Advanced Applications of Biobased Materials: Food, Biomedical, and Environmental Applications 0323916775, 9780323916776

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Advanced Applications of Biobased Materials

Advanced Applications of Biobased Materials Food, Biomedical, and Environmental Applications

Edited by

Shakeel Ahmed Assistant Professor of Chemistry, Higher Education Department, Government of Jammu and Kashmir; Assistant Professor, Department of Chemistry, Government Degree College Mendhar, Jammu and Kashmir, India

Annu International Research Professor, School of Mechanical Engineering, Yeungnam University, Gyeongsan, South Korea

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States Copyright © 2023 Elsevier Inc. 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 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. ISBN: 978-0-323-91677-6 For information on all Elsevier publications visit our website at https://www.elsevier.com/books-and-journals

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Contributors Atinafu Abayneh Department of Applied Chemistry, School of Applied Natural Science, Adama Science and Technology University, Adama, Ethiopia Frage Abookleesh Department of Food Science and Technology, Sebha University, Sabha, Libya Shruti Aggarwal Bharat Institute of Pharmacy, Pehladpur, Babain, Kurukshetra, Haryana, India Pablo Figuereido Aguilar Chemical Department, Faculty of Philosophy, Sciences and Letters at Ribeira˜o Preto, University of Sa˜o Paulo, Ribeira˜o Preto, SP, Brazil Shakeel Ahmed Department of Chemistry, Government Degree College Mendhar, Mendhar; Higher Education Department, Government of Jammu and Kashmir, Jammu, Jammu and Kashmir; University Center for Research & Development, Chandigarh University, Mohali, Punjab, India S. Wazed Ali Department of Textile and Fibre Engineering, Indian Institute of Technology Delhi, New Delhi, India C. Anandharamakrishnan Computational Modeling and Nanoscale Processing Unit, National Institute of Food Technology, Entrepreneurship and Management—Thanjavur, Ministry of Food Processing Industries, Government of India, Thanjavur, Tamil Nadu, India Annu International Research Professor, School of Mechanical Engineering, Yeungnam University, Gyeongsan, South Korea Reena Antil Department of Botany, Pt. Nekiram Sharma Government College Rohtak, Rohtak, Haryana, India E.O. Atoyebi Department of Biomedical Engineering, College of Engineering and Technology, Achievers University, Owo; Department of Biomedical Engineering, University of Ibadan, Ibadan, Nigeria Zaffar Azam Department of Zoology, Dr. Harisingh Gour Vishwavidyalaya (A Central University), Sagar, Madhya Pradesh, India Kalpana Baghel Department of Zoology, Dr. Harisingh Gour Vishwavidyalaya (A Central University), Sagar, Madhya Pradesh, India Satyaranjan Bairagi Department of Textile and Fibre Engineering, Indian Institute of Technology Delhi, New Delhi, India Sourav Banerjee School of Interdisciplinary Research, Indian Institute of Technology Delhi, New Delhi, India

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Contributors

Swagata Banerjee Department of Textile and Fibre Engineering, Indian Institute of Technology Delhi, New Delhi, India Larissa Rodrigues Beitum Chemical Department, Faculty of Philosophy, Sciences and Letters at Ribeira˜o Preto, University of Sa˜o Paulo, Ribeira˜o Preto, SP, Brazil Tanima Bhattacharya Innovation, Incubation and Industry Laboratory, Techno India NJR Institute of Technology, Udaipur, Rajasthan, India Neha Bhilare Department of Pharmaceutical Chemistry, Arvind Gavali College of Pharmacy, Satara, Maharashtra, India Karen Lopez Camas Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada Zaira Zaman Chowdhury Nanotechnology and Catalysis Research Centre (NANOCAT), Institute for Advanced Studies (IAS), University of Malaya, Kuala Lumpur, Malaysia T.T. Dele-Afolabi Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Universiti Putra Malaysia, UPM, Serdang, Selangor, Malaysia; Department of Mechanical Engineering, Faculty of Engineering, Ajayi Crowther University, Oyo, Oyo State, Nigeria Nisha Kumari Devaraj Faculty of Engineering, Multimedia University, Cyberjaya, Malaysia Hasan Ege Center for Nanotechnology and Biomaterials Application and Research (NBUAM), Marmara University; Department of Physiology, Institute of Health Sciences, Istanbul University-Cerrahpasa, Istanbul, Turkey Zeynep Ruya Ege Center for Nanotechnology and Biomaterials Application and Research (NBUAM), Marmara University; Department of Biomedical Engineering, Faculty of Engineering and Architecture, Istanbul Arel University, Istanbul, Turkey Gozde Enguven Center for Nanotechnology and Biomaterials Application and Research (NBUAM), Marmara University; Faculty of Chemical and Metallurgical Engineering, Department of Bioengineering, Yildiz Technical University, Istanbul, Turkey Abu Nasser Faisal Nanotechnology and Catalysis Research Centre (NANOCAT), Institute for Advanced Studies (IAS), University of Malaya, Kuala Lumpur, Malaysia Ana Laura Garcia Chemical Department, Faculty of Philosophy, Sciences and Letters at Ribeira˜o Preto, University of Sa˜o Paulo, Ribeira˜o Preto, SP, Brazil Shivani Garg Institute of Environmental Studies, Kurukshetra University, Kurukshetra, Haryana, India

Contributors

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Rupesh K. Gautam Department of Pharmacology, Indore Institute of Pharmacy, Rau, Indore, India Abbay Gebretsadik Department of Applied Chemistry, School of Applied Natural Science, Adama Science and Technology University, Adama, Ethiopia Rajat Goyal MM College of Pharmacy, Maharishi Markandeshwar (Deemed to be University), Mullana-Ambala, Haryana, India Surender Singh Gulia Department of Botany, Pt. Nekiram Sharma Government College Rohtak, Rohtak, Haryana, India Ravi Gundawar Department of Pharmaceutical Quality Assurance, Manipal College of Pharmaceutical Sciences, Manipal Academy of Higher Education, Manipal, Karnataka, India Oguzhan Gunduz Center for Nanotechnology and Biomaterials Application and Research (NBUAM); Department of Metallurgical and Materials Engineering, Faculty of Technology, Marmara University, Istanbul, Turkey Priyanka Gupta Department of Zoology, Dr. Harisingh Gour Vishwavidyalaya (A Central University), Sagar, Madhya Pradesh, India Reena Gupta Department of Biotechnology, Himachal Pradesh University, Shimla, India M.A. Azmah Hanim Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Universiti Putra Malaysia, UPM; Research Center Advance Engineering Materials and Composites, (AEMC), Faculty of Engineering, Universiti Putra Malaysia, Serdang, Selangor, Malaysia Yanet Rodrı´guez Herrero Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada Rabea Ikram Chemical Engineering, University of Malaya, Kuala Lumpur, Malaysia Aswathy Jayakumar Department of Materials and Production Engineering, The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangsue, Bangkok, Thailand; Department of Food and Nutrition, BioNanocomposite Research Center, Kyung Hee University, Seoul, Republic of Korea Mohd Rafie Johan Nanotechnology and Catalysis Research Centre (NANOCAT), Institute for Advanced Studies (IAS), University of Malaya, Kuala Lumpur, Malaysia Jasila Karayil Department of Applied Science, Government Engineering College West Hill, Kozhikode, India Manpreet Kaur Department of Biotechnology, Himachal Pradesh University, Shimla, India

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Contributors

Kiflom Gebremedhn Kelele Department of Applied Chemistry, School of Applied Natural Science, Adama Science and Technology University, Adama, Ethiopia Khalisanni Khalid Malaysian Agricultural Research and Development Institute (MARDI), Serdang, Selangor, Malaysia Jun Tae Kim Department of Food and Nutrition, BioNanocomposite Research Center, Kyung Hee University, Seoul, Republic of Korea Chin Wei Lai Nanotechnology and Catalysis Research Centre (NANOCAT), Institute for Advanced Studies (IAS), University of Malaya, Kuala Lumpur, Malaysia Jyoti Lathwal Department of Botany, Pt. Nekiram Sharma Government College Rohtak, Rohtak, Haryana, India Subhankar Maity Department of Textile Technology, Uttar Pradesh Textile Technology Institute, Kanpur, Uttar Pradesh, India M.U. Makgobole Chiropractic and Somatology, Durban University of Technology (DUT), Durban, South Africa P.S. Mdluli Department of Chemistry, Durban University of Technology (DUT), Durban, South Africa Danila Merino Smart Materials, Italian Institute of Technology, Genoa, Italy B.N. Mkhwanazi Dietetic and Human Nutrition, University of KwaZulu-Natal, Durban, South Africa J.A. Moses Computational Modeling and Nanoscale Processing Unit, National Institute of Food Technology, Entrepreneurship and Management—Thanjavur, Ministry of Food Processing Industries, Government of India, Thanjavur, Tamil Nadu, India N. Mpofana Chiropractic and Somatology, Durban University of Technology (DUT), Durban, South Africa H.C. Ananda Murthy Department of Applied Chemistry, School of Applied Natural Science, Adama Science and Technology University, Adama, Ethiopia; Department of Prosthodontics, Saveetha Dental College & Hospital, Saveetha Institute of Medical and Technical Science (SIMATS), Saveetha University, Chennai, Tamil Nadu, India Aswathy Narayanan Molecular Mycology Laboratory, Molecular Biology and Genetics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, Karnataka, India

Contributors

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Neelam Department of Zoology, Dr. Harisingh Gour Vishwavidyalaya (A Central University), Sagar, Madhya Pradesh, India Shubham Nimbkar Computational Modeling and Nanoscale Processing Unit, National Institute of Food Technology, Entrepreneurship and Management—Thanjavur, Ministry of Food Processing Industries, Government of India, Thanjavur, Tamil Nadu, India Nahid Nishat Inorganic Materials Research Lab, Department of Chemistry, Jamia Millia Islamia, New Delhi, India O.J. Ojo-Kupoluyi Department of Sugar Engineering, Nigeria Sugar Institute, Ilorin, Nigeria S.C. Okonkwo Shehu Idris College of Health Sciences and Technology, Makarfi, Nigeria S.C. Onwubu Department of Chemistry, Durban University of Technology (DUT), Durban, South Africa Riyaz Ali M. Osmani Department of Pharmaceutics, JSS College of Pharmacy, JSS Academy of Higher Education & Research, Mysuru, Karnataka, India Pintu Pandit Department of Textile Design, National Institute of Fashion Technology, Patna, Bihar, India Jyotishkumar Parameswaranpillai Department of Science, Faculty of Science and Technology, Alliance University, Bengaluru, Karnataka, India Ana Isabel Quilez-Molina Smart Materials, Italian Institute of Technology, Genoa, Italy Sabarish Radoor Department of Polymer-Nano Science and Technology, Jeonbuk National University, Deokjin-gu, Jeonju-si, Republic of Korea; Department of Materials and Production Engineering, The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangsue, Bangkok, Thailand Md Mahfujur Rahman Islamic Business School, IHM, University Utara Malaysia, Sintok, Kedah, Malaysia Jong Whan Rhim Department of Food and Nutrition, BioNanocomposite Research Center, Kyung Hee University, Seoul, Republic of Korea Nelson Pynadathu Rumjit Nanotechnology and Catalysis Research Centre (NANOCAT), Institute for Advanced Studies (IAS), University of Malaya, Kuala Lumpur, Malaysia

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Contributors

Vipin Saini MM College of Pharmacy, Maharishi Markandeshwar (Deemed to be University), Mullana-Ambala, Haryana, India Rutika Sehgal Department of Biotechnology, Himachal Pradesh University, Shimla, India Adnan Shahzaib Inorganic Materials Research Lab, Department of Chemistry, Jamia Millia Islamia, New Delhi, India Shaily Inorganic Materials Research Lab, Department of Chemistry, Jamia Millia Islamia, New Delhi, India Vibhuti Sharma Department of Biotechnology, Himachal Pradesh University, Shimla, India Mehdihasan I. Shekh College of Materials Science and Engineering, Shenzhen University, Shenzhen, People’s Republic of China Karishma Shetty Shobhaben Pratapbhai Patel School of Pharmacy & Technology Management, SVKM’S NMIMS (Deemed to be University), Mumbai, India Suchart Siengchin Department of Materials and Production Engineering, The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangsue, Bangkok, Thailand; Molecular Mycology Laboratory, Molecular Biology and Genetics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, Karnataka, India Ekta Singh Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch, Galveston, TX, United States P. Soma Yasaswi Shobhaben Pratapbhai Patel School of Pharmacy & Technology Management, SVKM’S NMIMS (Deemed to be University), Mumbai, India Apoorva Sood Department of Biotechnology, Himachal Pradesh University, Shimla, India D. Subhasri Computational Modeling and Nanoscale Processing Unit, National Institute of Food Technology, Entrepreneurship and Management—Thanjavur, Ministry of Food Processing Industries, Government of India, Thanjavur, Tamil Nadu, India Delia Rita Tapia-Bla´cido Chemical Department, Faculty of Philosophy, Sciences and Letters at Ribeira˜o Preto, University of Sa˜o Paulo, Ribeira˜o Preto, SP, Brazil Paul Thomas Nanotechnology and Catalysis Research Centre (NANOCAT), Institute for Advanced Studies (IAS), University of Malaya, Kuala Lumpur, Malaysia

Contributors

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Preeti Tyagi Nanotechnology and Catalysis Research Centre (NANOCAT), Institute for Advanced Studies (IAS), University of Malaya, Kuala Lumpur, Malaysia Aman Ullah Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada Muhammet Uzun Center for Nanotechnology and Biomaterials Application and Research (NBUAM); Department of Textile Engineering, Faculty of Technology, Marmara University, Istanbul, Turkey Unnati Walia Department of Biotechnology, Himachal Pradesh University, Shimla, India Khushwant S. Yadav Shobhaben Pratapbhai Patel School of Pharmacy & Technology Management, SVKM’S NMIMS (Deemed to be University), Mumbai, India Fahmina Zafar Inorganic Materials Research Lab, Department of Chemistry, Jamia Millia Islamia, New Delhi, India Luis Fernando Zitei-Baptista Chemical Department, Faculty of Philosophy, Sciences and Letters at Ribeira˜o Preto, University of Sa˜o Paulo, Ribeira˜o Preto, SP, Brazil

Preface Biobased materials refer to materials obtained partially or wholly from living matter that either occur naturally or are synthesized or processed from biomass. Today, as the world needs new sustainable alternatives to conventional materials that have a negative impact on the environment and human health, biobased materials are emerging as the solution. These ecofriendly and sustainable materials are occupying the mainstream end-users, altering the available materials in the 21st century and their use in different industrial sectors. Due to the increase in environmental and health awareness, and heavy demands in different sectors, the engineering of new biobased materials is considered to be an effective solution for the adverse effects caused by conventional practices. Such types of materials motivate scientists working in different fields to focus on the processing of biobased materials to convert them into value-added products. Biobased materials can make the economy more sustainable and will lower the dependence of human beings on conventional plastic, as these materials are nature inspired and adhere to nature’s circular principles of reusing, recycling, and biodegradation without waste generation. By 2030, it is expected that 20%–25% of biobased renewable composite materials will be utilized in different sectors of human life from industrial applications to biomedical applications. Despite the revolutionary usage of biobased materials, they possess limitations such as low compatibility, hydrophilic nature, and lower strength, which limit their applications to a few areas. In addition, extracting biofibers continuously from specific sources may lead to an imbalance in the ecosystem. Therefore, it is necessary to identify new bio-renewable materials from different sources to prevent their overuse and to overcome these limitations. There is a need to explore more avenues in the area of biobased materials. This book is divided into different sections, each of which discusses a particular area of biobased materials. Section 1 contains two chapters which discuss fundamental concepts to classification and modification of biobased materials. Section 2 consists of two chapters which consider the fabrication and characterization of these materials. In Section 3, various biobased materials are reviewed in terms of their food applications in six chapters. Section 4 consists of 12 chapters which focus specifically on biomedical applications such as wound healing, skin regeneration, tissue engineering, nerve regeneration, and osteoporosis. This section also gives an insight on the impact of biobased materials on human health along with their pros and cons. Section 5 contains four chapters discussing the environmental applications of biobased materials, while four more chapters in Section 6 consider their electronics, coating, catalysis and textile applications. The two chapters in Section 7 conclude by discussing the sustainability, life cycle assessment, circular economy, and future prospects of biobased materials. We hope that this book will be a useful resource for academicians, researchers, scientists, scholars, biologists, biotechnologists, nanotechnologists, food technologists, biomedical engineers, and others working in allied areas. It will also be useful for graduate and postgraduate students who are interested in exploring biobased materials for different applications.

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On behalf of Elsevier, we the editors of this book are very grateful to the authors for their outstanding contributions and dedicated efforts in completing this book. Finally, our thanks go to Elsevier for the publication of this book. Editors Shakeel Ahmed Annu

CHAPTER

Biopolymers: An overview

1

Mehdihasan I. Shekha, Annub, and Shakeel Ahmedc,d,e a

College of Materials Science and Engineering, Shenzhen University, Shenzhen, People’s Republic of China, International Research Professor, School of Mechanical Engineering, Yeungnam University, Gyeongsan, South Korea, c Department of Chemistry, Government Degree College Mendhar, Mendhar, Jammu and Kashmir, India, d Higher Education Department, Government of Jammu and Kashmir, Jammu, Jammu and Kashmir, India, eUniversity Center for Research & Development, Chandigarh University, Mohali, Punjab, India b

Introduction In the current scenario, the growing concerns of environmental and health hazards are key topics in the field of science. As the population increases, to fulfill daily needs, people unthinkingly use nonbiodegradable and easily available polymer-made plastics in their everyday life from the kitchen to the healthcare sector. Due to overuse of nonbiodegradable polymers, it is currently a significant challenge to deal with plastic waste. Additionally, this nonbiodegradable polymer waste increases the risk of health issues. With growing awareness of a healthy environment, researchers have developed sustainable and eco-friendly biopolymer-based green composites which are mainly engineered, or have functionalized raw biopolymers with other degradable synthetic or biosynthetic polymers (George, Sanjay, Srisuk, Parameswaranpillai, & Siengchin, 2020; Gurunathan, Mohanty, & Nayak, 2015; Moraes, Silva, & Vieira, 2020). By 2030, it is expected that 20%–25% of biobased renewable composite materials will be utilized in different sectors of human life from industrial applications to biomedical applications (Rajeswari, Stobel Christy, & Pius, 2021; Silva, Rodrigues, Fernandes, & Reis, 2020b; Varma & Gopi, 2021). These natural renewable green composites are biocompatible and biodegradable, and are widely applicable in the fields of food science (Augustine, Rajendran, Cvelbar, Mozetic, & George, 2013; Mangaraj, Yadav, Bal, Dash, & Mahanti, 2019), pharmaceuticals (Deb, Kokaz, Abed, Paradkar, & Tekade, 2019; Nayak & Hasnain, 2020), tissue engineering (Pattanashetti, Heggannavar, & Kariduraganavar, 2017; Silva, Rodrigues, Fernandes, & Reis, 2020a; Sohrabi, Khorasani, Ahmed, & Annu, 2021), and bioadsorbents (Donner, Arshad, Ullah, & Siddique, 2019; Singh et al., 2020). The word biopolymer comes from the Greek “bio” meaning “life” and “polymer” meaning “many parts.” Biopolymers are widely extracted or synthesized from living organisms which are mainly plants, animals, microorganisms, algae, fungi, etc. Additionally, the resources of biopolymers are agricultural waste, industrial biowaste, and forestry feed stocks. The main source of biopolymers are living organisms which make them biocompatible and biodegradable. Historically, biopolymers have been widely applicable in different fields (Deb, Al-Attraqchi, Chandrasekaran, & Paradkar, 2019). Advanced Applications of Biobased Materials. https://doi.org/10.1016/B978-0-323-91677-6.00026-X Copyright # 2023 Elsevier Inc. All rights reserved.

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Chapter 1 Biopolymers: An overview

For instance, the Egyptians and Babylonians demonstrated use of hemps, flax, and catgut in surgical science. Similarly, around 1600 BC Marathi Indians used natural rubbers to make balls. Joseph Priestly, Michal Faraday, and Charles Goodyear individually researched biobased rubbers and gave their views on biopolymeric structures and their applications. After this period, the era of synthetic polymers started and research grew day by day. From 1900 until now, numerous synthetic polymers were synthesized and extensively applied in different fields of daily life. Although synthetic polymers possess good mechanical, thermal, and antimicrobial properties, they also show toxic effects on human health and environment, which limits their biomedical application (Kalia & Averous, 2011; Reddy, Ponnamma, Choudhary, & Sadasivuni, 2021; Vinod, Sanjay, Suchart, & Jyotishkumar, 2020). Biopolymers are nontoxic, biocompatible, antimicrobial, and easily degradable in a variety of environments. These properties enhance their applicability in the biomedical field (Biswal, 2021; Liu et al., 2021; Reddy et al., 2021). In order to advance biomedical research, numerous works were carried out using biopolymer-based materials and their properties, benefits, and limitations were studied (Biswal, 2021; George et al., 2020; Gopi, Amalraj, Sukumaran, Haponiuk, & Thomas, 2018). For these, different kinds of biopolymerbased composites were synthesized with ceramics, metal oxides, and synthetic polymers. From this research it was deduced that different kinds of biopolymer-based structures can be extensively synthesized and applied for tissue engineering to drug delivery systems (Gopi et al., 2018; Kakoria & SinhaRay, 2018). These structures are mainly fibrous materials (Kakoria & Sinha-Ray, 2018; Khansari, Sinha-Ray, Yarin, & Pourdeyhimi, 2013; Shekh, Amirian, Stadler, Du, & Zhu, 2020), thin films/membranes (Akhter, Masoodi, Wani, & Rather, 2019; Taketa et al., 2020; Tomoda et al., 2020), foams (Gaserod, Anderson, & Myroveld, 2010; Rapp, Schneider, & Elsner, 2014), hydrogels (Amirian et al., 2021; Sivashanmugam, Arun Kumar, Vishnu Priya, Nair, & Jayakumar, 2015; Spicer, 2020), nanoparticles ( Jacob, Haponiuk, Thomas, & Gopi, 2018; Joye & McClements, 2014; McBain, Yiu, & Dobson, 2008; Nitta & Numata, 2013; Xie et al., 2014), and many more. This chapter focuses mainly on the detailed classification of biopolymers, their structural characteristics, and their possible applications in the biomedical field.

Classification of biopolymers and their structures Biopolymers are extracted or synthesized from living organisms. Different kinds of biopolymers are available which are mainly generated from renewable sources (Annu & Ahmed, 2021). Biopolymers are generally classified into three categories with respect to structures (see Fig. 1.1). Additionally, their classification is carried out through their origins (Averous & Pollet, 2013; Gross & Scholz, 2001; Silva et al., 2020b).

Polynucleotides Polynucleotides consist of nucleotide monomers which are joined together with covalent bonds. Each single polynucleotide has 14 or more nucleotide monomers in a chain structure. These monomers are arranged in such a manner that the final orientation of chain is in helical fashion. The two main examples of polynucleotides are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) (see Fig. 1.2). Generally, DNA consists of two helical polynucleotide chains while RNA consists of a single-stranded helical chain.

Classification of biopolymers and their structures

FIG. 1.1 Classification of biopolymers.

FIG. 1.2 Polynucleotides: (A) DNA and (B) RNA.

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Chapter 1 Biopolymers: An overview

Polypeptides/proteins Polypeptides/proteins are long chain biopolymers having amino acids as a monomeric unit. In the case of protein, a number of polypeptide chains join and a protein structure is generated. Between two amino acids, amide linkage is occurring; thus this biopolymer is also known as polyamides. The 20 different kinds of amino acids are decoded. Each polypeptide has three-dimensional molecular chain arrangements, which depend on the chemical compositions of the peptide chains. Polypeptides/proteins are mainly crucial biopolymers in living organisms, which facilitates regulation of gene expression, signal transduction, catalysis of reactions, transportation, and immunity-related functions (Deb, Al-Attraqchi, et al., 2019; Silva et al., 2020a). Proteins show 3D structural rearrangements from helical to complex polypeptide chain arrangements. This kind of chain arrangement is due to the presence of inter- or intramolecular hydrogen bonding, ionic interaction, salt bridges, and disulfide bonds. On the basis of their source or origin, proteins are divided into two types: animal source-based proteins (i.e., collagen, gelatine, silk fibroin, sericin, albumin) and agroproteins (i.e., soy protein, zein, gluten) (Shaik & Moussian, 2013; Sabater, Ro´denas, & Heredia, 2013). The source of the protein is generally animals’ bones, ligaments, tendons, blood vessels, skin, and tissues. For example, collagen is found in the skin of animals and fish. It is a main component of extracellular matrix and the most abundant protein in mammalian tissues. It contains amino acids (i.e., glycine, proline, and hydroxy proline-collagen type I) in the backbone (Fig. 1.3). Its main role is to provide mechanical strength to the tissues; it also stimulates cell adhesion and cell proliferation. Collagen is soluble in hot water but insoluble in cold water. Similarly, gelatine is a hydrolyzed form of collagen. It is extracted from cattle bones and fish skin. Gelatine is widely used in the food, pharmaceutical, biomedical, and cosmetic industries. On the basis of the extraction process, gelatine is divided into two types; acidic hydrolysis gives type A while alkaline hydrolysis gives type B. Gelatine contains repeating units of amino acids in the following order: alanine, glycine, proline, arginine, glycine, glutamine, hydroxy proline, glycine, and proline (-Ala-Gly-Pro-Arg-GLy-Glu-Hyp-GLy-Pro-).

FIG. 1.3 Protein chemical structures.

Classification of biopolymers and their structures

7

Silk is composed of fibroin and sericin proteins. Fibroin is a fibrous structure and sericin (a gummy protein) keeps the fibroin fibers together. Thus, silk fibroin consists of sericin in their structure. Silk fibroin consists of glycine, alanine, and serine amino acid units in random manner while sericin consists of serine, glycine, glutamic acid, aspartic acid, threonine, and tyrosine amino acids as repeating units. Silk fibroin is negatively charged on the surface, which provides electrostatic interactions with other materials. Sources of silk fibroin include silk worms (nonmulberry and mulberry), spiders, and some insects. Silk fibroin possess good elasticity, biocompatibility, and mechanical strength, and are thus widely applicable in tissue engineering and other biomedical fields. Sericin has attractive properties such as being pH responsive, antioxidant, and moisturizing; thus it is widely applicable in cosmetic and biomedical applications. Agroproteins are obtained from plants extracts (Sabater et al., 2013). Generally, these kinds of proteins have limited mechanical properties and different kinds of molecular arrangements to physical properties. Soy protein is extracted from soya beans. It contains 40% proteins and 20% oils. It is a water soluble and globular type of protein. Due to its oxygen barrier and UV protective properties, soy proteins are very commonly applied in food packaging, sport industries, and nonflammable thermal insulations. Another agroprotein is zein. This is a prolamine and is found in corn up to 10%. It is generally extracted from gluten meal, and is water-insoluble but soluble in a mixture of aqueous-organic solvents at pH 11. Zein is used extensively in paper industries, adhesives, laminations, and edible coatings. Other kinds of agroproteins are gluten (a wheat protein) and casein (a milk protein). Both proteins are water insoluble and are used in adhesives and laminations. Additionally, casein is extensively used in digestive enzyme preparations.

Polysaccharides Polysaccharides consist of many monosaccharide units which are joined together via glycosidic bonds. Each polysaccharide has unique monosaccharide repeating units, thus their physical and chemical properties differ vastly from their analogous polysaccharides. Generally, polysaccharides originate from renewable resources such as plants, animal shells, algae, fungi, etc. (Gross & Scholz, 2001; Kalia & Averous, 2011; Moraes et al., 2020; Silva et al., 2020a). Some polysaccharides may also be synthesized in laboratories. The biological functions of polysaccharides are mainly energy storage, cell wall formation, adhesives, and cell communications in plants and animals. Polysaccharides are further classified according to their origin. Table 1.1 lists different kinds of polysaccharides, their resources, characteristic features, and applications. The chemical structures of polysaccharides have similar kinds of main chain but substitution and linkage of two monomeric units are different (Gross & Scholz, 2001; Silva et al., 2020a). Two common structures of polysaccharides are shown in Fig. 1.4, while Table 1.2 reports the substitution of monomeric units and respective polysaccharide names.

Synthetic biopolymers (bioplastics) Synthetic biopolymers are classified as renewable or nonrenewable. They are mainly polyesters (i.e., poly lactic acid, poly(trimethylene terephthalate) (PTT), poly(butylene terephthalate) (PBT), and poly(butylene succinate) (PBS)), polyurethanes, polyhydroxy alkenoates (i.e., polyhydroxy butyrate (PHB) and polyhydroxy valerate (PHV), and polyamides (i.e., nylons) (Averous & Pollet, 2013). Normally, synthetic biopolymers are synthesized through fermentation of natural sources or biomass

Table 1.1 Characteristics of different polysaccharides. Name

Source

Physical characteristics

Structural characteristics

Applications

β-1,4-glycosidic-linked Dglucose units

Cellulose and its derivatives widely used in textile, food, paper, membranes, films, and wood products. Used as food thickening agent, adhesives, ink, and textile finishing formulations

Consist amylose + amylopectin as repeating unit

Use as thickener, adhesives, glazing agent in paper and textile industries, pharmaceutical industries

1,4-β-D-xylans + 1.4-β-Dmannans and araban + 1.3and 1,4-β-D-galactans as repeating unit

Used as food additives, emulsifiers, thickening agents, gelling agents, adhesives and adsorbents. Antitumor agents. Derivatives of HMC use in drugs Used as thickening agent in food and paper industries; Reduce blood cholesterol levels and gastrointestinal disorders

Resource: Plants/Woods Cellulose

Woods

• Neutral and linear • • •

Starch

Corn, potato, rice husk, wheat

• • • •

Hemicellulose

Plant cell walls, 20%–30% of wood mass

• • •

Pectin

Plant cell walls

polysaccharides High crystallinity Insoluble in water and organic solvent Easy to modify through esterification, grafting, and selective oxidation Neutral and branched polysaccharide Principal carbohydrate of plants Partially soluble in water Modification of starch alters its properties which make them widely applicable Neutral and linear polysaccharides Water soluble Amorphous in nature

• Ionization depends on pH and linear polysaccharide • MW: 50–180 kDa • Water soluble; forms viscous solutions • Forms very fast gel with calcium ions

α-1,4-D-Galacturonic acid units

Gum (guar gum, gum acacia, gum karaya, gum tragacanth, locust bean gum)

Plant extract, apple pomec and orange peel

• Neutral and branched

Cell walls of fungi, exoskeletons of arthropods and insects, radulas of mollusks, and beaks of cephalopods

• Neutral, crystalline,

Deacetylation of chitin

•

polysaccharides • Water soluble • Forms viscous solutions

Depends on gum derivative Guar gum: Mannose main chain with galactose branch after two units Gum arabic: highly branched polymer of galactose, rhamnose, arabinose, and glucuronic acid units Gum karaya: highly branched polymer of galactose, rhamnose, and partially acetylated glucuronic acid units Gum tragacanth: fucose, xylose, arabinose, and glucuronic acid units Locust bean gum: consist mannose main chain with galactose branches

Used as adhesives, emulsifiers, gels, flocculants, binders, films in food, textile, cosmetics, and pharmaceutical industries

β(1,4)-linked 2-acetamido2-deoxy-β-D-glucose monomeric units

Chitin and chitosan have vast applications. They are mainly used as drug, enzyme, and protein carriers. They possess antimicrobial, antifungal, antiviral, nontoxic, and nonallergic properties. Thus they widely used in the field of drug coatings, cosmetics and food industries. They are also used in fabrication of separation membranes and in agricultural field to control release essential metal ions

Resource: Animals Chitin

Chitosan

• •

• •

and linear polysaccharide Water insoluble Easily soluble in basic media and ionic liquids Ionization is pH dependent, i.e., acidic media- cationic Linear and amorphous polysaccharide Partially water soluble but soluble in slight acidic medium

β(1,4)-linked 2-amine-2deoxy-β-D-glucose monomeric units

Continued

Table 1.1 Characteristics of different polysaccharides—cont’d Name

Source

Hyaluronic acid (HA) (type of glycosaminoglycanGAGs)

Rooster comb and humors of cow’s eyes

Physical characteristics

• Anionic,

Brown algae including giant kelp, Macrocystos pyrifera, Asophyllum nodosum and Laminaria digitata. Up to 40% alginate with respect to dry weight

• Also known as

extracellular, and linear polysaccharides • Elastoviscous fluid • Nonallergic • Water soluble

Structural characteristics

Applications

D-Glucuronic

acid and N-acetyl-D-glucosamine as a repeating unit Sulfate derivatives of HA: heparin; heparan sulfate; chondroitin sulfate; dermatan sulfate and keratan sulfate

HA and its derivatives vastly applicable in the field of tissue engineering, drug carrier, orthopedics, cardiovascular aids, ophthalmic surgery, and wound healing. In nature, its function is to maintain the water level in soft tissues, improve mechanical properties, lubrication in synovial fluid and organs, and cell surface adhesions

β-(1,4)-linked Dmannuronic acid and α(1,4)-linked L-guluronic acid

Used as oxygen barrier, dehydrating agents, thickening and stabilizers in food industries and pharmaceuticals. Wound healants, dental impressions, and cell and enzyme immobilization

Sulfated and nonsulfated repeating units of galactose units and 3,6-anhydrogalactose; Types: iota-, kappa-, and lambda- carrageenan

Used as thickening, gelling, and stabilizing agents in food, pharmaceutical, and cosmetics industries

Resource: Algae Alginate

• • •

Carrageenan

Red algae

• • • •

alginic acid Anionic and linear polysaccharide Forms gels in the presence of divalent ions Possess immunogenicity and low toxicity Anionic and linear Polysaccharides MW: 100 k to 1 million Dalton Water soluble Iota and lambda types carrageenan forms gels at normal temp. While kappa carrageenan forms pH and temperaturesensitive hydrogels

Agar

Red seaweed

• Neutral and linear polysaccharide • Water soluble • Low gelling temp with thermoresponsive HG

Consist of two main copolymer units called agarose and agaropectin. Consist of repeating units of (1,3)-β-D-galactopyranose and (1,4)-3,6-anhydro-β-Lgalactopyranose. Also consist of side chains of 4,6O-(1-carboxyethylidene)-Dgalactopyranose or sulfated or methylated sugar residues

Used in dentistry, food industry, and microbiology

α-1,4-linked D-glucose trimers and some tetramers such as maltotriose and maltotetrose units

Used as viscosifier, binder, film forming agent, oxygen barrier coatings, adhesives in food and cosmetics industries; pharmaceutical tablet, fertilizers, paper, tobacco, and lithographic plates coating

α-1,4- and 1,3-linked Dglucan units

Used as low oxygen permeability coatings

Consist of β-1,3-D-glucose units with random branches of β-Ι,6-D-glueose units

Used as mobility control agent for enhancing the oil recovery; used as lubricants in drilling muds, ceramic glazes, paints and inks and in agriculture. Stimulate immune response and reduce the development of some forms of cancer

Resource: Fungi Pullulan

Extracellular product of Aureobasidium pullulans fungus

• Neutral and linear • • • • •

Elsinan

Extracellular product of Elsinoe fungus

Scleroglucan

Extracellular product of Sclerotium rolfsii, Sclerotium glucanicum, and Schizophyllum comm

• • • • •

polysaccharides Water soluble Nonhygroscopic, nontoxic, and odorless Excellent oxygen barrier Resistant to oil and greases Forms pseudoplastic solution in water Neutral and linear polysaccharides Water soluble Neutral and branched polysaccharides Water soluble and exists as triple helix conformation in water In water pseudoplastic behavior and viscosity unaffected up to 90°C

Continued

Table 1.1 Characteristics of different polysaccharides—cont’d Name

Source

Resource: Bacterial Bacterial cellulose (BC)

Gluconacetobacter xylinus or Acetobacter xylinum

Physical characteristics

• Neutral, extracellular, • • • •

Xanthan gum

Xanthomonas campestris

• •

Dextran

Fermentation of sucrose in the presence of lactic acid bacteria such as Leuconostoc mesenteroides and certain Streptococcus species

• Neutral, extracellular, •

•

Gellan

Sphingomonas paucimob/ elodea

and linear polysaccharide Water soluble Produced by gramnegative bacteria Large surface area High adsorption capability Anionic and branched polysaccharide Water soluble and solutions are pseudoplastics

• • •

and branched polysaccharides Highly soluble in water; however, their solutions possess low viscosity Forms highly stable complex with metal salts which are ineffective in salts or acidic or basic media with respect to broad temperature range Anionic, extracellular and linear polysaccharides Forms thermoreversible gels Water soluble

Structural characteristics

Applications

Glucan monomeric unit

Similar to cellulose, BC is also used as stabilizers and emulsifiers, and used as binders in pharmaceutical, food, and textile industries

Main chain of linear β-1,4D-glucose units with Dmannose and D-glucuronic acid with O-acetyl and pyruvyl residues

Used as thickener in food industry; stabilizers in food, agrochemicals, pesticides, paints, sprays, and pharmaceutical emulsions, etc. It is a blood plasma extender; crosslinked dextran beads used in separation field

α-1,6-D-glycopyranosyl repeat units with branches at α-1,2/1,3 and 1,4 positions

Consist D-glucopyranosyl, L-rhamnopyranosyl and Dglucopyranosyluronic acid units. Also possesses O-acetyl and L-glyceric acid substituents on Dglucopyranosyl units

Additives in meat products, frostings, jam, jellies, ice creams, candies, cheese, yogurt, pet foods, and sauces. Air-freshener gels, dental and personal care toiletries, degradants, and many more

Curdlan

Alcaligenes faecalis var. myxogenes, Agrobacterium radiobacter, Rhizobium meliloti, and Rhizobium trifolii

• Neutral, extracellular, and linear polysaccharides • Water insoluble but swell the water • Soluble in alkali, formic acid, DMSO, KI solution • Thermoresponsive gels forms

β-(1,3)-linked D-glucan

Used as additives to improve the texture of jellies, puddings, noodles, ice cream, fish paste, and meat products. Carboxymethylated derivatives have shown antitumor activity. Used for controlled drug delivery. Sulfated curdlan has shown antithrombotic and anti-HIV activity. Water purification

14

Chapter 1 Biopolymers: An overview

FIG. 1.4 Polysaccharide structure: (A) α-linked isomer and (B) β-linked isomer.

followed by reaction with petrochemical by-products. Bioplastic-based materials have similar properties to petrochemical-based polymers. The main advantage is their degradability in the environment. Thus, bioplastics are widely blended with polysaccharides to form high-strength scaffolds, thin films, membranes, etc. Thus, currently, bioplastic-based composite structures are widely used in the biomedical field, industrial parts, filtration membranes, and food packaging (Averous & Pollet, 2013; Deb, AlAttraqchi, et al., 2019).

Biopolymer-based composites and their applications Biopolymers possess properties such as biocompatibility, degradability, nontoxicity, antimicrobial, antifungal, adhesion, high adsorption capability, and high functionality. These advantageous properties make biopolymers valuable as raw materials in biomedical applications. However, they also show poor mechanical strength, which limits their individual applicability in the biomedical field. Numerous biopolymer-based composites with synthetic polymers, biodegradable polymers, carbon materials, and nanoparticles have been successfully fabricated and applied in drug delivery, tissue engineering, cosmetics, food packaging, and many other areas (Gross & Scholz, 2001; Silva et al., 2020a; Vinod et al., 2020). Biopolymer-based selective composite structures are schematically shown in Fig. 1.5. Table 1.3 represents the key advantages and disadvantages of each biocomposite material. The incorporation of nanoparticles in biopolymers further enhances their inherent properties and they are utilized in biomedical, environmental, textile, and food packaging applications (Annu, Ahmed, & Ahmed, 2021; Arfin, Bhaisare, Ahmed, & Annu, 2021; Bano, Sultana, Sabir, Khan, & Ahmed, 2021; Das et al., 2021; Maity, Pandit, Singha, Ahmed, & Annu, 2021; Osmani et al., 2021; Sohrabi et al., 2021; Theagarajan, Krishnamoorthy, Moses, Anandharamakrishnan, & Ahmed, 2021). Micelles consist of a hydrophobic core and hydrophilic shell. Micelles greatly enhance the delivery, bioavailability, solubility, and stability of the active compounds. Biopolymer-based micelles are extensively used in drug delivery, as emulsifiers in the food industry and as stabilizers in the pharmaceutical industry (Bu et al., 2021; Nayak & Hasnain, 2020; Spicer, 2020). For preparation of biopolymer-based micelles, it is necessary to functionalize the biopolymers with biocompatible polymers or long chain acids such as polycaprolactone, stearic acid, poly lectic acid, oleic acid, palmitic

Table 1.2 Polysaccharide names according to substitution. Name

Linkage

R1/R4

R2/R5

R3/R6

Starch Cellulose Pectin Chitin Chitosan Hyaluronic acid Heparin Heparan sulfate

α-(14)/(16) β-(14) β-(14) β-(14) β-(14) β-(14)/(13) α-(14) β-(14)/

–OH –OH –OH –OH –OH –OH –OH –OH

–CH2OH/–CH2–O– (16) –CH2OH –COOH/COOCH3 –CH2OH –CH2OH –COO /–CH2OH –COO / CH2OSO3 –COO /–CH2OSO3

Keratan sulfate Alginate Kappa (κ)carrageenan Lambda (λ)carrageenan Iota (I)carrageenan Pullulan Elsinan Scleroglucan Xanthan gum

β-(14)/α-(13) β-(14) α-(14)/α-(13)

–OH –OH –OH –NHCOCH3 –NH2 –OH/–NHCOCH3 –OSO3 /–NHSO3 –OSO3 /– NHCOCH3 –OH/–NHCOCH3 –OH –OH

–CH2OH/–CH2OSO3 –COOH –CH2OH/R6–CH2–O–C3

α-(14)/α-(13)

–OSO3

–OH/–O–(13) –OH –O–(13)/R6– CH2–O–C3 –OH/–O–(13)

α-(14)/α-(13)

–OH/–OSO3

–CH2OH/R6–CH2–O–C3

α-(14)/(16) α-(14)/(13) β-(13)/(16) β-(14)/(13)

–OH –OH –OH –OH

–O–(13)/R6– CH2–O–C3 –OH –OH/–O–(13) –OH/–O–(13) –OH

Gellan

β-(14)/(13)

Dextran Curdlan

β-(16)/(13) β-(13)

–OH/– OCOCH(OH) CH2OH –OH –OH

FIG. 1.5 Structures of biopolymer-based composites.

–OH/–O–(13) –OH/–O–(13) –O–(13)

–CH2OH/–CH2OSO3

–CH2OH//–CH2–O– (16) –CH2OH –CH2OH/–CH2–O– (16) –CH2OH/– CH2OOCOCH3/–COOH CH2OH/–CH2OOCOCH3/– COOH/–CH3 –CH2OH/–CH2–O– (16) –CH2OH

16

Chapter 1 Biopolymers: An overview

Table 1.3 Key advantages and disadvantages of biopolymer-based composites. Biocomposite Micelles

Nanofibers

Nanoparticles

Advantages

• Stimuli-responsive structure • Precise drug delivery with adequate • • • • • • • • • • • • •

Thin films/ membranes/ scaffolds

Hydrogels

Foams Bioinks

• • • • • • • • • • • • • • • •

bioavailability High drug loading Biocompatible 1D structure High surface area High surface area Light weight ECM-like structure Flexible Effective for transdermal drug delivery and wound healing Same size of domains as proteins High surface area Easy to modification of surface with desired functionalities Easily cross the cell barriers, thus used for distinctive drug delivery behavior especially in tumor cells Layer-by-layer assembly possible Good mechanical properties Used for wound healings, filtration, antimicrobial coatings, and drug delivery Flexible Biocompatible Biodegradable 3D structure Self-adhesion properties Biocompatible Biodegradable Well-defined cross-linked structure Used for wound healing, cells encapsulation, and drug delivery 3D porous structure Used for wound cleaning Viscous solution which can be modeled in any shapes Used for fabrication of selective tissue models and selective drug delivery models

Disadvantages

• Micro-size diameter • Limited use in targeted drug delivery • Tendency to aggregations, which limits their effectiveness

• Limited adhesive and mechanical properties • Sometimes poor distribution and release of active materials due to encapsulation of drug molecules into polymer structure

• • • •

Lower drug loadings Aggregations Difficult to scale up Limited size distribution

• Due to use of some other ingredients, it affects the toxicity of material

• Oxygen barrier properties and water permeability

• Limited surface area to porosity • Soft texture

• Limited application • Hard to implement • External environment required for solidification

• Difficult scaling-up process • Limited stability of bioinks

anhydride, and many more. Polysaccharides (i.e., chitosan, dextran, starch, hyaluronic acid, and alginate), proteins (i.e., casein, albumin), and peptides are widely used to prepare biopolymeric micelles (Bu et al., 2021; Gross & Scholz, 2001). Biopolymer-based micelles are synthesized through different techniques which are mainly direct dissolution, solvent evaporation, the dialysis method, ultrasound, and the film hydration method. Biopolymer-based micelles possess diameters of few nanometers to

Biopolymer-based composites and their applications

17

several hundred nanometers; they are nontoxic, biodegradable, show good compatibility, have a long blood circulation time, show nonimmunogenicity, and have high drug loading. One-dimensional (1D) nanostructures possess a high surface area and porous structure compared to microstructures. Nanofibrous membranes are one type of 1D nanostructure. Generally, nanofibers are fabricated through different techniques such as the drawing method, the template method, electrospinning, phase separation, and self-assembly techniques. Electrospinning is an easy and fast technique for fabrication of nanofibers. Generally, nanofibers are widely applicable for wound healing, drug delivery, adsorbents, filtration, and food packaging (Kakoria & Sinha-Ray, 2018; Khansari et al., 2013; Shekh et al., 2020; Vinod et al., 2020). The bare biopolymer-based nanofibrous structure of biopolymers is hard to fabricate due to poor dielectric properties and mechanical properties. For fabrication of biopolymer-based nanofibers, it is necessary to blend the biopolymers with degradable polymers such polycaprolactone, polyvinyl alcohol, poly 3-hydroxy butyrate (PHB), and many more. Biopolymerbased nanofibers are widely used in tissue engineering and transdermal drug delivery. Biopolymerbased composite nanofibers show great mechanical strength, light weight, self-adhesion, and many more advantageous properties (Aaliya, Sunooj, & Lackner, 2021; Kakoria & Sinha-Ray, 2018; Khansari et al., 2013; Vinod et al., 2020). Biopolymer-based thin films possess a low to high oxygen permittivity barrier, and their antimicrobial, antiallergic, and dehydrating properties make them very useful materials in food packaging. Biopolymer-based thin films are also used in membrane coatings, dental applications, antimicrobial coatings, etc. Biopolymer-based composite thin films possess adequate antimicrobial properties, good thermal properties, gas barrier, and mechanical properties. Normally for biodegradable thin films, biopolymers (i.e., pectin, chitosan, cellulose, starch, xylan, and lignin) are blended with degradable synthetic biopolymers, mainly polyhydroxy butyrate (PHB), poly lactic acid (PLA), poly caprolactam (PCL), polyhydroxy alkenoates (PHA), polyethylene glycol (PEG), polyethylene (PE), and polyvinyl alcohol (PVA) (Akhter et al., 2019; Bombaldi de Souza, Bombaldi de Souza, Bierhalz, Pires, & Moraes, 2020; Moraes et al., 2020; Taketa et al., 2020; Tomoda et al., 2020; Vinod et al., 2020). Biopolymer-based composite thin films are synthesized through solvent casting, sol-gel, and atomic layer deposition. Similar to nanofibers, biopolymer-based nanoparticles also possess a high surface area and good biodegradability and biocompatibility. An interesting feature of biopolymer-based nanoparticles is the changing of their physicochemical properties according to their particle size. Biopolymer-based nanoparticles are synthesized through different top-down (i.e., shredding, extrusion, and homogenization) and bottom-up approaches (i.e., antisolvent preparation, coacervation, inclusion complexation, drying, and fluid gel formation). Biopolymer nanoparticles are used for intensive drug delivery, especially for cancer, diabetes, allergies, infections, and inflammation (Gross & Scholz, 2001; Jacob et al., 2018; Joye & McClements, 2014; Nitta & Numata, 2013; Shekh et al., 2020; Xie et al., 2014). Additionally, they are widely used for gene delivery (Deb, Al-Attraqchi, et al., 2019; Joye & McClements, 2014; McBain et al., 2008). Polysaccharides (i.e., chitosan, alginate, heparin, pullulan, and starch), proteins (i.e., silk, collagen, zein, gelatine, and albumin), and protein-mimicked peptides are widely applied for fabrication of nanoparticles. Biopolymer-based composite membranes or scaffolds are fabricated through mixing of biopolymers with synthetic biodegradable polymers or with nonbiodegradable polymers, and also with inorganic nanoparticles to clay particles. Similar to thin films, biopolymer-based composite membranes show good thermal and mechanical properties. Due to the ionic nature of biopolymers, they are used

18

Chapter 1 Biopolymers: An overview

to prepare ionic membranes. These are widely used for filtration membranes, as well as providing ionic interactions with cells and improving cell adhesion and proliferation. Additionally, biopolymer-based membranes or scaffolds are extensively applied for chronic wound healing (Bombaldi de Souza et al., 2020; Moraes et al., 2020; Neffe, Wischke, Racheva, & Lendlein, 2013; Reddy et al., 2021; Shah et al., 2019; Yunus Basha, Sampath Kumar, & Doble, 2015). Another important form of biopolymer composites is hydrogels. These are three-dimensional crosslinked polymer networks which contain 80%–90% water. Different kinds of hydrogels dimensions are applied in biomedical applications, e.g., nanogels, microgels, and aerogels. Injectable hydrogels are also well-known for selective and critical diabetic wound healing. Furthermore, hydrogels are used for cell encapsulation, tissue engineering, drug delivery, wound cleaning, and ophthalmic use (Amirian et al., 2021; Gaserod et al., 2010; Neffe et al., 2013; Sivashanmugam et al., 2015). There are different ways to fabricate hydrogels, which mainly involve polymerization of modified biodegradable polymers in the presence of initiators (i.e., thermal or UV initiators). Additionally, modified biopolymers also obtain soft gels via Schiff base or ionic interactions (Neffe et al., 2013; Sivashanmugam et al., 2015). Soft foams are 3D porous structures which are generally used in the cleaning of wounds and curing of diabetic wounds. So far, composite foams of alginate, cellulose, starch, and poly lactic acid have been researched. Biopolymer-based foams are obtained through extrusion processing and blowing agent processing (Gaserod et al., 2010; Rapp et al., 2014). Bioinks are viscous solutions which consist of a polymer, active ingredients (i.e., living cells, gene, DNA), emulsion agents, and stabilizers. Bioinks are printable to desired shapes which enhance their applicability in the tissue engineering field (Donderwinkel, Van Hest, & Cameron, 2017). Bioink-based structures are desirable for selective and intensive drug deliveries, selective biomodels fabrications, and 3D tissues.

Conclusions As environmental concerns increase day by day, along with the need to decrease consumption of fossil fuels and their by-products, biopolymer-based materials are key and eco-friendly substitutions. The key properties of biopolymers are their large number of available sources, biocompatibility, biodegradability, nontoxicity, antiallergy, and high functionality. Additionally, their chemical constituents make them easy to modify with different organic compounds and polymers and they undergo different kinds of organic reactions (i.e., oxidation, esterification, alkylation, quaternization), which make them versatile raw materials in various fields of science. By modification with organic monomers or natural acids or lipids, biopolymers form micelles, which possess a high affinity toward drug release as well as being used as stabilizers and emulsifiers in the cosmetic, pharmaceutical, and food industries. Upon blending with synthetic or bioplastic polymers followed by fabrication of biopolymer-based 1D structures (i.e., nanofibers), they are widely used for filtration, adsorbents, face mask membranes, scaffolds, and transdermal drug delivery applications. Similar to nanofibers, biopolymer-based nanoparticles are also applied in pharmaceuticals, cosmetics, and food science in the delivery of active ingredients. Additionally, biopolymer-based nanoparticle surfaces are easy to modify with proteins or aptamers, making them further applicable for distinctive drug delivery carrier and biosensors. Flat sheet structures (i.e., thin films, membranes) and 3D structures (i.e., hydrogels, foams) of biopolymer composites are individually used as water-permeable cell coatings, laminations, wound healing, antimicrobial

References

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coatings, and oxygen barrier coatings to oxygen permeable coatings in the pharmaceutical, paper, textile, and food industries. Biopolymer-based bioinks are the future of biomedical applications-from drug delivery system to generation of selective tissues models and mimicking of organ structures. Not only are biopolymers applicable in biomedical or food packaging, but also ionic biopolymers are applied for preparation of polyelectrolyte membranes for energy harvesting devices as well as for environmental remediation.

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Donderwinkel, I., Van Hest, J. C. M., & Cameron, N. R. (2017). Bio-inks for 3D bioprinting: Recent advances and future prospects. Polymer Chemistry, 8(31), 4451–4471. https://doi.org/10.1039/c7py00826k. Donner, M. W., Arshad, M., Ullah, A., & Siddique, T. (2019). Unravelled keratin-derived biopolymers as novel biosorbents for the simultaneous removal of multiple trace metals from industrial wastewater. Science of the Total Environment, 647, 1539–1546. https://doi.org/10.1016/j.scitotenv.2018.08.085. Gaserod, O., Anderson, O., & Myroveld, H. (2010). FMC biopolymer AS. United States Patent. George, A., Sanjay, M. R., Srisuk, R., Parameswaranpillai, J., & Siengchin, S. (2020). A comprehensive review on chemical properties and applications of biopolymers and their composites. International Journal of Biological Macromolecules, 154, 329–338. https://doi.org/10.1016/j.ijbiomac.2020.03.120. Gopi, S., Amalraj, A., Sukumaran, N. P., Haponiuk, J. T., & Thomas, S. (2018). Macromolecular symposia. Vol. 380. Wiley. Gross, R. A., & Scholz, C. (2001). Biopolymers from polysaccharides and agroproteins. Copyright, foreword. Gurunathan, T., Mohanty, S., & Nayak, S. K. (2015). A review of the recent developments in biocomposites based on natural fibres and their application perspectives. Composites Part A: Applied Science and Manufacturing, 77, 1–25. https://doi.org/10.1016/j.compositesa.2015.06.007. Jacob, J., Haponiuk, J. T., Thomas, S., & Gopi, S. (2018). Biopolymer based nanomaterials in drug delivery systems: A review. Materials Today Chemistry, 9, 43–55. https://doi.org/10.1016/j.mtchem.2018.05.002. Joye, I. J., & McClements, D. J. (2014). Biopolymer-based nanoparticles and microparticles: Fabrication, characterization, and application. Current Opinion in Colloid and Interface Science, 19(5), 417–427. https://doi.org/ 10.1016/j.cocis.2014.07.002. Kakoria, A., & Sinha-Ray, S. (2018). Fibers, 6, 45. Kalia, S., & Averous, L. (2011). Biopolymers: Biom edical and environmental applications. Khansari, S., Sinha-Ray, S., Yarin, A. L., & Pourdeyhimi, B. (2013). Biopolymer-based nanofiber mats and their mechanical characterization. Industrial and Engineering Chemistry Research, 52(43), 15104–15113. https:// doi.org/10.1021/ie402246x. Liu, K., Chen, Y. Y., Zha, X. Q., Li, Q. M., Pan, L. H., & Luo, J. P. (2021). Research progress on polysaccharide/ protein hydrogels: Preparation method, functional property and application as delivery systems for bioactive ingredients. Food Research International, 147, 110542. Maity, S., Pandit, P., Singha, K., Ahmed, S., & Annu. (2021). Starch-based bionanocomposites in tissue engineering and regenerative medicines. In Woodhead publishing series in biomaterials (pp. 437–450). Woodhead Publishing. https://doi.org/10.1016/B978-0-12-821280-6.00029-5 (Chapter 22). Mangaraj, S., Yadav, A., Bal, L. M., Dash, S. K., & Mahanti, N. K. (2019). Application of biodegradable polymers in food packaging industry: A comprehensive review. Journal of Packaging Technology and Research, 77–96. https://doi.org/10.1007/s41783-018-0049-y. McBain, S. C., Yiu, H. H. P., & Dobson, J. (2008). Magnetic nanoparticles for gene and drug delivery. International Journal of Nanomedicine, 3(2), 169–180. Moraes, M. A. D., Silva, C. F., & Vieira, R. S. (2020). Biopolymer membranes and films: Health, food, environment, and energy applications. Elsevier. Nayak, A. K., & Hasnain, M. (2020). Advanced biopolymeric systems for drug delivery. Springer. Neffe, A. T., Wischke, C., Racheva, M., & Lendlein, A. (2013). Progress in biopolymer-based biomaterials and their application in controlled drug delivery. Expert Review of Medical Devices, 10(6), 813–833. https://doi. org/10.1586/17434440.2013.839209. Nitta, S. K., & Numata, K. (2013). Biopolymer-based nanoparticles for drug/gene delivery and tissue engineering. International Journal of Molecular Sciences, 14(1), 1629–1654. https://doi.org/10.3390/ijms14011629. Osmani, R. A. M., Singh, E., Hani, U., Chavan, S., Kazi, H., Menon, M., et al. (2021). Bionanocomposite hydrogels for regenerative medicine and biomedical applications. In Woodhead publishing series in biomaterials (pp. 91–118). Woodhead Publishing. https://doi.org/10.1016/B978-0-12-821280-6.00030-1 (Chapter 5). Pattanashetti, N. A., Heggannavar, G. B., & Kariduraganavar, M. Y. (2017). Smart biopolymers and their biomedical applications. Procedia Manufacturing, 12, 263–279. https://doi.org/10.1016/j.promfg.2017.08.030.

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CHAPTER

Chemical modification of proteinbased biopolymers for application in food packaging

2

Frage Abookleesha and Aman Ullahb a

Department of Food Science and Technology, Sebha University, Sabha, Libya, bDepartment of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada

Introduction Modern food packaging can be defined as multifunctional process that contain and protects food products from possible physical, chemical, and microbiological deterioration. Food packaging also play a key role in food supply chain and consumer awareness. Therefore, packaging becomes an integral part of our food systems, and packaging roles, forms, materials, etc. change with civilization growth, science, and technology. The need to contain, store, and transport has been around since the early time (Gupta & Dudeja, 2017). For example, until the early 1980s, milk was distributed as a bulk item and sold by directly filling the customer jars, jugs, or pails. The invention of packaging changed the food delivery scene, and today dairy and food items are sold in different forms, sizes, and types of packages. What will the food packaging of the future look like? The drive for sustainability, health and environmental concerns of implications of synthetic packaging materials is increasingly impacting packaging. In this scenario, eco-friendly packaging materials are beginning to develop and are highly likely to be employed (Chowdhury, Nag, Ashish, & Tripathi, 2017). Current packaging is made from synthetic materials, in particular petroleum-based plastics. Over the last few decades, petroleum-based plastic food packaging has become the most promising choice and their application growth on the expense of the other packaging materials due to their superior properties, such as low cost, light weight, versatility, durability, and easy manufacturing (Shin & Selke, 2014). Recently, worldwide plastic production has significantly increased. It was estimated that plastic production increased from 1.7 million metric tons (Mt) in 1950 to 407 million Mt in 2015. In 2015, about 8300 Mt was produced, 6300 Mt of plastic waste was generated, only 9% was recycled, 12% was incinerated, and 79% ended up in landfills or released into the natural environment. Among all the plastics produced in 2015, about 42% (146 Mt) was used for packaging (Geyer, Jambeck, & Law, 2017). If the current trends in manufacturing and disposal management continue, large quantities of plastic wastes will be released and accumulated by 2050. The major problems associated with the use of plastic are its nonbiodegradability and recyclability. Moreover, most food packaging is designed to be single-use and is not recycled; instead, packaging is discarded and released into the natural Advanced Applications of Biobased Materials. https://doi.org/10.1016/B978-0-323-91677-6.00008-8 Copyright # 2023 Elsevier Inc. All rights reserved.

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Chapter 2 Chemical modification of protein-based biopolymers

environment (Bodamer, 2016). The environmental impact of food packaging is enormous as it is nondegradable, and its disposal management is limited. Therefore, it is highly desirable for packaging materials to biodegrade under ambient environmental conditions in order to avoid accumulation and impacts on the natural environment (Zubair & Ullah, 2020). Over the last few decades, some dramatic shifts have occurred in the selection of materials by the manufacturing sectors and consumers alike. The reason behind these shifts is attributed to the massive environmental, health, economic stability, and sustainability problems that have resulted from the excessive use of synthetic fossil-based materials (Van der Meer, 2017). Recently, new forms of biobased, biodegradable packaging have received tremendous attention and are constantly being developed. Biobased materials are products that are essentially made from biomass, which includes food sources like proteins, fats, and carbohydrates and nonedible sources such as natural rubber. It may also refer to products made through various conversion processes. The most common biomass materials used are plants, wood, and wastes and their derived materials (Curran, 2010). Moreover, the production of biobased materials is characterized as a biowaste valorization strategy, which contributes to maximizing sustainability while minimizing health, economic, and environmental impacts (Dugmore, Clark, Bustamante, Houghton, & Matharu, 2017). Therefore, biobased materials are considered to be a green revolution of modern sciences and mankind due to their abundance, sustainability of feedstock sourcing, cost, reusability, recyclability and/or biodegradability, biocompatibility, and nontoxicity (Reichert et al., 2020). Among all biobased materials, proteins have been postulated as a viable source that offers an excellent prospect for developing protein-based bioplastics (Silva, Garcia, Amado, & Mauro, 2015). Moreover, biobased materials are abundant and can be sourced as low-cost by-products from different food industries. These include keratin from poultry feathers; wheat gluten, a by-product of the wheat starch industry; corn, canola, and soy protein, by-products of the oil industry; zein, a by-product of corn starch and corn syrup production; casein and whey, by-products of cheese production; and many other natural proteins and by-products (Zubair & Ullah, 2020). Protein-based plastics have many types of applications, like in packaging, agriculture, biomedicine, coating, and structural materials. Poor mechanical performance and high hydrophilicity are the greatest limitations of protein-based bioplastics that limit their wide application (Br€auer, Meister, Gottl€ober, & Nechwatal, 2007). Balancing the physical, thermal, and mechanical properties of protein biobased materials compared to synthetic ones is a crucial point of this innovation. Therefore, altering the protein characteristics in order to enhance their functionality using a particular method is highly required. Modification approaches can provide the opportunity to convert them into suitable materials for packaging by changing their physicochemical properties and addressing their limitations (Shahbazi & J€ager, 2021; Tomasik, 2003). These approaches are generally categorized into three main routes, which are physical, chemical, and biological. Chemical modification of proteins has been widely used due to its efficiency, low cost, and workability. Many different types of chemical modifications have been developed to modulate several kinds of protein materials and make them more suitable for polymeric applications. This has resulted in certain improved properties such as mechanical and thermal properties, solubility and targetability, and the overall performance (Rhim & Kim, 2013). In order to increase the range of their widely anticipated applications, it is necessary to enhance the properties and performances of proteins (Ullah, Vasanthan, Bressler, Elias, & Wu, 2011). Therefore, this chapter presents a review of those chemical modifications that have been the most applied for the use and application of protein biobased materials in food packaging.

Chemical structure, functional groups, and properties of proteins

25

Chemical structure, functional groups, and properties of proteins Unlike synthetic polymers, proteins are linear heteropolymers with a unique three-dimensional network. Their structures are formed by different combinations of 20 amino acids that are linked together in a specific order by peptide bonds to form a polypeptide chain. The amino acids present in proteins differ from each other in the structure of their side (R) chains. The sequence of amino acids within a protein plays a key role in its function and defines all its characteristics, such as its secondary structure, hydrophobicity, thermal stability, and solubility (Berg, Tymoczko, & Stryer, 2002). The four levels of a protein’s structure are primary, secondary, tertiary, and quaternary, as shown in Fig. 2.1. These levels

FIG. 2.1 Structure of protein. The four levels of a protein’s structure are primary, secondary, tertiary, and quaternary. It is helpful to understand the nature and function of each level of the protein structure in order to fully understand how a protein works. From BioRender. (2020). https://app.biorender.com/biorender-templates.

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Chapter 2 Chemical modification of protein-based biopolymers

are distinguished from one another by the degree of complexity in the polypeptide chain. In general, the primary structure is the sequence of amino acid residues in the protein. A vast number of primary structures can be constructed from these, which are classified by their side chains into polar, nonpolar, acidic, and basic groups (Dee, Puleo, & Bizios, 2002). The secondary structure of proteins is the three-dimensional form of the local segments of proteins. The most common secondary structural elements are alpha helices and beta sheets. The function of a protein is directly dependent on its threedimensional structure. Proteins fold up into unique three-dimensional structures by the formation of a set of inter- and intramolecular interactions among amino acid functional groups (Rychlewski, Jaroszewski, Li, & Godzik, 2000). Hydrogen bonds, ionic bonds, van der Waals attractions, and disulfide bonds lead to the formation of tertiary and quaternary protein structures. The ensemble of formations and folds in a single linear chain of amino acids is called the tertiary structure of a protein. Finally, the quaternary structure of a protein refers to those macromolecules with multiple polypeptide chains or subunits. Many weak bonds can act in parallel to hold two regions of a polypeptide chain tightly together. The stability of each folded shape is therefore determined by the combined strength of large numbers of such noncovalent bonds (Broglia & Tiana, 2001; Dorn, Silva, Buriol, & Lamb, 2014). Functional groups of amino acids allow for a series of different inter- and intramolecular forces, resulting in the complex structure of proteins. This implies that a successful modification of proteins is largely dependent on the ability to manipulate their structures. The conformation of a protein molecule is often important for its proposed industrial application, as structural changes typically lead to changes in the physical, chemical, or functional properties of the protein (Thatcher, 1994). These changes can be referred to as denaturation, which is the loss of the functional properties of a native protein resulting from the disordering or disruption of the noncovalent interactions that retain the protein in its active conformational state. The transformation of proteins into plastic materials largely relies on their structural changes (unfolding or denaturation) (Fig. 2.2). Unfolding the native structure of a protein can be achieved by small changes in environmental conditions, such as pH or temperature, by thermal or chemical means. In order to unfold the protein structure, multiple noncovalent and

FIG. 2.2 Denaturation of proteins. Denaturation of proteins is a process of transition from the folded to the unfolded state. It involves the breaking of many of the weak linkages, or bonds (e.g., hydrogen bonds), within a protein molecule that are responsible for the highly ordered structure of the protein in its natural (native) state. Created with BioRender.com.

Chemical structure, functional groups, and properties of proteins

27

covalent interactions need to be reduced, allowing the chains to unfold. This treatment converts the protein into a flexible polypeptide chain that has lost its natural shape. Once a protein is unfolded, the cooling down or drying will allow the formation of new protein-protein interactions, leading to the alignment of protein chains into a different three-dimensional network (Pain, 1983; Verbeek & Berg, 2009). A functional group is a specific group of atoms or bonds within a compound, which is responsible for the characteristic chemical reactions of that compound. Proteins contain a wide range of functional groups in the side chains of the amino acid residues, such as alcohols, thiols, thioethers, carboxylic acids, carboxamides, and a variety of basic groups. When these functional groups are joined in different sequences, they account for the wide range of functions that we see in (Felix, Perez-Puyana, Romero, & Guerrero, 2017) proteins (“The Chemistry of Life” through “Genomic Proteomics”; Lulu.Com, 2014). For instance, the chemical reactivity associated with these groups is essential to the function of enzymes, which are proteins that catalyze specific chemical reactions in biological systems (Berg et al., 2002). However, functional groups are frequently employed to modulate a compound, giving it different physiochemical properties than when it was in its natural state. In the field of biochemistry, there is an extensive prior history of chemically modified proteins in various functional groups for various applications. From a biobased material application perspective, the abundant functional groups in proteins have interesting applications, since these groups account for the vast majority and provide an excellent opportunity to create a specific chemical and physical environment. For example, the availability of polar residues in proteins can be reduced by turning them into hydrophobic groups. Such a modification can change the secondary structure and tertiary conformation of proteins and has shown dramatic improvements in their solubility and functional properties. Moreover, functional group modifications can result in some other improvements in the thermal stability and mechanical properties of proteins. The availability of functional groups can also serve to determine reactivity, stability, hardness, suitability, and/or other specific roles, tasks, or functions that lead to the expected application role (Felix et al., 2017; Jimenez-Go´mez & Cecilia, 2020; Tansaz & Boccaccini, 2016; Zhao, Ma, Yuen, & Phillips, 2004). The physical and chemical properties of any given functional group are strongly influenced by the nature of the local microenvironment. For example, when primary amines are present in a protein, these functional groups are not reactive, except in the freebase form. In other words, the proton present at neutral pH must be removed from the ε-amino group of lysine before this functional group can function as an effective nucleophile (Lundblad, 2004). The wide knowledge of physicochemical properties is used as the first step in the utilization of raw biobased materials and evaluation of the finished product. The physicochemical properties of proteins differ from one another and are influenced by amino acid composition and sequence, molecular weight, conformation, and content of polar and nonpolar groups of amino acids. This results in net charge, isoelectric point, solubility, stability, and hydrophobicity (Chen, Liu, Pantalone, & Zhong, 2020; Mohamad Ramlan et al., 2002). From a chemical perspective, all proteins can be regarded as folded polymers that have many nucleophilic functional groups on their surfaces. Amino acids are the building blocks of the protein structure, and each amino acid has its own physicochemical properties. The nature of the functional groups confers specific chemical and physical properties on those proteins. Amino acid profiles substantially differ between plant- and animal-based proteins. For example, corn zein contains high percentages of nonpolar amino acids, such as leucine (20%) and proline (10%), and basic and acidic amino acids in low proportions (Nehete, Narkhede, Bhambar, & Gawali, 2013), whereas keratin from chicken feathers has about 40% hydrophilic amino groups and 60% hydrophobic amino groups in

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Chapter 2 Chemical modification of protein-based biopolymers

its structure. Keratin is characterized by its content in the amino acids serine (16%), proline (12%), and cysteine (8.85%), with low concentrations of methionine and phenylalanine (Alahyaribeik & Ullah, 2020). Thus, the polar functional groups such as the hydroxyl, carboxyl, and amine groups dominate in determining the character of the proteins, making them highly polar and promoting their water solubility. For example, hydroxyl groups (OH) form H-bonds to promote their water solubility; carboxyl groups found in amino acids provide the ability to release hydrogen ions (H+), resulting in the negatively charged COOd group, which contributes to its hydrophilic nature. The hydrophilic nature of structural protein biopolymers will impact different properties such as stability and mechanical and thermal performance. However, improvements in raw protein biopolymers are always required to comply with their anticipated usage. By understanding the physicochemical properties of proteins, a particular chemical modification technique can be selected. In addition, the final structural and functional properties are highly dependent on the functional groups and amino acid composition. Knowledge of those amino acid properties that affect protein properties and also the roles that functional groups play in chemical reactions such as solubility, electronic, steric, and repulsion effects is essential (Kosbar, Gelorme, Japp, & Fotorny, 2000). These limitations need to be addressed before implementing these materials for applications in technological use in order to comply with the packaging standards and requirements. To accomplish this, chemical modification technology has been found to have a significant impact and, as such, provides an alternative platform and a good approach to overcome many of the technological issues. Moreover, chemical modifications have enabled the development and usage of new biodegradable materials that would have been unthinkable in the face of favorable competition from fossil fuel-based materials (Khosa, Wu, & Ullah, 2013). For the past few decades, different modification techniques have been used to alter the protein structure by changing its physical and chemical properties and by making numerous improvements, with some projected applications having been successfully achieved. These improvements are mainly concerned with the chemical modification of functional groups, since the characteristics of proteins are strongly related to the present functional group. Certain important properties can be altered through chemical modification reactions with functional groups, such as hydrophilic or hydrophobic characteristics, elasticity, adsorption, ion exchange capability, antimicrobial properties, thermal properties, and mechanical resistance (Du, Li, Zhang, Rempel, & Liu, 2016; Zahara, Arshad, Naeth, Siddique, & Ullah, 2021; Zink, Wyrobnik, Prinz, & Schmid, 2016). In this section, we will discuss the principal and main routes of protein chemical modification in the preparation of biopolymer materials for food packaging applications. The modification methods are presented and classified by reaction type. The principal mechanism of each reaction will be reviewed, and the enhanced properties will be highlighted for their intended packaging applications.

Plasticization Plasticization is one of the most important and widely used modifying techniques in the plastic industry. It has long been known for its effectiveness in enhancing the flexibility, distensibility, and processability of synthetic polymers and investigated bioplastics (Subramanian & Varade, 2017). A plasticizer is a low-molecular-weight nonvolatile organic compound that is added during bioplastic formation to improve its brittleness and flexibility (Fig. 2.3). Processing properties, such as glass transition temperature (Tg), melting temperature (Tm), viscosity, and the elastic modulus of the finished product, are greatly improved by the appropriate choice of plasticizer type and concentration, without altering the fundamental chemical character of the plasticized material (Wagh, Pushpadass, Emerald, &

Chemical structure, functional groups, and properties of proteins

29

FIG. 2.3 Plasticization of protein. A schematic representation of the effect of plasticization on the structure of the protein network. A brittle structure represents the interactions between protein chains by electrostatic interactions, hydrogen bonds, and disulfide bonds that generate a rigid and brittle film structure, and a flexible structure represents the disposition and interaction of the plasticizer with the protein chains, leading to a flexible and extensible film structure. Created with BioRender.com.

Nath, 2014). Many hypotheses have been proposed to explain the mechanism by which plasticizers work on polymers. Among the very best hypotheses, three plasticizing mechanisms have been widely accepted to describe the action of plasticizers on the polymeric network. In the gel theory, plasticizers disrupt the inter- and intramolecular hydrogen bonds that hold polymers loosely tied together, thus increasing the random motion of the polymer chains. In the lubricity theory, a plasticizer acts as a molecular lubricant to reduce friction, allowing the polymer chain to move freely past one another. In the free-volume theory, plasticizers act by increasing the free volume of resins and maintaining the free volume of the polymer-plasticizer mixture during cool down after processing (Daniels, 2009; Di Gioia, Cuq, & Guilbert, 1999; Sothornvit & Krochta, 2001). Typically, two main methods exist for plasticization of polymers: internal and external plasticization. The external method is the most commonly used due to its low cost, easy application, and freedom and flexibility to develop formulations (from semirigid to highly flexible) (Kl€ahn et al., 2019). Native protein properties, like those of all biobased materials, do not exhibit more satisfactory combinations of properties during their handling in manufacturing due to their brittle nature and poor flexibility. Therefore, extensive attempts to improve the limitations associated with both brittleness and flexibility are currently being made (Ghanbarzadeh et al., 2007; Ullah et al., 2011). Plasticization has become an interesting option to modify the thermal and mechanical properties of a protein-based polymer. The chemical structure of a plasticizer used together with its molecular weight, functional group, number, and positions of hydroxyl groups all play a vital role in its ability to plasticize a protein-based polymer (Hernandez-Izquierdo & Krochta, 2008; Mekonnen, Mussone, Khalil, &

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Chapter 2 Chemical modification of protein-based biopolymers

Bressler, 2013). There are several chemical families of plasticizers that are used for various types of polymer modifications. Glycerol is the most widely used and has been found to be particularly effective in plasticized hydrophilic polymers, in addition to its stability, safety, and low cost ( Jouki, Khazaei, Ghasemlou, & Hadinezhad, 2013; Murrieta-Martı´nez et al., 2019). Recently, other green polyols such as water, ethylene glycol, die-, tri-, tetra-ethylene glycol, polyethylene glycol, and sorbitol have been widely used for the production of many bioplastics. Both the type and concentration of a plasticizer strongly affect film formation and its final properties (Maulana, Mubarak, & Pujiastuti, 2021). Selection and utilization of a plasticizer is a fundamental step in achieving the desired physical and thermomechanical properties. Selecting a suitable plasticizer formulation mainly depends on the following factors: compatibility between the plasticizer and the protein in terms of solubility, molecular weight, polarity, hydrogen bonding, and stability in the formed film and efficiency in terms of the ratio that is required to plasticize the film. Hence, it is important to emphasize that both plasticizer compatibility and efficiency may differ from one protein to another (Kadhim, Shakheer, Fahim, & Kadhim, 2018). However, the effects that different plasticizers have on the properties and comparisons between plasticizer efficiencies have been systematically investigated for different prepared protein films using casting, compression molding, or extrusion techniques. Table 2.1 summarizes the common plasticizers for different plant- and animal-based proteins that have been used in the thermoplastic processing of proteins in the literature. Several advanced techniques, such as calorimetry, gravimetry, dynamic mechanical analysis, and tensile testing, were used to investigate the plasticization behavior and the thermal and mechanical properties of plasticized protein biobased films. Similar to many other biobased plastics, the thermal and mechanical properties of protein biopolymers were observed to be dependent on the type and amount of plasticizer used (Vieira, Da Silva, Dos Santos, & Beppu, 2011). An extensive study was conducted on the likely effect of different plasticizers (ethylene glycol, propylene glycol, glycerol, and diethyl tartrate) on the thermoplastic properties of bioplastics produced from quill keratin. Among the investigated polyol plasticizers, a remarkable reduction in Tg was achieved by ethylene glycol. Moreover, ethylene glycol exhibits a relatively larger interaction with keratin at the molecular level, exhibiting only one sharp glass transition, higher mechanical properties, and better visual effects compared to other plasticizers used. This is because ethylene glycol, with a lower molecular weight, remarkably reduces polymer-polymer associations, increases free volume, and interacts with polypeptide chains through hydrogen bonds. Conversely, glycerol contains more hydroxyl groups, which can form a greater number of hydrogen bonds. Therefore, its interactions with polypeptide chains may be more complex, which may ultimately affect mechanical properties. Hence, molecular weight variation, concentration, and the presence and position of polar groups of used plasticizers can positively interact with protein chains, consequently facilitating the compatibility between proteins and the plasticizer (Ullah et al., 2011). Another study compared the effects of four plasticizers (glycerol, triethanolamine (TEA), ethylene glycol, and polyethylene glycol) on the performance of the cottonseed protein (CP)/polyvinyl alcohol (PVA) blend films. All investigated plasticizers significantly altered the degree of interaction between CP and PVA, which changed the secondary structure of the CP but had little effect on the crystallinity of the CP/PVA blend films. The most efficiency in improving the elongation at break, tensile strength, and oxygen barrier properties of the CP/PVA blend films was observed on addition of TEA. This can be explained by the presence of a more electronegative tertiary amine group in the TEA molecule, which can form an intermolecular hydrogen bond between the H+ atoms on the N
and O
atoms in the CP/PVA macromolecular chain. However, this tertiary amine group can

Table 2.1 Overview of the commonly used chemical modifications and the mechanical properties of the biopolymers made.

Proteins Soy protein isolate

Agent

Amount

Young’s modulus (MPa)

Thiodiglycol Glycerol Ethylene glycol

25% 25% 2:4

582 436 –

Cross-linking

Genipin

1–10

Cross-linking

Trimethylolpropane-tris-(2-methyl1-aziridine) propionate and caffeic acid (CA) Citric acid 3-Glycidoxypropltrimethoxysilane Palmitic acid chloride Acrylic acid

1%–5%

128.163

4.3–6.5

60–137

Casting

10–30 0.2 g 16 mM 14%

– 47 – –

8.5–17.5 4.4 2.65 318

5 107 33 114

Casting Casting Casting Casting

8:2 20%

186

44 10.1

3.3