016. Global Status of Commercialized Biotech/GM Crops: ISAAA Brief No. 52. ISAAA, Ithaca, pp. 1–12.)

185

180 160

Area (million ha)

140 120

117

100 80 60 36

35

40 20 0 Soybean 78%

Cotton 64%

Conventional

Corn 33%

Canola 24%

Biotechnological Crop

damage such as stress cracks. Artificial drying is the most common practice to lower moisture content of cereal grains. Regardless of the dehydration technique, the principal factors to regulate are air temperature, relative humidity, airflow, depth of the grain, and the desired rate of dehydration. The cleaning system typically consists of air aspirators and sifters equipped with magnets to trap metals. Air aspiration removes most of the light contaminants such as plant material, glumes, and empty kernels, whereas milling separators are designed to remove contaminants larger and smaller than the grain. Turning is the process of moving bulk stored grains with conveyors within the storage facilities. The operation is practiced in order to break hot spots in storage, facilitate insect control, and make more efficient the aeration or ventilation operation. And finally, aeration is considered as the least costly prevention measurement for the preservation of grains. The aim of this operation is to equalize stored grain temperature to prevent moisture migration, remove sour and off-odors caused by molding, and cool the grain to prevent or minimize heat spots and insect and mold growth. Most aeration systems consist of perforated air ducts positioned in various configurations on the floor before the facility is filled (Serna-Saldivar, 2010c; Serna-Saldivar and Garcia-Lara, 2016).

GENERAL USES In contrast to rice and wheat, corn is mostly utilized for animal feeding and bioethanol production (Fig. 1.7). According to the Food and Agricultural Organization in 2016, approximately 85% of maize was used for animal feeds (see Chapter 23) and bioethanol (see Chapter 22). Of the approximately 320 million metric tons produced in the USA during 2016, 45%, 42%, and 13% were used respectively for animal feed, bioethanol, and food/seed/industrial purposes. The main use of corn is as a foodstuff for both monogastric and ruminant animals and diverse aquatic species that provide eggs, milk, meat products, fish, and crustaceans. In many prepared diets, ground or processed corn (i.e., reconstituted, steam flaked, pelleted, extruded, micronized, and popped) constitutes up to 70% of the diet. Corn is also used for the preparation of pet food. Corn is the preferred feedstock because it is relatively cheap, palatable, readily digested, and widely available around the globe. Cereals are bio-transformed into animal products that possess an excellent protein quality and digestibility and provide some essential nutrients that are scarce in cereal-based food (i.e., calcium, iron, vitamin B12). Additionally, the minerals and vitamins associated to animal products are more bioavailable to the human system. Poultry and swine diets usually contain up to 70% of maize products, whereas feedlot rations up to 90%. The feed industry formulates feeds from whole corn and the wide array of coproducts obtained from the dry-milling (see Chapter 15), wetmilling (see Chapter 18), and brewing and bioethanol industries (see Chapter 22). The main use of corn is as a source of highly digestible energy, although some by-products are rich in fiber, fat, or protein. Corn alone is not capable of

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Corn Immature and sweet corn Grain storage

Popcorn

Dry-milling

Snacks and confectionary products

Grits, meals and flours

Wet-milling

Nixtamalization

Starches

Fresh and dry Masa flour Brewing adjuncts

Modified starches Syrups maltodextrins, glucose, maltose and HFCS

Bakery products

Batters and breadings

Breakfast cereals flakes, puffs, pellets,shredded

Snacks second and third generation (puffs, collets, pellets)

Table tortillas

Snacks corn and tortilla chips

Brewing adjuncts

Lager and Ale Beers

Alcoholic spirits

FIG. 1.7 General scheme of the main food uses of corn.

sustaining growth in most domestic animals, especially in the early stages of development, because of the lack of the protein quality required for optimum growth. The corn protein is not well-balanced in terms of essential amino acids; therefore, most feeds are supplemented with legume or oilseed proteins. The most widely used sources are soybean protein for monogastrics and canola, cottonseed, and other defatted meals for ruminants (Serna-Saldivar, 2008). Most feed corns are yellow, dent, and soft-textured. These kernels are easier to mill into flour and have higher rate of both protein and energy digestibility. As a result, corn is considered to have the highest energy value for all domestic animals. The high-lysine and tryptophan corns, named QPM, can reduce the usage of protein feedstuffs such as soybean meal. Many studies have been conducted comparing regular corn versus QPM. Results clearly show that QPM has higher nutritional value due to improved protein quality. Dry matter, energy, and protein digestibility are comparable, but nitrogen retention improves due to the higher levels of lysine and tryptophan. Thus, diets based on high-lysine cereals require less protein supplementation, which provides an economic incentive especially for poultry and swine farmers (Serna-Saldivar, 2008). The recent boom in the production of corn bioethanol has increased the availability of the main coproduct known as dry distilled grains (DDGS). In the USA, nearly 40 million tons of DDGS were produced in 2016 with an estimated market value of 4 billion dollars. Corn DDGS is considered as an excellent energy and protein source for beef and dairy cattle and an important feed ingredient for use in swine and poultry (layer, broiler, duck, and turkey) diets where it contains approximately 85% of the energy value of corn (US Grain Council, 2015a, b). Large quantities of corn are channeled to biorefineries for the production of fuel ethanol. In the USA, more than 130 million tons were bioconverted into 52 billion liters of anhydrous ethanol for production of E10 gasolines. There are three corn-based feedstocks used for ethanol: whole grain known as dry grind, modified dry grind or use, or dry-milled fractions/ refined starch. The most practiced is the dry grind. In this process, the grain is simply ground and then subjected to the three sequential steps: starch conversion into glucose, yeast fermentation, and distillation. The yield of one ton of yellow dent maize ranges from 380 to 400 L. In the modified dry grind process, the grain is dry-milled with the aim of removing the pericarp and germ and the resulting endosperm pieces further ground into a meal that is processed similarly as the whole

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ground maize of the dry grind process. The advantage of this process is higher yields (410–420 L/ton), the beforehand separation of shelf-stable bran and germ coproducts, and the recovery of lower amounts of spent grains with lower fiber content. The least common way to obtain fuel ethanol is by converting starch slurries obtained after conventional wet-milling. The main disadvantage of using starch slurries is that the wet-milling process demands important amounts of energy and more capital investments. The advantages are the recovery of the typical wet-milling coproducts and the high ethanol yield. Approximately 540 L ethanol is obtained from 1 ton starch (see Chapter 22). The main use of fuel ethanol is to oxygenate gasoline instead of the hazardous methyl terbutil ether (MTBE). Most ethanol programs start with the substitution of MTBE in the gasoline, so E7.5 gasoline is produced. Then fuels with higher levels of ethanol are produced (E10, E15, and E20). When ethanol substitutes more than 15% or 20% of the gasoline, the motors have to be adjusted especially modifying the carburetor. From the environmental viewpoint, the ethanol burns more cleanly because it produces less carbon monoxide, nitrogen oxides, sulfur oxides, suspended particles, and other contaminating hydrocarbons. Other important advantage of ethanol is that, when accidentally spilled, it does not affect as much the ecosystems because it decomposes in approximately 1 week. The postharvest management of corn destined for direct human consumption typically comprises three sequential stages before reaching the consumer: storage, milling, and food manufacturing (Fig. 1.8). In most instances, corn is stored for different periods of time because it is usually harvested in specific periods of the year or, when imported, are usually acquired in large quantities. The storage practices of corn are aimed towards prevention of both intrinsic and extrinsic deterioration, which are costly due to dry matter losses and loss of quality as raw material for further processing. Corn is mainly channeled to three distinctive milling industries: dry and wet-milling and dry masa flour (see Chapters 15, 17, and 18 respectively). Most maize dry-milling processes consist of degerming kernels with the aim of obtaining an array of refined grits with different sizes, meals, and flours free of pericarp and tip cap tissues. These dry-milled fractions are widely used as raw materials for production of breakfast cereals, snacks, brewing adjuncts, bakery products, and as important ingredients for batters and breadings (see Chapter 16). Wet-milling is aimed towards the production of refined or prime corn starch (refer to Chapter 18) and generates important coproducts such as germ, bran, and corn gluten meal. The germ is usually channeled to the oil-crushing industries for the extraction of refined corn oil (see Chapter 21), whereas the other coproducts are widely used as animal feeds. Starch is the raw material for further production of sweeteners and modified starches (see Chapters 19 and 20). Most of the starch is enzymatically converted into maltodextrins, maltose, glucose, and high-fructose syrups. The production and utilization of these syrups have increased during the past decades because the soft drink industries prefer to use sweeteners instead of crystallized sugar. The milling of corn into fresh masa and shelf-stable dry masa flour is gaining popularity worldwide because this process yields tortillas and fried snacks such as corn chips and tortilla chips widely consumed all over the world (see Chapter 17). Three major products are industrially produced from lime-cooked corn: table tortillas, corn chips, and tortilla chips. Corn and tortilla chips are primarily produced and consumed in developed countries, where they have an important share within

Corn (1017 million tons)

Grain Storage

Seed (6.8 million tons)

Direct food uses (156 million tons)

Foods 125 million tons

Coproducts 31 million tons

FIG. 1.8 Postharvest losses and corn utilization in year 2013.

Animal feed (546 million tons)

Storage losses (40.7 million tons)

Bioethanol and other industrial products (189 million tons)

Coproducts 40 million tons

Industrial products 100 million tons

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the salted snack food market, whereas table tortillas constitute the staple food for large groups of people in Mexico and other Latin American countries. These products can be produced using fresh masa or industrially manufactured dry masa flour. The use of dry masa flour is rapidly growing because of its convenience (Serna-Saldivar, 2008, 2015). Specialty corns have been selected due to their unique properties (Table 1.5), the most important being popcorn, sweet, high-amylose, waxy, blue, and quality protein (see Chapter 10, Hallauer, 2000). Popcorn has been a favorite traditional snack worldwide for more than a century, whereas sweet corn is one of the most popular canned or frozen vegetables in the USA and Canada (Serna-Saldivar, 2008). Large quantities of waxy maize, which contains more than 95% amylopectin, are channeled to the wet-milling industry with the aim of obtaining starch with unique properties and functionality. As mentioned before, QPM contains almost twice as much lysine and tryptophan than regular counterparts. Thus, QPM-based food can upgrade the nutritional status of infants who consume cereals daily in marginal areas around the world. The future of QPM looks promising because of its upgraded nutritional value and the recent development of

TABLE 1.5 Major Uses and Properties of Regular and Specialty Corns Type of Corn

Uses

Yellow and White

Yellow dent corn is the most popular worldwide and is used for animal feed, starch production, and bioethanol. White corn is popular in several regions of the globe like Mexico. It is used for tortillas and production of traditional food. The Food-Grade yellow and white genotypes were developed for lime-cooking and dry milling

Popcorn

Special kind of flint corn. Yellow or white hybrids were bred to contain high proportions of translucent, flinty, or vitreous endosperm and give high expansion rates when popped. Most commercial popcorn has a 30- to 40-fold expansion. The pericarp and outer layers of the kernel participate directly in the popping action by serving as a pressure vessel enclosing the endosperm

Blue

Blue corn is a floury or soft endosperm type that generally grows in long ears (8–12 rows) in highlands. The aleurone layer contains anthocyanins that impart the blue appearance. Blue corn is especially prized as ceremonial maize by the North American Indian tribes and is currently being used to produce organic flours and food such as table tortillas and fried tortilla chips

Sweet

Sweet corn have recessive genes (sugary 1 or su1, sugary 2 or su2) that cause an alteration in the endosperm that results in higher levels of soluble sugars and reduced levels of starch in the kernel. Sweet corn hybrids have been developed specifically to produce corn with desirable color, sweetness, and tenderness for on the cob consumption or frozen or canned

Waxy

Waxy starch is composed of more than 95% amylopectin. It is utilized mainly by the wet-milling industry. Waxy starch has a higher hot viscosity and produce softer, more stable and clearer gels due to its lower retrogradation. It also has higher freeze-thaw stability

High-amylose maize

Also named amylomaize that expresses high quantities of linear amylose due to recessive ae gene. Amylomaize contain amylose from 37 to 65% and has potential for the paper, textile and adhesive industries, produces rigid opaque gels with potential for the confectionery industry and for production of biodegradable packaging materials that resemble polystyrene foam

Cuzco/Cacahuacintle

The Cuzco corn comes from 8-rowed ears that produce the largest known kernels. Cuzco corn grows at high altitudes and produces white kernels with soft endosperm texture and bland flavor. Cuzco corn is mainly used to manufacture Cornnuts™ and Cacahuacintle kernels for hominy and pozole production

Quality protein maize (QPM)

QPM has the opaque-2 gene that contains twice as much lysine and tryptophan compared to regular counterparts, and therefore, has better protein quality. Harder QPM corns are suited for dry-milling and alkaline cooking, while soft hybrids for use in wet-milling to produce sweeteners, starches, and alcohol would be desirable since the coproducts would be more valuable

High-oil corn (HOC)

Improved high-oil corn (HOC) genotypes contain more than 6% oil. HOC types have been bred for temperate, subtropical, and tropical environments using conventional recurrent selection. HOC hybrids contain more protein, lysine, fat, and metabolizable energy than normal corn. The main potential of Hoc is for animal feeding, especially monogastrics and probably for oil-crushing industry

Baby corn

Special maize varieties are grown and shucked immediately after pollination when the ears are 1–2 in. long. These small ears are used as pickles and other tasty snacks in salad bars. Most of the baby corn used is produced in Thailand and exported to Europe and North America

Source: Hallauer, A.R., 2000. Specialty Corns. CRC Press, Boca Raton, pp. 1–496. Lambert, R.J., 2000. High oil corn hybrids. In: Hallauer, A.R. (Ed.), Specialty Corns. CRC Press Inc., Boca Raton, pp. 123–145. Serna-Saldivar, S.O., 2010a. Physical properties, grading and specialty grains. In: Cereal Grains: Properties, Processing and Nutritional Attributes. CRC Press, Boca Raton, pp. 43–81.

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high-yielding varieties and hybrids that produce kernels with different physical properties. Blue maize has a pigmented aleurone that imparts an intense blue color and unique flavor. It has been traditionally dry-milled for production of flours or meals and also used for tortillas and chips. It has high levels of anthocyanins and other phenolics with proven nutraceutical properties (see Chapter 14).

CONCLUSIONS Undoubtedly, corn is the most relevant cereal crop in terms of annual production with yearly productions exceeding 1 billion tons. The great success of the crop is due to its wide adaptation to different ecosystems, the development of high-producing open-pollinated varieties and hybrids which include traditional and genetically modified maize, the great response to fertilization, and its high nutritional value especially in terms of digestible energy contribution to both humans and domestic animals. Corn evolved from wild teosinte about 10,000 years ago in Mesoamerica and was greatly responsible for the initiation of formal agriculture in Mesoamerica and the rapid growth of ancient cultures. We inherited from these native Mesoamerican cultures primitive corn races, including specialty types such as popcorn, sweet, pigmented, high oil, and quality protein, which constitute the genetic background for the production of high-yielding varieties and hybrids. From the utilization viewpoint, corn is mainly used by the feed, food, or biofuel industries. Corn utilized for production of both monogastric and ruminant feedstocks provides eggs, poultry and pork meats, beef, milk, and even fish and crustaceans. In terms of direct food use, corn is generally consumed on the cob or mature kernels channeled to the dry, wet, or nixtamalization milling industries that generate intermediate products that are further transformed into breakfast cereals, snacks, tortillas, bakery items, different syrups and sweeteners, beer, and potable alcoholic beverages. During the past decade, corn has gained relevance as industrial raw material for production of biofuels, particularly bioethanol. The future of corn looks bright because this C4 crop is one of the most versatile and high producing with very important nutritional and economic implications because it is the main staple for many people around the globe, constitutes the base for production of much needed animal products, and is gaining importance for production of value-added industrial products including renewable biofuels. The main constrains of corn are the climate changes, the need for more diverse biotechnological varieties, and novel strategies to face the relatively high losses still experienced during storage especially in developing countries and its high susceptibility to contamination with toxicogenic molds.

REFERENCES Abdalla, M., Osborne, B., Lanigan, G., Forristal, D., Williams, M., Smith, P., Jones, M.B., 2013. Conservation tillage systems: a review of its consequences for greenhouse gas emissions. Soil Use Manage. 29, 199–209. Benson, G.O., Reetz, H.F., 1984. Corn Plant Growth-From Seed to Seedling. National Corn Handbook, Purdue Univ. Coop. Ext. Serv, West Lafayette, pp. 1–240. Brummer, E.C., 2006. Breeding for cropping systems. In: Lamkey, K.R., Lee, M. (Eds.), Plant Breeding: The Arnel R. Hallauer International Symposium. Oxford, Blackwell Publishing, pp. 97–106. Carter, M.R., 1994. A review of conservation tillage strategies for humid temperate regions. Soil Tillage Res. 31 (4), 289–301. Comisio´n Nacional para el Conocimiento y Uso de la Biodiversidad, 2011. Recopilacio´n, generacio´n, actualizacio´n y ana´lisis de informacio´n acerca de la diversidad genetica de maı´ces y sus parientes silvestres en Mexico. CONABIO, Mexico. Available from: http://www.biodiversidad.gob.mx/genes/ proyectoMaices.html. (23 September 2017). Cuevas-Sa´nchez, J.A., 2011. Evolucio´n natural y antropogenica de Zea spp en Mesoamerica. Rev. Archaeobios 1 (5), 1–43. Dowswell, D.D., Paliwal, R.L., Camtrell, R.P., 1996. Maize in the Third World. Westview Press, Boulder, pp. 1–268. Farnham, D.E., Benson, G.O., Pearce, R.B., 2003. Corn perspective, culture. In: White, P.J., Johnson, L.A. (Eds.), Corn Chemistry and Technology. In: Vol. 2. American Association of Cereal Chemists Inc, St. Paul, pp. 1–33. Food and Agricultural Organization, 2018. FAOSTAT, FAO Statistical Databases. Available from: http://apps.fao.org/. (2 February 2018). Galinat, W.C., 1988. The origin of corn. In: Sprague, G.F., Dudley, J.W. (Eds.), Corn and Corn Improvement. American Society of Agronomy, Madison, pp. 1–31. Garcı´a-Lara, S., Serna-Saldivar, S.O., 2016. Insect pests. In: Caballero, B., Finglas, P., Toldra´, F. (Eds.), The Encyclopedia of Food and Health. Oxford, Academic Press, pp. 432–436. Hallauer, A.R., 2000. Specialty Corns. CRC Press, Boca Raton, pp. 1–496. Hoeft, R.G., Nafziger, E.D., Johnson, R.R., Aldrich, S.R., 2000. Corn as a crop. In: Modern Corn and Soybean Production. MCSP Publications, Champaign, pp. 1–28. Hsu, P.D., Lander, E.S., Zhang, F., 2014. Review: development and applications of CRISPR-Cas9 for genome engineering. Cell 157 (6), 1262–1278. International Service for the Acquisition of Agri-biotech Applications, 2016. Global Status of Commercialized Biotech/GM Crops: ISAAA brief No. 52. ISAAA, Ithaca, pp. 1–12. Lafitte, H.R., 1994. Identifying Production Problems in Tropical Maize: A Field Guide. CIMMYT, Mexico, pp. 1–48.

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Mangelsdorf, P.C., 1986. The origin of corn. Sci. Am. 22, 72–78. Manning, J.V., Fenster, C.R., 1983. What is conservation tillage? J. Soil Water Conserv. 38, 141–143. Mertz, E.T., Bates, L.S., Nelson, O.E., 1964. Mutant gene that changes the protein composition and increases the lysine content of maize endosperm. Science 145, 279–280. National Academies of Sciences, Engineering, and Medicine, 2016. Genetically Engineered Crops: Experiences and Prospects. The National Academies Press, Washington, pp. 1–606. Paliwal, R.L., Granados, G., Lafitte, H.R., Violic, A.D., Marathree, J.P., 2000. Tropical Maize: Improvement and Production. FAO, Rome, pp. 1–363. Paulis, J.W., Wall, J.S., 1977. Comparison of the protein compositions of selected corns and their wild relatives, teosintle and tripsacum. J. Agric. Food Chem. 25 (2), 265–270. Pingali, P.L., 2001. Meeting world maize needs: technological opportunities and priorities for the public sector. In: CIMMYT 1999/2000 World Maize Facts and Trends. CIMMYT, Mexico, pp. 1–60. Ribaut, J.M., Betran, J., Monneveux, P., Setter, T., 2009. Drought tolerance in maize. In: Bennetzen, J., Hare, S. (Eds.), Handbook of Maize: Its Biology. Springer, New York, pp. 311–344. Ritchie, S.W., Hanway, J.J., 1997. How a Corn Plant Develops. Spec. Rep. Iowa Coop. Ext. Serv, Ames. Sanchez, B., Rasmussen, A., Porter, J.R., 2014. Temperatures and the growth and development of maize and rice: a review. Global Change Biol. 20, 408–417. Sa´nchez, G.J.J., 2011. Diversidad del maı´z y teocintle. CONABIO, Mexico, DF. Available from: http://www.biodiversidad.gob.mx/genes/pdf/proyecto/ Anexo9_Analisis_Especialistas/Jesus_Sanchez_2011.pdf. (28 September 2017). Serna-Saldivar, S.O., 2008. Snacks from alkaline cooked maize products. In: Industrial Manufacture of Snack Foods. Kennedys Publications Ltd, London, pp. 183–234. Serna-Saldivar, S.O., 2010a. Physical properties, grading and specialty grains. In: Cereal Grains: Properties, Processing and Nutritional Attributes. CRC Press, Boca Raton, pp. 43–81. Serna-Saldivar, S.O., 2010b. Grain development, morphology and structure. In: Cereal Grains: Properties, Processing and Nutritional Attributes. CRC Press, Boca Raton, pp. 109–128. Serna-Saldivar, S.O., 2010c. Storage of cereal grains. In: Cereal Grains: Properties, Processing and Nutritional Attributes. CRC Press, Boca Raton, pp. 129–148. Serna-Saldivar, S.O., 2015. History of corn and wheat tortillas. In: Rooney, L.W., Serna Saldivar, S.O. (Eds.), Tortillas: Wheat Flour and Corn Products. American Association of Cereal Chemists, St. Paul, pp. 1–28. Serna-Saldivar, S.O., Garcia-Lara, S., 2016. Storage. In: Caballero, B., Finglas, P., Toldra´, F. (Eds.), The Encyclopedia of Food and Health. Academic Press, Oxford, pp. 716–721. Troyer, F., 2001. Temperate corn: background, behavior, and breeding. In: Hallauer, A.R. (Ed.), Specialty Corns, second ed. CRC Press Taylor & Francis Group, Boca Raton, pp. 393–446. US Grain Council, 2015a. A Guide to Distiller’s Dried Grains With Solubles (DDGS). US Grain Council. Available from: http://www.ethanolrfa.org/ wp-content/uploads/2015/11/2012_DDGS_Handbook-1.pdf. (28 September 2017). US Grain Council, 2015b. Annual Report. US Grain Council. Available from: http://www.grains.org. (28 September 2017). Vielle-Calzada, J.P., Padilla, J., 2009. The Mexican landraces: description, classification and diversity. In: Bennetzen, J., Hare, S. (Eds.), Handbook of Maize: Its Biology. Springer, New York, pp. 543–561. Wellhausen, E.J., Roberts, L.M., Herna´ndez, X.E., Mangelsdorf, P.C., 1951. Razas de maı´z en Mexico. Su origen, caracterı´sticas y distribucio´n. Oficina de Estudios Especiales-Secretarı´a de Agricultura y Ganaderı´a, Folleto tecnico No. 55, Mexico. Wilkes, H.G., 1972. Maize and its wild relatives. Science 177, 1071–1077.

FURTHER READING Lambert, R.J., 2000. High oil corn hybrids. In: Hallauer, A.R. (Ed.), Specialty Corns. CRC Press Inc., Boca Raton, pp. 123–145. Serna Saldivar, S.O., Rooney, L.W., 2015. Industrial production of maize tortillas and snacks. In: Rooney, L.W., Serna Saldivar, S.O. (Eds.), Tortillas: Wheat Flour and Corn Products. American Association of Cereal Chemists, St. Paul, pp. 247–272.

Chapter 2

Breeding, Genetics and Seed Corn Production L.L. Darrah*,†, M.D. McMullen*,† and M.S. Zuber†,a *Plant Genetics Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Geneva, NY, United States, † Department of Agronomy, University of Missouri, Columbia, MO, United States

INTRODUCTION Reproduction of the Corn Plant Corn (Zea mays L.) has a monoecious flowering habit. The male and female flowers are separate, but on the same plant. The staminate (male) flowers are borne in the tassel, and the pistillate (female) flowers are borne on the ears. Corn is predominantly cross-pollinated; pollen from any tassel can randomly pollinate the silks on the ears of adjacent plants or even its own silks. The average corn tassel produces 25 million pollen grains (modern hybrids have close to 750,000 to 1 million because of smaller tassels), and most ears have 500–1200 kernels. If an ear had 1000 kernels, about 25,000 pollen grains would be available for each kernel. Cells of a typical corn plant have nuclei with 20 chromosomes. Ten of these are derived from the egg cell (premature kernel) and 10 from the sperm nucleus (pollen grain) that fertilizes the egg. In the tassel, each spore mother cell (microsporocyte) divides once reductionally and once equationally (meiosis), forming four spores, with 10 chromosomes each. Each spore’s nucleus divides equationally (mitosis), forming a vegetative (tube) nucleus and a generative nucleus. The latter again divides equationally to form two sperm cells, so that a mature pollen grain has three haploid nuclei with 10 chromosomes each. Stepwise development of the male gamete is shown in Fig. 2.1. In the pistillate inflorescence (ear), a single spore mother cell (megasporocyte) of each functioning flower goes through meiosis and forms four spores, with each nucleus having 10 chromosomes. Three of these spores abort. The remaining spore undergoes three mitotic divisions to give an eight-nucleate embryo sac. The nuclei are separated into four at each end (steps 1–11 in Fig. 2.2). Next, the eight nuclei become organized in the embryo sac with three nuclei at each end and two in the center. These latter two polar nuclei fuse and are fertilized to eventually become the endosperm (step 13 in Fig. 2.2). One of the three nuclei at the basal end of the embryo sac enlarges and becomes the egg cell. The mature embryo sac, when ready for fertilization, contains a one-nucleate egg and two fused polar nuclei. The fertilized egg nucleus becomes the diploid zygote, and the fertilized polar nuclei become the triploid endosperm nucleus (step 14 in Fig. 2.2). Pollination occurs when silks protruding from the ear shoot intercept pollen grains from the tassel. Pollen grains germinate on the silk and send out a tube that grows down the center of an individual silk, from which it finally enters the embryo sac, ruptures, and releases two sperms, each carrying 10 chromosomes. The nucleus of one sperm fuses with the egg to form the zygote, which has 20 chromosomes. This number persists in the somatic cells of the plant, and the nucleus of all new cells that appear during growth has the 2n number of 20 chromosomes. The other sperm fuses with one of the two polar nuclei, which then fuses with the other polar nucleus, forming a primary endosperm nucleus with 30 chromosomes. This phenomenon is referred to as double fertilization (step 14 in Fig. 2.2).

Kernel Structure The corn seed is a single fruit called the kernel (see Chapter 6). It includes an embryo, endosperm, aleurone, and pericarp (Fig. 2.3; Kiesselbach, 1949). The pericarp (seed coat) is the transformed ovary wall, which covers the kernel and furnishes a. Deceased. Corn. https://doi.org/10.1016/B978-0-12-811971-6.00002-4 Copyright © 2019 AACCI. Published by Elsevier Inc. in cooperation with AACC International. All rights reserved.

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Pollen sac

Anther

Anther cross-section

Pollen mother cell Microspore dyad

Microspore mother cell

Microspore dyad

Microsporangium with tetrad

Microsporangium

MEIOSIS Pollen Stigma Sperms Tube nucleus Pollen grain Pollen grain FIG. 2.1 The development of the male gametophyte of higher plants. (Reprinted, with permission, from Kiesselbach, T.A., 1949. The structure and reproduction of corn. Nebraska Agric. Exp. Stn. Res. Bull. 161.)

protection for the interior parts. The pericarp is maternal tissue. Hence, it has no genetic contribution from the pollen grain that fertilized the ovule, but has a genotype identical to that of the plant on which the seed was borne. Pericarp thickness ranges from 25 to 140 mm among genotypes. The dry weight of the pericarp is usually 4,000,000 kg of hybrid seed produced (Table 2.3), representing about 16% of all hybrid seed used by U.S. corn producers. Other parental sources for inbred line development include the F2 of single crosses between (e.g., B73
Mo17) and within (e.g., B14A
B73) heterotic groups, three-way crosses, double crosses, open-pollinated cultivars, exotic
adapted crosses, adapted exotic cultivars (e.g., tropical germ plasm selected for earlier maturity), and synthetic or composite populations.

Evaluation of Experimental Material One of the most important tasks corn breeders have is to evaluate newly developed experimental materials. The difficulty in this task is to separate genetic and environmental effects. The usual procedure is to evaluate the material in performance trials conducted over 2 or 3 years at a minimum of six locations. More locations are preferred, but the number is determined by the resources available. Testing sites should be located in areas where the newly developed material is likely to be marketed or where traits of interest can be thoroughly evaluated.

Selection Trials Most breeders use a screening trial to eliminate genotypes that are obviously poor. Usually, large numbers of many genotypes are observed at a few locations. Sometimes inoculations with prevalent leaf diseases and stalk rot pathogens are included. Sprague (1952) reported that combining ability (yield) is determined early in the inbreeding process. For elite

TABLE 2.3 Public Inbred Line Usage in >4,000,000 kg of Hybrid Seed Corn Produced in 1984a Inbred Line

Pedigreeb

1984 Usage in Hybrid Production

Percent of Total Requirementc

B73

Iowa Stiff Stalk Synthetic C5

57,374,120

11.26

A632

[(Mt42
B14)B14(3)]

9,666,702

1.90

W117

643
Minnesota No. 13

7,724,373

1.52

Mo17

CI 187–2
C103

7,718,298

1.51

CM174

V3
B14(2)

6,801,817

1.33

CM105

V3
B14(2)

4,501,228

0.88

a

Adapted from Darrah and Zuber (1986), used by permission. Gerdes et al. (1993). c Based on an estimated corn hectarage of 33,677,500 in 1985. b

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pedigree improvement programs, most breeders screen S1 families visually, eliminate poor genotypes if they have the opportunity based on performance predictions and visual observations, and proceed with early-generation testing programs. A breeder’s ability to utilize performance prediction tools that encompass information on all types of trait attributes, in combination with his/her ability to integrate what has been learned from visual observations and his/her overall understanding of the germ plasm, is fundamental and necessary for success.

Experimental Hybrids Newly developed hybrids are usually placed in screening trials conducted at four to six locations. The elite performers are tested further at a larger number of locations over several years. Performance testing over a number of environments is likely to identify the weaknesses of a new hybrid. Those hybrids that survive rigorous testing are usually grown in larger strip tests for evaluation by farmers. Superior, selected hybrids enter pilot seed production and may be entered in state variety trials before being placed into large-scale production.

State Hybrid Performance Trials Almost every state in the United States where corn is grown conducts performance trials. The objective is to provide farmers, seed producers, and the extension staff with an unbiased estimate of a hybrid’s genetic potential for yield and other agronomic characteristics. Most states charge a “per entry” fee to cover expenses of conducting the trial and publishing the data. A company usually enters a hybrid after it has survived rigorous screening and is being considered for commercial release. Most states also include the most widely grown hybrids in the trials to provide comparative information on popular hybrids for which seed is available. Oftentimes, seed production of the newer hybrids is ramped up over 2–3 years; as performance is proven, availability is increased.

KERNEL MODIFICATION THROUGH BREEDING Single-Mutant Endosperm Genes Corn kernels can be altered by genetic means to give modifications in quantity and type of starch, protein, oil, and other aspects such as pericarp thickness or kernel hardness. During the last four decades, much interest has been generated in specific types of corn that are used by corn processors for specialty products.

Starch Modification Most of the alleles affecting endosperm composition are recessive. One exception is the floury allele Fl, which is partially dominant. Starch from normal dent or flint corn is composed of 73% amylopectin (the starch fraction with branched molecules) and 27% amylose (the fraction with mostly linear molecules). Waxy corn (having the wx allele) was introduced from China into the United States in 1908 (Alexander, 1988), but waxy mutations have also been found in American dent strains. Starch from this mutant is 100% amylopectin. Waxy corn is easy to identify. Its starch and its pollen grains stain a reddish brown when subjected to a dilute iodine-potassium iodide solution, whereas the starch and pollen grains from normal dent corn stain blue, the color difference being caused by differences in the way the iodine binds to the starch containing some amylose (normal corn) vs. all amylopectin (wx). Yields of the first waxy hybrids were somewhat less than those for their normal dent counterparts, but the newer waxy hybrids are comparable to the better dents. The endosperm mutant amylose-extender (ae), which increased the amylose fraction of the starch to 50% and above, was found by R.P. Bear in 1950 (Vineyard et al., 1958). The kernel of this corn is characterized by a tarnished, translucent, and partially full appearance. The ae allele, plus modifiers, gives a range in apparent amylose content of 50–80%, but the amylose content can be stabilized at various intermediate levels. For example, in class-V high-amylose corn, the apparent amylose content is 50%–60% and in class VII, it is 70%–80% (Fergason, 2001). Several other mutant alleles, either alone or in combination, affect starch composition by changing the amyloseamylopectin ratio (i.e., the ratio of mainly straight- vs. branched-chain molecules) and other fine structural characteristics. Among these are dull (du) and sugary-2 (su2). Both of these alleles have been studied in combination with wx and ae (Alexander and Creech, 1977), but commercial usage of these allelic combinations has not developed. Both waxy and high-amylose hybrids are grown under contract for corn wet milling. Since both genes are recessive, the fields in which they are produced must be isolated from normal dent corn. Limited acreages of waxy corn also are grown as feed for cattle and other livestock. Discussion of the products made from waxy and high-amylose corn starches is covered in Chapter 19.

Breeding, Genetics and Seed Corn Production Chapter

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Protein Modification Several endosperm mutants that alter the balance of amino acids have been identified. The most important of these is opaque-2 (o2). Mertz et al. (1964) reported that o2 reduced zein in the endosperm and increased lysine. Other mutant alleles with similar effects are floury-2 (fl2) and opaque-7 (o7). Kernels with the o2 gene are characterized by a soft, chalky, nontransparent appearance, with very little hard vitreous or horny endosperm. This type of kernel is more prone to damage by kernel rots, insects, rodents, and harvesting machinery. Much improvement has been made in increasing resistance to ear and kernel rots by selecting for more vitreous o2 types, with the work done mainly in the CIMMYT Maize Program (CIMMYT, 1982; Vasal, 2001). The improved, harder endosperm selections are known as quality protein maize (QPM). However, lysine levels tend to decrease, so selection for vitreous kernels must be accompanied by chemical endosperm analysis to retain high levels of lysine. Yields of the first o2 hybrids were 85%–90% of those of the normal dents. However, through selection, the yields of modified o2 CIMMYT material have been improved to about 98% of normal when compared over several years and test locations (Vasal, 2001). Germ plasm released from CIMMYT has included improved open-pollinated varieties and inbred lines used in hybrids. Several countries and seed companies offer QPM hybrids: China, Ghana, Mexico, South Africa, and the United States (primarily Crow’s Hybrid Corn Company, Kentland, IN). Others offer only QPM open-pollinated varieties. High-lysine corn can be an important source of balanced protein in the diets of nonruminants. Several nutritional studies have shown the potential value of high-lysine corn in helping meet human food needs in the less-developed countries. In the United States, the use of high-lysine corn has been restricted because it yields less than normal dent corn and because a nutritionally balanced protein from corn is not needed when soybean (Glycine max (L.) Merr.) meal is economical and readily available. The trade-off in production of high-lysine corn is that calories per hectare are lost in exchange for a gain in higher-quality protein.

Altering Kernel Composition and Integrity by Selection Oil The oil content of hybrids from the U.S. Corn Belt ranges from 3.1% to 5.7%, with an average of about 4.3% (dry-weight basis; Watson, 1987). The long-time Illinois bidirectional selection experiment (Dudley et al., 1974; Dudley and Lambert, 1992) showed that oil content can go from 6% oil content) were lower yielding than hybrids with 1700 (Sharopova et al., 2002) with >2000 expected by the end of 2001. This advancement will provide corn with a more detailed SSR resource than for any other crop plant. Aligned genetic maps showing the position of 1200 SSR markers are available from MaizeDB. SSR markers generally have replaced RFLPs as the method of choice for phenotypic mutant and QTL mapping for corn and for establishing relatedness among corn lines and populations (Senior et al., 1998; Bernardo et al., 2000).

Single-Nucleotide Polymorphism Markers Single-nucleotide polymorphisms (SNP, pronounced “snips”) are the most common genetic polymorphisms available for use as genetic markers. Estimates have been made that a SNP occurs, on average, every 70 nucleotides in the 30 regions of corn genes (Rafalski, 2002). Single-nucleotide polymorphism discovery and mapping projects have been initiated in several public and private corn laboratories. Single-nucleotide polymorphism markers are expected to become the standard approach for high-throughput applications because of the highly parallel-process genotyping methods (Cho et al., 1999; Fan et al., 2000; Pastinen et al., 2000).

Genetic Maps for Corn Research Classical and Cytological Maps for Corn The first genetic map for corn was published in 1935 (Emerson et al., 1935). This map consisted of 62 loci of visual phenotypic variants crossed against each other to establish the 10 linkage groups for corn. From this base, the number of phenotypic mutants has increased steadily. Coe et al. (2001) reported that 845 genetic loci have been mapped for corn. In addition to the phenotypic mutants, corn has a well-developed cytological map consisting of B-A translocations (Roman and Ullstrup, 1951; Beckett, 1991), A-A translocations (Longley, 1958, 1961), and other cytological structures that total 2307 loci (Coe et al., 2001). The most detailed and elegant presentation of the genetic and cytological maps, along with the history of corn genetics and color illustration of the phenotypic variation present in corn, is given in Mutants of Maize (Neuffer et al., 1997). This book is an essential reference for anyone with an interest in corn genetics or biology.

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Molecular Maps for Corn The first DNA-based-marker map for corn was published by Helentjaris et al. (1986a, b) and included 116 loci. The linkage groups of the molecular map were oriented relative to the classical or cytological map by use of monosomics (Helentjaris et al., 1986a, b) and B-A translocations (Weber and Helentjaris, 1989). Many groups followed the lead of Helentjaris, including major public RFLP mapping efforts at Brookhaven National Laboratory (BNL) (Burr et al., 1988) and University of Missouri-Columbia (UMC) (Gardiner et al., 1993). Starting from developing anonymous markers for trait mapping, the RFLP mapping efforts soon switched focus to the mapping of sequenced cDNAs or ESTs and isolated genes of known function. A new era of linking gene structure to phenotype emerged. The BNL map grew to 1699 loci (summarized by Coe et al., 2001) and the UMC map to 1736 loci (Davis et al., 1999). The BNL map is a composite of two recombinant inbred line (RIL) mapping panels of 41 and 48 individuals, while the UMC map represents an “immortalized” panel of 54 F2 individuals. Because of the limited number of total meioses represented in the populations for the BNL and UMC maps, resolution of order is essentially saturated. This has prompted the corn research community to adopt a new mapping population as the community standard. The intermated B73
Mo17 (IBM) population includes approximately 300 individual RIL lines derived from a population that underwent four rounds of random mating at the F2 stage (Lee et al., 2002). The random mating results in threefold map expansion (Liu et al., 1996). The increased number of lines and the map expansion from the rounds of random mating result in a map resource with 15 times the order-resolving power of the prior BNL and UMC map standards. The IBM map currently consists of >1000 RFLP loci (G. Davis, T. Musket, S. Melia-Hancock, N. Duru, N. Sharopova, L. Schultz, M. McMullen, H. Sanchez, S. Schroeder, and A. Garcia, unpublished data), >800 SSRs (Sharopova et al., 2002), and >200 miniature inverted repeat transposable elements, better known by the acronym “MITEs” (Casa et al., 2000). The IBM population will serve as the germ plasm framework for developing a public physical map for corn based on integration of germ plasm, genetics, and genomics.

The Bin Concept The “bin” concept for the corn genetics map was first proposed by Gardiner et al. (1993). Bins are approximately 20 centiMorgan regions of the corn genome bound by RFLP markers known as the “core markers.” Core markers were chosen based on map position, low-copy number, and high polymorphism across inbred lines. As the genetic map became more refined, the core markers, and therefore the bin boundaries, were adjusted to more accurately fulfill the goals of the bin concept (G. Davis, T. Musket, S. Melia-Hancock, N. Duru, N. Sharopova, L. Schultz, M. McMullen, H. Sanchez, S. Schroeder, and A. Garcia, unpublished data). In MaizeDB, all genetic entities with a map position are placed in bins, leading to a composite genetic map for corn regardless of the population in which the entity was originally positioned (Coe et al., 2001). QTL often have confidence intervals that are approximately one bin in length. It is common practice in the corn research community to report QTL position by bin. The bin concept has been used primarily for comparing mutant, EST, gene, and QTL positions to identify candidate genes for phenotypes or QTLs.

The Corn Physical Map The next step in the evolution of genetic resources for the corn community is the development of a physical map for corn. Three bacterial artificial chromosome (BAC) libraries totaling >450,000 clones and representing 27 genome equivalents are available from Clemson University (http://www.genome.clemson.edu) and from Children’s Hospital of Oakland Research Institute (http://www.chori.org). All of these clones are in the process of being fingerprinted by HindIII digestion, and the fingerprinted BACs are represented as contigs on the Clemson website (http://www.genome.clemson.edu/projects/ maize/fpc). The BAC contigs are being anchored to the genetic map through a combination of RFLP, EST, amplified fragment length polymorphisms, SSR, and SNP markers (http://cafnr.missouri.edu/mmp). In addition to the BAC libraries, a three-genome-equivalent yeast-artificial-chromosome library is available for corn researchers (Edwards et al., 1992b).

Quantitative Trait Locus Analysis in Corn While study of the rich resource of discrete morphological variation of corn has captivated corn geneticists and physiologists, most of the traits of interest to the corn breeder show quantitative or continuous distribution of phenotype. Before the advent of molecular markers, the genes underlying quantitative variation could be studied only as the sum of the gene effects (Mather and Jinks, 1982). This situation was changed, first with isozymes, then more dramatically with the use of DNA-based markers. Many reviews of QTL analysis in plants have been published (Kearsey and Farquhar, 1998; Paterson, 1997). >100 QTL papers about corn have been published in the last decade, and numerous unpublished studies have been done. Clearly, any in-depth review of QTL studies in corn would require its own chapter or book. In this section,

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we highlight some of the themes that have emerged from QTL studies in corn, particularly those analyses that have contributed to our general understanding of the genetic basis of quantitative traits. One reason for the large number of QTL papers is that corn has many features that make it an excellent organism for studying quantitative variation. Along with self-fertility, separation of male and female inflorescences allows for ease in making controlled crosses, and the large number of progeny per cross makes corn ideal for establishing the structured populations for study. Numerous inbred lines with distinct morphological and agronomic properties provide ready starting material for population development. All but closely related inbred lines exhibit levels of marker polymorphism conducive to complete linkage map construction. The limiting factors for population size in corn have generally revolved around the cost of genotyping and field requirements for replicated trials, rather than limitations in population construction. Early attempts were made to link chromosome position to genes for complex traits by chromosomal translocations (Scott and Nelson, 1971). However, the difficulties in establishing the necessary stocks and pleiotropic effects of the translocations made this approach impractical for routine use. The advantage of neutral markers was immediately evident with studies using isozymes as genetic markers (Edwards et al., 1987). These studies quickly challenged many assumptions of classical quantitative theory and established several themes for the QTL studies that followed. Instead of a very large number of small, additive gene effects controlling agronomic traits, individual marker loci accounted for variable percentages of the total variation and exhibited a continuous range of gene action. Although the initial populations studied were crosses between very different lines to optimize isozyme polymorphism (Edwards et al., 1987), similar results were found for populations formed by elite crosses (Abler et al., 1991). The majority of QTL experiments published for corn have used population sizes of 100–400 families. The population structures have included F2, F2:F3 (F2-derived F3), or F2:F4 RIL families, and so on. Each of these classes can be analyzed as classes, or as back-crosses or test-crosses to the original parents or tester lines. The ability to generate complex population structures with large amounts of seed for replicated phenotypic testing, together with the economic importance of corn, makes corn the leading crop plant for QTL studies. As reviewed by Beavis (1998) and Kearsey and Farquhar (1998), the genetic basis for the full range of quantitative traits is generally a few (one to three) loci with >10% (sometimes as high as 40%–50%) of the phenotypic variance accounted for and a larger number of QTL with smaller effects. The gene action of QTLs ranges from additive to overdominance. Comparing the locations of QTLs for the same trait across any two populations usually highlights differences, but when comparisons are made across large numbers of populations, common regions of the genome emerge. Examples for plant height and yield have been previously reviewed (Beavis, 1998). Another interesting example is QTLs for resistance to stem-boring insects in corn (Khairallah et al., 1998; Bohn et al., 2000; Cardinal et al., 2001). There are now a dozen publications on resistance to either the leaf-feeding or the stalk-tunneling stages of corn-boring insects. The germ plasm for the inbred parents of the populations includes tropical
tropical, tropical
temperate, and temperate
temperate. Multiple insect specie
corn population combinations were examined. In each study, approximately 3–12 QTLs were found, with a wide range of variation and differing types of gene action. Although only a subset of QTLs are common for the same insect between two populations, QTL positions have recurred in studies with different insects. Cardinal et al. (2001) point out that QTLs for stalk tunneling by European corn borer share QTL positions with leaf-feeding studies of tropical stem borers as often as with other European corn borer tunneling studies. As pointed out by Beavis (1998), based on simulation studies, and by Melchinger et al. (1998), based on replicated tests, individual QTL experiments as currently structured have limited power to detect QTLs; generally they identify only a subset of the QTLs present and often overestimate the contribution of the QTLs detected. Individual QTL experiments must be interpreted as a sampling of significant loci. In addition, QTL studies can detect loci only if variation exists between the two lines used to form the studied population. If individual experiments provide limited information, how should we utilize the QTL studies conducted to date? For traits such as insect resistance, plant height, maturity, and yield, many studies are available from MaizeDB. Examination of the studies identifies consistent genome regions in which genetic variability for the trait exists across corn germ plasm. These data are best used to identify candidate genes within the regions for analysis and manipulation. In July 2001, 134 plant-height QTLs were shown in MaizeDB. Ten of these QTLs map to bins 9.03–9.04. Bin 9.03 also contains the map position for the phenotypic mutant dwarf3. The dwarf3 gene has been cloned and demonstrated to encode an enzyme in gibberellin biosynthesis (Winkler and Helentjaris, 1995). These results suggest that natural variation at dwarf3 may provide the genetic basis for height variation in corn inbreds. A major justification for developing molecular markers and for conducting QTL studies was the potential to perform marker-assisted selection (MAS) on quantitative traits, which has turned out to be a difficult task for several reasons. First, as detailed in the previous discussion on QTL, experiments give us only a partial understanding of the genetic basis of a trait. Second, most QTL experiments either have ignored or have limited power to detect epistatic interactions in the populations under study and have essentially no predictive value for revealing epistatic effects in crosses to other lines

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(Tanksley, 1993; Holland, 2001). While MAS is used extensively to manipulate transgenes and single-gene traits, it is clear that most initial attempts at MAS for QTLs lacked adequate understanding of the genetics involved. The most notable exception was the success of Stuber and colleagues in enhancing yield potential of inbred lines by MAS (Stuber, 1994, 1995). MAS is used extensively now when phenotypic assessments are not technically feasible, and markers can identify which progeny contain the trait of interest and most closely resemble the recurrent parent.

Current Trends in QTL Analysis Despite more than a decade of QTL studies, this scientific pursuit has yet to make a major impact on corn breeding. The contributing causes have been outlined. Geneticists have approached quantitative variation one cross at a time, and even when multiple populations were studied, little has been done to determine the variation that exists across corn germ plasm as a whole, the palette of interest to the corn breeder. A new set of analytical approaches and molecular tools is beginning to revitalize QTL studies. These tools and approaches have been referred to by Stuber et al. (1999) as the “synergy of breeding, MAS, and genomics.” Genomic projects underway for corn will provide extensive EST resources and a physical map to efficiently map these ESTs. Together, these tools will provide candidate gene identities and map positions for a large subset, and in the near future, for nearly all corn genes. We argue that QTL studies will continue to play a major role as a gene discovery tool. Of the possible genes affecting a biochemical process, which possess the allelic variation useful to breeders? Quantitative trait analysis remains a powerful tool for separating candidate genes affecting a particular trait from candidates with limited allelic variability. Large-scale EST sequencing and SNP development also form the basis of a new statistical approach, known as “association analysis,” to identify genes based on the diversity present across germ plasm, rather than by linkage disequilibrium measures. Association analysis was pioneered for the study of complex human diseases (Lander and Schork, 1994) and has recently been used to demonstrate that sequence variation at the dwarf8 locus is associated with flowering time in corn (Thornsberry et al., 2001). Classic QTL analysis works to identify a target region approximately 20 cM in size; genomics provides a list of candidate genes within that region. Association analysis provides a means to sort through those candidates to identify the genes with variation affecting trait expression.

Seed Production Seed production requires special care. Hybrid plants with the same pedigree but from seed produced by two different companies or from two differing locations can vary as much as two different hybrids because of different production or conditioning techniques. After the seed producer chooses the desired hybrid, parental seed stocks must be located. Many large companies produce their own seed stocks, but smaller producers may buy seed from foundation seed stock companies that specialize in developing inbred lines and producing seed of public inbred lines. Seed of parental inbred lines is sold on a thousandviable-kernel basis. For example, if the germination is 90%, the number of seeds is adjusted to 1111 kernels to provide 1000 viable kernels.

Crossing Techniques The planting patterns used in hybrid seed production are sometimes a function of planting equipment, whereby the number of male rows may be one to two and the number of female rows may be four to eight. Tassels are removed from the female rows by hand, with workers either walking or riding a special apparatus that carries six or eight workers through the field at one time. Mechanical cutters and pullers also are used, but usually require a follow-up by a walking crew to remove tassels that were missed. An alternative method to tassel removal is the use of male sterility, which can be genetic or cytoplasmic. Genetic male sterility has not been used to a great extent. Before 1970, >90% of the corn seed in the United States was produced in Texas male-sterile cytoplasm. But after the 1970 catastrophe, in which southern corn leaf blight (Cochliobolus heterostrophus (Drechs.) Drechs. ¼ Helminthosporium maydis Nisikado and Miyake) race T caused damage to hybrids made using Texas male-sterile cytoplasm, cytoplasmic male sterility was not used for a few years. In 1971, male-sterile cytoplasms were found that did not confer susceptibility to any foliar diseases. Since that time, the smaller producers have partially returned to the use of cytoplasmic male sterility. Some of the cytoplasmic male-sterile sources now used belong to the “C” and “S” groups (Beckett, 1971). The larger producers have not returned to the use of cytoplasmic male sterility because of the attached stigma. They also are involved in development of constitutive male sterility systems in which sterility is normally expressed, and specific conditions are required to confer male fertility. These systems are considered commercially viable.

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One problem associated with seed production via the cytoplasmic male-sterile method is the need to restore pollen fertility in the farmers’ fields. This step is accomplished by breeding into the male parent a restorer gene (Rf) or by blending (usually 1:1) seed produced by the cytoplasmic male-sterile method with seed of the same hybrid produced in normal cytoplasm on detasseled plants. Most seed producers use the latter method.

Isolation Requirements A seed-production field should usually be isolated from other corn by a distance of not 100 generations. The change in oil has been substantial. Up to 20% oil in the kernel has been achieved from the typical level of 4%, and the low oil-producing line has almost zero content of oil. To explain the large response in changes at the

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individual gene loci, a team of scientists from the Monsanto Company and the University of Illinois reported the identification of quantitative trait loci (QTLs) regions of the genome where genes influence the trait. It is challenging to identify the genes and the molecular changes that cause many small but significant changes in quantitative traits. However, it is these small differences that generate variability in populations, providing basis for making genetic selection (Hill, 2005). The Illinois HOC line had about 20% oil; however, with selection only for oil, the yield of HOC fell significantly compared to that of commercial hybrids. The development of high-oil corn hybrids advanced considerably in the 1990 and early 2000. There are also a few recent studies on increasing oil content. Chai et al. (2012) reported that although a few major multiple QTL with large additive effects have an important role in increasing kernel oil content and altering fatty acid composition, a larger number of minor QTL and some epistatic QTL also additively contribute to these oil traits. The gene encoding acyl-CoA:diacylglycerol acyltransferase (DGAT1–2) was shown to be a key quantitative trait locus that controls oil content and oleic-acid composition in corn kernels. Chai et al. (2012) sequenced the DGAT1–2 region responsible for oil variation in a corn landrace set and in 155 inbred lines (35 highoil and 120 normal lines). Association analysis detected significant effects of two PCR-based functional markers on kernel oil content and oleic-acid composition. Then, marker-assisted backcrossing was performed to transfer the favorable allele from the high-oil line. Oil content of homozygous kernels containing the high-oil DGAT1–2 allele increased by 27%–37% compared to the parents. Zheng et al. (2008) also showed that a high-oil QTL affected corn oil and oleic-acid contents encode DGAT1–2, which catalyzes the final step of oil synthesis. Ectopic expression of the high-oil DGAT1–2 allele increases oil and oleic-acid contents by up to 41% and 107%, respectively. Yang et al. (2012) characterized QTL for kernel oil content using recombinant inbred population derived from a cross between normal line B73 and high-oil line By804. Eight main-effect QTL were identified for kernel oil content and embryo oil content. Genome-wide association was used to extensively examine the genetic architecture of corn oil biosynthesis (Li et al., 2013) in a study using 1.03 million SNPs in 368 corn inbred lines (including high-oil lines). A total of 74 loci were identified that are significantly associated with kernel oil concentration and fatty acid composition which were subsequently examined using QTL mapping, linkage mapping, and coexpression analysis. Twenty six loci were identified to relate to oil concentration, and they could explain up to 83% of the phenotypic variation in oil content. These results provide insights into the genetic basis of oil biosynthesis in corn kernels that will facilitate marker-based breeding for oil quantity and quality. Qin et al. (2005) conducted corn inbreeding for three generations and obtained some new super-high-oil lines and this trait could be inherited. The mean oil content was 22%. The study of the correlation between the mean grain weight and oil content of ears showed no correlation. Zhang et al. (2010) was able to transform corn with the wheat puroindoline genes that control the hardness of wheat seeds. The transformed corn had significantly increased germ size without negatively impacting seed size. Germ yield increased 33.8%, while total seed oil content was increased by 25.2%. Four subtropical white and yellow HOC populations were studied for the effect of selection on yield, kernel physical properties, oil content, and fatty acid profile (Preciado-Ortiz et al., 2013). Eight cycles of recurrent selection for high-oil content and agronomic traits in kernels increased oil content, which had a significant positive correlation with the germ size, with 33%–60% more oil compared to original line. The agronomic traits showed a low but significant increase of grain yield. This work suggested that it is feasible to develop high-yielding subtropical high-oil content corn and acceptable agronomic performance and grain physical properties. In recent years, studies on oil accumulation in vegetative tissues have been increasing. Since certain transcription factors in Arabidopsis including Wrinkled 1 (Wri1) and Leafy Cotyledons 2 (LEC2) are involved in the synthesis of fatty acids and/or for packaging of the oil bodies, Alameldin et al. (2017a,b) overexpressed three major genes involved in the TAG biosynthesis and accumulation, (1) diacylglycerol acyltransferases 1 as a key enzyme in TAG biosynthesis, (2) transcription factor Wri1 that is involved in supplies of fatty acids for TAG biosynthesis, and (3) oleosin (Ole) gene which encodes for protein that protects TAGs from degradation. The three genes were integrated in corn genome to allow the production of oil bodies in corn vegetative biomass. An increase in the total leaf fatty acid content by 71% (from 1.35 to 2.31 mg/g dry weight) in the engineered line was produced. This is the first report of increasing TAG accumulation in corn vegetative biomass by genetic engineering, and it may lead to new effort in greatly increasing oil productivity in whole corn plant. Value of HOC is in animal feeding. Risley and Bajjalieh (1996) and Lohrmann et al. (1998) reported faster weight gains of pigs, reduced feed intake, and improved efficiency of feed utilization of HOC over conventional corn diets. The growth performance was essentially the same for the HOC and soybean meal. The HOC diets simplify animal ration formulations and eliminate handling, storing, and mixing problems associated with the addition of oils or fats to feedstuffs. However, diets containing high level corn oil can produce soft belly and oily carcasses that are unacceptable for conventional processing. Lactating dairy cattle fed diets containing 6% HOC had a 12% greater intake of dry matter than did cattle fed a 4%

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oil corn diet (Atwell et al., 1988), thus an increase in body weight from 4 to 20 weeks postpartum, whereas the normal diet generated a decrease in body weight during this period. Substitution of HOC for normal corn in the finishing rations of beef cattle increased carcass quality grades, marbling scores, and unsaturated fatty acid proportions in the longissimus muscles, but did not affect other carcass or sensory properties of the muscles (Andrae et al., 2001). In general, feeding trials conducted over the past several decades all demonstrate an advantage from feeding HOC versus normal corn to chickens, swine, dairy cattle, and sheep. The disadvantages of HOC come from lower corn yields (up to 10% reduction), increased kernel damage, and the potential for increase in insect damage (Heiniger and Dunphy, 2017). The increase in embryo vs the hard endosperm results in a softer kernel that is more prone to damage. Trials have shown a significant increase in kernel damage in the Midwest. Softer kernels and high oil also make this corn attractive to insect feeding. Dupont recommended increasing seeding rates to obtain higher plant populations that make up for the loss of productive plants. The reduction in yield potential leads to the necessity for market premiums, but there seems to be no such structure in place currently. There is no new market information on HOC since 2000, and there is no commercial production of high-oil corn today. Nonetheless, traits-stacked grain and oilseeds (having altered fatty acid composition, oil content, and elevated levels of micronutrients) are currently being developed and may be released for commercial production (personal communication with Professor Edgar Cahoo of University of Nebraska). The development of fast assay methods has contributed to the progress in genetic selection of corn for HOC. 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Lipids of the Kernel Chapter

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FURTHER READING Christensen, S.A., Huffaker, A., Kaplan, F., Sims, J., Ziemann, S., Doehlemann, G., Ji, L., Schmitz, R.J., Kolomiets, M.V., Alborn, H.T., Mori, N., Jander, G., Ni, X., Sartor, R.C., Byers, S., Abdo, Z., Schmelz, E.A., 2015. Maize death acids, 9-lipoxygenase–derived cyclopente(a)nones, display activity as cytotoxic phytoalexins and transcriptional mediators. PNAS 112 (36), 11407–11412. Moreau, R.A., Singh, V., Hicks, K.B., 2001b. Comparison of oil and phytosterol levels in germplasm accessions of corn, teosinte, and Job’s tears. J. Agric. Food Chem. 49, 3793–3795. Shintani, D., 2006. Engineering plants for increased nutrition and antioxidant content through the manipulation of the vitamin E pathway. In: Setlow, J.K. (Ed.), Genetic engineering: principles and methods. Brookhaven National Laboratory, New York, pp. 231–242. USDA, 2017. World Agricultural Supply and Demand Estimate (WASDE). Available from:https://www.usda.gov/oce/commodity/wasde/> [26 October 2017].

Chapter 14

Minor Constituents and Phytochemicals of the Kernel Beatriz A. Acosta-Estrada*, Janet A. Guti
errez-Uribe*,† and Sergio O. Serna-Saldivar* *Centro de Biotecnologı´a FEMSA, Escuela de Ingenierı´a y Ciencias, Tecnologico de Monterrey, Monterrey, Mexico, † Tecnologico de Monterrey, School of Engineering and Science, Puebla, Mexico,

INTRODUCTION The minor food components associated to the corn kernel can exert significant effects from the functional, nutritional, and nutraceutical viewpoints. Just because something is less abundant does not mean that its influence is not relevant and such is the case with micronutrients and phytochemicals present in our diet. Micronutrients such as vitamins and minerals are minor constituents of food that play vital roles in basic physiology and nutrition, whereas phytochemicals or nutraceuticals are compounds that exert proven positive effects on human health. Minerals are inorganic substances that must be acquired by the diet. They include major minerals such as calcium, phosphorus, magnesium, and potassium and other named traces that are daily required in few milligrams or even micrograms. These include iron, zinc, copper, manganese, and selenium, among others. Minerals play numerous roles in the body because they are constituents of vital molecules, like iron in hemoglobin (red blood cells), phosphorus that is required for the synthesis of adenosine triphosphate (ATP), iodine for thyroid hormones, and zinc, copper, and selenium as key elements for the production of metaloenzymes. Vitamins are organic molecules that act as cofactors for enzymes which play fundamental roles in human metabolism. In the early part of the last century, the term “vitamin” was formed from “vital amines,” when it was thought that all vitamins were constituted by amines. The continuous deprivation of vitamins B1 (thiamin) and B3 (niacin) incited potentially fatal diseases as beriberi and pellagra, respectively. These diseases have been very common throughout human history. A subset of vitamins can be stored in body fat (e.g., vitamins A and E) and are, therefore, named fat-soluble. The most relevant are vitamins A and E, the first considered the most deficient vitamin worldwide and the second one the main mechanism to protect the human body against oxidative stress. Plants through primary or secondary metabolic pathways produce phytochemicals, generally to help them thrive or thwart competitors, predators, or pathogens. The name is derived from the Greek word phyton, meaning plant. Phytochemicals, also known as nutraceuticals, are not essential nutrients, but have protective or disease preventive properties. Phytochemicals are divided into phenolics, flavonoids, anthocyanins, phytosterols, phospholipids, policosanols, carotenoids, and xantophylls, among others. Most of these chemical compounds prevent oxidative stress, considered the main causal of most chronic diseases (e.g., cardiovascular diseases, cancer, high blood cholesterol), which has resulted in about 60% of the current deaths, experienced globally. Cereal-based food are the most important source of nutrients for mankind (FAO, 2018). Most diets are based on one particular cereal grain as the main substance in most countries around the world. The cereals more widely consumed are rice, wheat, and corn (Ranum et al., 2014). Corn (Zea mays) is a staple food for more than a billion people worldwide, especially for populations in Latin America and Southern Africa where this crop provides almost one-third of their caloric needs (Dı´az-Go´mez et al., 2017b). Corn provides significant quantities of most B-vitamins, tocopherols, essential minerals, and phytochemicals and unfortunately lacks some other nutrients, such as vitamin B12, vitamin C, and it is a poor source of calcium, zinc, and iron. The pericarp, germ, and aleurone layer are the anatomical parts that contain the highest concentration of most micronutrients; unfortunately, these anatomical parts are commonly removed during milling (see Chapter 15). In addition to physical loses, thermal treatments usually reduce the content of important vitamins. The different types of vitamins are lost due to pH, ultraviolet light, oxygen, and the enzymatic or fermentative action of microorganisms. This is the main reason why, in Corn. https://doi.org/10.1016/B978-0-12-811971-6.00014-0 Copyright © 2019 AACCI. Published by Elsevier Inc. in cooperation with AACC International. All rights reserved.

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countries where deficiencies are considered moderate or severe public health problems, the enrichment of corn flour and cornmeal with selected vitamins and minerals has been used to improve micronutrient intake and prevent deficiencies (Serna-Saldivar, 2010; Ranum et al., 2014). Classical examples of vitamin deficiencies comprise scurvy (vitamin C), beriberi (vitamin B1), pellagra (niacin), night blindness and xeropthalmia (vitamin A), rickets (vitamin D), and pernicious anemia (vitamin B12) (Brinch-Pedersen et al., 2007). Currently, the ‘hidden hunger’ brought by the lack of essential micronutrients is attracting increasing attention since close to 2 billion of the world’s population suffer from malnutrition not only caused by deficient caloric or good quality protein intake, but by an insufficient ingestion of essential micronutrients. Great efforts have been devoted to the development of new corn genotypes with improved levels of micronutrients, through biofortification (Wen et al., 2016). Biofortification is a term that encompasses four major strategies: fertilizers, conventional breeding, mutagenesis, and transgenic methods. Breeding for chemical composition is being extended beyond traditional targets of oil and protein to include components such as vitamins and antioxidant secondary metabolites with considerable purported consequences for human health (Wen et al., 2016). Plant breeding nowadays focuses on nutritional improvement and selection of key phytochemicals, which have proven health benefits. Improved blue maize hybrids have 2.6-fold increased anthocyanin content compared to native populations of pigmented maize (Urias-Peraldı´ et al., 2013). Anthocyanins have antioxidant, antiinflammatory, and hypoglycemic activities and reduce cancer cell proliferation (Urias-Peraldı´ et al., 2013). Transgenic corn plants in which the levels of three vitamins were increased 169-fold the normal amount of b-carotene, sixfold the normal amount of ascorbate, and double the normal amount of folate have also been created (Naqvi et al., 2009). The new trend of the cereal industry is the development of new nutraceutical or functional food. Most cereal processors face the challenge of developing new food if they want to subsist in the market. Nowadays, there are commercial products as Benecol, a dairy product with stanols from cereals including corn which lowers blood cholesterol or Mazola corn oil with 0.77% (w/w) of phytosterols that diminish cholesterol absorption (Ostlind et al., 2002). There are other products as a pan bread enriched with corn bran with elevated levels of calcium and ferulic acid, the last recognized as antioxidant, antiinflammatory, and anticarcinogenic (Acosta-Estrada et al., 2014b). The purpose of this chapter is to summarize vitamins, minerals, and phytochemicals associated with corn and their role in preventing health deficiencies, oxidative stress, and chronic diseases. Moreover, the bioavailabilities of these minor compounds as affected by diverse food processing methods and strategies are also addressed.

MINERALS Humans require >22 mineral elements, which should all be supplied by an appropriate and balanced diet. However, the diets of populations subsisting on cereals, or inhabiting regions where soil mineral imbalances occur, often lack Fe, Zn, Ca, Mg, Cu, I, or Se (White and Broadley, 2005). The amounts of Mn and Se in whole corn kernels vary according to the soil composition. Phosphorus, potassium, and magnesium are the most prevalent minerals found in corn providing nearly 85% of the total ash content (Nuss and Tanumihardjo, 2010). Total iron, zinc, and calcium levels are negligible and the concentrated germ phytate levels lower the bioavailability of these and other essential minerals (Dei, 2017). The pericarp, germ, and aleurone layer are the anatomical parts with the highest concentration of minerals (SernaSaldivar, 2010). The inorganic or mineral component of the corn kernel constitutes 2500 years. Hippocrates, the Greek Philosopher and father of medicine, postulated that food had a great impact on health. The new trend in the cereal processing industry is the development of nutraceutical or functional food. Nutraceutical food are those that contain chemical compounds (phytochemicals) that exert a positive effect on human health. These chemicals are not considered nutrients that have been traditionally associated to deficiencies such as vitamins and minerals discussed above. The main nutraceuticals are those with proven positive effects to combat oxidative stress, chronic diseases, and cancer. In some instances, the scientific evidence of the positive effects is solid and so overwhelming that regulatory agencies allow processors to declare them on the nutritional label (Serna-Saldivar, 2010). For example, phytosterols can be declared in the USA labels and policosanols are approved dietary supplement in Cuba, and they are currently commercialized in Caribbean and South American countries (Leguizamo´n et al., 2009). In most instances, the nutraceuticals are intrinsic to the food such as corn germ rich in phytosterols, tocopherols, and policosanols (Serna-Saldivar, 2010). Modern humans are more prone to oxidative stress because they are exposed to many oxidative agents such as air contamination, stress, cigarette smoke, and others. In addition, the human body constantly produces free radicals that can cause cell membrane oxidation and DNA damage that exacerbates mutations of protoncogenes and aging and increases the probability of cancer and chronic diseases (Serna-Saldivar, 2010, 2016). The nutraceutical compounds related to corn are classified according to their chemical properties. Besides the nutritional attributes of corn, this cereal contains an array of nutraceuticals such as phenolics compounds, carotenoids, phospholipids, phytosterols, and other minor nutrients such as policosanols. The health beneficial properties of maize

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phytochemicals have been mainly attributed to their high antioxidant and antiradical activities, and also to many other mechanisms such as antimutagenesis, anticarcinogenesis, and antiinflammatory activities, inhibition of enzymes, and induction of detoxification enzymes. These phytochemicals are partially lost during storage, milling, and processing.

Phenolic Compounds Phenolics are the most widely distributed secondary metabolites present in corn (Table 14.7). These phytochemicals can be divided into three major categories: simple phenolics, flavonoids, and tannins, although the last class is not present in corn. Simple phenolics are usually derived from benzoic or cinnamic acids (Fig. 14.3), whereas flavonoids including anthocyanins are built from two units: a C6-C3 component from cinnamic and a C6 fragment from malonyl-CoA (Fig. 14.3). Recently, Zavala-Lopez et al. (2018) evaluated soluble and bound phenolic compounds in an array of 22 teosintes, which are the wild ancestors of modern corn. Total soluble phenolic compounds in all teosinte accessions were higher compared to the maize counterparts, ranging from 2.01 to 4.47 mg gallic acid equivalents (GAE)/g dw. Interestingly, even the teosinte accession (Z. luxurians) with the lowest phenolics contained twice as much content than commercial corn. Total bound phenolic compounds in teosinte ranged from 13.17 to 30.27 mg GAE/g dw, while the highest content in corn reached only 8.01 mg GAE/g dw. Teosinte’s phenolic profile showed that p-coumaric acid was the predominant phenolic acid form with soluble concentrations around 17 to 31 mg/g dw, whereas concentrations of bound ranged from 215 to 238 mg/g dw. Moreover, most teosinte accessions contained higher soluble and bound trans-ferulic acid contents compared to the corn accessions. Teosinte’s antioxidant capacities were higher for bound phenolics with values ranging from 50 to 82 mmol trolox equivalent (TE)/100 g dw compared to only 7–17 mmolTE/100 g dw observed in corn. The high phenolics assayed in the teosintes were consequence of the glumes that were not removed before extraction, since it has been stated that the increased hardening of these external structures is correlated with a thicker abaxial mesoderm of lignified cells (Doebley, 2004). Most phenolics in corn are associated to cell walls in the pericarp and the monolayered aleurone (Serna-Saldivar, 2010). Phenolic compounds occur mostly as soluble conjugates (glycosides) and insoluble forms, covalently bound to sugar moieties or cell wall structural components. In nature, simple phenolics occur mostly in the insoluble or bound forms, whereas flavonoids present as glycosides with a single or multiple sugar moieties linked through an OH group (O-glycosides) or through carbon-carbon bonds (C-glycosides) (Acosta-Estrada et al., 2014a). About 85% of the total phenolics present in corn are in the insoluble bound forms, with ferulic acid, a simple phenolic, being the major compound (Adom and Liu, 2002; Guti
errez-Uribe et al., 2010).

Simple Phenolic Compounds (Phenolic Acids) The most common simple phenolic compounds found in whole grain are phenolic acids. Corn phenolics acids include caffeic, coumaric, hydroxybenzoic, protocatechuic, syringic, vainillic, sinapic, syringic, gallic, and ferulic acids (Ndolo and Beta, 2014; Nile and Park, 2014). Total phenolic acids in corn average 255 mg/100 g (Table 14.7), ferulic acid being the major compound representing about 70% of the total (Ndolo and Beta, 2014). Ferulic acid is a hydroxycinnamic acid associated to cell walls of pericarp (Table 14.7). It is mainly found in bound or conjugated forms (>80%) (Guti
errez-Uribe et al., 2010). The insoluble-bound ferulic forms such as diferulic, trifeluric, or pentaferulic are covalently linked to polysaccharides mainly in the pericarp and aleurone layers, crosslinking and strengthening cell walls (Serna-Saldivar, 2010; Acosta-Estrada et al., 2014a). Regardless of the ferulic acid form, it has a wide range of therapeutic effects. It is considered a potent antioxidant and a nutraceutical that prevents inflammation, cancer, LDL oxidation, and neuron degeneration. Among major cereals, corn exerts the highest antioxidant activity and contains up to three times more phenolics compared to wheat, rice, and oats (Adom and Liu, 2002). They inhibit the generation of ROS or directly scavenge free radicals. Through this process, antioxidant compounds themselves become radicals, though much less reactive, preventing damage to cellular molecules (Tan et al., 2011). This antioxidant potential can be usually attributed to the chemical structural features. Phenolic nucleus and unsaturated side chain can readily form a resonance-stabilized phenoxy radical. Most phenolic antioxidant compounds exert their chemopreventive action, inducing cellular defense detoxifying and antioxidant enzymes (phase II enzymes) in the organism. The phenolic extracts of raw corn are capable of inducing quinone reductase activity in order of effectiveness purple corn < white corn < red corn < blue corn (Lopez-Martinez et al., 2011). Nejayote, a corn byproduct of the lime-cooking process to produce tortillas (see Chapter 17), also induced quinone reductase. The free phenolics extract of white maize nejayote induced BPrc1 cells quinone reductase and exerted a higher chemopreventive index compared to free and bound extracts of yellow, blue, red, high-carotenoid, and quality protein corns

Minor Constituents and Phytochemicals of the Kernel Chapter

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TABLE 14.7 Nutraceutical Content in Corn Kernels Nutraceutical Compound Family/Class

Compound

Phenolics compounds (simple phenolics)

Total phenolic acids

Phenolics compounds (flavonoids)

p-Coumaric acid

Anatomical Part/Corn Type

mg/ 100 g

Reference

Whole yellow corn

255.0

Ndolo and Beta (2014)

Ferulic acid

178.8

Sinapic acid

13.3

p-Hydroxybenzoic acid

2.0

Vainillic acid

20.1

Syringic acid

11.6

Ferulic acid

Yellow corn pericarp

1840.0

Ndolo and Beta (2014)

Total anthocyanins

Red corn

5.1

Li et al. (2017)

Total anthocyanins

Blue corn

36.8

De la Parra et al. (2007)

Total anthocyanins

Purple corn

130– 1640

Li et al. (2017) and Lao and Giusti (2016)

Cyaniding-3-glucoside

Purple corn

113.5

Li et al. (2017)

Pelargonidin-3-glucoside

11.6

Peonidin-3-glucoside

28.5

00

Carotenoids

24.2

Cyanidin 3-O-(6 malonyl-glucoside)

39.9

Pelargonidin 3-O-(600 malonyl-glucoside)

5.1

Peonidin 3-O-(600 malonyl-glucoside)

14.5

Total carotenoids g-Carotene

Whole white corn

0.30 0.09

a-Carotene

0.01

b-Carotene

0.04

Luteine

0.06

Zeaxanthin

0.03

Total carotenoids Lutein

Whole yellow corn

6.60

0.53

b-Cryptoxanthin

0.41

13-cis-b-Carotene

0.09

all trans-b-Carotene

0.30

9-cis-b-Carotene

0.10

Lycopene g-Carotene

Whole highcarotenoids corn

Taleon et al. (2017)

0.21

Zeaxanthin

Total carotenoids

Dı´az-Go´mez et al. (2017a, b) and Naqvi et al. (2009)

6–9.5 2.28

Burt et al. (2010); Dı´az-Go´mez et al. (2017a, b) and Naqvi et al. (2009)

0.48 Continued

388

Corn

TABLE 14.7 Nutraceutical Content in Corn Kernels—cont’d Nutraceutical Compound Family/Class

Phytosterols

Compound

mg/ 100 g

a-Carotene

0.72

b-Carotene

5.93

a-Cryptoxanthin

1.34

b-Cryptoxanthin

0.52

Luteine

1.46

Zeaxanthin

3.57

Total phytosterols b-Sitosterol

White/yellow corn germ

311

65

Stigmasterol

17

24-Methylencholesterol

2

D7-Campesterol

1

Campesterol

White/yellow corn germ oil

840

13

Stigmasterol

54

Sitosterol

503

Sitostanol

30

Campesterol

White/yellow corn oil

1109

74

Stigmasterol

46

Sitosterol

510

Sitostanol

184

Campesterol

White/yellow corn fiber oil

7939

1182

Stigmasterol

142

Sitosterol

1897

Sitostanol

2964

Phosphatidylinositol

White/yellow corn germ oil

Moreau et al. (2009)

Moreau et al. (2009)

594

Campestanol

Total phospholipids

Moreau et al. (2009)

135

Campestanol

Total phytosterols

Giordano et al. (2016)

151

Campestanol

Total phytosterols

Reference

198

Campesterol

Total phytosterols

Phospholipids

Anatomical Part/Corn Type

243.25 56.19

Phosphatidylethanilamine

25.54

Phosphatidylglycerol

15.81

Phosphatidylcholine

138.65

Harrabi et al. (2010)

Minor Constituents and Phytochemicals of the Kernel Chapter

14

389

TABLE 14.7 Nutraceutical Content in Corn Kernels—cont’d Nutraceutical Compound Family/Class

Compound

Policosanols

Total policosanols Docosanol C22

Anatomical Part/Corn Type

mg/ 100 g

Reference

White/yellow whole corn

2.01

Harrabi et al. (2009)

0.09

Tetracosanol C24

0.34

Hexacosanol C26

0.15

Octacosanol C28

0.12

Triacontanol C30

0.36

Dotriacontanol C32

0.61

(Rojas-Garcı´a et al., 2012). Particularly, feruloyl putrescines (coumaroyl-feruloyl putrescine and feruloyl-feruloyl putrescine) isolated from nejayote solids exerted 105% higher chemopreventive effect than nejayote phenolic extract (Acosta-Estrada et al., 2015). Moreover, ferulic acid has an inhibitory effect in proliferation and migration of human lung cancer cells cultured in vitro (Fong et al., 2016), whereas gallic acid exerts antiangiogenic effects in ovarian cancer cells in vitro in a concentration-dependent manner (He et al., 2016). Hydroxycinnamic acid derivatives isolated from corn bran (coumaric acid, ferulic acid, dicoumaroyl-putrescine, and diferuloylputrescine) have proven antiinflammatory activity in lipopolysaccharide-stimulated Raw 264.7 macrophages (Kim et al., 2012). Likewise, ferulic acid attenuated chronic neuroinflammation and induced neural progenitor cell proliferation both in vitro and in vivo (Wenk et al., 2004; Yabe et al., 2010). Chronic neuroinflammation and oxidative stress contribute to the neurodegeneration associated with Alzheimer’s disease (Wenk et al., 2004). Simple phenolic acids possess antidiabetic affects. They have been shown to increase glucose uptake and glycogen synthesis, improving glucose and lipid profiles related to obesity and cardiovascular diseases. They decreased blood glucose levels, glucose-6-phosphatase and phosphoenolpyruvate carboxykinase activities, and glucose and lipid peroxidation and increased glycogen and insulin (Senaphan et al., 2015; Vinayagam et al., 2016). Corn phenolics are partially lost during processing. The tortilla chip-making process has a clear reduction of these compounds, especially after lime-cooking. Lime-cooking, tortilla baking, and chip frying reduced 39%, 4%, and 10% total phenolics, respectively, with a total accumulated loss of 53% (De la Parra et al., 2007). Moreover, lime-cooking of corn kernels to produce tortillas changed the ratio between free and bound phenolics in masa compared with raw corn. The average content of free phenolics in masa increased at least 20% of the concentration originally present in raw kernels. Bound ferulic acid present in masa was approximately one-third of that present in whole kernels, whereas free ferulic acid was concentrated at least 10 times in masa compared to raw kernels (Guti
errez-Uribe et al., 2010). Mora-Rochin et al. (2010) researched the effects of traditional nixtamalization and extrusion lime-cooking on bound and free total phenolics of two Mexican pigmented (blue and red) and two commercial (white and yellow) corns processed into dry masa flours and tortillas. Tortillas prepared from extruded flours retained 88% of total phenolics compared to 62% in conventionally made tortillas. Results clearly indicate that the proposed lime-cooking extrusion strategy retained higher levels of phenolics in all tortillas. Additionally, in extruded whole masa flours, antioxidant activity of free phenolic extracts increased, while bound phenolics decreased in comparison with the unprocessed samples (Rochı´n-Medina et al., 2012). The FDA classifies ferulic acid as an antioxidant in the list of food additives (Fazary and Ju, 2007). Thus, phenolic compounds can be alternatively used as functional ingredients to improve the antioxidant capacity of processed food and to provide the health benefits associated with these phytochemicals. Agro-industrial corn by-products are good sources of phenolic acids, particularly bound moieties, which can be further extracted and released from cell walls. For example, the nejayote solids have been used to improve ferulic acid and antioxidant capacity contents in pan bread. The addition of 7.2% of the nejayote solids contained about 745 times more free ferulic acid and increased approximately 70% their antioxidant capacity (Acosta-Estrada et al., 2015). Furthermore, process like germination and fermentation could aid in improving phenolic content in food intended to be used as functional ingredients. Germinated and fermented corn with B. longum increased phenolic levels threefold to 28.6 mg/100 g (Hiran et al., 2016). Likewise, cold pressed oil from corn germ retained 3.3 times more phenolic acids than conventional refined corn oil; the first could be used as functional ingredient (G€ uneser et al., 2017).

390 Corn

FIG. 14.3 Chemical structures of bioactive phytochemicals associated to corn kernels.

Anthocyanins: Pigmented Flavonoids Cereals may contain significant amounts of flavonoids such as flavanols, flavanones, flavones, and anthocyanins. Anthocyanins are a class of water-soluble flavonoids responsible for attractive colors such as red, orange, purple, scarlet, violet, mauve, and blue (Lao and Giusti, 2016; Nile and Park, 2014). They are water-soluble glycosides of polyhydroxy and polymethoxy derivates of 2-phenylbenzopyrylium or flavylium salts (Fig. 14.3). The red, blue, and purple-pigmented corn kernels are known to contain significant amounts of these antioxidants. These molecules are set apart from other flavonoids because they contain a net positive charge in acidic solutions. Anthocyanins aglycones are known as anthocyanidins. The

Minor Constituents and Phytochemicals of the Kernel Chapter

14

391

anthocyanins of corn are mainly located in the aleurone layer or pericarp, greatly affecting the color of the kernel, and they could be separated into anthocyanin-rich fractions for use as functional colorants or food ingredients (Nile and Park, 2014). Colored corn is one of the richest sources of anthocyanins, with concentrations ranging from 51 mg/kg in red corn to 1300–16,400 mg/kg in purple corn and 368 mg/kg in blue corn (Table 14.7) (De la Parra et al., 2007; Lao and Giusti, 2016; Li et al., 2017). The main anthocyanins in corn are cyanidin and peonidin glycosides. Cyanidin 3-glucoside is the most abundant in blue and purple corns with ACN concentrations varying from 15.4 to 1135.4 mg/kg (Abdel Aal et al., 2006; Pedreschi and Cisneros-Zevallos, 2007; Li et al., 2017). Other relevant anthocyanins are cyanidin-3-(60 -malonylglucoside), cyanidin-3-O-glucoside-2-malonylglucoside, peonidin-3-O-glucoside, peonidin-3-(60 -malonylglucoside), pelargonidin-3-(600 -malonylglucoside), and peonidin-3-(dimalonylglucoside) (Li et al., 2017). Studies have shown that these antioxidants possess anticancer, antiobesity, and antiinflammation effects. Their health benefits have been related to their high antioxidant and antiradical activities. The antioxidant effect of anthocyanins is attributed specifically to the presence of hydroxyl groups in position 30 of the C ring and 30 , 40 , 50 of the B ring (Cone, 2007). In general, the antioxidant of anthocyanins (aglycones) is superior to that of glycosylated forms and decreases as the number of carbohydrates residues is higher in the molecule (Serna-Saldivar et al., 2015). Anthocyanins stimulate the protective phase II enzyme system, glutathione peroxidase, glutathione reductase, and glutathione S-transferase through the activation of the antioxidant response element (Shih et al., 2005; Wang and Stoner, 2008). Lopez-Martinez et al. (2011) assayed total phenolics and anthocyanins contents, antioxidant activity and quinone reductase induction in the murine hepatoma (Hepa 1 c1c7 cell line) as a biological marker for phase II detoxification enzymes of white, blue, red, and purple corns lime-cooked into masa and further baked into tortillas. All samples induced quinone reeducate; surprisingly, the blue variety and its corresponding masa and tortillas did not induce quinone reductase. Moreover, anthocyanin-rich purple and red corn extracts inhibit human colon cancer cell proliferation through promoting apoptosis and suppressing angiogenesis, being the red corn genotype with the highest potential (Mazewski et al., 2017). Anthocyanins in purple corn increased fecal butyric acid and prevented liver inflammation in high-fat diet-induced obese mice. They also prevented bodyweight gains (body weights decreased 9.8%), elevated the HDL cholesterol concentration and hepatic SOD and GPX activities, significantly decreased lipid peroxidation, and downregulated the gene expression levels of inflammation markers TNFa, IL-6, iNOS, and NF-кB. Therefore, anthocyanins can meliorate dietinduced obesity by alleviating both oxidative stress and inflammation (Wu et al., 2017). Anthocyanins and the corresponding aglycones are prone to degradation. The easy oxidation of anthocyanins, due to the antioxidant properties of these molecules, leads to degradation during processing. Processing of blue maize into tortillas reduced the amount of anthocyanins in >50% and these losses were correlated to the loss of antioxidant capacity (r ¼ 0.94). Most of these nutraceuticals leached into the cooking liquor or nejayote during lime-cooking and steeping. Del PozoInsfran et al. (2006) processed a white and two blue (Mexican and American) corn genotypes into dough or masa, tortillas, and chips (see Chapter 17). Anthocyanins losses during the preparation of masa, soft tortillas, and tortilla chips were 39%, 53%, and 78%, respectively. Using an acidification strategy with fumaric acid reduced phytochemical degradation for the overall process. However, the production of tortillas from nixtamalized flours obtained via thermoplastic extrusion significantly reduced the losses of anthocyanins (Mora-Rochin et al., 2010). Wet- and dry-milling affect anthocyanin distribution in colored corn fractions. When dry-milling purple corn, most anthocyanins are present in the pericarp (45.9% of total anthocyanins), while in wet-milling they concentrate in the steeping water (79.1% of total anthocyanins) (Li et al., 2017). Because corn processing generates a large amount of anthocyanins-rich coproducts, and the demand to use natural colors as an alternative to controversial artificial/synthetic dyes has increased significantly in the food market, colored corn is becoming an attractive potential source to extract anthocyanins at low cost (Lao and Giusti, 2016; Li et al., 2017). Aside from being use as functional ingredient for their color and health benefits, anthocyanins (maysin and maysin-30 -methyl ether) have shown antimicrobial activities (Nessa et al., 2012). Anthocyanins as functional ingredients have been used in colored cookies made from anthocyanin-rich corn flour (Van and Zili, 2016).

Carotenes and Xanthophylls Carotenoids (refer to Fig. 13.6, Chapter 13) are polyisoprenoids containing 40 carbons that provide color to plants. In cereal grains, they provide the yellow color to the endosperm. Carotenoids are divided into carotenes and xanthophylls. The molecular structure of xanthophylls is similar to that of carotenes, but they contain oxygen atoms, while carotenes are purely hydrocarbons with no oxygen (Dı´az-Go´mez et al., 2017a) (Fig. 14.3). Carotenoids are very minor constituents of corn (see Chapter 13). White corn is practically devoid of carotenes, whereas yellow genotypes contain significant amounts of both carotenes and xantophylls. Owing to the importance and relevance of

392

Corn

B-carotenes and other carotenoids, plant breeders have developed high-carotenoid genotypes via conventional breeding and via genetic modification (Burt et al., 2010; Zhu et al., 2017). The high-carotenoid corns can help to diminish deficiency of vitamin A, especially throughout the underdeveloped world, and used to supplement lutein, zeaxanthin, and other relevant related nutraceuticals. The use of high-carotenoid corn can also help to naturally pigment egg yolk and broiler skin and produce lutein-enriched eggs (Leeson and Caston, 2004). Burt et al. (2010) assayed concentrations and types of carotenoids associated to regular yellow corns and highcarotenoid corns and studied the impact of postharvest practices on their fate for 18 months storage. The yellow and high-carotenoid kernels are contained from 50 to 80 mg/g and 95 to 120 mg/g of total carotenoids, respectively. As expected, most carotenoids were associated to the endosperm. The carotenoids remained fairly stable during prolonged storage. The further study of three drying and storage regimes (freeze-drying and storage at
80°C; room temperature drying and storage; 90°C drying and room temperature storage) indicated that extreme caution is required to maintain carotenoid levels during storage because kernels dried at 90°C and stored for 18 months loose up to 40% of their original concentration. A genetically engineered high-carotenoid corn-based diet fed to mice reduced hepatomegaly and steatosis and promoted the repartitioning of fatty acids in the liver, away from triacylglycerol storage. At the molecular level, the high-carotenoid diet clearly reduced lipogenic gene expression, boosted catabolism, and increased hepatic retinoic acid levels and is likely a natural treatment for nonalcoholic fatty liver disease (Eritja et al., 2016). Carotenoids in nonphotosynthetic plant tissues are mainly found in chromoplasts, dissolved in oil droplets. Corn carotenoids are also present in substantial levels in amyloplasts, plastids specialized for storage of starch granules (Dı´az-Go´mez et al., 2017a). They are found primarily in the corneous endosperm (74%–86%), followed by the floury endosperm (9%– 23%), germ (2%–4%), and pericarp (1%) (Serna-Saldivar, 2010). White corn is practically devoid of carotenoids with only 3 mg/g of total carotenoids, whereas common yellow and high-carotenoid kernels contain up to 66 and 95 mg/g of total carotenoids (Table 14.7) (Burt et al., 2010; Dı´az-Go´mez et al., 2017a; Taleon et al., 2017). The predominant types in corn are lutein, zeaxanthin, and b-carotenes (Table 14.7), and since corn is important both as a human staple and as animal feed, it is an ideal source of dietary carotenoids. The absorption of these compounds is not regulated; therefore, their concentration in blood and peripheral tissues reflects ingestion. The main nutraceutical property of carotenoids in humans is the antioxidant molecular protection, especially because of their ability to quench singlet oxygen and interact with free radicals (Brinch-Pedersen et al., 2007). From the nutritional viewpoint, the most important metabolite is b-carotene because one molecule is converted in the human system into two molecules of the active form of vitamin A or retinol (Dı´az-Go´mez et al., 2017a). Furthermore, b-carotenes can regenerate the activity of vitamin E and possibly other oxidized antioxidants. b-Carotenes also act as an antioxidant that scavenges free radicals deep in human LDL and HDL as well as in cell membranes (Serna-Saldivar, 2010). As explained before, vitamin A is considered the most important liposoluble vitamin for human nutrition and health. The supplementation of vitamin A or b-carotenes prevents partial and complete blindness, xerophthalmia, cancer and CVD and strengthens the immune system. The intake of lutein, zeaxanthin, and cryptoxanthin prevents age-related macular degeneration (AMD) or dystrophy associated to blindness especially in geriatric patients (Serna-Saldivar, 2010). In addition, their high AOX activity protects the skin against ultraviolet radiation. The unsaturated structure of carotenoids makes them susceptible to degradation under high temperature, low pH, light, and reactive oxygen species (Dı´az-Go´mez et al., 2017a). The tortilla chip-making process has a significant effect on carotenoids content (De la Parra et al., 2007). The lime-cooking process significantly decreased the lutein content between 9% and 69% in yellow, red, and high-carotenoid corns. Levels of zeaxanthin decreased in yellow maize after lime-cooking as well as after baking and frying, adding up losses of 81%. Some corn products are fermented to facilitate grain processing and avoid bacterial contamination. Fermentation reduced carotenoid content due to the lower or acidic pH, while cooking of porridges for 10 min at a temperature of 95°C enhanced the liberation and extractability of carotenoids (Dı´az-Go´mez et al., 2017a). Oils extracted by cold pressing rich in carotenoids could be used as functional food. Cold pressing is environmentally friendly and yields good quality oil, but it is poor in overall oil yield. Hence, it is only preferable when special purpose oils are demanded. Cold pressed oils retain most of bioactive components such as carotenoids, making it a highly valued product. The total carotenoids in cold press corn oil were 7.41 mg/kg, 53 times higher compared to refined corn oil (G€ uneser et al., 2017).

Phytosterols Phytosterols include plant sterols and stanols; they are natural components of plant membranes. These compounds are also covered in Chapter 13 of this volume. Plant sterols are C-28 or C-29 sterols (Fig. 14.3), differing from cholesterol (C-27)

Minor Constituents and Phytochemicals of the Kernel Chapter

14

393

due to presence of an extra methyl or ethyl group on the cholesterol side chain. Stanols are saturated sterols, having no double bonds in the sterol ring structure (Fig. 14.3) (refer to Fig. 13.5, Chapter 13 for more detailed chemical structures). There has been much interest in the health benefits of consuming phytosterols, especially since the FDA issued a health claim for their use. Phytosterols compete for cholesterol absorption, and therefore, are considered hypocholesterolemic and preventive against cardiovascular diseases (Table 14.8). A daily intake of 2 g of plant sterols inhibit the absorption of cholesterol from the small intestine, thus effectively lowering total blood cholesterol by 5%– 20%. In addition, the intake decreases oxidized low-density lipoprotein (LDL) by 10%–15% and apolipoprotein B (Brufau et al., 2008; Ferretti et al., 2010; Serna-Saldivar, 2010). The supplementation of 0.2% b-sitosterol decreases the occurrence of chemically induced colon tumors. Stigmasterol inhibits several proinflammatory and matrix degradation mediators typically involved in osteoarthtitic-induced cartilage degradation, through the inhibition of the NF-kB pathway (Gabay et al., 2010). Other investigators have confirmed that lipoprotein changes after diet supplementation with phytosterols are associated with a decrease in plasma isoprostanes, markers of free radical-initiated lipid peroxidation (Mannarino et al., 2009). Phytosterols exert an inhibitory effect against lipid peroxidation of human low-density lipoproteins (Ferretti et al., 2010). Most phytosterols are associated to the oil located in the germ. The oil constitutes from 3.1% to 5.7% of the raw corn kernel weight. The total phytosterols content of the germ is 310 mg/100 g (Table 14.7). The predominant sterols are b-sitosterol (60.75%), campesterol (19.60%), and stigmasterol (6.44%). Other reported sterols are campestanol, D-7-campesterol, D-5,23-stigmastadienol, chlerosterol, brassicasterol, sitostanol, D-5-avenasterol, D-5,24-stigmastadienol, D-7-stigmastenol, and D-7-avenasterol (G€ uneser et al., 2017). The heat treatment of crude corn oil for 30 min at 140°C produced 12% losses of phytosterols (Giordano et al., 2016). When raw corn oil is subject to the regular refining process of degumming, neutralization, bleaching, and deodorization, 50% of phytosterols are removed (Moreau et al., 2009). Conventional commercial corn oil extracted from corn germ is different in composition to “new generation corn oils”. The levels of total phytosterols in corn fiber oil (hexane-extracted) and corn kernel oil (ethanol-extracted) were 9.5 and 1.3 times higher compared to commercial (germ) corn oil, respectively (Moreau et al., 2009). The fiber oil also contained important amounts of ferulated phytosterols esters, free phytosterols, and fatty acid phytosterols esters that lower serum cholesterol in laboratory animals. The most common class are ferulated phytosterols esters dominated by sitostanyl ferulate (Rose et al., 2010a), which is considered more efficient in lowering cholesterol. “New generation corn oils” could be used as ingredient of functional food. Nowadays, there are commercial products as Benecol, a dairy product (e.g., margarines) with stanols from cereals, including phytosterols from maize germ that lower cholesterol, or Mazola corn oil with 0.77% (w/w) of phytosterols that lower cholesterol absorption (Ostlind et al., 2002). A baked corn snack has been developed in which its consumption lowered serum lipids and differentiated liver gene expression in mice fed a high-fat diet (Domı´nguez-Uscanga et al., 2017).

Phospholipids Phospholipids are a class of lipids that can form bilayers and are a major component of all cell membranes. Like triglycerides, the backbone of phosphoglycerides is glycerol (a three-carbon alcohol), but only the primary and secondary alcohol residues of glycerol are esterified to fatty acids (long-chain carboxylic acids); the third site is esterified to a phosphate group (Fig. 14.3), which in turn is linked to a head of choline (PC), ethanolamine (PE), serine (PS), inositol (PI), or glycerol (PG) (Harrabi et al., 2010) (refer to Fig. 13.2, Chapter 13 for more detailed chemical structures). Phospholipids have a wide array of food and nonfood applications, mainly as nontoxic biodegradable emulsifiers, industrial lubricants, and nutrition supplements (Harrabi et al., 2010). In food, phospholipids increase the oxidative stability of fats and oils and high-fat food and act synergistically with tocopherols and phenolic antioxidants, such as flavonoids (Pokony, 2003). They have been used as functional ingredients in infant formulas (e.g., Nestl
e NAN) (Billeaud, 2014) and patents for corn phospholipidsemulsifiers have been filed (Schoeppe et al., 2014). Since phospholipids are natural emulsifiers, they are ideal “carriers” of healthy active ingredients for enhancing the dose efficiency and the potency of other bioactive compounds (Ting et al., 2014). Phosphatidylcholine, a generally recognized as safe (GRAS) substance, is the main constituent of “phytopharmaceutical-phospholipid” complexes, commercially named Phytosome (Indena, Italy). The Phytosome formulation increases the absorption of ingredients, improving their systemic bioavailability, for example Leucoselect Phytosome are procyanidins-phospholipids complex designed towards the cardiovascular system. Extract-phospholipid complex tested in vitro resulted in 54 times more cell permeability than the extract alone. In vivo, extract-phospholipid complex had 20 times higher plasma levels and five times higher brain levels than the extract alone (H€usch et al., 2012). Phospholipids have positive effects on human health; from the majority of the studies, it became evident that dietary supplementation has a positive impact in several diseases, for example, coronary heart disease, inflammation, or cancer (K€ ullenberg et al., 2012). Moreover, phospholipids reduce liver lipid levels, being able to interfere with sterol absorption

394 Corn

TABLE 14.8 Major Nutraceuticals Associated to Maize, Their Therapeutical Effect, and Novel Application as Functional Food Nutraceutical Compound

Anatomical Part

Preventive or Therapeutic Effect

Phenolics compounds

Simple phenolics (e.g., ferulic acid)

Pericarp and aleurone

Potent antioxidants and a nutraceutical that prevents inflammation (attenuate chronic neuroinflammation and induce neural progenitor cell proliferation), cancer (phase II enzymes inducers, and antiangiogenic), and LDL oxidation

FDA classifies ferulic acid as an antioxidant in the list of food additives. Corn nejayote (7.2%) improved ferulic acid and antioxidant capacity contents in pan bread by 745 times and 70%, respectively. Cold pressed germ oil retained 3.3 times more phenolic acids than conventional refined corn oil that could be used as functional ingredient

Flavonoids (e.g., anthocyanins)

Aleurone of blue-, purple-, and red-colored maize

Anthocyanins have antioxidant, anticancer, anti-obesity, and antiinflammation effects. Anthocyanins stimulate the protective phase II enzyme system; inhibit human colon cancer cell proliferation through promoting apoptosis and suppressing angiogenesis. Anthocyanins prevent liver inflammation, bodyweight gain; elevated the HDL cholesterol concentration and increase fecal butyric acid contents

Colored corn is becoming an attractive source to extract anthocyanins to be used as natural colors and for their health benefits. Anthocyanins have been used in colored cookies made from anthocyanin-rich corn flour

Carotenoids

Carotenes (e.g., b-carotene) and xantophylles (e.g., lutein, zeaxanthin, cryptoxanthin)

Starchy endosperm in yellow maize

b-Carotenes are converted to vitamin A or retinol. Carotenes prevent cancer, cardiovascular disease and strengthen the immune system. Prevent age-related macular degeneration and cataracts (opacity of the crystalline lens of the eye). Slow down symptoms of retinitis pigmentosa

Oils rich in carotenoids extracted by cold pressing with 53 times higher total carotenoid content than refined corn oil

Phytosterols

Sterols and stanols (e.g., b-sitosterol, stigmaesterol, campesterol)

Germ, pericarp, and aleurone

Compete with cholesterol for absorption (hypocholesterolemic). Prevents cardiovascular diseases. Decrease oxidized low-density lipoprotein (LDL). Reduce apolipoprotein B. Decrease chemically induced colon tumors. Inhibits proinflammatory involved in osteoarthritic-degradation. Decrease in plasma isoprostanes. Inhibitory effect against lipid peroxidation of LDL

Benecol, a dairy product (e.g., margarine) with stanols from cereals, including maize that lower cholesterol. Mazola corn oil with 0.77% (w/w) of phytosterols that lower cholesterol absorption. A baked corn snack that lowered serum lipids and differentiated liver gene expression in mice fed a highfat diet

Functional Food or Ingredient

Minor Constituents and Phytochemicals of the Kernel Chapter

14

395

TABLE 14.8 Major Nutraceuticals Associated to Maize, Their Therapeutical Effect, and Novel Application as Functional Food—cont’d Nutraceutical Compound

Anatomical Part

Preventive or Therapeutic Effect

Functional Food or Ingredient

Phospholipids

Phosphatydil Choline, Phosphatydil ethanol amine, Phosphatydil inositol, Phosphatydil serine

Germ, pericarp

Phosphatydil choline (lecithin), ethanol amine, inositol, and serine are essential for proper function of cell membranes and brain, are considered hypocholesterolemic, cardioprotective, and anticarcinogenic. Reduce liver lipid levels being able to interfere with sterol absorption in the intestinal lumen. Stimulate bile acid and cholesterol secretion and have the ability to increase plasma. Their deficiency is related to increased susceptibility to hepatic cancer. Choline positively affects brain and mental development, is one of the most important neurotransmissions. Phosphatidyl inositol and serine reduce blood triglycerides, fatty liver, bipolar disorders, and neurodegenerative diseases.

Used as functional ingredients in infant formula (e.g., Nestl
e NAN) and patents as phospholipids-emulsifiers from corn have been filed by Cargill. “Phytopharmaceutical
phospholipid” complexes, commercially named Phytosome (Indena, Italy), have been developed with four times more cell permeability, 20 times higher plasma levels, and five times higher brain levels of compounds

Policosanols

Long-chained alcohols (waxes): Octacosanol, Tricontanol, Hexacosanol, Dotriacontanol

Pericarp and germ

Have beneficial physiological activities such as reducing blood lipid levels and platelet aggregation

Corn and their distillers dried grain with solubles (DDGS) contain policosanols, which could be used to develop healthpromoting dietary products. Currently, a number of dietary supplements containing policosanol are commercially available in the US market

Arabinoxylans

Ferulated copolymers of arabinose and xylose

Pericarp cell walls

Arabinoxylans improve colon function and prevent diabetes mellitus, cardiovascular diseases, some sorts of cancer, and immunological disorders. Arabinoxylans have strong prebiotic effect by increasing Lactobacillus and Bifidobacterium populations, reducing gut infections and colon cancer, and increasing levels of intestinal short chain fatty acids which are known to reduce blood cholesterol

Corn arabinoxylans have been used for the improvement of the properties of gluten-free breads. These breads contained the highest amounts of dietary fiber (approximately 1 g total fiber/30 g bread); and more importantly, approximately 84% of this dietary fiber contribution was soluble

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in the intestinal lumen. Phospholipids stimulate bile acid and cholesterol secretion and have the ability to increase plasma HDL (Cohn et al., 2008). Phospholipid isolates could be used as hepatoprotective nutraceuticals. Particularly, phosphatidyl choline or lecithin helps to keep the proper functioning of the liver and to transport lipids and its deficiency is related to increased susceptibility to hepatic cancer (Serna-Saldivar, 2010). Lecithin and choline lower the risk of cardiovascular disease and positively affect brain and mental development of both the fetus and infants and their chronic inadequacy may be related to Alzheimer’s disease. Choline released from lecithin during metabolism is considered as one of the most important neurotransmitters and is commonly supplemented to geriatrics in order to maintain proper brain function (SernaSaldivar, 2010). Both phosphatidyl inositol and serine reduce blood triglycerides, fatty liver, bipolar disorders, and neurodegenerative diseases. The deficiency of these phospholipids is also related to increased susceptibility to hepatic cancer (Phillippy, 2003). Inositol, from phosphatidyl inositol or from the enzymatic hydrolysis of phytic acid by phytases, is known as a potent nutraceutical because it is essential for brain functioning, and therefore, is especially recommended for newborn babies and geriatrics. Inositol is considered a potent biological active compound and, by some nutritionists, as part of the B-vitamin complex because it helps to maintain cell membrane integrity and other important metabolic functions such as part of phosphatidyl inositol required for the proper functioning of the cerebrum and heart. Furthermore, it helps in the synthesis of RNA and to transport lipids and cholesterol. As a result, inositol is considered hypocholesterolemic, cardioprotective, and anticarcinogenic (Serna-Saldivar, 2010). Regular corn kernels commonly contain 243 mg/100 g of total phospholipids (Table 14.7). Most of these are associated to the lipid fraction which contains between 5.2% and 8.7% of total phospholipids. The major types found in corn are phosphatidyl choline (PC), inositol (PI), and ethanolamine (PE). PC is the most abundant class accounting for 51.4%–70.6% and is mainly found in the germ and pericarp, followed by PI (11.3%–25.1%) and PE (8.4%–12.6%). In contrast, phosphatidylethanolamine was found to be the most abundant class in the endosperm fraction (41.4%–48.5%), followed by phosphatidylcholine (30.2%–33.4%) and phosphatidylinositol (13.2%–14.4%). Unfortunately, most of these phospholipids are lost during the first step or degumming of the oil refining process (refer to Chapter 21) (Harrabi et al., 2010).

Policosanols A considerable amount of wax-like material that contains significant amounts of policosanols can be extracted from maize kernels. The wax is mainly associated to the outer pericarp layers and germ. The yield of this wax-like material from corn is about 10 mg/100 g of dry kernels (Serna-Saldivar, 2010). Policosanols are the chemical name for a mixture of long-chained aliphatic primary alcohols (Fig. 14.3), containing mostly docosanol (22:0), hexacosanol (26:0), octacosanol (28:0), triacontanol (30:0), and dotriacontanol (32:0) (Leguizamo´n et al., 2009). They are commercially obtained from sugarcane and cereal germs from the milling industries. Total policosanol content of corn kernels varied from 15.2 to 20.5 mg/kg (Table 14.7) and the major identified components are dotriacontanol, triacontanol, and tetracosanol (Harrabi et al., 2009). The corn pericarp contained higher policosanols (72.7–110.9 mg/kg) compared to the endosperm (4.0–16.2 mg/ kg) and germ (19.3–37.1 mg/kg) (Harrabi et al., 2009). Corn pericarp policosanols were mainly triacontanol, dotriacontanol, and octacosanol. In contrast, the corn germ fraction contained mostly dotriacontanol (>50%) and no triacontanol. The main components of corn endosperm policosanols were triacontanol and hexacosanol (Harrabi et al., 2009). There has been significant recent interest in policosanols as nutraceuticals. Their relevance in human health (Table 14.8) stems from a demonstrated effectiveness in physiological activities such as reducing serum lipid levels and platelet aggregation (Mannarino et al., 2014). There are numerous research studies indicating that the daily consumption of 1–20 mg of policosanols is effective in lowering total blood cholesterol, LDL-cholesterol, and insulin resistance in elderly people (>75 years) (Marazzi et al., 2011; Serna-Saldivar, 2010). Policosanols have been attributed with plasma cholesterollowering properties in humans (Leguizamo´n et al., 2009). Primary reported policosanols that have been suggested to contribute to the lowering serum cholesterol levels are octacosanol (C28), triacontanol (C30), and hexacosanol (C26). These compounds were first approved as a dietary supplement in Cuba, and they are currently commercialized in Caribbean and South American countries (Leguizamo´n et al., 2009). Moreover, policosanols improve mood state, which also seems to influence the efficacy of central processing, improving reactivity, and reducing reaction time in attention tests (Fontani et al., 2009). Policosanols have immense nutraceutical value as antioxidants, endorse proper arterial endothelial cell function, restrain platelet aggregation and thrombosis, and act as effectual treatment for sporadic claudication. Policosanols reduce cholesterol by inhibiting endogenous cholesterol biosynthesis via enzyme 3-hydroxy-3-methyl-glutaryl CoA (HMG-CoA) reductase activity (Kaur et al., 2014; Pasha et al., 2013). Corn and their distillers dried grain with solubles or DDGS (refer to Chapter 22) contain policosanols, which could be used to develop health-promoting dietary products (Leguizamo´n et al., 2009). Currently, a number of dietary supplements containing policosanol are commercially available in the US market.

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Arabinoxylans Arabinoxylans are the main soluble fiber components of corn and are mainly located in cell walls of pericarp where they play an important structural and functional role. These compounds are usually linked to phenolics like ferulic acid (Fig. 14.3), and therefore, also exert antioxidant properties. The bran coproducts obtained after dry-milling (refer to Chapter 15) or wet-milling (refer to Chapter 18) contain about 50% heteroxylans, 20% cellulose, 1%–2% lignin, 9%– 23% starch, 10%–13% protein, 4% dehydroxycinnamic acids, 2%–3% lipids, and 2% ash (Saulnier and Thibault, 1999). Arabinoxylans differ in their arabinose to xylose ratio and the degree and pattern of substitution of the arabinose residues along the xylan backbone. Their structural heterogeneity is not limited to arabinose substitution, but also for ferulic acid (Izydorczyk and Biliaderis, 1995). The corn fiber arabinoxylans yield ranges from 19% to 39% and in corn these molecules have a moderately branched structure of 0.5–0.8 arabinose/xylose with a sugar composition of arabinose 20%–35%, xylose 35%–55%, galactose 3%–7%, and glucose 1%–5%. Carvajal-Milla´n et al. (2007) reported that the most abundant diferulic isomer of corn fiber arabinoxylans was 5–50 , while Lapierre et al. (2001) reported a 8–80 moiety. Yadav et al. (2007) demonstrated that corn fiber hydrocolloids could contain over 4% proteins, up to 0.15% phenolics (ferulic and p-coumaric acid), and 0.43% lipids containing sterol-fatty acid esters, triacylglycerols, and free fatty acids. Arabinoxylans have relevant physicochemical characteristics such as solubility, viscosity, gelling, and hydration properties, which are closely related to their chemical structure, molecular size, conformation, and molecular interactions, which affect functionality and nutraceutical attributes. Arabinoxylans have been used to produce functional food and for the improvement of the properties of gluten-free breads. Ayala-Soto et al. (2017) assessed the role of corn arabinoxylans in production of gluten-free breads and concluded that these compounds increased water-binding capacity of flour and yielded breads containing 1 g total dietary fiber/30 g with higher specific volume and softer crumb texture. These quality parameters were best rated with the addition of 6% arabinoxylans to flours. This important source of soluble fiber containing ferulic acid moieties is known to exert health benefits like improving colon function and preventing diabetes mellitus, cardiovascular diseases, some sorts of cancer, and immunological disorders (Ogawa et al., 2005; Nin˜o-Medina et al., 2010; Rose et al., 2010a, 2010b; Saeed et al., 2011). The most noteworthy nutraceutical property is the strong prebiotic effect that shifts the dynamics of the intestinal bacterial population by increasing beneficial species of Lactobacillus and Bifidobacterium. As a result, arabinoxylans reduce gut infections and colon cancer and increase levels of intestinal short chain fatty acids or SCFA (Lopez et al., 1999; Rose et al., 2010a, 2010b). A study showed that arabinoxylans from corn were more fermentable in vitro compared to counterparts associated to wheat and rice bran. Corn arabinoxylans were more efficiently converted to SCFA by the intestinal microbiota (Rose et al., 2010b). The SCFA with higher production were acetate and propionate, which are known to reduce blood cholesterol through the downregulation of 3-hydroxy-3-methylglutaryl-CoA reductase (Lopez et al., 1999).

CONCLUSIONS Corn is a relevant resource of minor nutrients and phytochemicals known to enhance health and prevent metabolic diseases and cancer. The corn caryopsis contains significant amounts of most B-vitamins, provitamin A, tocopherols (vitamin E), and essential macro and microminerals which impact health among people who consume large amounts of this cereal grain. White, yellow, specialty (i.e., pigmented, high carotenoid, high oil), and nutritionally enhanced GMO corns vary in the amounts of these important compounds (see Chapter 10). Yellow endosperm genotypes provide significant amounts of b-carotenes or provitamin A, which prevents night blindness and susceptibility to infectious diseases, and three major xanthophylls (lutein, zeaxanthin, and cryptoxanthin), which exert antioxidant properties and prevent macular degeneration. Blue corn contains important amounts of different types of anthocyanins, which can also significantly decrease oxidative stress and the incidence of chronic diseases. The bioavailability of phosphorus, iron, zinc, and copper is questionable due to the presence of phytic acid, which has been genetically manipulated to lower its amounts in certain types of corns. In addition, corn is practically devoid of calcium, so people, especially preschool children, who depend on this cereal are more prone to develop anemia, stunt growth (infantilism), and osteoporosis. Additionally, whole corn contains relevant amounts of nutraceuticals such as simple phenolics (ferulic and cinnamic acids), flavonoids/anthocyanins, arabinoxylans, phytosterols, phospholipids, and policosanols, which prevent oxidative stress, inflammation, cancer and most chronic diseases responsible for >60% of the deaths experienced worldwide. Most of these phytochemicals are associated to the pericarp, germ, and aleurone layer, which are usually totally or partially removed during traditional or commercial drymilling procedures (see Chapter 15). Likewise, the lime-cooking process for production of corn tortillas and related

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products (see Chapter 17) significantly diminish levels of these important nutrients and phytochemicals. In short, the amounts of micronutrients and phytochemicals of corn-based food are mainly affected by the type of corn and traditional or industrial processes covered in other chapters of this book.

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Zavala-Lopez, M., Lopez-Tavera, E., Figueroa-Cardenas, J.d.D., Serna-Saldivar, S.O., Garcı´a-Lara, S., 2018. Screening of major phenolics and antioxidant activities in teosinte populations and modern maize types. J. Cereal Sci. 79, 276–285. Zhu, C., Farre, G., Zanga, D., Lloveras, J., Michelena, A., Ferrio, J.P., Voltas, J., Slafer, G., Savin, R., Albajes, R., Eizaguirre, M., Lopez, C., CanteroMartınez, C., Dıaz-Gomez, J., Nogareda, C., Moreno, J.A., Angulo, E., Estany, J., Pena, R.N., Tor, M., Portero-Otin, M., Eritja, N., Arjo, G., Serrano, J.C.E., Matias-Guiu, X., Twyman, R.M., Sandmann, G., Capell, T., Christou, P., 2017. High-carotenoid maize: development of plant biotechnology prototypes for human and animal health and nutrition. Phytochem. Rev. https://doi.org/10.1007/s11101-017-9506-4.

FURTHER READING Ayala-Soto, F.E., Serna-Saldı´var, S.O., Garcı´a-Lara, S., P
erez-Carrillo, E., 2013. Hydroxycinnamic acids, sugar composition and antioxidant capacity of arabinoxylans from different maize fiber sources. J. Food Hydrocolloid. 35, 471–475. Kale, M.S., Pai, D.A., Hamaker, B.R., Campanella, O.H., 2010. Structure-function relationships for corn bran arabinoxylans. J. Cereal Sci. 52, 368–372. Nin˜o-Medina, G., Carvajal-Milla´n, E., Lizardi, J., Rasco´n-Chu, A., Ma´rquez-Escalante, J., Gardea, A., Martı´nez-Lo´pez, A., Guerrero, V., 2009. Maize processing wastewater arabinoxylans: gelling capability and crosslinking content. Food Chem. 115, 1286–1290. White, P., Weber, E.J., 2003. Lipids of the kernel. In: White, P.J., Johnson, L.A. (Eds.), Corn Chemistry and Technology. American Association of Cereal Chemists, St. Paul, pp. 355–395.

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Chapter 15

Corn Dry Milling: Processes, Products, and Applications Brian Anderson and Helbert Almeida Bunge Milling, Inc., St Louis, MO, United States

HISTORY OF CORN DRY-MILLING The history of corn milling follows the history of corn crop domestication and development very closely, which most experts agree originated in North and Central America, and the need to develop various new applications. Corn was probably not introduced into Europe until after Columbus discovered the New World. This history goes back several thousand years, as recorded by several investigators. Mangelsdorf et al. (1964) reported the discovery of 7000-year old plant remains, which they identified as a wild progenitor of modern corn. More than 20,000 specimens of corn, about half with intact cobs, have been found in several caves in both the Tehuacan valley of Mexico and the southwestern United States. These corn samples have been dated as being between 4000 and 6500 years old (Mangelsdorf et al., 1967; Mangelsdorf, 1974). In addition to fossil corn, artifacts used with corn have been found. Belt (1928) observed that the ancient Indians of Nicaragua buried the stones they had used for grinding corn along with their dead. Undoubtedly, these stones were believed indispensable for the person’s future life. They were essentially the first rudimentary means of milling corn. For a look at the key developments of early corn dry-milling, one can examine the implements used in pioneer America. Initially, the early settlers adopted the use of the Indian “metate,” which was only a slight improvement over the early grinding stones. With this device, the corn was ground between a handheld stone and a concave bedstone. The world owns a repository under deep freeze conditions of thousands of ancient wild and modern domesticated corn lines at CIMMYT (International Center for the Improvement of Corn and Wheat) in Mexico. This is a world source of germplasm for potential of further genetic and agronomic development and new applications. Much opportunity lies at CIMMYT germplasm for further development of corn materials that address current available technologies and consumer needs. One step up from the “metate” was the hominy block. Early directions for making this device were quite simple, as recorded by Hardeman (1981): Near the cabin, cut off a hardwood tree 3 or 4 ft above the ground and hollow out the top. From a springy limb of another tree extending over the stump, tie a pestle or block of wood by a strong line. The hominy block was operated by repeatedly plunging the wood pestle into the hollow stump until the corn had been sufficiently crushed into meal. The hominy block was eventually replaced by a single-family, stone device called a quern (pronounced “kwern”). This was a small, burred-stone grinding apparatus, apparently invented in ancient Rome. It was operated by pouring corn through the cone-shaped axle hole at the top. An offset handle was used to rotate the cap-stone on the stationary “netherstone,” and the corn meal worked out between the stones and fell into a tub surrounding the quern. The principle of this type of revolving stone mill was applied on a much larger scale, as early as 1620 (Hardeman, 1981). It was further developed to become the local grist mill, which was eventually used to process both corn and wheat. Energy to operate the mill was supplied by livestock, occasionally by humans, and by water. By the mid-1800s, most of the mills in the United States were operated by water, although steam-driven mills were used in some sections of the country. Some of these grist mills are still used to grind corn today, particularly in the southern states (Larsen, 1959). As was the case in pioneer America, the mills are relatively small, and their packaged product distribution is limited to a fairly localized geographic area. This limitation is largely dictated by shelf life considerations, because these “full-fat” or “bolted” products

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(described in more detail later in this chapter) still contain most of the corn germ and associated enzyme systems and are, therefore, subject to rancidity, especially in hot, humid weather, if improperly stored. In the late 1800s and early 1900s, the above-described milling systems gradually gave way to more sophisticated “tempering-degerming” milling systems in which the corn germ and corn bran were more completely removed from the endosperm portion of the kernel. This process is described in more detail later in this chapter. These newer milling methods were developed to meet the demands of the evolving brewing and ready-to-eat cereal markets, which required lower fat, higher-starch products with longer shelf life. One such development was the “hominy mill,” which was invented by John Beall of Decatur, IL. On February 19, 1901, he was awarded US Patent 668,252 for this device, which consisted of a truncated cone with conical protuberances that rotated within a housing or “concave” (Beall and Crea, 1901). In this patent, Beall claimed that the “salient parts of the cones tend to break the grains and remove the germ; the rounded surfaces act to denude and scour the broken grain.” With various improvements over the years, the “Beall Degerminator” is still in regular use today, more than 100 years after the original patent was issued.

INDUSTRY OVERVIEW As has been the trend in many other industries (brewing, flour milling, dairy, etc.), the corn dry-milling industry in the United States has evolved from small mills in virtually every community, serving the local market, to the current situation in which much fewer, larger mills serve wider geographic markets. This consolidation within the industry is the direct result of the longer shelf life of degermed corn products, along with the economies of scale, which have allowed the successful and economical shipments of dry-milled products for greater distances in larger quantities. It is also worthy to note that in today’s milling terminology and industry data documentation, traditional “dry corn milling” for food ingredients can be confused with dry corn milling and/or fractionation for fuel alcohol production. According to Brekke (1970a), there were 152 dry corn mills in the United States with a daily capacity of 50 cwt or more in 1965. By 1969, this number had dropped to 115. As of 1984, only 88 mills were in operation, and of these, 66 were smallcapacity mills located primarily in the South and Southeast (Anonymous, 1984). The remaining larger-capacity mills were located primarily in the Midwest (i.e., in the Corn Belt). By 1997, the number of corn dry mills operating in the United States had dropped to 51 (Anonymous, 1997a), and by 2017, this number had further decreased to only 41 (Anonymous, 1984; North American Millers’ Association, 2017). Table 15.1 lists the principal dry-milling facilities in the United States as of 2017, grouped into “daily grind” categories based on unpublished industry data. The facilities are further ranked within the categories based on unpublished information and our knowledge of the industry. Note that most of these facilities are located in the Midwest region of the United States in areas where corn is most readily available and of the highest quality. This table lists 12 mills out of the 41 in operation in 2017. The remaining 36 mills have grind capacities of less than 12,000 bu (305 metric tons [t]) per day and, in many cases, considerably less than that. It is estimated that the 12 largest facilities shown in Table 15.1 have a combined daily grind capacity of about 525,000 bu. (13,335 t), and that this capacity represents over 80% of the total U.S. dry-milling capacity. Most of these large mills utilize the previously mentioned tempering-degerming milling process. This tempering-degerming process is most effective and efficient when the mill is operated under constant load and steady state conditions. Therefore, the miller would prefer to add or delete days from the weekly grind schedule rather than significantly change the number of bushels processed per day. If it is assumed that the 12 largest mills account for 83% of the total bushels milled, this would mean that the total U.S. dry-milled grind is approximately 632,000 bu (16,050 t). Further assuming an average 5-day-per-week “grind schedule,” this would equate to an annual volume of corn consumed by the U.S. corn dry-milling industry of about 164 million bushels (4.165 million tons). This number is consistent with recent estimates of the North American Millers’ Association, which referenced 165 million bushels per year in a statement before the EPA Scientific Advisory Panel hearing on StarLink corn (North American Millers’ Association, 2001). To put this figure in perspective, it represents less than 2% of U.S. annual corn production (9.54 billion bushels [242.3 million tons] in 2001) and compares with annual grinds of about 85 million bushels (2.16 million tons) in the 1930s and about 125 million bushels (3.175 million tons) in the 1960s for the U.S. corn dry-milling industry (Brekke, 1970a). A notorious advancement in the corn dry milling industry is the propagation of formal collaborations across the whole supply chain starting from seed and grain sourcing and ending with consumer packaged goods companies and consumers (Fig. 15.1). Consumers are not only more aware of health and nutrition of food, but also traceability and general corporate responsibility practices. This awareness drives much of consumer acceptance or rejection of food nowadays.

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TABLE 15.1 Principal Corn Dry-Milling Facilities and Locationsa Company

Mill Location

50,000 bu per day (1271 tons) or more Bunge

Atchison, KS Crete, NE Danville, IL

Cargill

Paris, IL

Lifeline Foods LCC

St. Joseph, MO

36,000–50,000 bu per day (915–1271 tons) Agricor

Marion, IN

SEMO

Scott City, MO

12,000–36,000 bu per day (305–915 tons) ADM

Lincoln, NE

Didion

Cambria, WI

Iowa Corn

Glidden, IA

Wilkens Rogers Inc.

Elicott City, MD

The Quaker Oats, Co

Cedar Rapids, IA

a

Data from Anonymous (2001) and updated.

North American dry milled corn supply chain

Dry mill streams Whole grain Growing contract

Value stream (further processed) Extrusion - pre gel flour - inclusions

Bran Germ Grit/Germ

Corn farmer base

Seed

WaterCrop protection

Storage

Grit

Food processor - cereals - snacks - brewing Animal feed market - dairy - beef cattle - poultry

Credit

Miller/ Processor

Feed/Food/Industrial channels

Flour Meals

Retail - hot cereal mix - rice alternative

+ Whole/cleaned seed

Fertilizer

6 Major mill streams 3 Value added streams 5 Potential Food/Feed/Industrial Channels

Industrial - binders - oil drilling

Government food aid - program - emergency

FIG. 15.1 Typical supply chain spectrum for the North American corn dry-milling industry (Anderson, 2014).

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CORN GRAIN QUALITY FOR DRY-MILLING A critical initial step in modern industrialization of corn is securing and monitoring the quality of the grain with the purpose of achieving and maintaining efficiencies, effectiveness, and competitiveness. Selected grain quality properties for drymilling are shown in Table 15.2. As a general guidance, a few selected desired grain attributes are large and/or uniform size, relatively easy pericarp removal, minimum stress cracks, maximum hard endosperm within the dent corn category, minimum foreign materials, minimum breakage, and no odors and mycotoxins. As more analytical instrumentation becomes available, other properties can now be measured and related to process effectiveness and finished ingredient functionality (Table 15.3). Corn traits around the world vary and dry-millers develop their own specifications depending on corn varieties available to them, their

TABLE 15.2 Corn Grain Quality Properties for Dry-Milling Incoming Corn Specifications Maximum

Optimal

Test weight, kg/hL

75.9

72.1–73.4

Moisture, %

16.0

15.5

Small kernel (through US 5/16 wire), %

15.0

10.0

Stress cracks

5.0%

None

Total damage

2.0%

2.0%

Infestation

None

None

Aflatoxin

None

None

Soybeans

None

None

Odor

None

None

None

None

Mold Density, g/cm

3

1.27

Contamination (wood/metal)

None

None

Heat Damage (Carmel/black), kernels/500 g

3

None

TABLE 15.3 Analytical Methods Useful to Monitor Corn and Ingredient Properties TADD (Tangential Abrasive Dehulling Device)

Grain hardness from weight removed by abrasive milling of kernels with a Dehulling Device (TADD). High values indicate soft kernels

Thousand kernel weight

TKW useful to estimate kernel size

Floaters

Proportion of kernels that float in a solution of a given density. Endosperm is naturally packed loosely in soft kernels with high floater values

Test weight

Bulk density of grain expressed in pounds per bushel in the US. High values indicate high amount of large, plump kernels with a greater proportion of starch-rich endosperm

Translucency

Visual observation of kernels over a light box and rating against a set of standards. Universal use and highly valuable among experts

Stress Cracks

External and internal damage caused by abrasion, mechanical stresses, and cuts that cause physical rupture of the endosperm or pericarp

RVA (Rapid Viscoamylograph)

Pasting properties by heating and slow mixing. Hard corn produces lower viscosity peaks and smaller ascending slopes

Density

Density of kernels calculated after their true volume is accurately measured by gas displacement with a Pycnometer

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processing equipment, and the types of corn dry-milled ingredients demanded by their market. Finally, uniformity of grain properties is an essential for the massive flow, processing, and controls practiced at large-scale dry-milling facilities; this gives operators opportunity to adjust and maintain the process at steady state. The overall process takes hours to achieve steady state after any given adjustment along the line which forces operators to minimize these changes to maintain consistent quality of milled corn products.

Dry-Milling Processes Nowadays, there are a number of different dry-milling processes that can be used to grind corn kernels for human food applications. The resulting milled products (which are typically referred to as “prime products” or “white goods”) differ slightly in their attributes depending upon the milling method utilized. Accordingly, some of these different products each have their own Standard of Identity sections within the Code of Federal Regulations (CFR, 2000) and can generally be categorized as full-fat, bolted, or degermed corn products. Other relatively new dry-milled corn ingredients are flours of corn bran, pregel, viscosity, and whole grains with a variety of functional food properties. The grain-based food market continues to evolve and demands new functional corn ingredients. It is the job of all supply chain players to develop and adapt processing technologies, to respond to the demands of the market, and participate on driving the trends with state-ofthe-art science and technology that delivers value to consumers. The milling systems used to produce the above products are each reviewed in more detail, but they all share several basic process steps (Fig. 15.2). All starts with the receipt of the raw material-shelled yellow or white dent corn. When a truckload of corn arrives at the mill, a representative sample is taken, typically via a sample probe (manual or hydraulic). This sample is then tested to determine whether the load meets the miller’s specifications. These “milling quality” specifications vary between mills, but the attributes measured usually include certain aspects of corn quality (test weight, moisture), corn defects (broken kernels, heat damage, stress cracks, etc.), foreign material (soybeans, other grains, rodent pellets, etc.), and evidence of infestation. Additionally, a ground portion of the corn sample would be viewed under UV light and/or tested by an enzyme-linked immunosorbent assay (ELISA) “quick test” to check for the possible presence of aflatoxin (see Chapter 9). Finally, depending on specific circumstances, tests for other mycotoxins (i.e., fumonisin) or unapproved genetic modifications (i.e., StarLink) might also be conducted using the ELISA technology. An adverse finding for any of the abovementioned tests could result in the rejection of that load of corn. If the representative sample meets all of the required specifications, the load of corn is accepted, dumped, and placed into storage. Depending on the size of the mill (and many other considerations), on-site corn storage could be as small as several thousand bushels or as large as several million (Anonymous, 1997b). The actual milling process is usually preceded by a rigorous mechanical cleaning of the corn kernels. This step typically utilizes aspiration to remove dust, fines, cob particles, and stalk pieces; size separation to remove coarse particles, broken kernels, and other foreign material; and magnets to remove tramp metal, rust chips, and other ferrous particles from the sound, whole kernels. In many cases, a destoner is also used to remove stones, glass, nonmagnetic metal, and other heavy extraneous material (Wanzenried, 1986) from the corn stream. The ultimate objective of this cleaning step is to provide the milling process with clean, sound, whole kernels that are essentially free of extraneous material.

Full-Fat Milling Process As the name implies, this milling process yields products that contain virtually all of the “fat,” or corn oil, originally present in the corn kernel. The Code of Federal Regulations (21CFR137.250) describes one such product, white corn meal, as follows: (a) White corn meal is the food prepared by so grinding cleaned white corn that, when tested by the method prescribed in paragraph (b) (2) of this section, not less than 95% passes through a no. 12 sieve, not less than 45% through a no. 25 sieve, but not more than 35% through a no. 72 grits gauze. Its moisture content is not more than 15%. In its preparation, coarse particles of the ground corn may be separated and discarded, or reground and recombined with all or part of the material from which they were separated, but in any such case the crude fiber content of the finished corn meal is not less than 1.2% and not more than that of the cleaned corn from which it was ground, and its fat content does not differ more than 0.3% from that of such corn. The contents of crude fiber and fat in all the foregoing provisions relating thereto are on a moisture-free basis. Likewise, yellow corn meal is described in 21CFR137.275 as follows:

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FIG. 15.2 Basic unit operations for commercial dry-milling of corn.

FIRST BREAK DEGERMINATION

THRU STOCK

TAIL STOCK

ASPIRATOR

SIFTER

GRAVITY TABLE

TEMPERING

COLOR SORTER

Water & Stream

ASPIRATOR Germ/Fines

Bran

Discolored Grits

Flour

CORN SCALE Bu/Hr

Flour

SIFTER

Bran

DRYER/COOLER

ASPIRATOR Germ

CLEANING

Bran

FINISH/COOLER

GRAVITY TABLE

Grits

REDUCTION ROLLS STORAGE Germ

SIFTER

Grit meal

DRYER/COOLER

Bran

WHOLE CORN

ORIGIN

Meal

ASPIRATOR DRYER/COOLER

REDUCTION ROLLS

Flour

DRYER/COOLER

SIFTER

Hominy feed

Yellow corn meal conforms to the definition and Standard of Identity prescribed by Sec. 137.250 for white corn meal except that cleaned yellow corn is used instead of cleaned white corn. Note that these standards of identity descriptions require that the fat content of the milled products differs by not more than 0.3% from that of whole corn. Because most of the corn oil is located in the germ, this implies that all (or certainly most) of the germ must remain in the milled product. As a result, this milling process is sometimes referred to as the “nondegerming process” (White and Pollak, 1995). Also, these standards allow for some reduction in the crude fiber content. As the crude fiber is most highly concentrated in the bran coat (pericarp) and tip cap, this implies that some of the larger bran and tip cap pieces can be removed from the milled product. With the full-fat, or nondegerming, process, millstones were traditionally used to grind the corn and, to a large extent, that remains true today. As a result, these products are often referred to as “stone ground” corn meals. While this milling

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process is limited primarily to small mills serving local retail markets in the south-east portion of the United States, it is still widely used in Africa, Latin America, and Asia (White and Pollak, 1995). Typically, white dent corn would be stone ground into a meal. In some cases, a small amount of the larger bran pieces would then be removed by “bolting” (sifting), and the resulting full-fat corn meal, exhibiting a rich, full flavor and soft texture, would be packaged into paper bags (2, 5, 10, and 25 lb [0.91, 2.27, 4.54, or 11.35 kg, respectively]) for the local or regional retail trade. As noted earlier, full-fat corn meal has a relatively short shelf life because of the high fat content, large surface area, and the action of the native corn germ enzymes that are present (Brekke, 1970a). Collectively, these factors can induce rancidity, which is an off-flavor quality in food related to the enzymatic or oxidative breakdown of fats. These products may also be sold as “enriched” (21CFRI37.260) with the proper addition of thiamin, riboflavin, niacin, folic acid, and iron (only in forms that are harmless and bioavailable) as summarized below: (a) Enriched corn meals are the food, each of which conforms to the definition and Standard of Identity prescribed for a kind of corn meal by Secs. 137.250, 137.255, 137.265, 137.270, 137.275, 137.280, 137.285, and 137.290, except that: (1) it contains in each pound (454 g) not less than 2.0 mg (mg) and not more than 3.0 mg of thiamin, not less than 1.2 mg and not more than 1.8 mg of riboflavin, not less than 16 mg and not more than 24 mg of niacin or niacinamide, not less than 0.7 mg and not more than 1.0 mg of folic acid, and not less than 13 mg and not more than 26 mg of iron (Fe); (2) it may contain in each pound not less than 250 U.S.P. units and not more than 1000 U.S.P. units of vitamin D; and (3) it may contain in each pound not less than 500 mg and not more than 750 mg of calcium (Ca); provided, however, that enriched self-rising corn meals shall contain in each pound not more than 1750 mg of calcium (Ca). Iron and calcium may be added only in forms which are harmless and assimilable. The substance referred to in this paragraph (a) (3) and in paragraphs (a) (1) and (2) of this section may be added in a harmless carrier, which does not impair the enriched corn meal; such carrier is used only in the quantity necessary to affect an intimate and uniform admixture of such substances with the kind of corn meal used. Dried yeast in quantities not exceeding 1.5% by weight of the finished food may be used. (b) The name of each kind of enriched corn meal is the word “Enriched” followed by the name of the kind of corn meal used which is prescribed in the definition and standard of identity therefore. (c) Label definition. Each of the ingredients used in the food shall be declared on the label as required by the applicable sections of parts 101 and 130 of this chapter. The products may also be sold as “self-rising” (21CFR137.270 for white corn meal and 21CFR137.290 for yellow corn meal) with the proper addition of sodium bicarbonate, an acid-reacting phosphate, and salt. A portion of 21CFR137.270 for self-rising white corn meal is summarized as follows: (a) Self-rising white corn meal is an intimate mixture of white corn meal, sodium bicarbonate, and one or both of the acid-reacting substances, mono-calcium phosphate and sodium aluminum phosphate. It is seasoned with salt. When it is tested by the method prescribed in paragraph (b) of this section, not less than 0.5% of carbon dioxide is evolved. The acidreacting substance is added in sufficient quantity to neutralize the sodium bicarbonate. The combined weight of such acidreacting substance and sodium bicarbonate is not more than 4.5 parts to each 100 parts of white corn meal used. In many cases, the corn meal is both enriched and self-rising, and it may further be mixed with wheat flour to result in an enriched self-rising corn-meal mix. As noted above, these mixes would be small-packaged for the local retail market. Typically, these various full-fat corn-meal products would be used by the home baker to make such goods as corn bread, corn muffins, corn cakes, hush puppies, corn dogs, breading mixes, stuffing mixes, and many other related items.

Bolted Milling Process For this milling process, the word “bolted” refers to the use of “bolting cloth” which, according to the Dictionary of Milling Terms, is defined as: The woven material used to sift, or classify by size, milled cereal products. The materials used to produce bolting cloth include silk, nylon, polyester, iron, phosphor bronze, copper, stainless steel, or tin-plated steel (Wingfield, 1989). In this context, the sifting process is used to remove some of the larger particles, predominantly bran and tip cap pieces and germ fragments, from the milled corn. Again, the Code of Federal Regulations provides guidance and clarification. The standard of identity for bolted white corn meal, as defined in 21CFR137.255, is as follows: (a) Bolted white corn meal is the food prepared by so grinding and sifting cleaned white corn that: (1) its crude fiber content is less than 1.2% but its fat content is not less than 2.25%; and (2) when tested by the method prescribed in Sec. 137.250(b) (2), except that a no. 20 standard sieve is used instead of the no. 12 sieve, not less than 95% passes through a no. 20 sieve, not less than 45% through a no. 25 sieve, but not more than 25% through no. 72 XXX grits gauze. Its moisture

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content is not more than 15%. In its preparation, particles of ground corn which contain germ may be separated, reground, and recombined with all or part of the material from which it was separated, but in any such case the fat content of the finished bolted white corn meal does not exceed by more than 0.3% the fat content of the cleaned corn from which it was ground. The contents of crude fiber and fat in all the foregoing provisions relating thereto are on a moisture-free basis. The definition for bolted yellow corn meal (21CFR137.280) is equally straight forward: Bolted yellow corn meal conforms to the definition and Standard of Identity prescribed by Sec. 137.255 for bolted white corn meal except that cleaned yellow corn is used instead of cleaned white corn. The key requirements in these descriptions are the crude fiber content and the fat content. For full-fat corn meal, the crude fiber content must be more than 1.2%, dry basis (db), but for bolted corn meal, it must be less than 1.2%, db. Additionally, full-fat corn meal must exhibit the fat content of whole corn (about 4.0%, db) plus or minus 0.3%, whereas bolted corn meal can have a fat content as low as 2.25%, db. Obviously, these requirements for bolted corn meal can be met only when a certain amount of the corn bran and corn germ are removed from the milled product stream. Although millstones may be used to grind the corn for bolted products (as is the case for full-fat products), roller mills or hammer mills are more typically used. This grinding step is followed by a bolting, or sifting step, where a portion of the germ and bran are removed. Additionally, other process steps, such as aspiration, may be utilized to achieve this separation. The standards of identity also say that fine corn flour (i.e., the material that goes through a 72-mesh sieve) is allowed in bolted corn meal (25%, maximum) than in full-fat corn meal (35%, maximum). Therefore, the bolting process may also produce additional milled products such as corn flour and hominy grits. The standard of identity for white corn flour (21CFR l37.21l) is as follows: (a) White corn flour is the food prepared by so grinding and bolting cleaned white corn that when tested by the method prescribed in paragraph (b) (2) of this section, not less than 98% passes through a no. 50 sieve and not less than 50% passes through no. 70 woven-wire cloth. Its moisture content is not more than 15%. In its preparation, part of the ground corn may be removed, but in any such case, the content (on a moisture-free basis) of neither the crude fiber nor fat in the finished white corn flour exceeds the content (on a moisture-free basis) of such substance in the cleaned corn from which it was ground. As has been the case with other standards, yellow corn flour (21CFR137.215) is simply defined by replacing the words “cleaned white corn” with “cleaned yellow corn” in the above description. Because these particular standards of identity are very general and contain no minimums for crude fiber or fat contents, the word “bolted” (or “degermed,” if appropriate) is sometimes unofficially added to more definitively describe the particular product (and milling process). No standard of identity exists for hominy grits, but these products generally exhibit larger granulation than corn meals. With industry concurrence, the standards of identity for “corn grits” (21CFR137.230) and “yellow grits” (21CFR137.245) were revoked in 1990 due to unnecessary granulation constraints and other issues. Today, any dry-milled corn product that is larger in particle size than corn meal can be called “corn grits.” As was the case with full-fat products, most bolted products utilize white corn, although some yellow bolted products are manufactured, particularly outside of southeastern United States. Most bolted products are packaged in paper bags (2, 5, 10, and 25 lb equivalent to 0.90, 2.25, 4.54, and 11.35 kg) for the retail trade, although some quantity is sold in larger bags (51 or 100 lb. equivalent to 23.1 o 45.4 kg) or in bulk to the industrial market (i.e., hush puppy mix, breading mix, etc.). Finally, these bolted products may also be enriched (21CFR137.260) with the addition of thiamin, riboflavin, niacin, folic acid, and iron, and they may be sold as self-rising (21CFR l37.270 for white corn meal and 21CFR137.290 for yellow corn meal) with the addition of sodium bicarbonate and an acid-reacting phosphate salt. In many instances, the corn meal is both enriched and self-rising, and it can also be mixed with enriched wheat flour to result in an enriched self-rising mix for the retail market. The applications are similar to those described for full-fat corn meal.

Tempering-Degerming Milling Process As the name implies, this milling process involves adding moisture to the corn kernel (tempering) to facilitate the removal of the germ and bran coat (degerming). The Code of Federal Regulations again provides helpful insight into this product category. The standard of identity for degermed white corn meal (21CFR137.265) describes the following product: (a) Degerminated white corn meal, degermed white corn meal, is the food prepared by grinding cleaned white corn and removing bran and germ so that: (1) On a moisture-free basis, its crude fiber content is less than 1.2% and its fat content is less than 2.25%. (2) When tested by the method prescribed in Sec. 137.250(b)(2j), except that a no. 20 standard sieve is used instead of a no. 12 sieve, not less than 95% passes through a no. 20 sieve, not less than 45% through a no. 25 sieve, but not more than 25% through no. 72 XXX grits gauze. Its moisture content is not more than 15%.

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(b) For the purpose of this section, moisture, fat, and crude fibers are determined by methods therefore referred to in Sec. 137.250(b)(l). For degermed yellow corn meal (21CFR137.285), the words “cleaned white corn” are replaced by “cleaned yellow corn.” The first observation from these standards of identity is that the words “degerminate” and “degerm” are interchangeable, but the limits on crude fiber and fat are probably of greater significance. These maximums imply that the fiber and fat contents should be as low as possible so that the starch content can be as high as possible; tempering is a key process in achieving this goal. Tempering aids in fractionating and separating the corn kernel into its components-endosperm, germ, and pericarp (or bran coat) because the texture, density, and grinding characteristics of each component are slightly different, and tempering magnifies these differences (Giguere, 1993). This fact is critically important because the goal of the degerming process is to remove the pericarp, tip cap, and germ portions from the endosperm portion of the corn kernel as completely as possible, while recovering the maximum amount of low-fat, low-fiber endosperm as large pieces (Brekke, 1970a; White and Pollak, 1995). Considerable research has been conducted on this tempering step. In the 1960s and 1970s, research was aimed at optimizing this process (Brekke et al., 1961, 1963; Brekke and Weinecke, 1964; Brekke, 1966, 1967, 1968, 1970a, b; Brekke and Kwolek, 1969), and more recently, the research has been aimed at better understanding it (Eckhoff and Okos, 1989; Ruan et al., 1992). It has been determined, for example, that moisture mainly enters the kernel through the tip cap area and moves to the crown of the kernel via capillary action. The moisture diffuses into the seed coat and outer aleurone layer and then moves into the endosperm. Because the movement of moisture into the kernel requires time, temper time is critical. Too short a temper time may be inadequate to achieve the necessary level of moisture nonuniformity; too long a time may allow the moisture content to re-equilibrate, thereby defeating the entire reason for tempering (Mehra and Eckhoff, 2001; Mehra et al., 2001). Therefore, the proper temper duration is essential for the effectiveness of this process. Likewise, the quantity of tempering water, its temperature, and its method of addition are important factors. Much of the scientific literature on tempering cites a three-stage tempering procedure (Brekke, 1970b; Brekke et al., 1963), but work on a two-stage procedure has also been conducted (Brekke, 1967). Ultimately, because of variations in corn age, hardness, breakage susceptibility, moisture content, and kernel size, tempering continues to be a significant portion of the “art” of corn drymilling. In addition to the “miller’s art,” the quality and consistency of the starting corn determine, to a large extent, the efficiency of the dry-milling process and the quality and consistency of the dry-milled products. The age-old concept that “corn is corn” is rapidly changing as millers strive to meet customers’ ever-increasing demands. While the manufacturing process for degermed corn products has not fundamentally changed since the introduction of the degerminator in the early 1900s, the customers’ expectations in terms of quality, consistency, and functionality have changed. The dry-milling industry is addressing this demand for higher quality with large investments in specialized equipment and, more importantly, the procurement of higher quality, uniform corn. What constitutes “high-quality corn” to the dry-miller? Considerable research has been undertaken over the years to help answer that question. Brekke (1968) reported that stress crack formation had an adverse effect on degerminator performance, especially as it relates to flaking-grit yields. Paulsen and Hill (1985) showed that flaking-grit yield was significantly increased by selecting corn with low breakage susceptibility and high test weight, based on full-scale milling trials. Peplinski et al. (1992) confirmed the above findings and further reported that first-break grit yield was higher for corn with test weight above 75 kg/hL or 58 lb/bu (and breakage below 16% as measured by the Stein breakage test). Peplinski also noted that corn is less susceptible to breakage when its density is high (as measured by low flotation and high test weight) and when the percentage of stress-cracked kernels is low. Wu and Berquist (1991) showed that corn density and hardness are positively correlated with milling yields, and Kirleis and Stroshine (1990) concluded that corn kernel density was the best single predictor of dry-milling quality. Additionally, Dorsey-Redding et al. (1991) reported that kernel hardness showed a significant correlation with protein content, test weight, and kernel density, and Wehling et al. (1996) reported that near-infrared reflectance (NIR) spectroscopy can be used to measure some combination of the properties discussed above to predict dry-milling characteristics for initial screening purposes. Finally, Yuan and Flores (1996) showed that protein content, true density, and the ratio of hard to soft endosperm have high correlations with dry-milling yields. From the above overview, it is obvious that a significant number of grain traits affect milling quality. These include test weight, kernel size, kernel density, kernel hardness, percent horny endosperm, protein content, and stress cracks. Other factors such as kernel shape and uniformity, as well as low mycotoxin levels, are also important. Unfortunately, a number of factors (some controllable and some not) affect corn quality before it reaches the mill. These include corn variety, weather and climate, disease pressure, insect damage, harvesting conditions, drying methods, and additional cleaning and handling of the grain. The combination of these factors determines final grain quality.

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In response to these many variables, there has been a trend among dry corn millers to develop well-defined evaluation and selection protocols for purchasing “milling quality” corn. Several of the above-mentioned attributes, such as test weight and stress cracks, can be quickly and accurately measured at the probe stand. These properties, therefore, could be part of a miller’s corn quality specifications (and premium program) because they can be measured truckload by truckload in real time. Other millers have developed lists of approved hybrids from which growers may choose, and some have set up sophisticated “identity preserved” programs, which incorporate extensive documentation and allow complete traceability. In the future, the relationships among the seed company, the grower, the miller, and the end user is becoming stronger. Several tempering-degerming systems are in commercial use, and each has its strengths and weaknesses. There are trade-offs, for example, between acceptable fat and fiber levels and acceptable yields; trade-offs between the capability to produce large endosperm pieces (i.e., flaking grits) and capital and energy requirements; and trade-offs between the capability to produce many different product granulations and plant space availability. These various systems are reviewed individually in this chapter, but ultimately, the choice of a milling system is based on each milling company’s particular market needs.

Beall Degerminating System Although other types of degerming equipment have been developed since 1901 (and are discussed later in this section), the Beall degerminator continues to be the mainstream for U.S. milling companies utilizing the tempering-degerming system. It was directly responsible for the dry-milling industry’s consolidation from numerous small, locally owned and operated grist mills with limited capacity and distribution to the larger, more efficient facilities in existence today. It also allowed for the marketing of high-quality, low-fat dry-milled corn products with greatly extended shelf life and product stability to customers to whom those attributes were important, such as the ready-to-eat (RTE) and brewing industries. For a very detailed discussion of all aspects of the Beall degerminating process, see the reviews by Stiver (1955) or Brekke (1970a). As was mentioned earlier, the Beall degerminator, or hominy mill, was patented in 1901 and began to see use in the U.S. corn dry-milling industry in 1906 (Larsen, 1959). This degerminator evolved from a corn shelling machine, known as the “western corn sheller,” which Beall developed in 1872. The original hominy mill, shown in Fig. 15.3A, bears little external resemblance to the Beall degerminators in service today at most of the major U.S. corn dry mills. However, its internal configuration, consisting of a truncated cone surfaced with numerous conical protrusions (or “pearling knobs”), which rotates within a similarly shaped housing (shown in Fig. 15.3B and C from the original patent), is virtually identical to the Beall degerminators in use today (Fig. 15.3D). Corn kernels are fed into the small diameter end of the machine and work their way toward the large diameter end as they are subjected to abrading action between the moving rotor and the stationary housing. When properly cleaned and tempered kernels are processed in the Beall degerminator, this combination of physical and mechanical abrading action on the kernels results in the release and separation of the various components and allows for their individual recovery (Brekke, 1970a). For optimal separation, studies have shown that the final moisture content should be in the 20%–22% range (Brekke, 1970a; Wells, 1979; Peplinski et al., 1984; Mehra et al., 2001). The abrading action peels the germ and bran away from the endosperm while leaving the endosperm portion largely intact (this fact is very critical if flaking grits are to be recovered from the milling process). This initial separation results in two streams exiting the degerminator: “tail stock,” which is primarily large pieces of endosperm that exit the tail end of the degerminator; and “through (or ‘thru’) stock,” which is made up of the germ, bran, and smaller endosperm pieces that pass through the perforations in the degerminator housing. These streams are then subjected to additional processing steps to further enhance the separation, which started at the degerminator. For the tail stock stream, subsequent steps include drying, cooling, aspirating, density separating (i.e., gravity tables), and sizing to produce flaking grits and other coarse grits. The parameters for optimizing flaking-grit yields have been widely studied and regularly reported (Brekke, 1966; Brekke and Kwolek, 1969; Peplinski et al., 1984). The remainder of this stream is sent to roller mills for reduction into smaller fractions, including brewers’ grits, fine grits, meals, and flours. Each of these fractions undergoes an additional sizing step (and possibly additional drying and cooling) to meet customer specifications. The thru-stock stream may also undergo a drying and cooling step, followed by aspirating to remove the bran and density separating (via gravity tables) to further separate germ pieces from recoverable endosperm pieces. In addition, the corn bran mentioned above can be further refined (concentrated), milled, and sized for human food applications. The composition of this corn bran product is discussed in more detail later in this chapter. Further release of the adhering germ and bran from endosperm can be accomplished via gradual size reduction by using corrugated roller mills followed by additional sifting steps (Brekke, 1970a).

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Fig.1.

4 2 3 5

1 Fig.2. 4 3

2

5

(A)

6

1 11

(B)

Fig.3. 3 10

9

8

4

8

7

7

X

Fig.4.

10 12

9

2

12 8

7

Fig.5. 9 2

3

(D)

11

Fig.6.

(C)

9

FIG. 15.3 (A) Original Beall combination hominy mill, sifter, and aspirator (around 1905). (B) Degerminator housing, US Patent 668,252 (Beall and Crea, 1901). (C) Degerminator cone, US Patent 668,252 (Beall and Crea, 1901). (D) Beall degerminator. (Parts A and D: Courtesy Beall Degerminator Co., Decatur, IL.)

416

Corn

The germ can then be screw-pressed or hexane-extracted to remove the oil, and the germ cake or spent germ becomes one of the coproduct streams. Some corn dry-millers do not further process the germ, but sell it to other companies for processing. The fines separated from the thru-stock endosperm are usually high in oil, fine fiber, and tip caps, and they become one of the coproduct streams known as “standard meal” or “fine thru stock.” The bran, germ cake, standard meal, and broker corn (isolated from the whole corn in the cleaning step) are combined, dried, and ground up together to become the main by-product of the corn dry-millers, which is known as “hominy feed.” Hominy feed is widely used in dairy feed mixes, where it is considered a high-energy replacement for whole corn. It is also used in swine feed mixes, feeder cattle mixes, and aquatic feeds, where it functions as a palatable preground, high-energy replacement for corn (some nutritionists place a higher feed value on hominy feed than on corn). Since none of the dry-millers currently refine corn oil, the crude oil obtained from either screw pressing or extraction is sold to one of several oil refiners in the United States, where it is refined into a pale yellow, bland-tasting, premium liquid oil. The remaining portion of the endosperm isolated from the thru stock is processed in much the same way as the tail stock fraction to produce prime grits, meals, and flours. In several of the major corn dry-milling plants, corn grits and flours are further processed in acid-modification systems, in extrusion cookers, or similar systems to provide a variety of value-added modified corn products for both food and nonfood uses (Wells, 1979). As indicated by Stiver (1955) and others, after the degerminator, the roller mills and sifters are the core of the corn drymilling system. With this system, the miller has numerous options in producing a wide range of prime products from flaking grits to specialty corn flours. Although the capital costs and energy requirements associated with such a temperingdegerming system are relatively high, the miller enjoys the greatest flexibility in producing a broad spectrum of highquality products. Most of these products are sold in bulk rail or bulk truck, although some portion of the prime products from the large tempering-degerming mills are sold in multiple- ply, heat-sealed paper bags (25, 50, and 100 lb [11.35, 22.7, and 45.4 kg, respectively]) or in supersacks (2000–2500 lb [908–1135 kg]). Degermed corn products are widely used in the manufacture of RTE breakfast cereals, extruded snacks, beer, prepared mixes, breading and batter mixes, and fortified food, as well as various other nonfood industrial applications (see Chapter 16). These applications are discussed in more detail later in this chapter.

Buhler Degerminating System Buhler is a name that is widely recognized and well-respected in the cereal grain milling and oilseed processing industries throughout the world. First established in 1860 as a foundry in Uzwil, Switzerland, Buhler has been supplying roller mills and related equipment to the flour milling industry since 1876. The company also manufactures several types of degerminators (or “maize decorticators”) for milling corn. According to the Dictionary of Milling Terms (Wingfield, 1989), the word “decorticator” is defined as: Any one of several designs of machines which removes most or all of the bran and germ from a grain kernel, leaving the endosperm, or groat, intact. One of these Decorticator units is fabricated by Buhler where, in contrast to the truncated cone configuration of the Beall degerminator, the Buhler technology utilizes a cylindrical design, with a central rotor running horizontally the length of the machine, to which rows of spiked fingers, or “beater bars,” are attached. This rotor/beater bar assembly is enclosed in a perforated screen housing or “decorticator jacket.” As with the Beall system, corn kernels must be rigorously cleaned and properly tempered before introduction to the decorticator. Again, uniform tempering to the optimal moisture level for the proper amount of time is critical in achieving effective bran removal and germ release. Typically, tempering is undertaken via a two-stage process. The first temper step incorporates a hold phase of 1–10 h and is intended to optimize germ release. The second temper step is of much shorter duration, and its purpose is to toughen the bran coat to aid in its release from the endosperm portion of the corn kernel. The final moisture content upon entering the decorticator is typically in the 18%–20% range. When properly conditioned corn kernels enter the decorticator, they are intensely rubbed between the jacket and the spiked fingers on the rotor. The decortication effect is achieved by the attrition action of kernel against kernel, the rubbing action of kernels against the perforated decorticator jacket, and by the direct action of the spiked fingers. The desired attrition back pressure is regulated by adjusting the discharge slide gate, which is located at the exit end of the device. Bran pieces, germ particles, and broken kernels fall through the perforations in the decorticator jacket and leave the decorticator as throughs (or thrus). The debranned and degermed kernels leave the machine as tailings (or “tail stock”) to be further processed. As with the Beall degerminator, these additional processing steps include drying, cooling, aspirating, density separating, roller milling, and sizing.

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With the decorticator system, the tail stock tends to be composed of slightly smaller endosperm pieces compared to those produced by the Beall unit, and bran removal is generally less complete. For these reasons, flaking grits are not typically one of the prime products recovered from this decorticator system. On the other hand, the thru-stock stream tends to contain larger and more intact germ pieces as well as larger bran pieces, making separation of these fractions easier. Finally, the Buhler decorticating system is less energy-intensive than is the Beall degerminator, and in many instances, produces higher prime product yields (brewers’ grits, snack grits, corn meal, and corn flour). The packaging and shipping options are essentially the same as those discussed in the previous section. Buhler also manufactures degerminators/decorticators with further development of previous models, with a redesign of the screen, retarding device, and outlet area. No preconditioning (tempering) of the corn is required with this new design. The grinding chamber consists of an eccentric rotor and a special perforated screen design. The combination results in a high degree of degermination and a wide range of milled products, from flaking grits to low-fat corn flours, and no product drying is required.

Satake Degerminating System As with Buhler, the name Satake is widely recognized and respected in the cereal grain-milling industry. Started in Hiroshima, Japan, by Riichi Satake, rice milling equipment has constituted this company’s core business, beginning with the industry’s first power-driven rice-milling machine in 1896. Today, Satake manufactures equipment for all steps in the ricemilling process, from paddy cleaners and destoners to rice polishers and color sorters. In 2000, based on its extensive experience in removing the bran and germ from rice, Satake entered into the corn dry-milling business with the introduction of the VBF maize degerminator, shown in Figs. 15.4 and 15.5. FIG. 15.4 Satake VBFIOA vertical degerminator. (Courtesy Satake USA, Houston, TX.)

418 Corn

FIG. 15.5 Satake VBFIOA degerminator, internal view. (Courtesy Satake USA, Houston, TX.)

Screen

Inner frame

This new corn dry-milling process incorporates the Satake hydrator for precise tempering control to “precondition” the corn kernels for optimal separation of bran and germ from the endosperm. The tempering step is followed by the Satake maize degerminator, a cylindrical device that is oriented vertically instead of horizontally, as is the case with the Buhler decorticator. In many respects the systems are similar, in that a “degerming roll” rotates within a perforated housing. Likewise, two product streams exit the degerminator. They are identified as “thrus,” composed of germ fragments and bran pieces that are forced through the perforated screen section, and “overtails,” comprised primarily of the decorticated endosperm pieces that exit the tail end of the machine. As has occurred over the years with the Beall degerminator, research is currently under way to determine the optimal screen perforation shape, size, and configuration (i.e., round holes vs. rectangular slots). According to the company, this system features higher prime-product yields and lower installation and operating costs than do other competing systems, but the technology has yet to be proven in the field. The steps following degermination include aspiration, gravity separation, and final sizing. In principle, this system, although a somewhat shorter flow than some other systems, should be capable of producing a full range of degermed corn products.

Other Degerminating Systems In addition to the systems previously described, a number of other degerminating systems are in use around the world. Brekke (1970a) described the Ocrim degermer, manufactured by Ocrim S.P.A. of Cremona, Italy (and now marketed by CETEC Cereal Technologies, Inc., Millersville, MD). According to Brekke, this machine consists of two horizontal drums operating in parallel inside one housing. Each drum consists of a paddle-type rotor and a surrounding cylinder made either of impact bars or perforated steel plates. Such a system is typically referred to as an “impact degermer.” Degermination can be undertaken with the corn kernels completely dry or partially wet (i.e., tempered), depending on the milledproduct properties required and the total plant investment made. This impact degerming system allows for the recovery of essentially whole-germ pieces with a minimum amount of fines generated. The fractured endosperm pieces are subsequently classified with the use of gravity tables, aspirators, and sifters. Also described by Brekke (1970a) was an impact mill manufactured by the Entoleter Company of Hamden, CT. This mill consists of a horizontal, disk-type rotor with vertical pins turning within a stationary housing. For degerming corn,

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Brekke noted that the horizontal rotor typically had two rows of pins arranged concentrically that intermesh with a single row of pins pointing downward from a stationary overhead disk. Corn kernels are subjected to impact between the moving and stationary pins, with the germ released as a result of this impact. While this impact mill does an excellent job of dislodging the germ from the endosperm, it does a less effective job of bran removal. Additionally, the Entoleter impact mill does not require that the corn kernels be tempered, although the degerming process is improved slightly with tempering. However, the energy required by the impact mill is somewhat higher than for other degerming systems. As a result of the above-mentioned factors, this milling system, while widely utilized in the U.S. corn wet-milling industry, is not extensively used by U.S. corn dry-millers. The technology does, however, find considerable acceptance by corn dry-millers in Africa. The final degerminating system to be discussed is one that is patented and available under a licensing arrangement. This system was patented by R. J. Giguere and assigned to Cereal Enterprises, Inc. of Kansas City, MO (Giguere, 1993). The patent describes a degerminating process wherein the grain kernels are crushed from the thin edges toward the center while avoiding pressure on the relatively flat side surfaces of the kernel. According to the patent, compressive force so applied acts to release the germ from the endosperm essentially intact. The machine for carrying out this process is made up of rotating disks with corrugations in their facing surfaces, which serve to catch and crush the corn kernels along their thin edges (an alternative system which achieves the same end result utilizes centrifugal force and a series of vanes to properly orient each kernel). The need for tempering is eliminated in some situations and reduced in others, thus reducing the expenses associated with drying. However, the debranning effectiveness is related to the particular corn hybrid and the kernel’s general condition, as well as the degree of tempering used. The patent further notes that germ separation is, in fact, improved when the corn kernel is tempered to 15%–20% moisture, using known techniques. Finally, the patent claims a prime-product yield substantially higher than that attainable with a Beall degerminator system (72% vs. 55%), but with a more limited range of products. This technology is currently utilized by several medium-sized mills in the United States.

DRY-MILLED PRODUCTS Categories and Composition As just discussed, a number of dry-milling processes can be used to mill corn for human consumption, and these processes yield products that are different in several functional properties and applications. For example, milled products can be significantly different in their proximate composition (i.e., full-fat corn meal vs. degermed corn meal), their physical characteristics (i.e., degermed flaking grits vs. corn flour), and various combinations of the above. Generally speaking, however, the three categories of milled products (full-fat, bolted, and degermed) fall into distinctly different ranges with regard to their fat, crude fiber, ash, and carbohydrate contents. The differences in proximate composition (Table 15.4) are a direct indication of the amount of germ and bran removed during the milling process. The differences in protein content are not as great as one might expect, because a substantial amount of protein is also present in the endosperm matrix. Note the significantly higher starch content (carbohydrates) in the degermed corn meal is a direct result of the more complete germ and bran removal accomplished with the tempering-degerming process. As would be expected, the lowest-fat, highest-starch product also exhibits the longest shelf life. The values in Table 15.4 are essentially valid for

TABLE 15.4 Typical Composition of Dry-Milled Corn Products (% As Is)a Component

Full-Fat Corn Meal

Bolted Corn Meal

Degermed Corn Meal

Moisture

13.0

13.0

12.0

Protein

7.8

7.5

7.0

Fat

3.5

2.4

0.7

Crude fiber

1.5

0.9

0.5

1.3

1.0

0.4

72.9

75.2

79.4

Ash Carbohydrates a

b

Compiled from unpublished data. Carbohydrates are determined by subtracting other proximate values from 100. This is sometimes referred to as “starch by difference.”

b

420

Corn

both yellow and white milled products. The primary significant difference between milling-quality yellow and white dent corn is the presence/absence and/or concentration of carotene, a fat-soluble vitamin, which is responsible for the pigmentation in yellow corn. The widest range of product sizes (from flaking grits to corn flour) is possible from the tempering-degerming systems, with the Beall-type process providing the widest spectrum of products. The granulation profiles of these various degermed products exhibit typical bell-shaped curves. This profile can be accurately defined by minimum and maximum specifications for the amount of product retained on a series of precision-testing sieves beginning with the largest openings and continuing to the smallest openings. The profile culminates with a maximum specification on the amount of product passing through the finest sieve and retained in the pan. This scheme is precisely how a product granulation profile is described in a specification or a technical data sheet. However, the granulation profiles of these products can also be described (without much loss of precision) by simply listing the sieve size through which the product passes and the sieve size on which the product is retained. For example, a degermed corn meal, which has a granulation defined on the technical data sheet with typical values and ranges for the 16, 20, 25, 30, 40, and 50 mesh U.S. sieves, might be equally well-identified simply as a “20/40 meal.” That is to say, the major portion of the product passes a U.S. 20 sieve and is retained on a U.S. 40 sieve. This method of defining the granulation profile is used in Table 15.5 for a number of degermed corn products (using their common names) produced by the tempering-degerming process. A sieve size on which corn flour is retained is not applicable, because only the coarse end of the bell-shaped curve is controlled for corn flour, with the tail end of the particle-size-distribution curve extending down to discrete starch granules. Table 15.5 provides a general overview of the range of products available from the corn dry-milling industry. Each milling company, however, might offer many more products, as the product granulation profiles can be tailored to meet individual customers’ requirements. Within the family of degermed corn products described in Table 15.4, there exists relatively minor differences in proximate composition. These differences occur because the various products originate from different areas within the corn kernel. The products from the horny, or vitreous, endosperm portion of the kernel, for example, exhibit the lowest fat content, whereas those products primarily from the soft floury endosperm portion of the kernel (i.e., break flour) have higher fat contents (Brekke, 1970a). The protein differences in these degermed products are related to the presence or absence of endosperm proteins (zeins and glutelins, primarily) rather than to germ proteins (Landry and Moureaux, 1980). The typical compositions of various degermed corn products are summarized in Table 15.6. It has been said that the corn dry-miller can control only three attributes of the milled product: granulation profile, moisture content, and fat content. Table 15.6 shows that this is a slight oversimplification. For example, break flour, as was discussed earlier, has a relatively low protein content and a relatively high (for degermed products) fat content. This product has very little starch damage and is unavoidably produced during the roller milling of degermer stock (Brekke, 1970a). When slurried with water at a specific concentration, break flour would yield a batter with a very thin viscosity. TABLE 15.5 Typical Granulation for Degermed Corn Productsa US Sieve

Microns

US Sieve

Microns

On

Product Name

Through

Flaking grits

31-S

5660

6

3350

Cereal grits

6

3350

12

1680

Coarse grits

10

2000

18

1000

Brewers’grits

12

1680

30

590

Snack meal

20

840

40

420

Fine corn

30

590

60

250

Corn cones

40

420

80

180

Corn flour

60

250

N/A

N/Ab

Fine corn flour

100

150

N/Ab

N/Ab

a

From unpublished industry data. Not applicable.

b

b

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TABLE 15.6 Typical Composition of Various Degermed Corn Products (% As Is) Component

Flaking Grits

Brewers’ Grits

Corn Meal

Corn Cones

Break Flour

Moisture

13.8

11.7

12.0

11.5

12.0

Protein

7.5

7.7

7.0

8.0

6.0

Fat

0.4

0.7

0.7

0.6

2.2

Crude fiber

0.3

0.4

0.5

0.4

0.6

0.2

0.3

0.4

0.3

0.6

77.8

79.2

79.4

79.2

78.6

Ash a

Carbohydrates a

Carbohydrates are determined by subtracting other proximate values from 100. This is sometimes referred to as “starch by difference."

Any of the other products shown in Table 15.6, however, could be made into corn flour by additional grinding. The resulting product, generally referred to as “reduction flour” (Brekke, 1970a), would obviously have the composition of the starting raw material and would also exhibit considerable starch damage because of the additional grinding step. If this corn flour were slurried with water at the same concentration as noted above for break flour, a batter with a much thicker viscosity than that of the break flour would result. This fact is useful in preparing blends of break flour and reduction flour for the purpose of controlling batter thickness. Such products are known as “viscosity-controlled” corn flours. Another category of products that can be produced by the corn dry-miller is “pregelatinized” (or “pregel”) corn products. These products have traditionally been made by the larger tempering-degerming mills because degermed products are a desirable starting material for the pregelatinization process. Smaller mills using shorter flow systems, however, are also capable of manufacturing pregelatinized products. Typically, degermed (or partially degermed) corn flour and corn meal are processed through an extruder (sometimes referred to as a “cooker-extruder” or “extrusion cooker”) to yield a product with a highly gelatinized starch component. The extrusion cooking process is discussed in more detail in the next section of this chapter. The material discharged from the extruder (“extrudate”) is cooled and subsequently milled to the desired particle size. Pregel corn products are available in granulations from fine corn flour up to medium corn meal and serve to provide cohesiveness and adhesiveness in a wide range of food and industrial applications. To some extent, the properties of pregel corn products (such as degree of gelatinization, density, viscosity, green strength, and water absorption) can be modified and controlled by such process variables as extrusion moisture, temperature, screw speed, die configuration, and starting raw material. Obviously, the proximate composition of pregel products would be essentially the same as that of the starting raw material, except that the moisture content would tend to be lower. These products exhibit higher water absorption than do their nongelatinized counterparts and are used in applications in which higher water absorption, increased water retention, or greater adhesion are important. With the cooker-extruder, the dry-miller has some flexibility in the composition of the starting raw material. This flexibility, along with the higher value of pregel products, has made the extruder an important processing tool for the corn drymiller, as it provides a means to convert corn flour and other standard mill products into premium products (Roberts, 1967). The final category of value-added products from the corn dry-milling process is corn bran. As was briefly mentioned earlier, corn bran is present in the thru-stock stream from the Beall degerminator. Because of density differences between the germ and bran, this raw corn bran can be recovered via aspiration from the bran-germ-fines stream for additional refining and sizing. The refining step is actually the mechanical removal of the nonbran components (tip cap, germ, endosperm) that might adhere to the bran pieces. The net result of this refining, or concentrating, step is a corn bran product relatively low in corn oil, protein, ash, and starch and high in total dietary fiber (TDF). Table 15.7 shows a typical analysis of high-TDF dry-milled corn bran (Burge and Duensing, 1989). The product (like the endosperm portion of the kernel) can be sized to meet the granulation requirements for a number of different applications. A “coarse” granulation (through the U.S. no. 20 sieve and on the U.S. no. 60 sieve) can be used to add fiber content to RTE cereals and other extruded products, whereas an “ultrafine” granulation (through U.S. no. 200 sieve) could find application in high-fiber baked goods and lowcalorie drink mixes. The dietary fiber in dry-milled corn bran is essentially insoluble (approximately 18% cellulose and 67% hemicellulose), with a water-holding capacity of about 2.4: 1, varying slightly with particle size (Burge and Duensing, 1989).

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TABLE 15.7 Typical Analysis of Dry-Milled Corn Bran With High Total Dietary Fibera Component

Dry Basis (%)

Protein

3.8

Oil

1.0

Ash

1.0

Crude fiber

17.2

Total dietary fiber

88.0

a

From Burge and Duensing (1989).

DRY-MILLING INFERENCES FOR SELECTED CORN FOOD CATEGORIES History and main milling implications of grain and milled fractions for some selected food categories are presented; a more specific, extensive review is presented in Chapter 16. The total product volume of the U.S. corn dry-milling industry is quantified to provide an “order of magnitude” sense of the volumes involved. By using the “annual grind” figure of 165 million bushels (4.19 million tons) for 2000, an average test weight for corn of 56 lb/bu (72 kg/hL), and a “shrink factor” of 0.97 (that is, corn is purchased at 15% moisture and milled products are sold at 12% moisture), the total quantity of drymilled products produced in 2000 can be calculated as 165 million bushels
56 lb/bu
0.97 ¼ 8963 million pounds (4069 million kg). Thus, the total quantity of products sold by the U.S. corn dry-milling industry in 2000, including prime products, hominy feed, and crude corn oil, was almost 9 billion pounds (4.1 billion kg). This figure was calculated to be about 6 billion pounds (2.7 billion kg) for 1977. A significant portion of this 9 billion pounds is sold as hominy feed, and that amount can be estimated by first calculating the total quantity of milled products that are sold as prime products. Based on unpublished industry data, the largest 15 mills primarily utilize tempering-degerming technologies resulting in prime product yields of about 55% (approximately 40 kg/hL or 30.8 lb/bu), and these mills are responsible for about 90% of the total industry grind. From these assumptions, the degermed prime product volume for 2000 can be calculated as 165 million bushels x 56 lb/bu
0.9
0.55 ¼ 4574 million pounds (2077 million kg). Likewise, the full-fat and bolted prime product volume for 2000 can be calculated for the remaining 10% of the industry annual grind, using an estimated prime product yield of 80% (44.8 lb/bu) as 165 million bushels
56 lb/bu
0.1
0.8 ¼ 739 million pounds (336 million kilograms). Finally, by subtracting these calculated prime product values from the industry total, 8963  (4574 + 739), the annual volume for hominy feed (and crude corn oil) in 2000 was about 3650 million pounds (l657 million kg). Because the values calculated above are based on a number of assumptions, all of which are difficult to precisely confirm, the estimate for calendar year 2000 is more generally summarized as follows: total milled products, 8.95 billion pounds (4.06 billion kg); hominy feed and oil, 3.65 billion pounds (1.66 billion kg); full-fat and bolted prime products, 0.75 billion pounds (0.34 billion kg); and degermed prime products, 4.55 billion pounds (2.07 billion kg). The commercial applications for full-fat and bolted products (retail small packages) and hominy feed (animal feeds) have been previously discussed. This section focuses on the commercial applications of the 4.55 billion pounds (2.07 billion kg) per year of degermed prime products-grits, meals, and flours produced by this segment of the USA corn dry-milling industry. In general, degermed corn products are primarily destined for human consumption within a limited number of commercial categories.

RTE Breakfast Cereals The milled corn products utilized for RTE breakfast cereals include flaking grits, degermed corn grits, degermed corn meals and corn cones, degermed corn flours (either yellow or white for all of the aforementioned), pregel corn products, and corn bran. RTE breakfast cereals are shelf-stable, lightweight, and convenient to ship and store. Most RTE cereals can be grouped into eight general categories relating to their manufacturing processes: (1) flaked cereals (corn flakes, wheat flakes, and rice flakes, including extruded flakes), (2) gun-puffed whole grains, (3) extruded gun-puffed cereals, (4) shredded whole grains, (5) extruded and shredded cereals, (6) oven-puffed cereals, (7) granola cereals, and (8) extruded expanded cereals (Fast, 1990). Those RTE cereals utilizing degermed corn products include flaked, puffed, and extruded types.

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Corn flakes are one of the most common (and earliest) examples of an RTE cereal made from the endosperm of the corn kernel. In 1903, W. K. Kellogg learned that a stable, good-tasting flake could be made from degermed corn grits (Fast, 1999). Today, the properly sized pieces of endosperm suitable for corn flake production, called “flaking grits,” are the largest pieces of horny endosperm, typically one-half to one-third the size of the original corn kernel, recovered from the milling process. Flaking grits are commonly called “4 grits” in the trade. The large pieces of raw corn endosperm, however, are unsuitable for flaking until they are properly prepared. A typical formula for corn flakes might include: 100 lb (45.4 kg) flaking grits, 6 lb (2.7 kg) granulated sugar, 2 lb (0.9 kg) malt syrup (or malt flour), 2 lb salt, and sufficient water to yield cooked grits at a moisture content of 28%–32% (Fast, 1990). After these ingredients are mixed, the flaking grits are cooked under pressure with steam in specially designed rotary cookers (see Chapter 16). This cooking step is most efficient (and the most uniform flakes result) when the flaking grits are of uniform size and moisture content and when they are essentially free of attached germ, attached hull, and other defects such as free germ pieces, cob particles, and soybeans. As a result, most RTE cereal companies have developed specifications that include limits on these various defect categories. Many RTE cereals are also made with corn meal or corn flour using an extrusion process, i.e., continuous forming by forcing a plasticized material through an opening designed to produce a desired shape; an extruder with one or two screws rotating within a tight-fitting barrel. The screw is driven by a drive composed of an electric motor and a speed-reducing gearbox that contains bearings to absorb the thrust exerted by the screws. Raw materials, which may have been moistened with water or steam in a preconditioning cylinder, are metered into a cooking extruder via a feeder. The flights of the screw convey the material forward into the extruder. The extruder adds heat by the viscous dissipation of mechanical energy, conduction through the barrel wall, and direct steam injection into the barrel. The application of heat and shear to starch-based materials ruptures the starch granules and transforms them into a gelatinized dough. Typically, this dough is pumped through one or more dies to form a desired shape, as the extruder screw generates the pressure needed to overcome the resistance of the opening, or die, at the discharge of the extruder. Finally, rotating knives cut the formed extrudate into individual pieces, which can be further processed into finished products. One such finished product is a corn flake produced from corn meal or corn flour. In this case, the appropriate degermed corn product is extruded and cut into small cylindrical pieces that resemble cooked flaking grits. Other examples of extruded RTE cereals made with degermed corn products include the various shaped and colored types, which are generally presweetened and marketed primarily to children. In most cases, these products are also fortified with vitamins and minerals. Such products could result from a two-step process (that is, extrusion followed by oven puffing) or from a single-step direct-expansion process. Extrusion technology has evolved considerably since the late 1980s, resulting in an increasing array of colors, textures, sizes, and shapes of RTE cereals made from degermed corn products. As these product shapes (and the necessary die configurations) become more complex, tighter control of the granulation profile of degermed corn meals and even control of the water absorption characteristics of the degermed corn meal or corn flour are increasingly important. The RTE cereal industry has the potential to utilize virtually every product, from flaking grits to corn bran, manufactured by the corn dry-miller and to use them in large quantities. Consequently, this commercial application is one of the most important to the corn dry-milling industry.

Brewing Adjuncts The U.S. brewing industry was, for many years, the largest user of prime products from the corn dry-milling industry, which clearly shows the significance of this commercial application. The importance of brewing adjuncts to the brewer is also interesting because the word “adjunct,” according to Webster, means something secondary, or nonessential. The Dictionary of Milling Terms (Wingfield, 1989), however, defines adjunct as follows: “One of several carbohydrate based fillers used in the brewing of beer to impart certain desirable characteristics.” In The Practical Brewer (Bradee, 1977), the definition is even more positive, with adjuncts defined as nonmalt carbohydrate materials of suitable composition and properties, which beneficially complement or supplement the principal brewing material which is malt. These definitions indicate that brewing adjuncts are not simply tolerated because of economics, but that they actually have a desirable and beneficial impact in the brewing of beer. This fact has been understood by the U.S. brewing industry for many years. Corn grits, corn meal, and corn flakes (also known, respectively, as “brewers’ grits,” “brewers’ meal,” and “brewers’ flakes”) have been widely used by U.S. brewers since the late 1800s (Bradee et al., 1999). Although the brewing industry has historically been the largest user of prime products from the corn dry-milling industry, that position has been taken over by the RTE cereal industry in recent years. Early in the history of North American brewing, brewmasters learned that “allmalt” formulations using U.S.-grown malted barley resulted in beers with poor physical and chemical stability. They also

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learned that this problem could be mitigated by adding other starch sources with lower soluble protein content, such as degermed corn grits. Today, it is generally acknowledged that brewing adjuncts provide the following benefits (Bradee, 1977): economical source of fermentable extract, improved flavor profile and palate fullness, improved physical and chemical stability, and increased production capabilities. In the United States, brewers’ grits typically exhibit a moisture content of about 12%, a fat content of less than l%, and carbohydrates of about 81% (Table 15.4). Additionally, this product is passed through a U.S. no. 12 sieve and retained on a U.S. no. 40 sieve, although individual specifications vary (Bradee et al., 1999). Brewers’ meal has traditionally been used by the Canadian brewing industry in the past because of tariff considerations, although this situation is changing as a result of the North American Free Trade Agreement. As can be seen in Table 15.5, the primary difference between brewers ‘grits and brewers’ meal is one of size; to qualify as corn meal, at least 50% of the product must pass through a U.S. no. 25 sieve, according to Canadian custom requirements (Bradee et al., 1999). When degermed corn grits (or meal) are utilized in beer production, the first step involves cooking the grits, a step required to gelatinize the starch so that it can subsequently be further hydrolyzed to fermentable sugars by the action of malt enzymes. The cooked grits are then added to the malt mash, where the enzymatic breakdown occurs. The solubilized sugars are then separated from the “spent grains” (i.e., nonstarch components) in a filtering, or lautering, step. The resulting solution, called “wort,” is combined with hops in the brew kettle. After boiling, the hopped wort is filtered, cooled, and “pitched” (or inoculated) with brewers’ yeast. From this point, the soluble sugars are converted by the yeast into alcohol (ethanol) and carbon dioxide during the fermentation process. The resulting beer is then aged for several days at nearfreezing conditions before it is filtered, pasteurized, and packaged. A detailed review of this process has been written by Macleod (1977). Brewers’ flakes are used by some brewers because they do not require a cooking step. The corn dry-miller manufactures this product by preconditioning coarse corn grits with hot water or steam and subsequently passing the conditioned grits through heated flaking rolls. This process renders starch more available, thereby eliminating this step in the brewery (as well as eliminating the need for the cereal cooker). Following gelatinization, brewers’ flakes are dried, cooled, and sized to customer specifications. The use of brewers’ flakes by the U.S. brewing industry also dates to the late 1800s (Bradee et al., 1999). Increasingly, brewers’ flakes (or “flakes of maize”) are finding greater acceptance and usage within the microbrewing community in the United States, as these brewers recognize the desirability of making their products more physically stable, slightly lighter, and less satiating. Also, “flakes of maize” adds mystique to the label. Dry-milled adjuncts from corn have long been the traditional adjunct of choice because they are “prime” products of the corn dry-milling industry. As such, they are extremely consistent in terms of quality, composition, and availability. In recent years, however, the use of “brewers’ syrups” by a number of U.S. brewers has adversely affected “brewers grits” market share in this important commercial segment. Brewers’ syrups, which are actually a family of products manufactured by the corn wet-milling industry, do not require a cereal cooker and can be added later in the brewing process. In some instances, this option can help resolve brewhouse bottlenecks and increase brewery throughput (Pollock and Weir, 1976; Swain, 1976; Pfisterer et al., 1978). It has been reported that brewhouse capacity can be increased by as much as 25% through a concept called “high-gravity brewing” (Bradee et al., 1999). Finally, specialized wet-milled adjuncts (i.e., dextrose) are available to meet the requirements for light beers (Chantler, 1990). Nevertheless, the United States, Canadian, and Mexican brewing industries have been, and continue to represent, a large and important commercial application for degermed corn products from the United States corn dry-milling industry.

Extruded and Sheeted Snacks Early patents and other literature regarding extruders describe their use in preparing products for industrial applications (Stickley and Griffith, 1966; Bradley and Downhour, 1970), fortified cereal applications (Anderson et al., 1969, 1970; Bookwalter et al., 1971; Bookwalter, 1977), and protein-fortified beverage applications (Hauck, 1980), but it seems that the snack-food industry may have been the primary beneficiary of the versatility offered by the modern extruder. The snackfood industry is able to produce snack products in a wide variety of sizes, shapes, colors, textures, and densities from a variety of starting raw materials. Foremost among the starting materials, however, are degermed corn grits, degermed corn meals, and degermed corn flours, both yellow and white. Corn meals and flours have been shown to be particularly useful in the manufacture of corn chips (Sanderude, 1969; Scales, 1982; Stauffer, 1983), corn puffs (Williams, 1977; Toft, 1979; Scales, 1982), extruded onion rings (Sanderude, 1969; Williams, 1977), and second- and third-generation snacks (Toft, 1979; Hauck, 1980; Matson, 1982) via extrusion processes. The food extrusion process can be categorized as cooking or forming, low or high-shear, low or high moisture, and low or high pressure. One of the most prevalent uses for extruders in snack-food manufacture is in the high-shear, low-moisture,

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high-pressure, direct expansion of puffed snacks, which are typically called “corn curls” or “cheese curls” in the trade. The extruded pieces (properly called “collets”) can also take other shapes like balls, rods, rings, and clubs among others. These products are typically manufactured via direct expansion on short-barrel single-screw extruders from degermed yellow corn meal tempered to approximately 16% moisture (see Chapter 16). Corn is an excellent starting material because of its high expandability. This mixture of corn meal and water forms a plastic dough under the conditions of heat, pressure, and shear in the extruder barrel. When the dough exits the extruder at the die, the pressure rapidly drops and instantly generates steam, which expands the extrudate and forms the collet. The collets are cut to the desired length by a rotating cutter arrangement; the resulting individual pieces are uniform in size and shape with a low bulk density. The collets are then baked or fried, after which a cheese slurry is applied. The range of flavors for this coating step is expanding. As the die shape becomes more complicated (twists, tubes, wheels, stars, etc.) and the starting raw material becomes more complex (i.e., blends with other cereal flours or corn bran, etc.), both single-and twin-screw extruders are increasingly used to form the collets. The more complex and expensive twin-screw extruder was introduced in the late 1970s, and it was felt at that time that this technology would replace all other competing technologies in a matter of 10–15 years. The products produced by the twin-screw extruder often were perceived to be better, but better is different, and different can be bad when it comes to the consumer (Beecher and Starer, 1998). Nowadays, both single and twin-screw extruders are competitive in the market for snack food. An additional application of degermed corn products (and twin-screw extruders) is in the manufacture of “half products,” “pellets,” or “third-generation” snacks (see Chapter 16). This process generally comprises two steps, wherein the dough mass is first cooked and then shaped. The resulting pellets (or other shapes) are then dried to a shelf-stable moisture content optimum for later expansion (8%–14%). They are finished at some later point by puffing in hot oil, hot air, or with a puffing gun, followed by a flavor-coating step. This process is less economical than direct expansion, but it allows for greater control of shape formation at the extruder die and develops unique crunchier expanded food textures. Additionally, these half products can be efficiently shipped to smaller regional processors, where custom flavoring and packaging can be tailored to the local market. As noted earlier, degermed corn products, including corn meals, corn flours, and even pregel products, are used in the manufacture of third-generation snacks. “Fabricated chips” are products that can also be made using a process similar to that described above. In this case, the cooked dough is formed into a continuous sheet from which the individual pieces are cut. These wafers are ultimately baked or fried and seasoned to make the finished product. Fabricated chips are part of a broader category called “sheeted snacks,” in which the starting raw materials (including dry-milled corn products) are cooked and formed into a dough sheet, from which the snack pieces are cut. These pieces can then be further shaped or formed while in a flexible state before being fried to yield three-dimensional snack pieces. Considerable research has been done in the field of snack-food extrusion. Zhang and Hoseney (1998) reported that the particle size of corn meal could adversely affect extrusion, but that poor expansion could be overcome with additional tempering. Matthew et al. (1999) showed that the particular corn hybrid and its growth environment can significantly affect extrudate characteristics and that higher starch content is related to increased expansion. Garber et al. (1997) measured the impact of corn meal particle size on extruder performance and concluded that the twin-screw extruder performs well over a fairly wide range of particle sizes. This commercial application of degermed corn products is a large and dynamic market, but it is currently dominated by a small number of major food manufacturers, and the demands for product uniformity and consistency, and innovation are ever-increasing.

Breadings, Batters, and Prepared Mixes According to Suderman (1983), breading is defined as a dry mixture of flour, starch, and seasonings, coarse in nature, and applied to moistened or battered food products prior to cooking

and batter is defined as a liquid mixture comprised of water, flour, starch, and seasonings into which food products are dipped prior to cooking.

A number of batter types exist (conventional, adhesion, crispy, corn dog), as do breadings (home-style, extruded, corn flake, predust, etc.), but, in general, these are cereal flour- and starch-based preparations that are used to coat other food (Burge, 1990). Coating, in this context, is defined as “the batter and/or breading adhering to a food product after cooking” (Suderman, 1983); the food products so coated include fish, seafood, poultry, meats, cheese, mushrooms, vegetables

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Corn

(i.e., onion rings, cauliflower, etc.), and other food products. Commercially coated food products are usually quick frozen before distribution to the retail and food service markets. These mixes are typically formulated with wheat flour, corn flour, and a number of minor ingredients (starch, salt, sugar, gums, oil, corn meal, dairy powders, etc.) to meet the color, flavor, texture, and crispness requirements for the particular coated food product (see Chapter 16). At the extreme, the wheat flour or the corn flour component could be as high as 100% (Burge, 1990), but intermediate blend ratios are more common. Consistent and predictable water absorption characteristics are important for these mixes so that uniform coating thickness and frying properties are possible when the batter is prepared for use. Viscosity-controlled corn flours play an important role in making this possible. These products, described earlier in this chapter, are blended to meet customer specifications for controlled water absorption (also referred to as viscosity or fluidity) and are widely used in the breading and batter industry for this purpose. Prepared mixes constitute a broad category of products that are made by dry blending a number of ingredients in precisely controlled amounts. These mixes are subsequently packaged in small boxes or pouches for the retail market or are packaged in larger boxes or bags for the food-service market. Examples of such products include corn bread, corn dog, corn muffin, waffle, pancake, dusting meal, fish coating, and hush puppy mixes, as well as related ethnic products such as polenta. As noted earlier in this chapter, some bolted corn products are used in these applications, but degermed corn grits, meals, and flours are widely used in prepared mix formulations because of tight granulation control and shelf life considerations.

Fortified Food During the late 1950s and early 1960s, a number of changes occurred within the government food aid programs that had a major effect on the corn dry-milling industry. In this period, the shortage of nonfat dry milk (NFDM) resulted in the search for alternate sources of low-cost protein (Senti et al., 1967). The government assisted industry with the passage of the Food for Peace Act of 1966 (Public Law 480, or PL480), which broadened the range of commodities eligible for donation to underdeveloped countries. Even before passage of the new legislation, the corn dry-millers had developed several corn-based prototypes (Tollefson, 1967), so that in 1966 they were ready to produce the first of several proteinfortified food. The first product that received worldwide distribution and acceptance was corn soy-milk (CSM). The original formula for this material consisted of 64% partially cooked corn meal (PCM); 24% defatted, toasted soy flour; 5% NFDM; 5% soy oil; and 2% vitamins and minerals. The product was well-balanced from a carbohydrate-protein-fat standpoint, and the protein contained a particularly good amino acid profile (Cantor and Roberts, 1967). The combination of corn, soy, and milk proteins resulted in a protein efficiency ratio essentially equivalent to that of casein. It is believed that the combination of acceptable flavor and excellent functional and nutritional properties resulted in the success of CSM. Because of the success of this initial product, additional corn-based fortified food were developed over the ensuing years. Table 15.8 summarizes the various products, which were developed for the PL480 program, along with their year of introduction and their original composition. Likewise, Table 15.9 provides an idea of the relative volumes of the various PL480 products sold to the U.S. government over the past 30 years. Obviously, the total volume of fortified food (and the actual product mix) varies considerably year to year, and Table 15.9 is intended only to show several general trends. It can be observed, for example, that between 1980 and 1990 a dramatic shift from CSM to corn-soy blend (CSB) occurred. This happened because the government reserves of NFDM were essentially depleted in the late 1980s, with the resulting switch to CSB. Some small quantity of CSM was again produced in 2000. Also, apparent from Table 15.7 is the large food volumes of the PL480 program over the past decades. Before about 1967, the PCM used to make CSM was generally produced on hot rolls (Anderson, 1982), the commercial products being made on gas-fired rolls. Since 1967, most of the PCM and instant PCM (used to make instant CSM) have been made in extrusion cookers of the type described in the preceding section and by Conway (1971a, b). Other forms of cooking have been described by Anderson et al. (1969, 1970), although the extruder appears to be the most versatile and practical cooking equipment for dry-milled corn products. Although soy flour and soy grits have been the main protein supplement used in PL480 products (alone or in combination with NFDM), other protein sources have been investigated. Cantor and Roberts (1967) described the use of fish protein concentrate in producing materials equivalent to CSM in protein efficiency ratio. They also discussed the possible use of amino acid fortification. Hayes et al. (1978, 1983) examined the replacement of soy flour in both corn- and wheat-based products with both defatted cottonseed and peanut flours. Whey protein concentrate was also tested and eventually approved as a replacement for NFDM and for use in a whey-soy drink mix (Bookwalter, 1981). The main objective of the Food for Peace Legislation (PL480) has been to provide nutrition, in the form of both total calories and high-quality protein, to the millions of people in the Third World who do not have enough food. The various

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TABLE 15.8 Corn-Based Fortified Food Development for US PL480 Programs Year Introduced

Composition

Corn meal, enriched

1957

99+% corn meal, 1/4 oz. vitamin-mineral premix per hundred weight

Processed corn meal, enrichedb

1963

99+% PCM, 1/4 oz. vitamin-mineral premix per hundred weight

Celaproc

1965

58% Corn meal, 25% soy flour, 10% durum flour, 5% NFDMd, 2% vitamin-mineral premix

Corn-soy-milk (CSM)

1966

59.2% PCM, 17.5% soy flour, 15% NFDM, 5.5% soy oil, 2.8% vitamin-mineral premixe

Instant CSM

1971

63% PCM, 23.7% soy flour, 5.0% NFDM, 5.5% soy oil, 2.8% vitamin-mineral premixe

Instant sweetened CSM

1971

53% PCM, 27.5% soy flour, 7.35% sucrose, 5.0% NFDM, 5.0% soy oil, 2.0% vitaminmineral premix, 0.15% vanilla flavor

Soy-fortified corn meal

1972

85% corn meal, 15% soy grits

Corn-soy-blend

1973

67% PCM, 25% soy flour, 5.0% soy oil, 3% vitamin-mineral premix

2012

78.5% PCM, 20% whole soy flour, 0.20% vitamin-mineral premix

2014

58% PCM, 20% soy flour, 8.0% dried skim milk powder, 9.0% sugar, 3.0% soy oil, 0.40% vitamin-mineral premix

Product a

Corn-soy-plus f

Super cereal plus a

According to Tollefson (1967), between 1957 and 1967, approximately 140 million tons were sold for US aid programs. The product was tested in more than 30 countries, but never purchased under PL 480. Processed corn meal. d Nonfat dry milk. e The original formulas for these products called for 64% PCM, 24% soy flour, 5.0% NFDM, 5.0% soy oil, and 2.0% vitamin-mineral premix. The present requirements were described by Bookwalter (1981). f Super cereal plus was developed specifically for infant & lactating mothers, package design was modified from standard 55 kg bag to bag in box, 10–1.5 kg bags, labeling was added with graphic infant feeding instructions. b c

TABLE 15.9 Corn-Based Fortified Food (million kg) Sold to Government Agencies Under PL480a Year (million kg) Product

1970

1980

1990

2000

2016

Corn meal, enriched

–

3.67

24.10

47.76

36.13

Soy-fortified corn meal

–

49.12

24.42

18.61

0.68

Corn-soy blend (CSB)

–

–

238.21

295.00

2.27

Corn-soy-milk (CSM)

174.11

112.27

–

7.90

–

Corn-soy-plus (CSB +)

–

39.67

–

–

55.02

Super cereal plus

–

–

–

–

8.58

Instant CSM

–

–

–

–

–

Instant sweetened CSM

–

–

–

–

–

Annual total

174.11

202.48

286.75

369.28

102.69

a

From Bookwalter (1983).

cereal products purchased for the program have been distributed to most of the countries in the world through the Agency for International Development, local governments, and various volunteer agencies, such as World Food Program CARE, UNICEF, and Catholic Relief Services. The products get to the people through various programs, including church-related schools, school-lunch programs, and mother-child care centers. Based on the results achieved to date, this program has been very successful and it is likely to continue into the foreseeable future.

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NONFOOD APPLICATIONS Although the primary objective of the corn dry-milling process is to manufacture products for human consumption, a significant amount of each bushel of milled corn is used in nonfood or industrial applications. The largest and most obvious of these nonfood applications is hominy feed, but a number of other industrial applications (utilizing prime products, in most cases) also exist. Many of these nonfood uses have been reviewed in the past by Brockington (1970), Alexander (1974), and Rankin (1982), and the most significant of these applications are discussed here.

Animal Feeds As previously noted, hominy feed is produced in substantial quantities by the U.S. corn dry-milling industry, as measured both from a percentage standpoint (up to 45% for some systems) and also from an absolute volume standpoint (3.65 billion pounds [1.66 billion kg] in 2000). This product, composed of corn germ (full-fat or expelled/extracted), corn bran, fine thrustock, and ground corn cleanings, is a palatable, high-energy, premilled replacement for corn in numerous animal rations (see Chapter 23). Hominy feed competes with many other corn by-products, such as corn gluten feed, spent brewers’ grains, and distillers’ dried grains, in feed applications (Shroder and Heiman, 1970). It is readily available, however, competitively priced and of consistent composition. As a result, it is an important option for U.S. (and international) feed formulators. The high carotenoid content of hominy feed from yellow corn is especially desirable in chicken feeds, because it produces eggs with bright yellow yolks. Hominy feed is widely used in feed formulations for dairy cattle, beef cattle, and hogs and is also utilized in aquatic feeds. In some instances, prime products, such as degermed corn grits or degermed corn meals, are used in premium dog food and cat food formulations, especially in extruded types. Additionally, degermed corn flour can be used in various dog treats, such as baked dog biscuits. Coarse corn grits are also used in bird-feed mixes, in which the grits may be dyed and mixed with other seeds. Finally, degermed corn products are used as the attractant and bait in extruded rodenticides and as a carrier for certain insecticides.

Gypsum-Board Starch This application, also known as “core starch,” utilizes acid modification (typically HCI acid) to modify the solubility and change the functionality of degermed corn flour. Such acid-modified corn flours have been widely used in the manufacture of gypsum board (or “dry wall”) for a number of years. These traditional products have been described by Slotter (1952) and Wimmer and Meindl (1959), and chemically modified and acid-modified flours have also been described by Ferrara (1976). In many cases, acid-modified corn flours are preferred to other starch-based products because of price and functional advantages. Gypsum-board starches are typically added at the mixer with the powdered stucco and water at a usage rate that equates to 6–12 lb of starch per 1000 ft2 (2.7–5.4 kg/92.9 m2) of finished half-inch board. Although this addition rate is only 0.4%– 0.8% of the final board weight, the gypsum-board starch performs a very important function as the gypsum crystals are growing to form the board. The acid-modified corn flour, already partially dextrinized, is further solubilized in the board drying oven, where it controls the rate of water loss (Alexander, 1974) from the board. The solubilized carbohydrates migrate to the board’s surface, where they protect the gypsum crystals, which form at the gypsum/paper interface, by preventing their loss of crystallinity. This complex process results in a strong bond between the facing paper and the gypsumboard core.

Pregelatinized Binders When degermed corn products are gelatinized (typically via extruder cooking), the resulting pregel corn product, when ground to a fine granulation, exhibits excellent adhesive properties. These pregel products, collectively referred to as “binders,” find commercial use in a number of industrial applications. One such application is as a “core binder” to the foundry industry. In this application, pregel corn flours, sold under a variety of trademarks, serve as the primary binder for sand cores until they are baked (Alexander, 1974). The ability to provide “green strength” to the sand core during this vulnerable period has made core binders valuable to the foundry industry for many years. The introduction of a family of petroleum-based “no-bake” and “quick-set” binders in the 1970s, however, resulted in dramatic industry changes. The new binders did not require heat for curing, which resulted in no thermal-related expansion, shrinkage, or warpage of cores and

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molds. This process improvement allowed the production of more precise and delicate castings. Additionally, the new quick-setting binders utilized a two-part system in which the liquid resin was mixed with the sand and blown into the core box. This step was followed by the introduction of the catalyst gas, which resulted in an almost instantaneous hardening of the resin-coated sand, allowing for quick release of the cured mold. In recent years, however, there has been some concern about the toxic nature of the chemicals involved. The above-mentioned green strength attribute of pregel corn flour has also been utilized in producing charcoal briquettes (Senti, 1965; Alexander, 1974), where charcoal powders are pressed into briquette shapes with the aid of such a binder. In a similar application, pregel corn flour has been used in the pelletizing and agglomerating of coal fines into a more useable product form. Pregel corn flour has also been evaluated in conjunction with a pellet mill on numerous other powders, including rice hull ash. Additionally, pregel corn products have found application in oil well drilling (Alexander, 1974). In this application, the precooked starch or flour minimizes water loss in the drilling mud. The mud cools and lubricates the drill bit, suspends and removes the cuttings from the bottom of the hole, and coats the hole with an impermeable layer. It also controls subsurface pressures in the hole, supports part of the weight of drill pipe and casing, and minimizes adverse effects on the formation adjacent to the hole. The precooked flours used in this application have been produced using either drum dryers or hot rolls (Roemer and Downhour, 1970a, b) or extrusion cookers (Bradley and Downhour, 1970; Roemer and Downhour, 1970a, b). Chemically modified flours, such as described by Smith et al. (1962, 1969), are thought to be improved agents for decreasing water loss because of their increased water-holding capacities. In extremely deep holes, where mud temperatures in the 200–300°C range are reached, corn flours (Wimmer, 1959b) or starches (Hullinger, 1967) that have been cross-linked are preferred. Pregel corn flours have also been used in a variety of applications associated with the building products or construction industry, including insulation or fiber board (Naffziger et al., 1963; Alexander, 1974), plywood and related laminating adhesives (Senti, 1965), and compression-molded particleboard (Alexander and Krueger, 1976) and wafer board. Pregel flours also have been used in ceiling tile, as edge pastes in gypsum-board production, and as binders in gypsum-based taping compounds (Cummisford, 1973).

Starch Conversions Dry-milled corn products serve as starch sources for a number of fermentation processes and related starch conversions. Corn flour and corn meal have been used in substantial quantities in the production of citric acid, for example. Likewise, corn flour serves as the starting material for various pharmaceutical fermentations of animal antibiotics and related products. In this case, the high starch content and the smaller quantity of protein are important considerations. Although whole corn is typically utilized, dry-milled corn products could also be used in ethanol production, either potable or industrial (see Chapter 22). This application could be helpful in addressing mill balance issues, and it would provide a ready outlet for off-quality milled products as well as rejected truckloads of corn. Other Industrial Applications A number of special processes for making corrugating adhesives from corn flours have been reported. Wimmer (1959a) used corn flour plus sodium chloroacetate in the carrier portion of the adhesives to make an improved product. Horner (1961) described the use of waxy starch or flour in the carrier in combination with a cereal flour, preferably from sorghum, to produce a nonthixotropic adhesive. Another process (Fortney and Hunt, 1966) employs fine-grind corn flours with a special granulation profile to produce a superior adhesive. Likewise, several patents by Ware and Hill (1973a, b) describe the development of a novel, viscosity-stable corrugating adhesive from cooked flour. To our knowledge, however, corn flour is not currently utilized for this application in the United States. Other industrial applications for dry-milled corn products have been reported, including ore refining, where corn flour can be used in the beneficiation of aluminum ore ( Jones, 1960); rigid and flexible polyurethane foam extenders (Bennett et al., 1967; Hostettler, 1978); textile sizing (Rankin et al., 1963); and as an abrasive agent in industrial hand soaps (Alexander, 1974).

FUTURE TRENDS AND DEVELOPMENTS Dry corn milling will have a growing importance going forward based on its capability and versatility to create corn-based ingredients that meet numerous demands from a fast world population growth rate, growing interest on agronomic and industrial sustainability, dynamic leading health and wellness trends, and constantly changing consumer needs.

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New and technologically advanced corn-based final food products will play an important role in meeting world population growth that is expected to be 9.6 billion by 2050. To meet this population growth expectations, predict that food production must also grow by 70% by 2050. In North America, genetically modified corn hybrids are actively playing a critical role for world food production growth. This has been seen in central US corn fields with the rapid rise in bushels per acres from 140 to 170 to current levels of over 250. This rapid acceleration in genetic advancement has created challenges for the dry corn miller. Kernel size, hard endosperm ratios, and density have all been affected is some degree. In addition to the physicochemical shifts, the dry corn miller has been challenged in terms of genetic regulatory approvals (StarLink in 2000; Enogen in 2011) that have been disruptive in terms of food and feed approval (in the case of StarLink a split approval) and/or a functionality for food production (in the case of Enogen elevated alpha amylase content to increase carbohydrate breakdown into simple sugars for fuel alcohol production). In both of these examples, the dry-milling industry learned that “absolute” segregation is virtually impossible for commodities such as corn, which are pollinated in an open environment, planted in adjoining fields, transported in shared equipment, and moved through common elevators. The understanding and appreciation of this fact will become even more important in the future as millers consider evolving niche markets, such as organic and non-GMO. Increasing corn production for food utilization will also present future challenges to meet sustainability requirements, which in today’s age is a table stake. Essentially, a bigger corn crop will have to be grown on a smaller environmental footprint. This will require further advancements in plant anatomy and composition, breeding, genetic modifications, water usage, and fertilizer. In addition, corn dry-milling equipment will need to be enhanced to higher throughputs, lower power requirements, and more automation. At the same velocity, corn dry mills will have to be modified or green field constructed to be highly flexible to handle a variety of end products from multiple sources or varieties of raw materials, i.e., seed color, genetics, organic, non-GMO, and nutritionally enhanced hybrids. As bio-fortification becomes more relevant in the food market place to address current consumer health and wellness, needs for corn and corn products are an excellent potential vehicle to deliver a variety of unique nutrients. The pericarp, the aleurone layer, and germ of appropriately selected corn varieties can deliver antioxidants, carotenoids, phytoesterols, policosanols, and others. Genetic selection must be coupled with adequate processing technologies that include and preserve those nutrients. Current players of the world corn dry-milling industry are fully aware of this fact and are working in this direction. Consumer demands for food products that are made out of dry-milled corn ingredients are growing rapidly. Snacks in particular are driving the growth. On-the-go handheld portable snacks have been growing at a sustained 3.0% rate for the past 5 years. Also, this trend is driving specialty dry corn ingredients such as non-GMO, organic, gluten-free, and natural seed colors. Many opportunities exist for the traditional dry corn miller to expand into bolt on platforms to roast/toast, flake, and extrude numerous corn-based products. Partnerships among players across the whole corn dry-milling supply chain have become a need as the market complexity and dynamics require collaboration of various types. Some of the factors of that complexity are that the world has become more conscious and proactive about the criticality of conservation and, in some instances, the improvement of our ecosystems, newly developed technologies are available and commercially practical, practices of agronomic and corporate sustainability are a reality in many areas of the world, a pressed need for minimized costs of industrial transformation, the search for technologies to achieve maximum production efficiencies, the need for versatile technologies, the existence of practically a single market that encompasses a world with little borders, and the existence of extremely extensive regionalized regulatory systems. Partnerships among seed companies, machine manufacturers, dry-millers, manufacturers of consumer packaged goods, government offices, universities and research centers, and other key global players are an advantageous reality.

CONCLUSIONS Current corn dry-milling is a well-established technology deployed in many regions around the world with a variety of investment levels depending on market demands. Utilization and versatility of current assets is a constant topic of discussion. The global food market continues to demand more cost savings, processing efficiencies, new alternative value-added corn dry-milled ingredients, and milling capabilities suitable for new grains beyond typical cereal grains, which all together pose a variety of technology opportunities. Opportunities for new corn dry-milling techniques include areas on equipment design, flexible processing capabilities, and control of precooking degree as examples among others for future research and technology development investment.

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Flexible processing technologies are fundamental to support a constantly changing food market that moves from typical cereal grains into pseudo-cereals and then ancient grains with different anatomical morphology. Collaborations across the supply chain from agronomy through milling and to finished food product will continue to evolve into more committed, more sustainable relationships that secure involvement of the right type and level of expertise early enough even during definition of food concepts and technology needs. More than ever, this generation faces the chance for food scientists, agronomists, engineers, regulatory, market research, and other key disciplines to work together in the construction of the next grains dry-milling technology.

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FURTHER READING Alexander, RJ & Cummisford, RG. 1971. Cationic cereal flours and a method for their manufacture. US Patent 3,578,475. Anderson, R.A., Watson, S.A., 1982. The corn milling industry. In: Wolff, I.A. (Ed.), CRC Handbook of Processing and Utilization in Agriculture. Part I. Plant Products. In: vol. II. CRC Press Inc., Boca Raton, pp. 31–61. Russell, CR, Buchanan, RA & Rist, CE. 1964. Cellulosic pulps comprising crosslinked xanthate cereal pulps and products made therewith. US Patent 3, 160,552. Tsen, C.C., Mojiban, C.N., lnglett, G.E., 1974. Defatted corn germ flour as a nutrient fortifier for bread. Cereal Chem. 51, 262–271. Wimmer, EL & Sussex, JL. 1968. Process for manufacturing corn flour. US Patent 3,404,986.

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Chapter 16

Food Uses of Whole Corn and Dry-Milled Fractions Sergio O. Serna-Saldivar and Esther Perez Carrillo Centro de Biotecnologı´a FEMSA, Escuela de Ingenierı´a y Ciencias, Tecnologico de Monterrey, Monterrey, Mexico

INTRODUCTION Maize or corn is the leading grain crop in the world and in the United States with annual productions in 2014 exceeding 1037 and 361 million metric tons, respectively. About 15% of the crop is directly consumed by humans (FAO, 2018). Corn is staple for large groups of people in Africa and Latin America where it is used for the production of numerous traditional and industrialized food. Corn originated in Mesoamerica (see Chapter 1) and has been an integral part of native diets centuries before the discovery of the American Continent in 1492. After the discovery of the Americas, corn was readily introduced into Africa and Asia after the dissemination of corn cultivars by Portuguese and Spaniards in their colonies (Serna Saldivar, 2015). Corn food are characterized by their unique distinctive flavor unduplicated by other cereal. In developed countries around the globe, corn is mainly used for production of animal feeds and fuel ethanol. For example, of the approximately 361 million metric tons of corn produced during 2014 in the United States, 39% and 30% were channeled for animal feeds (see Chapter 23) and biorefineries (see Chapter 22), respectively. Only 3.5%, 2.2%, 1.7%, 1.5%, and 1.1% of the USA corn are used for HFCS, other sweeteners, starch, breakfast cereals, snacks, tortillas, and alcoholic beverages, respectively (USDA, 2016). The use of corn as an ingredient in ready-to-eat (RTE) breakfast cereals, snacks, and mixes has increased as consumers look for convenience food which meet nutritional and health requirements. Recently, this grain has been viewed as an excellent choice for production of gluten-free products recommended to avoid maladies commonly experienced by celiacs. The dry-milling industry and food processors are demanding corns with increased yields and quality to improve end product attributes. Some unique types such as blue corn are becoming increasingly popular in specialty food stores. Quality protein maize (QPM) hybrids and lines have excellent improved nutritional value and have been processed into excellent food. Recent references of general interest on food uses of corn and its dry-milled fractions are available (Serna Saldivar and Perez Carrillo, 2016; Serna Saldivar, 2016, 2008a). This chapter summarizes information related to the use of corn in human food, with special emphasis on utilization of whole corn and refined dry-milled fractions. Dry and wet-milling processes, food uses of starch and production of lime-cooked tortillas, and related food are thoroughly covered in other sections of this volume (see Chapters 15 and 17–19).

HUMAN CONSUMPTION OF CORN Over the past three decades, significant progress has been made in advancing corn production as well as productivity, resulting in increased per capita availability in many developing countries. However, the direct human utilization of corn expressed on total production has been practically the same (FAO, 2018). The current overdependence on cereal-based diets coupled with inadequate intake of more expensive and less available animal products or pulses still leads to serious nutritional deficiencies in several parts of the globe, especially in terms of protein quality and essential micronutrients such as iron, zinc, and vitamin A. However, nowadays one of the major concerns related to corn consumption is in terms of chronic and acute mycotoxicoses (see Chapter 9). Undoubtedly, cereals are the main source of calories and protein for the world population. Among cereals, wheat, milled rice, and corn are the main contributors. According to the FAO (2018), the average per capita daily consumption of wheat, rice, and corn in 2013 were 179, 148, and 49 g, respectively. Interestingly, unlike the other major cereals which are more homogenously consumed throughout the different countries and continents, the consumption of corn in some regions of the Corn. https://doi.org/10.1016/B978-0-12-811971-6.00016-4 Copyright © 2019 AACCI. Published by Elsevier Inc. in cooperation with AACC International. All rights reserved.

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globe is very high, whereas in others practically nil. Basically, the majority of the corn consumption by humans takes place in developing countries where the GDP is relatively low. In fact, corn is considered a primary source of calories in the diets of 230 million inhabitants of developing countries (81 million in sub-Saharan Africa, 141 million in South Asia, and 8 million in Latin America). Table 16.1 summarizes the daily human consumption of corn with the caloric and protein contributions and the main corn-based food products consumed in different cultures. Inhabitants of countries of Lesotho, Malawi, Republic of Moldova, Mexico, Zambia, and South Africa have daily consumptions exceeding 250 per person, which supply >650 kcal and 16 g protein. These caloric and protein intakes represent at least 32 and 28% of the recommended daily allowances for adults, respectively. In Africa and America, most of the consumed corn is in the form of porridges/gruels and nixtamalized products (see Chapter 17), respectively. According to the FAO (2018), the highest per capita daily consumption of corn is recorded in people living in Lesotho (433 g), Malawi (354 g), Zambia (325 g), and Mexico (319 g). In these countries, corn is domestically produced and cheaper than rice or wheat and therefore widely used as staple.

SPECIALTY CORNS Food-Grade White and Yellow Corns Today, white and yellow corn hybrids with markedly better yields, adaptability, and improved processing quality are available because commercial hybrid seed companies have spent significant efforts in breeding hybrids with improved dry-milling and alkaline cooking properties (Poneleit, 2001; Rooney and Serna Saldivar, 2015). These food-grade types usually have higher test weight (>76 kg/hL), 1000 kernel weight (320 g), true density (1.26 g/cm3), and harder endosperm texture compared to the typical US dent corn. In addition, the cobs of these hybrids are white-colored. These food-grade corn hybrids are usually sold by farmers with a small premium, have improved processing efficiencies in dry-milling (see Chapter 15) plants, and because of their better quality, demanded by large breakfast and snack food companies.

Popcorn Popcorn is a special kind of flint corn that was selected by Indians in ancient Western civilizations and likely was the first snack food prepared by humankind. The major traits that distinguish popcorn from other genotypes are the size and shape of the kernels and the ability of sound kernels to explode and produce large puffed flakes when heated (Ziegler, 2003). The regular dent corn kernels weigh at least twice as much as the flint popcorns used by the industry. In contrast, the hectoliter weight of popcorn kernels (82–83 kg/hL) is at least 10–12 kg higher than that of regular dent corns (Serna Saldivar, 2008a, 2010a). Popcorn production greatly increased when farmers shifted from open-pollinated varieties to hybrids. Other major advantages of growing hybrids are better plant standing ability and poppability and more uniform kernel type and maturity (Ziegler, 2000). The germ, endosperm, and pericarp commonly comprise 12%, 81%, and 7% of the dry weight, respectively. The pericarp protects the kernel and, when it is damaged, negatively affects the popping performance. Hybrids or varieties with high proportions of translucent or vitreous endosperm give higher expansion rates (Pordesimo et al., 1990). Most hybrids possess practically 100% vitreous or corneous endosperm, although some bisected kernels show a small area of floury endosperm neighboring to the scutellum. The hard endosperm cells contain tightly packed small starch granules with polyhedral or angular forms. The endosperm cell also contains a thin fibrous and rectangular-shaped cell wall that encases the angular starch granules, protein bodies, and protein matrix. The tightly packed starch granules have indentations that look like small cavities from the protein bodies and the protein matrix holds the internal structure (Serna Saldivar, 2008a). Popcorn is merchandized in three kernel types: white, small yellow, and large yellow. Color differences in popcorn kernels result from genetic differences in the pericarp, aleurone, and endosperm. Kernels of white popcorn are usually rice-shaped, while small and large yellow popcorns are pearl-shaped. The range of thousand kernel weight for the large, medium, and small popcorn kernels are 149–152, 133–147, and 95–131 g, respectively. In order to produce the best quality popcorn, farmers should harvest kernels when reached full maturity and kernels contain about 17% moisture (Serna Saldivar, 2010c). The harvesting operation is especially vital because it should minimize kernel damage. Kernels must be dried slowly to prevent stress cracks from developing, but fast enough to prevent mold development (Serna Saldivar, 2008a). Kernels should not be dried below 11% moisture, otherwise poppability will not be attained. Structural damage to the popcorn kernel due to mechanical harvesting, shelling, and during handling drastically diminishes expansion volume and augments the percentage of unpopped kernels (Cretors, 2001).

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TABLE 16.1 Types of Corn Food and Statistics of Corn Consumption With Its Supply of Calories and Proteins in Year 2013 for Inhabitants of Different Continents and Selected Countries Around the World (FAO, 2018) Type of Corn-Based Food

Region/ Countrya

Corn Supply (g/ capita/ day)

Calories (kcal/ capita/ day)

Protein (g/capita/ day)

WORLD

49.0

147

3.6

Africa

121.9

388

9.9

Angola

106

338

8.9

Pirao, Fuba, Funge

Benin

116

351

9.3

Akassa, Amiwo, Akpan

Botswana

105

335

8.8

Kabu, Bogobe, Ting, Seswaa

Porridge/ Polenta/ Gruel/ Dumplings

Beverage

Bread

Nixtamalized

Kissangua

Burkina Faso

187

596

15.7

T^ o

Cabo Verde

106

338

8.9

Cachupa, Xerem

Cameroon

115

325

8.6

Corn fufu, Sangah

Egypt

171

596

15.7

Couscous

Ethiopia

115

398

9.2

Gonfo

Tella, Kerari

Kenya

208

663

17.5

Ugali, Uji, Irio, Githeri

Busaa

Lesotho

433

1379

36.3

Mielie pap, Ting

Malawi

354

1125

29.6

Nsima, Ubwali, Mgaiwa phala

Mali

104

331

8.7

T^ o

Morocco

99

273

7.0

Badaz

Mozambique

150

438

11.5

Ncima

Namibia

118

357

9.4

Oshifima, Mielie pap

Nigeria

90

285

7.5

Omi ukpoka, Tuwo Masara, Ogi

South Africa

274

858

21.9

Mieliepap, Putupap, Umnggusho

Mageu

Swaziland

191

642

16.9

Sishwala, Incwancwa,

Umcombotsi Emahewu

Fallahi, Shamsi, Eish merahrah Dabo, Kollo, Injera, Kitta

Leqebekoane Thobwa

Harsha Pombe

Mosa, Kokoro Meali, Cheesy corn bread, Umphokogo

Continued

438 Corn

TABLE 16.1 Types of Corn Food and Statistics of Corn Consumption With Its Supply of Calories and Proteins in Year 2013 for Inhabitants of Different Continents and Selected Countries Around the World—cont’d

Region/ Country

Corn Supply (g/ capita/ day)

Type of Corn-Based Food Calories (kcal/ capita/ day)

Protein (g/capita/ day)

Porridge/ Polenta/ Gruel/ Dumplings

Beverage

Bread

Nixtamalized

Sitfubi, Emasi etinkhobe temmbila, Sidvudvu, Tinkhobe Togo

191

572

15.1

Akume

Uganda

134

415

9.8

Posho (Kawunga)

United Rep. Tanzania

160

523

12.4

Ugali

Zambia

325

999

26.3

Nshima ya mgayiwa, Ubwali

Munkoyo

Zimbabwe

256

743

19.6

Bota, Isitshwala, Sadza

Whawha

Cornmeal cake

Bolivia

95

290

7.0

Choclos, Incachapi, Tujure, Mote

Api, Chicha

Chuspillo, Tortitas de maı´z, Pasankalla

Brazil

77

240

6.3

Cuzcuz, canjica, polenta (Angu)

Mingau

Bolo, Carantanta, Pomonha

Colombia

83

255

5.9

Mazamorra, Chorotes

Cuba

77

265

6.9

El Salvador

192

659

17.2

Guatemala

239

820

21.4

Honduras

213

733

19.1

Mexico

319

986

25.4

Kenkey (or kormi, kokoe, dorkunu), P^ate, Ablo, Djenkoume

Samp

America Humitas, baked tamales

Arepa, Bollo, Garullas, Pan de maı´z, Almoja´banas Majarete, Frituritas

Tamales

Atol

Riguas, Pasteles

Pupusas

Atol

Paches, Chuchitos, Torrejas Totoposte

Atole, Pinole, Tejate, Champurrado

Tesguino, Pozol

Pan de Elote

Tortillas, tamales, tostitos fritos

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TABLE 16.1 Types of Corn Food and Statistics of Corn Consumption With Its Supply of Calories and Proteins in Year 2013 for Inhabitants of Different Continents and Selected Countries Around the World—cont’d Type of Corn-Based Food

Region/ Country

Corn Supply (g/ capita/ day)

Calories (kcal/ capita/ day)

Protein (g/capita/ day)

Porridge/ Polenta/ Gruel/ Dumplings

Nicaragua

188

643

16.7

Paraguay

163

551

Venezuela

151

Asia

Beverage

Bread

Nixtamalized

Tiste

Chicha, Atol, Pinolillo

Rosquillas. G€ uirila, Yoltamales, Perrerreque

Tortilla, Quesillo Nacatamal, Tamugas

14.4

Mazamorra, Bori bori, mbaipy, Kyrype

Abati

Chipa Guasu, Sopa paraguaya

368

8.2

Funche, Majarete

27

76

1.8

Democratic Rep. of Korea

126

369

8.9

Georgia

75

243

5.6

Mchadi

Indonesia

97

239

5.9

Corn fritter (bakwan jagung)

Nepal

119

342

8.3

Ato, Dhido, Satoo

Timor-Leste

229

580

14.4

Batar Da’an (boiled corn)

Europe

20

54

1.3

Bosnia and Herzegovina

212

631

14.6

Kacˇamak

Rep. of Moldova

251

684

15.8

Ma˘ma˘liga˘

Romania

111

314

7.3

Ma˘ma˘liga˘

Slovenia

90

260

6.0

Polenta, Zganci, Mocˇnik

Oceania

12

38

1

Kenke

Arepas, Cachapas Hallacas, Mandoca

Maize porridge

Marring

Cocoloşi

a

Selected countries with at least 75 g/capita daily corn consumption in 2013 (FAO, 2018).

Sweet Corn The agronomics, composition, and plant breeding of specialty sweet corns are thoroughly covered by Tracy (2000) and Szymanek (2012). Sweet corn hybrids have been developed specifically to produce corn with desirable color, sweetness, and tenderness (see Chapter 10). Its ability to retain sweetness longer than regular dent corn when picked at the kernel milk stage has made sweet corn a highly desirable food. However, sweet corn cultivars generally yield lower compared

440

Corn

to regular hybrids. A recessive gene (sugary1 or su1) causes an alteration in the endosperm of corn that results in higher levels of soluble sugars and reduced levels of starch in the kernel. Currently, at least eight genes that affect carbohydrate synthesis in the endosperm are being utilized (Tracy, 2000). As compared to other varieties, sweet corn is characterized by possessing a lower pericarp thickness and a larger germ, which constitutes about 15% of the volume or 11.5%–14% of the kernel weight (Szymanek, 2012). From the moment of pollination until harvesting, the kernels undergo numerous physical and chemical transformations which largely affect their organoleptic properties. The flavor is particularly affected by the amounts of sugars and their gradual transformation into dextrins and starch during maturation. With respect to the content of sugars, three types of sweet corn cultivars are recognized; the normal sweet cultivar named type su or sugary which contains 4%–6% sugars, the sugar-enhanced cultivars commonly known as type se (sugary enhancement) with 6%–8%, and the sweetest cultivars named sh2 (shrunken 2) which contain 8%–12% sugar. In addition to these sugar contents, the fresh sweet corn kernels contain 3%–20% starch, 2.1%–4.5% protein, 1.1%–2.7% fat, 0.9%–1.9% cellulose, and significant amounts of essential minerals and vitamins including ascorbic acid (9–12 mg). Sweet corn has the highest nutritional value in the phase of milk ripeness. The content of soluble sugars and starch decreases and increases as kernels mature in the field. The sweet kernels contain about 3.03 sucrose, 0.34 glucose, and 0.31% fructose (Suk and Sang, 1999; Szymanek, 2012). Besides the sugar-starch composition, cultivars are selected based on the softness of the pericarp, fresh kernel color, and the facility to mechanically separate kernels from the cobs. The cut kernels commonly constitute between 30% and 40% of the total corn on the cob weight.

Quality Protein Maize >50 years have passed since Mertz et al. (1964) discovered the opaque-2 mutant genes that significantly increased the levels of lysine and tryptophan in corn (Atlin et al., 2011). The opaque 2 mutation increases the proportion of these amino acids by reducing zein synthesis, which results in increased synthesis of other protein fractions that are richer in lysine and tryptophan (Gibbon and Larkins, 2005). Unfortunately, the opaque-2 corn possessed a chalky, soft, and opaque endosperm which caused lower grain yields, poor milling properties, higher susceptibility to insects and diseases, and poor storability and processing properties (Rooney and Serna Saldivar, 2003). The increased levels of these essential amino acids prompted corn breeders to backcross the gene into many inbred lines and open-pollinated cultivars, but it soon became apparent that the mutation was associated with deleterious pleiotropic effects resulting from softer endosperm, including increased susceptibility to insect damage, higher ear rot incidence, and a yield penalty of approximately 25% due to reduced grain density (Vasal, 2000; Prasanna et al., 2001). After years of continued effort, new improved populations of QPM with improved grain hardness and agronomic performance were developed. These yellow and white QPM populations have been incorporated into high-yielding hybrids in Brazil, Mexico, Ghana, and other countries, while open-pollinated varieties are grown in Africa and Central America (Vasal, 2000). Drs. Vasal and Villegas were granted the World Food Prize in fall of 2000 for their significant contributions to world agriculture through the development of QPM. Harder QPM corns are suited for dry-milling and alkaline cooking, while soft hybrids for use in wet-milling to produce sweeteners, starches, and alcohol would be desirable since the coproducts would be more valuable, especially in terms of protein quality (Melesio Cuellar et al., 2008; Rooney and Serna Saldivar, 2003). De Groote et al. (2014) compared the organoleptic acceptance of QPM staple food in Tanzania (Ugali), Kenya (Githeri), and Ethiopia (Injera) with counterparts produced from regular corn. The results showed that African consumers differentiated sensory attributes of QPM products from their conventional counterparts. Analysis by ordinal mixed regression models showed that consumers found QPM acceptable and even preferable compared to conventional maize. Barragan-Delgado and Serna Saldivar (2000) determined the essential amino acid scores of weaning food produced from regular corn or QPM and found a 23 units difference in favor of the QPM. Weanling rats fed the QPM weaning food had 2.2 PER, whereas counterparts fed regular corn 1.2. Recently, Ortiz-Martı´nez et al. (2017) observed that protein hydrolysates obtained from QPM maize had more antioxidant activity than a regular counterpart. QPM-based food can upgrade the nutritional status of many infants who consume cereals daily due to the better protein quality. The dramatic improvement in the nutritional value of QPM food is easily worth the plant-breeding efforts currently being made throughout the world. Unfortunately, the adoption of QPM has been limited despite the development of highyielding yellow and white open-pollinated varieties and hybrids adapted to tropical and temperate ecosystems of the planet.

Blue and Pigmented Corns Indigenous meso and north American cultures have recognized the value of blue corn since ancient times. For example, the Aztec and Hopi civilizations related blue pigmented corn with religious cults to their Gods of subsistence. Likewise, Mayan

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people related it with cosmic directions where blue corn represented the cardinal point West (Arellano-Va´zquez et al., 2003). An anonymous Huichol tale describes that the origin of pigmented corn is associated with the 5 Mothers of Corn, the blue being the most beautiful and sacred of them all. Blue corn is a floury or soft endosperm type that generally grows in long ears (8–12 rows). Most blue varieties of corn are planted in the highlands of Mexico and Peru and are still landraces or criollo types inherited by past generations dating back to prehispanic times. The major withdraws of blue corn varieties are that plants are more prone to lodging, yield lower amounts of grain, and that kernels are soft-textured. It has been estimated that only 3% of the Mexican corn production is blue, black, or purple-colored. With the available technology based on indigenous or landraces types, corn yields reach between 2 and 3.5 ton/ha (Miguel et al., 2004). Due to the increased interest in blue corns, plant breeders have developed high-yielding hybrids adapted to other ecosystems such as subtropical regions. These hybrids with excellent yield potential produce harder kernels with higher concentrations of anthocyanins (Garcia-Lara et al., 2012; Urias-Peraldı´ et al., 2013; Urias-Lugo et al., 2015a, b, c). The blue corn pigments are most often found in the aluerone layer Betran et al., 2000), but in some cases they can also be found in the pericarp (see Chapter 14). Blue corn owes its coloration to the presence of glycosylated and acylated anthocyanins (Cevallos-Casal & Ciseneros-Zeballos, 2003). The recent interest for blue corns is due to their nutraceutical and health-promoting properties (Urias-Peraldı´ et al., 2013). Urias-Lugo et al. (2015b) reported antiproliferative activity effect of anthocyanins and phenolics acids of blue maize on mammary, liver, colon, and prostate cancer cells, whereas Guzma´n-Gero´nimo et al. (2017) concluded that blue corn extracts enhanced high-density lipoprotein cholesterol and decreased systolic blood pressure, serum triglycerides, total cholesterol, and epididymal adipose tissue weight in laboratory rats. Blue corn is crushed with stone mills and the resulting fractions sifted to remove some of the very coarse pericarp to produce refined meals and flours. These flours are used to produce Pika, a ceremonial paper bread, by Navajos in the southwestern US. The fine corn meal or flour is made into a thin batter; boiling water is added to form a thin paste, which is spread on a hot, flat stone or metal griddle that has been previously brushed with vegetable oil. The thin layer after baking is peeled off and folded or rolled into thin wafers and accompanied with beans or stew. Blue corn is also utilized to produce thick and thin porridges such as Chaqueque, Atole, and Pinole. Chicos are made from immature blue kernels steamed in the husk and dried. Chicos are generally cooked with beans, peppers, and green onions or used in stews (Rooney and Serna Saldivar, 2003).

Giant Cuzco Corn The Peruvian Giant Cuzco race yields 8-rowed ears with the largest known corn kernels (Grobman et al., 1961). The preferred genotypes are those that yield a white kernel, although in Peru and Mexico blue and red-colored types are also produced. Cuzco corn was named as Cacahuacintle by the Aztec culture and widely used for the production of many food. This type of corn is still planted at high altitudes and generally sold for production of pozole or for the manufacturing of Cornnuts (see Chapter 17). In the USA, Cuzco corn was introduced in 1964 and transformed into high-yielding hybrids after 9 years of painstaking breeding work. Kernels are harvested when the moisture content of the grain is