Mediterranean Fruits Bio-wastes: Chemistry, Functionality and Technological Applications 3030844358, 9783030844356

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Mohamed Fawzy Ramadan Mohamed A. Farag   Editors

Mediterranean Fruits Bio-wastes Chemistry, Functionality and Technological Applications

Mediterranean Fruits Bio-wastes

Mohamed Fawzy Ramadan • Mohamed A. Farag Editors

Mediterranean Fruits Bio-wastes Chemistry, Functionality and Technological Applications

Editors Mohamed Fawzy Ramadan Deanship of Scientific Research Umm Al-Qura University Makkah, Saudi Arabia

Mohamed A. Farag Pharmacognosy Department Cairo University Cairo, Egypt

ISBN 978-3-030-84435-6 ISBN 978-3-030-84436-3 https://doi.org/10.1007/978-3-030-84436-3

(eBook)

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

Biomolecules from fruit biowastes include pectin, enzymes, fibers, oils, phenolics, carotenoids, and other bioactive compounds. These biomolecules are helpful for the food industry and human health. Efforts have been made for harnessing fruit industrial biowaste, and studies have reported the utilization of peels, seeds, and pomace from Mediterranean fruits. Nowadays, the attention towards beneficial reuse of fruit biowastes aims to recover added-value molecules before their energetic purposes provide close-tozero-waste biorefinery. Recent investigations have been focused on developing new techniques to explore applications of the bioactive compounds obtained from fruit biowastes and their valorization to even other novel added-value products. Food products have been fortified with bioactive compounds from fruit biowastes, since there is a growing interest in using natural additives with health-enhancing properties. On the other hand, feeding fruit by-products has neutral or positive effects on animal growth and meat quality attributes compared to conventional fibers (i.e., soybean hulls, maize bran, wheat bran, and straw). The Mediterranean climate is ideal for cultivating several fruits, wherein the Mediterranean food pattern is characterized by high consumption of fresh and processed fruits. Citrus is an important example of Mediterranean fruit. Citrus is the largest fruit crop worldwide, with annual production exceeding 124.3 million tons. Every year about 120 million tons of citrus biowastes are generated worldwide from the citrus processing industries. Citrus industrial biowastes are readily available and a cheap source of renewed biomass. Citrus peel (ca. 50% of fruit weight) is a source of health-enhancing compounds, particularly phenolics (flavanones, flavanone glycosides, and polymethoxylated flavones), oils, fibers, minerals, and carotenoids. Apple is another example of Mediterranean fruits. Apple pomace (ca. 30% of apple weight) is a rich source of added-value compounds (i.e., flavanols, flavonols, procyanidin, phloridzin, and chlorogenic acid). In addition, apple pomace is used for animal feeding, and it was proposed as fuel for steam generation in processing plants. Given the association between oxidation and aging and age-related diseases and the health-promoting effects of the Mediterranean fruits, the antioxidant v

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potential of Mediterranean fruit biowastes (Med-Fruit-Waste) may be responsible for health benefits and contribute to expanding the life span of consumers. This book aims to create a multidisciplinary forum for discussion on Med-FruitWaste, particularly emphasizing phytochemistry, functionality, health-promoting properties, and applications. The impact of traditional and innovative processing techniques on recovering high added-value compounds from Med-Fruit-Waste is reported. Besides, chapters of this book discuss the potential applications of MedFruit-Waste in functional food, cosmetics, and pharmaceuticals. Intending to provide major reference work for those of the scientific community involved in horticulture, food science, pharmacology, and nutrition, as well as for undergraduate and graduate students, this book presents a comprehensive review of the aspects and results that have led to the advancements in Med-Fruit-Waste chemistry, functionality, and uses. We hope that the book will be a valuable source for people involved in all kinds of related disciplines. We sincerely thank all authors for their valuable contributions and their cooperation during the book preparation. The Springer Nature staff’s help and support, especially Daniel Falatko and Sofia Valsendur, was essential for completing our task and is highly appreciated. Makkah, Saudi Arabia Cairo, Egypt

Mohamed Fawzy Ramadan Mohamed A. Farag

Contents

Part I 1

2

Introduction to Mediterranean Fruits Bio-wastes: Chemistry, Functionality and Techno-Applications . . . . . . . . . . . . . . . . . . . . . . Diaaeldin M. Elimam, Mohamed Fawzy Ramadan, Ahmed M. Elshazly, and Mohamed A. Farag Potentials of Biowaste Carbohydrates in Gut Health Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Marwa El-Hindawy

Part II 3

4

5

6

General Aspects 3

29

Olive Bio-wastes: Chemistry, Functionality and Technological Applications

Olive Fruit by-Products: From Waste Streams into a Promising Source of Value-Added Products . . . . . . . . . . . . . . . . . . . . . . . . . . . Trabelsi Najla, Mariem Habibi, Maryem Hadj Ammar, Leila Abazza, and Ridha Mhamdi Anaerobic Digestion Technology of Solid and Liquid Forms of Olive Wastes in the Mediterranean Region . . . . . . . . . . . . . . . . . Ouahid El Asri, Soufiane Fadlaoui, and Mohamed Ramdani Agronomic Olive Bio-waste Management: Combination of Olive Mill Wastewater Spreading and Compost Amendment – Effects on Soil Properties and Olive Tree Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Salwa Magdich and Emna Ammar

47

67

91

Olive Waste as a Promising Approach to Produce Antioxidants, Biofertilizers and Biogas . . . . . . . . . . . . . . . . . . . . . . 115 Ayoub Haouas, Anas Tallou, Amin Shavandi, Mounir El Achaby, Khalid Aziz, Ayoub El Ghadraoui, and Faissal Aziz vii

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Contents

Part III

Citurs Bio-wastes: Chemistry, Functionality and Technological Applications

7

Citrus Biowastes: Applications in Production and Quality Enhancement of Food from Animal Sources . . . . . . . . . . . . . . . . . . 133 Tawanda Tayengwa, Chenaimoyo L. F. Katiyatiya, Leo N. Mahachi, Obert C. Chikwanha, and Cletos Mapiye

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Valorization of Grapefruit (Citrus 3 paradisi) Processing Wastes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Nuria Zarate-Vilet, Emilie Gué, Michèle Delalonde, and Christelle Wisniewski

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Citrus Bio-wastes: A Source of Bioactive, Functional Products and Non-food Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 Ines Ellouze

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Citrus sinensis (Sweet Oranges) Wastes: The Orange Wealth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 Shimaa Mohammad Yousof, Rasha Atta, Islam A. Khalil, Mohamed A. Zayed, and Asmaa Seddek

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Tangerine (Citrus reticulata L.) Wastes: Chemistry, Properties and Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 Ahmad A. Omar, Abdelaleim I. ElSayed, and Azza H. Mohamed

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Lemon (Citrus limon) Bio-waste: Chemistry, Functionality and Technological Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 Massimo Lucarini, Alessandra Durazzo, Amirhossein Nazhand, Johannes Kiefer, Roberta Bernini, Annalisa Romani, Eliana B. Souto, and Antonello Santini

Part IV

Apple and Pear Bio-wastes: Chemistry, Functionality and Technological Applications

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Valorisation of Apple (Malus domestica) Wastes . . . . . . . . . . . . . . . 325 Cristina Ghinea and Ana Leahu

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Apple (Malus domestica) By-products: Chemistry, Functionality and Industrial Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349 Pedro A. R. Fernandes, Dulcineia F. Wessel, Manuel A. Coimbra, and Susana M. Cardoso

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Chemistry, Functionality and Technological Applications of Pear Bio-waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375 Rahman Qadir, Farooq Anwar, Mian Anjum Murtaza, and Muhammad Fayyaz ur Rehman

Contents

Part V

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Date Palm Bio-wastes: Chemistry, Functionality and Technological Applications

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Valorization of Date Palm (Phoenix dactylifera) Wastes and By-Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391 Buket Aydeniz-Güneşer

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Date Palm (Phoenix dactylifera L.) Wastes Valorization: A Circular Economy Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403 Wadii Abid and Emna Ammar

Part VI

Bio-wastes from Grape and Berries: Chemistry, Functionality and Technological Applications

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An Insight into the Brilliant Benefits of Grape Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433 Maii AbdelNaby Ismail Maamoun

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Grape (Vitis vinifera) Biowastes: Applications in Egg, Meat and Dairy Production and Products . . . . . . . . . . . . . . . . . . . . 467 Obert C. Chikwanha, Trust M. Pfukwa, Tawanda Tayengwa, Chenaimoyo L. F. Katiyatiya, and Cletos Mapiye

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Vaccinium Berry Processing Wastes: Composition and Biorefinery Possibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505 Linards Klavins and Maris Klavins

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Strawberry Fruit Waste: Chemistry, Functionality and Technological Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523 Wei Ting Jess Ong and Kar Lin Nyam

Part VII

Prunus Bio-wastes: Chemistry, Functionality and Technological Applications

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Apricot (Prunus armeniaca L.) Kernel: A Valuable by-Product . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547 Mustafa Kiralan and Onur Ketenoglu

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Valorization of Sweet Cherry (Prunus avium) Wastes as a Source of Advanced Bioactive Compounds . . . . . . . . . . . . . . . . . . . . . . . . . 559 Esra Gençdağ, Ahmet Görgüç, and Fatih Mehmet Yılmaz

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Peach (Prunus persica) Bio-Waste: Chemistry, Functionality and Technological Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581 Alessandra Durazzo, Massimo Lucarini, Amirhossein Nazhand, Johannes Kiefer, Roberta Bernini, Annalisa Romani, Eliana B. Souto, and Antonello Santini

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Contents

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Valorization of Peach (Prunus persica) Fruit Waste . . . . . . . . . . . . 589 Muhammad Imran, Muhammad Kamran Khan, Muhammad Haseeb Ahmad, Rabia Shabir Ahmad, Muhammad Rizwan Javed, Mahr Un Nisa, Muhammad Nadeem, Faheem Liaqat, Usama Ahmad, and Muhammad Abdul Rahim

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Plum (Prunus domestica L.) Wastes . . . . . . . . . . . . . . . . . . . . . . . . . 605 Francisc Vasile Dulf

Part VIII

Cucurbitaceae Bio-wastes: Chemistry, Functionality and Technological Applications

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Leveraging the Cucumis melo Wastes . . . . . . . . . . . . . . . . . . . . . . . 627 Bruna Laratta, Domenico Pignone, and Filomena Monica Vella

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Citrullus Lanatus (Watermelon) Wastes: Maximizing the Benefits and Saving the Environment . . . . . . . . . . . . . . . . . . . . 647 Doaa Attia Elsayed, Shimaa Mohammad Yousof, Islam A. Khalil, Eman Kolieb, and Mohamed A. Zayed

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Pumpkin Bio-Wastes as Source of Functional Ingredients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667 Shahira M. Ezzat, Riham Adel, and Essam Abdel-Sattar

Part IX

Bio-wastes from Other Fruits: Chemistry, Functionality and Technological Applications

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Avocado (Persea Americana) Wastes: Chemical Composition, Biological Activities and Industrial Applications . . . . . . . . . . . . . . . 699 Natascha Cheikhyoussef and Ahmad Cheikhyoussef

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Industrial Pomegranate Wastes and their Functional Benefits in Novel Food Formulations . . . . . . . . . . . . . . . . . . . . . . . . 721 Ahmet Görgüç, Esra Gençdağ, and Fatih Mehmet Yılmaz

32

Valorization of Persimmon (Diospyros kaki) Wastes to Be Used as Functional Ingredients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 739 Lucía Seguí, Claudia Bas-Bellver, Cristina Barrera, and Noelia Betoret

33

Carob-Agro-Industrial Waste and Potential Uses in the Circular Economy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765 Artemis Palaiogianni, Marinos Stylianou, Dimitrios Sarris, and Agapios Agapiou

Contents

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34

Utilization of Tomato (Solanum lycopersicum) by-Products: An Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799 Mustafa Kiralan and Onur Ketenoglu

35

Valorization of Guava Fruit Byproducts: Chemical Composition, Bioactive Components, and Technical Concerns to the Food Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . 819 Ibrahim Khalifa and Asad Nawaz

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841

About the Editors

Mohamed Fawzy Ramadan is a Professor of Biochemistry and consultant of international publishing at the Deanship of Scientific Research, Umm Al-Qura University, Makkah, Saudi Arabia. Since 2014, Professor Ramadan is a Professor in the Agricultural Biochemistry Department, Faculty of Agriculture at Zagazig University, Egypt. Prof. Ramadan obtained his Ph.D. (Dr. rer. nat.) in Food Chemistry from Berlin University of Technology (Germany, 2004). Prof. Ramadan continued his postdoctoral research in ranked universities, such as the University of Helsinki (Finland), Max Rubner-Institut (Germany), Berlin University of Technology (Germany), and the University of Maryland (USA). In 2012, he was appointed to be Visiting Professor (100% teaching) in the School of Biomedicine, Far Eastern Federal University in Vladivostok, Russian Federation. Prof. Ramadan published more than 280 research papers and reviews in international peer-reviewed journals as well as several books and book chapters (Scopus h-index is 43 and more than 5300 citations). He was an invited speaker at several international conferences. Since 2003, Prof. Ramadan is a reviewer and editor in several highly-cited international journals, such as Journal of Medicinal Food and Journal of Advanced Research. Prof. Ramadan received Abdul Hamid Shoman Prize for Arab Researcher in Agricultural Sciences (2006); Egyptian State Prize for Encouragement in Agricultural Sciences (2009); European Young Lipid Scientist

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About the Editors

Award (2009); AU-TWAS Young Scientist National Awards (Egypt) in Basic Sciences, Technology and Innovation (2012); TWAS-ARO Young Arab Scientist (YAS) Prize in Scientific and Technological Achievement (2013); and Atta-ur-Rahman Prize in Chemistry (2014).

Mohamed A. Farag is a Professor at the Faculty of Pharmacy, Cairo University, Egypt. Specializing in metabolomics, natural products chemistry, and plant biochemistry, Mohamed A. Farag completed his Ph.D. at Texas Tech University, USA, in 2003. In 2005, after spending time as a postdoctoral fellow at the Samuel Roberts Noble Foundation, USA, and the James Graham Brown Cancer Center, USA, he became an Assistant Professor at the Faculty of Pharmacy, Cairo University, Egypt. Since 2009, Dr. Farag has been working as a parttime Visiting Professor at the Technical University of Munich, Germany, to participate in teaching plant metabolomics and chemometrics modeling for master students. In 2009–2010, he held the Alexander von Humboldt fellowship at the Leibniz Institute of Plant Biochemistry, Germany. Dr. Farag now works full-time as a Visiting Professor at the Chemistry Department, American University in Cairo (AUC). His research work focuses primarily on applying innovative biochemical technologies (metabolomics) to help answer complex biological questions in medicine, herbal drug analysis, and agriculture. Dr. Farag has been recognized with several awards, including Abdul Hameed Shoman award (2016), Egypt Excellence Award in medical sciences (2018), Higher State Incentive Award (2012), Cairo University Incentive Award (2009), TWAS award in science diplomacy (2014), and the Mass Spectroscopy Performance Award, TTU, USA (2004). In addition, for his highly cited publications of more than 5000 citations and an hindex of 39, Dr. Farag was selected as a top researcher in the field of plant biology in Africa by the American Society of Plant Biologists, USA. Dr. Farag is a current TWAS Fellow in Agriculture from Egypt. He is the managing editor of the esteemed Journal of Advanced Research, along with editorial board membership in several other plant journals.

Part I

General Aspects

Chapter 1

Introduction to Mediterranean Fruits Bio-wastes: Chemistry, Functionality and Techno-Applications Diaaeldin M. Elimam, Mohamed Fawzy Ramadan and Mohamed A. Farag

1.1

, Ahmed M. Elshazly,

Description and Contents of the Mediterranean Diet

Mediterranean diet (MTD) is a collection of eating habits prevalent in Mediterranean Sea countries (olive-growing areas), which builds mainly upon consumption of high amounts of fruits and vegetables and lower quantities of meat, fish, and their products modest or no consumption of alcoholics. MTD was scientifically described in the very first place by the American physiologist Ancel Keys as a high vegetable oils/low saturated fat-based diet. The pattern of MTD can be discriminated by four essential parameters, namely, Ratio of unsaturated/saturated fatty acids (around 2.0);

D. M. Elimam Department of Pharmacognosy, Faculty of Pharmacy, Kafrelsheikh University, Kafr El-sheikh, Egypt School of Pharmacy and Medical Sciences, Faculty of Life Sciences, University of Bradford, Bradford, UK M. F. Ramadan (*) Deanship of Scientific Research, Umm Al-Qura University, Makkah, Saudi Arabia Agricultural Biochemistry Department, Faculty of Agriculture, Zagazig University, Zagazig, Egypt e-mail: [email protected] A. M. Elshazly Department of Pharmacology, Faculty of Pharmacy, Kafrelsheikh University, Kafr El-sheikh, Egypt M. A. Farag (*) Pharmacognosy Department, Faculty of Pharmacy, Cairo University, Cairo, Egypt Chemistry Department, School of Sciences & Engineering, The American University in Cairo, New Cairo, Egypt e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 M. F. Ramadan, M. A. Farag (eds.), Mediterranean Fruits Bio-wastes, https://doi.org/10.1007/978-3-030-84436-3_1

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phytosterols (370–555 mg/day); antioxidant capacity (3500–5300 Trolox eq./day) and dietary fibres (41–62 g/day) (Tous & Ferguson, 1996). In terms of daily servings, typical MTD comprises about 3–9 vegetables, 1/2 to 2 fruits, 1 to 13 cereals, and 2–8 olive oil. On the energy level, MTD provides nearly 9.3 MJ/day, gained from carbohydrates (43%), total fats (~ 37%), and proteins (15–20%) (Davis et al., 2015).

1.2

Fruits of the Mediterranean Diet

Since ever, the Mediterranean region has been reckoned as a site of fruit production, active consumption, and commerce. The basin is the source of hundreds of fruits, presented in versatile forms, either fresh, dried or fruit products (jams, juices, cakes, etc.). Some botanical fruits may be termed “vegetables” in culinary parlance. These fruits are either native to the Mediterranean basin or in other regions with nearly similar climates but then were transferred to Mediterranean countries by cultivars (Tous & Ferguson, 1996). Figure 1.1 represents an annotated collection of the most distinguished Mediterranean fruits discussed within this book.

Fig. 1.1 An annotated collection of most distinguished Mediterranean fruits

1 Introduction to Mediterranean Fruits Bio-wastes: Chemistry, Functionality. . .

1.3

5

Mediterranean Diet as a Functional Food

MTD may protect against many progressive disorders, especially cardiovascular and cancer. Active compounds of the MTD (e.g., phenolics, flavonoids, and phytosterols) are all known to have health-positive effects; thus, they can be used to formulate functional food. However, identification and standardization of these constituents and studying the pharmacological properties of the minor components of this diet (e.g., vitamins) are crucial aspects in the process of functional-food formulation. A nutraceutical, food-derived drug is a preparation of pharmaceuticals (tablets, capsules, and elixirs) containing the active constituents found in functional foods (extracted/isolated, and bio-assayed) (Ortega, 2006). For instance, carob can be consumed as a functional-food, or as a nutraceutical. It can be consumed as a beverage for its health effects, a functional food. On the other hand, its phenolic contents, carbohydrates, or benzodiazepine-like substances can be extracted, formulated, and used as a nutraceutical drug (Ortega, 2006).

1.4

Epidemiological Studies

Many studies concluded that consumption of natural product-based food led to a decrease in mortality rate, especially from chronic diseases and cancers. This could be related to their immense content of phenolics, antioxidants, natural fibers, etc., in addition to pharmacologically active metabolites. MTD is considered a vital source of such compounds. Studies have shown that Mediterranean populations have a lower risk of major chronic diseases and a longer life expectancy. Martinez-Gonzalez et al. analyzed 19 large prospective studies and 2 large cohort studies and reported that MTD consistently reduced the risk of myocardial infarction, heart failure, stroke, disability, and total mortality. In addition, PREDIMED, the largest randomized trial with MTD, reported its advantages in preventing cognitive diseases and some cancers (Martinez-Gonzalez & Martin-Calvo, 2016). In a 13-years clinical follow-up epidemiological study (above 40,000 individuals) concerned with polyphenolic flavonoids effects on cardiovascular diseases, the European Prospective Investigation of Cancer and Nutrition (EPIC, the Spanish branch) reported a 29% mortality-decrease from cardio-vascular diseases upon consumption of high flavonoid diet (Buckland et al., 2011). Furthermore, a systematic meta-analysis of 143 prospective observational studies concerning dietary flavonoid intake and cancer has shown that isoflavones significantly reduced lung, stomach, breast, and colorectal cancers, while total flavonoids showed a nonsignificant decrease in breast cancer risk (Grosso et al., 2017). Sofi et al. in 2013, conducted a comprehensive review (80 studies with over four million population subjects) to investigate the association between the MTD and health status. The Cohort prospective study demonstrated that MTD was associated with 8% overall mortality decline, 10% reduced cardiovascular disease risk, and 4%

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decrease in cancer diseases (Sofi et al., 2014). On the same line, a study calculated that, in Western countries populations (northern Europe and North America), the incidence of colorectal cancer and breast cancer would be reduced by 25% and 15%, respectively as well as the prostate, pancreas, and endometrial cancers by
10% if the populations shifted to MTD (Trichopoulou et al., 2000). Upon analysis of approximately 200 studies that correlate fruit and vegetable intake (main MTD components) with lung, GIT, breast, and reproductive system cancers, it was shown that individuals who highly consume fruit and vegetables significantly suffer less in developing such cancers (about half the risk compared to lower consumers). The studies provided strong evidence of consistent protective effect against lung cancer (24 out of 25 included studies), GIT (77 out of 89 studies), reproductive system cancers (11 of 13 studies), and breast cancer (meta-analysis) (Block et al., 1992). The mitigation of the risk might be attributed to their wellknown antioxidant micronutrients (Steinmetz & Potter, 1991). In Italy and Finland, intervention studies have persuasively demonstrated an improved risk profile of coronary heart disease (decreased blood pressure and cholesterol) by MTD (Crete diet) with 70% lower mortality (all-causes) compared to the control diet (Kok & Kromhout, 2004). In another meta-analysis study, Psaltopoulou et al. included 22 eligible studies that cover: stroke (11), depression (9), cognitive impairment (8), and Parkinson’s disease (1). Strong adherence to MTD showed a consistent correlation to reduced risk for stroke, depression, and cognitive impairments. The protective effect of high adherence to MTD in terms of reduced risk for ischemic stroke, mild cognitive impairment, dementia, and particularly Alzheimer’s disease was emphasized by further subgroup analyses. Metaregression analysis suggested that stroke prevention was more significant among males. However, less adherence to MTD almost diminished the protective effect against stroke but retained the reduced risk for cognitive impairment and depression (the effect appeared to wane with elder ages) (Psaltopoulou et al., 2013). Giugliano et al. conducted a study that illustrates the relationship between MTD and metabolic diseases (obesity, type-II diabetes, and metabolic syndrome) and the potential mechanisms of MTD in these diseases’ prevention and treatment. The growing evidence indicated a positive effect on obesity and type-II diabetes. Moreover, a lower prevalence of metabolic syndrome is associated with dietary patterns rich in fruits, vegetables, whole grains, dairy products, and unsaturated fats. MTD reduced adult obesity and had a significant role in attenuating the inflammatory burden associated with type-II diabetes. Epidemiological and interventional studies have shown a positive effect of the MTD in chronic inflammation, suggesting a key mechanism of MTD protective effects on discussed disorders (Giugliano & Esposito, 2008). An inverse relation between MTD consumption and body mass index (BMI) in the Spanish population sample was reported by Schröder. MTD overall is a low-energetic diet, which might explain its prevention of weight gain. Some mechanistic studies suggest that a high intake of MTD leads to higher ingestion of dietary fiber, antioxidants, magnesium, and unsaturated fatty acids, which potentially explains its positive effects in obesity and type 2 diabetes. Evidence from

1 Introduction to Mediterranean Fruits Bio-wastes: Chemistry, Functionality. . .

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epidemiological studies and several mechanistic explanations confirm a protective effect of MTD on obesity and type-II diabetes (Schröder, 2007). In a randomized intervention trial over 4.5 years, MTD enhanced endothelial function and considerably reduced blood glucose level, insulin, BMI, and metabolic syndrome (Esposito et al., 2004; Schröder, 2007). Furthermore, in a controlled randomized clinical trial on type-II diabetic postmenopausal patients, Toobert et al. reported the ability of a MTD to reduce risk factors of cardiovascular diseases (improved lipid profile, BMI, and glycated hemoglobin levels) (Toobert et al., 2003). However, Trichopoulou et al. reported that no relation was observed among a larger sample of the Greek population (Trichopoulou et al., 2005).

1.5

UN Sustainable Development Goals and Promoting Environmental-Friendly Food Production

Fruit processing results in a vast amount of bio-wastes such as seeds, peels, and stones. The disposal of bio-waste represents a further aggravated problem by legal restrictions due to the negative environmental impact of such wastes. However, using this bio-waste to produce natural edible additives or supplements with nutritional value has gained interest because the recovery of these bioactive compounds might be economically valuable. The United Nations Sustainable Development Goals (SDG) comprises a vision of a peaceful, fairer, and sustainable world (https://sustainabledevelopment.un.org). Regarding the food sector, aspects of the value-added chain, including the way crops are planted, processed, transported, marketed, stored, and consumed, are the main link between people and the development of sustainable economics (Ramadan, 2021). Efficient, inexpensive, and environmentally friendly fruit industry bio-wastes are cost-effective and minimize the environmental effect. This approach agrees with United Nations SDG, called “Good Health and Well-Being” that aims to enhance human well-being by using health-promoting crops and environmentally-friendly methods in food processing (https://sdgs.un.org/goals/goal3).

1.6

Definition, Main Sources, and Statistics of MTD Wastes

Worldwide, fruits and vegetables can be considered the most consumed agricultural products. Due to the abrupt population growth and different diet habits, the production and processing of fruits and vegetables have significantly increased. They are utilized (either totally-, minimally- or un-processed) due to their nutritional values and health-promoting effects. According to Food and Agriculture Organization (FAO), the 2019-global production reached ~880 million metric tons for fruits (compared to 500 million in the year 2000), and about ~1 billion metric tons for

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vegetables (compared to 600 million, in the year 2000). Interestingly, around 15% of fruits and vegetables were produced in the region of the Mediterranean basin (FAO, 2019). The increased production levels, alongside the shortage of suitable processing techniques, have generated enormous losses and wasted such vital resources. These losses and wastes are principally comprised of crops’ rind (skin, e.g., citrus, banana), pomace (e.g., grape, olives), and/or seeds (e.g., peach, mango). For instance, the FAO has estimated that about a third of fruits and vegetables are wasted as by-products; annotating them with the highest loss-share amongst all types of food (about 400 million metric tons, ~ 60% of all lost food around the world), (Gustavsson et al., 2011; Sagar et al., 2018). Crop loss and waste can arise throughout all the supply and processing stages: harvesting, transportation, storage, retailing, processing, and/or a consumer. The term loss can be distinguished from waste; it refers to any unintended damage during the sequence of production and supply (technical limitations from producer till before consumption; more in developing countries). On the other hand, waste is the discarded portion of ready-to-consume food and is generally related to consumers or retailers (deliberately or through negligence; more in developed countries). Crop reduction in mass or volume (reduced amount of food available for consumption) is known as quantitative (loss or waste), while qualitatively, they are characterized by reduced: value (nutritional, caloric, and/or economic), customer satisfactoriness, or edibility which all eventually lead to discarding (Parfitt et al., 2010). Over and above nutritional concerns, the issue is growing into severe environmental and commercial problems because of losing essential resources such as working hands, energy, farming area, water, and fertilizers in addition to increased landfills-decomposition as these wastes are prone to microbial spoilage (offensive odors) and subsequently emission of harmful greenhouse gases (Venkat, 2011; Vilariño et al., 2017). According to different studies conducted in Germany (Eberle & Fels, 2016), Denmark (Edjabou et al., 2016), and the United kingdom (Quested et al., 2013), fruit and vegetables are responsible for almost half of households’ food waste. De Laurentiis et al. in their study on European countries, have quantified and differentiated between unavoidable (never been normally edible) and avoidable wastes (disposed edible) to aid and design management and prevention strategies. On average, about 29% of household fruits and vegetables were wasted (about 35 kg/ person/year), half of which was an avoidable waste that could be decreased by applying targeted prevention strategies. On the other hand, a significant percentage of the waste is generated by the inedible parts (e.g., rind, pomace), that could not be decreased without changing consumption patterns, or these products had gone under higher processing level (e.g., canning or freezing) which would have shift-up the waste generated at industrial level (De Laurentiis et al., 2018). According to the USA department of agriculture, economic research service (USDA/ERS), Hodges et al. reported that avoidable loss from edible Fruits and vegetables in the USA in 2008 reached 35% of the total available crops (81,355 tons/

1 Introduction to Mediterranean Fruits Bio-wastes: Chemistry, Functionality. . .

9

year); distributed as 15% retail-related loss (5728 tons/year), and 20% consumerrelated loss (11,577 tons/year) (Hodges et al., 2011).

1.7

Key Molecules and Bioactive Compounds in MTD-Fruit-Waste

Fruit processing results in excessive quantities of wastes/by-products, for instance, rinds, pomace, seed, and oil waste-water/cakes, which are usually rich sources of valuable molecules. Lately, this by-product was seriously considered; for being a valuable source of dietary fibers, phenolics, natural pigments, vitamins, and minerals, etc., which potentially have desired effects on oxidative stress, cardiovascular system, metabolism, microbial infections (phytoalexins), and different cancers (Sagar et al., 2018). Dietary fibers are diverse chemical components derived from plant cell walls that human gut enzymes cannot completely digest. They have two major categories: soluble and insoluble fibers and are composed mainly of complex polysaccharide and polysaccharide derivatives (e.g., cellulose, hemicellulose, and pectin). For decades, dietary fibers have been studied because of their versatility and potential benefits for human health and the prevention of several diseases. Cellulose and pectin comprise the most relevant dietary fiber in fruits (Massiot & Renard, 1997; Medicine, 2001). Cellulose and hemicellulose dietary fibers were abundantly found in grape pomace (Kammerer et al., 2005). González et al. reported that the red grape pomace has had the highest dietary fiber content among 10 studied grape varieties (37% fruit weight) (González-Centeno et al., 2010). Deng et al. studied the grape pomace fiber content after fruit drying and found the ratio around 50% (Deng et al., 2011). Comparably, Llobera et al. reported that red grape pomace contained about 77% dietary fiber by the fruit dry mass (Llobera & Canellas, 2007). Pectin is the most re-utilized compound from apple pomace, juice production waste, but the enzymatic browning of apple pectin may limit its industrial applications (Renard et al., 1997). Similarly, the peels contained high dietary fiber content (even higher than the pulp 0.91% fresh weight) (Gorinstein et al., 2001a, 2001b). In peach, dietary fibers constituted about 30% of the dry mass, with pectin, one-third that percentage, as the main cell wall polysaccharide (Chang et al., 2000; Kurz et al., 2008). Orange peels contain 57% dietary fiber per dry mass, with both cellulose and pectin polysaccharides as main components (Chau & Huang, 2003), while for lemon peel, according to Gorinstein, it was only 14%. However, it remained higher than the pulp (~7%) (Gorinstein et al., 2001a, 2001b). Contrary wise this, Russo et al. reported the amount to be higher in the pulp, with a total of 77% compared to the peels, 53% (Russo et al., 2014). The dietary fiber contents in various fruit wastes are briefly reviewed in Table 1.1 and Fig. 1.2.

Fruit Apple

Pear

Tomatoes

Banana

No. 1.

2.

3.

4.

Peel

Skin

Pomace

Pomace

Pomace

Nature of the waste Peel

Dietary fibers46–48 (50%), high sugar content. Phenolic compounds (~40): Hydroxycinnamic acids6, Flavonoids1,1`,2 and catecholamines

Dietary fibers46–48 (50%), Carotenoids (lycopene22). Carotenoids (lycopene22)

Bio-active compound (structurea) Dietary fibers (Pectins48, Cellulose46), (0.91%). Dietary fibers46–48 (88.5%). Phenolic compounds (~60): Flavonoids1,2/glycosides, Quinic acid derivatives5, Chalcones10, Cinnamic acids6/derivatives, Coumaric acid derivatives11, Catechins3, Cyanidins8. Dietary fibers46–48 (43.9%). Major phenolics: chlorogenic acid5b, vanillin27, epicatechin3b, catechin3a, and caffeic acid6c.

Table 1.1 Major potential bio-active compounds in MTD-Fruit-Waste

Martin-Cabrejas et al. (1995), Yuan et al. (2011), Banerjee and Chattopadhyay (2019)

Phenolics: Antioxidant and antimicrobial. Vanillin: second most popular flavoring agent, personal care products. Herbicide, ripening agent, an antifoaming agent. Carotenoids: Potent antioxidants, photo-protectants, modulate gene activity (protection from experimentally-induced inflammatory damage and neoplastic transformation). Pro-vitamin A activity (immunebooster, effective in degenerative diseases and cardiovascular disease). Sugars: Bio-fuel production. Phenolics: Antioxidant and antimicrobial. Carotenoids: Antioxidant, photo-

Wachirasiri et al. (2009), Subagio et al. (1996), Hix et al. (2004), Vu et al. (2018), Palacios et al. (2017)

Del Valle et al. (2006), Strati and Oreopoulou (2011), Hix et al. (2004), Sharma and Le Maguer (1996)

Reference Gorinstein et al. (2001a, 2001b), Renard and Thibault (1991), BenitoGonzález et al. (2019), Schols and Voragen (1996), Jitpukdeebodintra and Jangwang (2009)

Potential use Maintain a healthy digestive system (Prevent constipation, laxative) Pectins: lower cholesterol, remove heavy metal, stabilize blood pressure, control body weight. Induce apoptosis in colon cancers.

10 D. M. Elimam et al.

Date

Grapes

Citrus (Lemon, orange)

5.

6.

7.

Peel

Skin

Pomace

Seeds

Seeds

(Dopamine25a, L-dopa25b), Carotenoids (xanthophyll21b) (xanthophylpalmitate, caprate, laurate)21c Dietary fibers46–48 (57–92.4%). Phenolic acids (gallic acid4a, protocatechuic acid-TBDMS24, p-hydroxybenzoic acids4, canillic4b acid25a, caffeic acid6c, coumaric acids11, ferulic acid6b). Dietary fibers46–48 (40%). Procyanidin7, Cyanidin 3-glucoside8, Catechin, Epicatechin, Gallic acid, Chlorogenic acid, and Homogentisic acid. Dietary fibers37–39 (77.9%), Catechins3, Anthocyanins33, Stilbenes (Resveratrol)26, and flavonol glycosides1. Catechin3a, Epicatechin3b, Epigallocatechin3c, Epicatechin gallate3d, and Kaempferol1b. Dietary fibers46–48 (14–57%). Flavonoids (hesperidin2c, naringin2a, eriocitrin2b), Limonene40. Naringin: antioxidant, antiinflammatory, antiapoptotic, antiatherogenic, anti-diabetic, effective in cardiovascular, neurodegenerative, osteoporosis, and rheumatological disorders. Limonene: antimicrobial, antioxidant, analgesic, anti-inflammatory, gastroprotective, antineoplastic, and antidiabetic effects.

Anthocyanins: coloring agent, antioxidant, Cytotoxic (breast, lung, and GIT), Cytoprotective (chemical-induced toxicity).

Antifungal, Acaricide, Insulinreleasing agent, hepatoprotective.

protectants, and pro-vitamin A activity

(continued)

Gorinstein et al. (2001a, 2001b), Chau and Huang (2003), Matharu et al. (2016), Bharti et al. (2014), Forgács et al. (2012), Vieira et al. (2018)

Bagchi et al. (2002), Valiente et al. (1995), Schieber et al. (2001), Souquet et al. (1996), Dimitrić-Marković (2007), Deng et al. (2012)

Al-Farsi and Lee (2008), Lima et al. (2018), Sharma (2011)

1 Introduction to Mediterranean Fruits Bio-wastes: Chemistry, Functionality. . . 11

Fruit Clementine

Tangerine

Grapefruit

Pomegranate

No. 8

9.

10.

11.

Peel

Peel

Peel

Nature of the waste Peel

Table 1.1 (continued)

Furanocoumarins: Epoxybergamottin14, Aurapten12, Meranzin13a, Sibiricin13b and 3,5,6,7,8,30 ,40 -heptamethoxy flavone1i, and Limonene40. Flavonoids1,2, anthocyanidins (Pelargonidin)8, High molecular weight ellagitannins: Punicalagin32, Tellimagrandin-I37, Strictinin38, Casuarinin39, and Corilagin36.

Highly methoxylated flavonoids (nobiletin1h, and tangeretin1g), and Hesperidin2c.

Bio-active compound (structurea) Narangin2a, Rutin1c, and Hesperidin2c (most abundant polyphenol), transFerulic6b, and p-Coumaric acids11.

Selective bacteriostatic/bactericidal, antioxidant Prebiotic: a reservoir of valuable therapeutic agents, food preservatives, stabilizers, supplements, and probiotics. Casuarinin and corilagin exhibit antiviral properties (Herpes simplex).

Potential use Hesperidin: Protective against metabolic syndrome and associated diseases, reduce the diastolic blood pressure, and improve microvascular endothelial function, antiinflammatory, antioxidant, antimicrobial, anticarcinogenic, cell aggregation inhibitor, antiallergic, UV protecting, and radioprotection. Nobiletin: Treat bulbectomy-induced memory impairment. Nobiletin and Tangeretin: Potent antineuroinflammatory (Neurodegenerative diseases: Alzheimer’s and Parkinson’s diseases) Epoxybergamottin: Potent cytochrome P 450 3A4 (CYP3A4) inhibitor.

Akhtar et al. (2015)

Wangensteen et al. (2003)

Nagase et al. (2005), Ho and Kuo (2014)

Reference Gómez-Mejía et al. (2019), Karim et al. (2021)

12 D. M. Elimam et al.

Olive

Watermelon

Peach

Apricot

Avocado

12.

13.

14.

15.

16.

Seed

Peel

Seeds

Pomace

Rind and seed

Pomace

Oil wastewater Seed (Stone)

Dietary fibers46–48 (35.8%), Amygdalin29, Kernel oil (57.2%), Oleic44, Linoleic45, and Palmitic acids43. Phenolics (62.8%): Gallic acid, chlorogenic acid, catechin, epicatechin, caffeic acid, and p-coumaric acid11. Phenolics (54.8%): Chlorogenic acid5b, Cyanidin 3-glucoside8

Hydroxy-tyrosol16b, Tyrosol16a, Nuezhenide18, methoxylatednuezhenide18, nuezhenide-11methyloleoside19, and Oleuropein17. Phenolics: Tyrosol16a, Apigenin1d, Oleuropein17, Squalene23. Phenolic acids (Chlorogenic5b, Vanillic4b, Sinapic6d, Cinnamic6a, p-Coumaric11a, Syringic4c, Caffeic6c, Ferulic6b, Gallic, 4-Hydroxybenzoic4)acids, Quercetin1a, Gingerol15, Anthocyanin33, and Phenolic glycosides (Lanatusosides C30a and D30b) Dietary fibers46–48 (54.5%). Amygdalin29, Polyphenolics: Flavonoids1,2,3, Anthocyanins33 and Carotenoids21.

Oleuropein17 and hydroxy-tyrosol derivatives16b.

Pagan and Ibarz (1999), Plazzotta et al. (2020), Halenár et al. (2021), Vargas et al. (2017), Strati and Oreopoulou (2011)

Amygdalin: anticancer, antiinflammatory, treatment of hypertension, diabetes, respiratory diseases, leprosy, cerebral function, and cerebrovascular lesions. Antimicrobial, antioxidant, photoprotectants, and pro-vitamin A activity. Maintain a healthy digestive system. Food ingredient (non-traditional potential oil sources) Inhibit the release of the inflammatory mediator (NO) and pro-inflammatory cytokine (TNF-α). In cosmetic and food fields.

(continued)

Deng et al. (2012), Saavedra et al. (2017), Colombo and Papetti (2019)

Seker et al. (2010), Musa (2010)

Zamuz et al. (2021)

OMAR (2010), Ruiz et al. (2017), Visioli et al. (1998), Wang et al. (2020), Bu et al. (2007)

In vitro antioxidant activity and potential microbiota modulation. Lanatusosides (antitumor activity, antidiabetic).

Oleuropein: antioxidant, antiinflammatory, anti-atherogenic, anticancer, antimicrobial, antiviral, hypolipidemic, and hypoglycemic. Tyrosols: Antioxidant and neuroprotective. Nuezhenide: Anti-inflammatory (NF-κB pathway).

1 Introduction to Mediterranean Fruits Bio-wastes: Chemistry, Functionality. . . 13

Fruit

Guava

Melon

Strawberry

Persimmon

Plum

No.

17.

18.

19.

20.

21.

Seeds

Peel and Calyx

extrudate

Seeds

Peels

Seed

Peel

Nature of the waste

Table 1.1 (continued)

3a

Homogentisic acid , Catechin , and Epicatechin3b. Phenolic compounds (~37): Ellagic acid9 (major), Catechin3a, Galangin1f, and Homogentisic acid11b. Cyanidin 3-glucoside8, Gallic acid4a, Kaempferol1b, Flavonols3, and Condensed tannins35. Dietary fibers: (lignin34, cellulose46, hemicelluloses47, pectin48). Phenolics: Luteolin1e, Chlorogenic acid5b, Apigenin-7- Glycoside1d, β-Carotene21b. High level of polyunsaturated fatty acids (PUFA)42 (~63%), Phenolics Anthocyanins33, Quercetin-3glucoside1a, Ellagic acid derivatives9, Kaempferol1b, and Pelargonidin-3glucoside8b. Phenolics, condensed tannins (proanthocyanidins)35, Lycopene22, and β-carotene22b. Amygdalin29, Rutin1c, Epigallocatechin3c, Epicatechin3b, Ferulic acid6b, Syringic acid4c, Caffeic acid6c, and Coumaric acid acids11.

161b

Bio-active compound (structurea)

Conesa et al. (2019), Lee et al. (2006)

Antihyperglycemic (lipid metabolism and organ functions in STZ-induced diabetic rats). Amygdalin: antitumor. Antioxidant and antimicrobial.

Savic and Gajic (2021)

Vázquez-González et al. (2020)

Rolim et al. (2018, 2020)

Deng et al. (2012), Lima et al. (2019)

Reference

Antioxidant and antimicrobial

Prebiotic activities, production of sweets, high antioxidant capacity in vitro, and antiproliferative

Antioxidant and antimicrobial.

Potential use

14 D. M. Elimam et al.

a

Carob

kibbles

Seeds

Flavonols (quercetin1a and kaempferol1b), flavanols (catechins3a and procyanidins7), Gallic acid4a, hydrolyzable tannins31, Fatty acids (oleic44, linoleic45, and palmitic43), γ-tocopherol20, Sterols (β-sitosterol28b and Stigmasterol28a). Bio-oil (88%) from kibbles liquefaction at high temperatures. Anti-glycation activity, antioxidant, and antimicrobial, and bio-fuels.

Güzel et al. (2015), Santonocito et al. (2020), Mateus et al. (2019)

Superscript numbers and letters indicate the compound structure in Fig. 1.2, retrieved from PubChem online database

22.

1 Introduction to Mediterranean Fruits Bio-wastes: Chemistry, Functionality. . . 15

16

D. M. Elimam et al.

Fig. 1.2 Potential compounds isolated from MTD waste material

The phenolic compounds fall amongst the largest/most diverse biologically active groups. Structurally, they contain at least one aromatic ring and one hydroxyl group, ranging from simple phenolic to higher complex polymers (polyphenolics) (Ignat et al., 2011). Polyphenolics are classified into several classes: flavonoids, stilbenes, lignans, phenolic acids, and tannins. Deng et al. assessed the possibility of fruit wastes as a source of polyphenolics by systematically evaluating the total phenolic content and antioxidant capacities of 50 fruit wastes (rinds and seed). The outcomes revealed that wastes have disparate antioxidant potencies. Major compounds were cyanidin 3-glucoside, catechin, epicatechin, chlorogenic acid, gallic acid, homogentisic acid, and kaempferol flavonoid. Interestingly, many waste antioxidant capacities outweighed those of the used

1 Introduction to Mediterranean Fruits Bio-wastes: Chemistry, Functionality. . .

17

parts of the fruit, suggesting an economical (neglected) source of various active constituents (Deng et al., 2012). Such findings are not surprising, as such phenolics are the fruit 2ry metabolites that contribute to its physical properties (color and smell) (Naczk & Shahidi, 2006) and serve a defensive mechanism, which logically would be higher in skins (rinds as attractants) and seed (allelochemicals in future contact with the soil), (Mann, 1998; Popa et al., 2008). This supports the finding of Gorinstein et al. and Soong et al. who found the rinds of citrus fruits and grapes, and the seeds of avocados and other fruits contain >15% higher phenolic content than that of the used part (Gorinstein et al., 2001a, 2001b; Soong & Barlow, 2004). Citrus industrial processing generates waste of about 50% of the total fruit weight (Bocco et al., 1998). These by-products, if optimally recovered, will be the main resource of phenolic compounds. For example, banana peels were found to contain four folds the percentage of phenolics compared to its pulp, alongside catecholamines, dopamine, and L-dopa (González-Montelongo et al., 2010; Someya et al., 2002). Similarly, Li et al. reported pomegranate peels to contain ten folds the phenolic content of the pulp (Li et al., 2006). Date seeds were recognized as an outstanding resource of phenolic antioxidants (Al-Farsi & Lee, 2008). Besbes et al. extracted the date seed oil and described its high phenolic content among edible oils as the second most after olive oil (Besbes et al., 2005). Wolfe et al. found that dry apple peels contain phenolic compounds up to 3.3% w/w (Wolfe & Liu, 2003), while Schieber et al. reported about 10% w/w recovered phenolics from dry apple pomace (Schieber et al., 2003). Tomato by-product (pomace) presents about 4% of the fresh-fruit weight and consists of skin and seeds. Most of the principal carotenoid in tomato, lycopene (characteristic red color) confines mainly in the skin and is water-insoluble, which increase its loss during juice production (Baysal et al., 2000; Sharma & Le Maguer, 1996). Hence, extraction of tomato skin can lead to a maximum recovery of lycopene (around 50%) of the dry weight (Strati & Oreopoulou, 2011). The phenolic contents in various fruit wastes are briefly reviewed in Table 1.1 and Fig. 1.2.

1.8

Major Application Fields of MTD-Fruit-Waste

Fruit processing (pressing, canning, drying, and jams production) produces solid wastes (pomace, peels, and seeds) or liquid wastes (wash/chilling water/chemicals, and saps), which are highly prone to decay and fermentation, primarily due to high moisture content (>80%), sugars (>50%) and proteins (>20%) and able to cause significant environmental and economic risk. On the other hand, they encompass a significant amount of valuable materials such as dietary fiber, phenolics, pigments, organic acids, and oils, which can be retrieved and utilized in pharmaceutical manufacturing, food industries, and biofuel production (Campos et al., 2020). For instance, carotenoids from tomato peels (lycopene, red) and banana peels (xanthophyll, yellow) can be used as efficient and safe natural coloring agents, in addition to their beneficial health effects (Ho et al., 2015; Sharma & Le Maguer,

18

D. M. Elimam et al.

1996; Subagio et al., 1996). Medicinally, Carotenoids are considered pro-vitamin A, which provide immune-stimulant effects and protection against degenerative and cardiovascular disease. Moreover, they are potent antioxidants, photo-protectants, and gene activity modulators (protector against induced inflammation and neoplastic transformation) (Hix et al., 2004; Vu et al., 2018). Limonene, a flavoring/aromatic agent in perfumery, cosmetics, pharmaceutical manufacturing, and food industries, is essential oil isolated from citrus peels (John et al., 2017a, 2017b). The citrus peel oil is the richest source for limonene (up to 90%), standing as the principal industrial source (Craig, 2006). Additionally, limonene proved to have antimicrobial, antioxidant, analgesic, anti-inflammatory, gastroprotective, antineoplastic, and antidiabetic effects, along with other positive health effects (Vieira et al., 2018). Tannins, either hydrolyzable (mainly from pomegranate peel) or condensed (from persimmon pomace and guava seeds), are major valuable polyphenolics in fruit wastes. Industrially, tannins are used in leather/textile tanning and dying, inks (ferric-based), and as coagulators in rubber production. In food processing, they are used as an antioxidant preservative and participant to clarify fruit juices and liquors. Therapeutically they are used as astringents, haemostatic, anti-diarrhetic, anti-inflammatory, and antiseptic. In addition, tannins can be used as an antidote in heavy metals and several alkaloid oral poisoning to precipitate them. Recently, tannins are reported to have antiviral, antibacterial, and antitumor activities. High molecular weight ellagitannins (such as punicalagin, which is unique to pomegranate) were reported to have selective bacteriostatic/bactericidal activities, antioxidant, prebiotic (reservoir of valuable therapeutic agents, food preservatives, stabilizers, supplements, and probiotics). Casuarinin and corilagin were also reported to exhibit antiviral properties (Herpes simplex) (Akhtar et al., 2015; Khanbabaee & Van Ree, 2001). Flavonoids, natural polyphenolic compounds, are well recognized for their colors, flavors, aromas, and health-promoting effects, which established them as an indispensable component in medicinal, pharmaceutical, cosmetic, and nutraceutical applications. Anthocyanidins and their glycosides anthocyanins, the most widely spread class of flavonoids, are intensively colored compounds responsible for the red and blue colors in plants. They are abundant in grapes, strawberries, pomegranate, peach, persimmon. . .etc., mainly in the outer layer of the fruit (attractant). For example, the peels in pomegranate contain more than 30% of all fruit anthocyanidins content. Anthocyanidins and anthocyanins can change color depending on the pH (acid-base indicator) and are one of the 13 approved natural pigments in the European food industry (Akhtar et al., 2015; Dimitrić-Marković, 2007). Flavonoids have antioxidative, anti-inflammatory, antimicrobial, anti-allergic, anticancer, cell aggregation inhibition, anti-mutagenic, and radioprotective and their health-promoting activities in cardiovascular, neurodegenerative, osteoporosis, and rheumatological disorders. Flavonoids can modulate many essential cellular enzyme functions such as cyclo-oxygenase, lipoxygenase, xanthine oxidase, and phosphoinositide-3-kinas (Panche et al., 2016). Naringin, flavonoid glycoside

1 Introduction to Mediterranean Fruits Bio-wastes: Chemistry, Functionality. . .

19

containing Naringenin aglycon, is abundant mainly in grapefruit peels (and some oranges) and responsible for its bitterness (Izawa et al., 2010). Naringin exerts antiapoptotic, anti-diabetic, cytochrome P450 enzyme inhibition activities (Bharti et al., 2014). Hesperidin, flavanone glycoside with hesperitin aglycon, is dominant within oranges, ranging in sweet oranges, sour oranges, lemons, and tangerines (Yumol & Ward, 2018). Hesperidin proved to have protective effects against metabolic syndrome and associated diseases (Karim et al., 2021). Nobiletin and tangeretin, highly non-polar methoxylated flavonoids, demonstrated potent antineuroinflammatory in neurodegenerative diseases, especially Alzheimer’s and Parkinson’s diseases. Alongside their anti-inflammatory effects, they have been shown to act via several other mechanisms such as countering cholinergic deficiencies, decreasing neurotoxic amyloid-beta peptide’s abnormal accumulation, treatment of ischemic injuries, and modulation of various signaling cascades and receptor functions. Nobiletin demonstrated potential activity to treat bulbectomy-induced memory impairment (Ho & Kuo, 2014; Nagase et al., 2005). It is noteworthy that which is grapefruit potent cytochrome P450-3A4 (CYP3A4) inhibition activity is due to Furanocoumarins (Epoxybergamottin) rather than flavonoids (Wangensteen et al., 2003). Phenolic acids, free (rare) or bound (amides, esters, or glycosides), constitute about 30% plant phenols. They are categorized under two major groups, hydroxybenzoic acids (p-hydroxybenzoic, gallic, protocatechuic, vanillic, and syringic acids), either soluble (e.g., conjugated with carbohydrates) or embedded in the cell wall (e.g., bound with lignin); and hydroxycinnamic acids (caffeic, ferulic, and sinapic acids) in addition to coumaric acids (Ignat et al., 2011). Chlorogenic acid is the most abundant soluble hydroxycinnamic acid (caffeic acid with and quinic acids). Compared to hydroxycinnamic acids, hydroxybenzoic acids are generally found in low concentrations in red fruits. Phenolic acids have been used for improving the flavor, astringency, hardness, color in food industries. Also, they affect fruit maturation, prevent enzymatic browning, and act as food preservatives. Generally, caffeic (free/esterified) acids are the most abundant phenolic acids found in nearly all fruits (Dimitrić-Marković, 2007). For example, phenolic acids from watermelon peel have shown very potent in vitro antioxidant and potential microbiota modulation activities, while its phenolic glycosides (Lanatusosides C and D) were reported to have antitumor and antidiabetic activities (Zamuz et al., 2021). Avocado peel phenolic acids Inhibited the release of the inflammatory mediator (NO) and pro-inflammatory cytokine (TNF-α) (Colombo & Papetti, 2019). Additionally, cinnamic acid and benzoic acid esters in dates oil and other fruits sowed antifungal, acaricide, insulin-releasing, and hepatoprotective activities (Al-Farsi & Lee, 2008; Kumar & Goel, 2019; Lima et al., 2018; Sharma, 2011). Tyrosol derivatives (seco-iridoid glycosides) can be isolated in reasonable amounts from oil wastewater, pomace, and seed. Tyrosols have shown antioxidant and neuroprotective effects. Oleuropein is reported to have several pharmacological activities such as antioxidant, anti-inflammatory, anti-atherogenic, anti-cancer, antimicrobial, antiviral, hypolipidemic, and hypoglycemic effects (Omar, 2010). In

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addition, Nuezhenide showed potent anti-inflammatory activity through the NF-κB pathway (Wang et al., 2020). Amygdalin, the major component of Prunus family seeds such as apricots, peaches, plums, and apples, is a cyanogenic glucoside that contains benzaldehyde (analgesic effect) and a hydrocyanic acid (anticancer effect). It is reported to have anti-cancer, anti-inflammatory, antimicrobial (leprosy), hypotensive, and antidiabetic effects in addition to its role in the treatment of respiratory diseases (asthma, emphysema, and bronchitis), cerebrovascular lesions, and restoration of cerebral functions (Halenár et al., 2021). Pectin, polysaccharides commercially isolated from citrus peels and apple pomace, in addition to other potential sources as banana and melon peels, are extensively utilized as emulsifying, gelling, and thickening agents in food industries, cosmetics and pharmaceutical manufacturing and precursors in biofuel production (John et al., 2017a, 2017b; May, 1990; Raji et al., 2017; Schols & Voragen, 1996). Lignin, in addition to cellulose and hemicellulose, can be salvaged from lignocellulosic biomass as olive and peach kernels and banana peels. Carob kibbles acidcatalyzed liquefaction at high temperatures produces about 88% oil by its dry weight that can be utilized as bio-oils. Even though bio-oils have lower values than conventional diesel, they can be used as a fuel in diesel engines, turbines, and boilers for heat and electricity (Mateus et al., 2019). However, the most commercial application of lignin is bio-fuel valorization and other applications such as polymers (polyurethane foams) and polymer building blocks (aromatic monomers: phenol, benzene, toluene, and xylene). Also, lignin is an essential source of vanillin carbon fibers and wood adhesives (Manara et al., 2014). Cellulose is used directly (or after processing and refinement) in paper manufacturing and pharmaceuticals (Kamel et al., 2008). In addition, cellulose partial-hydrolysis produces organic acids, oligosaccharides (cellodextrin), and disaccharides (cellobiose) which are used in drug delivery systems (dendrimers) and raw material for cosmetics (Manara et al., 2014), while cellulose complete-hydrolysis into glucose monomers (saccharification) through microbial fermentation can be used to produce bio-fuel (ethanol) (Kareem & Rahman, 2013; Olsson & HahnHägerdal, 1996). The health benefits of dietary fiber (cellulose, hemicellulose, pectin, etc.) rely on which type has been consumed. For example, insoluble fibers (cellulose, hemicellulose) absorb water, thicken fecal mass and act as a bulk laxative (Medicine, 2001), while soluble fibers, on the other hand (e.g., pectin), is used to control body weight, lower cholesterol levels, chelate heavy metals, and stabilize blood pressure (Jitpukdeebodintra & Jangwang, 2009; Schols & Voragen, 1996). Interestingly, dietary fibers also have a pre-biotic capacity; in the colon, they are fermented by probiotic bacteria maintaining their beneficial action and producing secondary fermentation metabolites (e.g., short-chain fatty acids), which can induce apoptosis in colon cancer cells and produce diverse actions on gastrointestinal health. Furthermore, antioxidant molecules may be linked (glycosylated) to dietary fibers, which synergize their antioxidant capacity and act as a delivery system (gastric bypass

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conditions) to be released in the intestine, absorbed to exert an action (BenitoGonzález et al., 2019). Plant oils can be obtained from non-conventional sources. For instance, apricot seed encompasses more than 50% kernel oil with high contents of oleic, linoleic, and palmitic acids (Musa, 2010). On the other hand, melon seeds contain about 30% oil by dry weight, with oleic and linoleic acids as major fatty acids. Besides, the oils contain considerable amounts of phytosterols, flavonoids, and tocopherols, making them alternative oil sources that may serve as raw material for edible food/other industrial applications (Mallek-Ayadi et al., 2018). The structure and potential uses/ biological activities of different compounds isolated from fruit waste products are summarized in Table 1.1 and Fig. 1.2.

1.9

Anticipated Output and Potential Impact on the Economy and Environment

Fruit waste recycling is considered a practical approach to reduce food losses, which is considered a promising measure to enhance future food security and increase resource efficiency in food production. The successful, efficient crop-wastes valorization should decrease the animal feeding cost, increase farmer’s income, retrieve value-added products, and reduce environmental pollution. The losses affect many resources, for instance, freshwater, farming lands, and fertilizers. The waste reduction could decrease such environmental issues (Vilariño et al., 2017). The production of wasted food consumes about 250 billion m3 of water yearly (Mekonnen & Hoekstra, 2011), with approximately 25% of freshwater supplies (27 m3/person/ year) and 20% the fertilizers (4.3 kg/person/year) used in the production of crops. Also, 20% of farming land used is lost (1980 billion m2 per year) (Mekonnen & Hoekstra, 2011). Kummu et al. reported that North Africa, nearly half of the Mediterranean region, contributes the most to freshwater and farming-land losses (Kummu et al., 2012). Wasted crops also have climatic impacts; they account for about 8% of total world greenhouse gas emissions. Therefore, more inclusive waste management approaches play an essential role in the circular economy. According to FAO, the direct economic cost of 1.3 billion tons of lost food is about $1 trillion a year, with externalities of around $900 billion and environmental damages at around $700 billion (FAO, 2014). By any means, if crop wastes could be reduced to half, there would be enough food for roughly extra one billion individuals. Furthermore, the waste reduction would consequently decrease energy expenditure, greenhousegas emissions, soil degradation, and farming-land (which will protect natural forests and biodiversity) (Wadhwa & Bakshi, 2013).

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Aims and Features of the Book

This book aims to create a multidisciplinary forum of discussion on the biochemistry, functional properties, health-promoting effects of bioactive compounds in Med-Fruit-Waste, and the food and non-food applications of Med-Fruit-Waste. The book capitalizes mainly on the features of Med-Fruit-Waste, mainly from a food science perspective. Thus, the scientific fundamentals of the health-promoting benefits and applications of Med-Fruit-Waste will be unveiled. Furthermore, the book will review the relevant recovery issues and different techniques to develop new applications. In addition, the economy will be promoted by integrating MedFruit-Wastes into industrial activities (food production, pharmaceutical, livestock production, and cosmetic). The tentative book chapter submission has diverse developments in food science, environmental chemistry, and horticultural research. Therefore, the editors invited expertise and highly-cited researchers to write chapters with the major purpose of letting the readers of this book know more about this specific area of science. Each chapter covered the following main topics: (1) introduction and economic values of each discussed fruit waste, (2) chemical composition and bioactive compounds of waste extracts, (3) biological and functional properties of extracts and bioactive compounds from fruit bio-wastes, (4) food and non-food applications of extracts and bioactive compounds from fruit wastes, and (5) valorization of fruit waste for non-health purposes, i.e., source of bioenergy.

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Chapter 2

Potentials of Biowaste Carbohydrates in Gut Health Enhancement Marwa El-Hindawy

Abbreviations ASPS DON FOS GOS H2O2 HMOS HRP IECs IL-2 IL-4 IL-6 LPS NASH OBPS SCFAs TEER TLR4 TM TNBS TNF-α WJPS ZO-1

Acanthopanax senticosus polysaccharides Deoxynivalenol Fructooligosaccharides Galactooligosaccharides Hydrogen peroxide Human milk oligosaccharides Horseradish peroxidase Intestinal epithelial cells Interleukin 2 Interleukin 4 Interleukin 6 Lipopolysaccharides Non-alcoholic steatohepatitis Ommastrephes bartrami polysaccharides Short-chain fatty acids Transepithelial electrical resistance Toll-like receptor 4 Transmembrane 2,4,6-trinitrobenzene sulfonic acid Tumor necrosis factor-alpha Wild jujube polysaccharides Zonula occludens-1

M. El-Hindawy (*) Whistler Center for Carbohydrate Research, Purdue University, West Lafayette, IN, USA e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 M. F. Ramadan, M. A. Farag (eds.), Mediterranean Fruits Bio-wastes, https://doi.org/10.1007/978-3-030-84436-3_2

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2.1

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Barrier Function and Intestinal Permeability

Intestinal epithelial cells (IECs) compose the surface lining the gastrointestinal tract (GI) and are considered to be the largest barrier separating the inner mammalian content from the outside milieu (Turner, 2009). There are two basic ways to control selective transport by IECs (Anderson, 2001). One way is by modulating transcellular transport, facilitated by different and specific transporters for electrolytes, sugars, amino acids, and short-chain fatty acids (SCFAs). The second way is by modulating paracellular transport, which includes the passage through space between adjacent cells without entering the cells (Anderson, 2001). Thus, the intestinal barrier works as a discriminating mesh that allows the paracellular translocation of small dietary nutrients, including electrolytes and water molecules, into the bloodstream. In addition, the barrier protects against bacterial translocation and the passage of unsafe intraluminal toxins and antigens (Peterson & Artis, 2014). The paracellular route of selective permeability is regulated by intercellular protein complexes recruited alongside the lateral membrane junction (Bischoff et al., 2014). These protein complexes control the space between the adjacent cells and are divided into three ultrastructural proteins: adherens junctions, tight junctions, and desmosomes (Bischoff et al., 2014). Although adherent junctions and desmosomes are more important locations of intercellular connections that tie together adjacent IECs, tight junctions abundant on the apical membrane are thought to be the junctional complexes that seal the intercellular space and alter selective paracellular permeability (Antoni et al., 2014). The tight junction complexes include both transmembrane proteins (TM) and scaffolding proteins within the cytosol. The extracellular subunits of TM proteins, including occludins, claudins, tricellulin, and junctional adhesion molecules, interact with their adjacent counterparts either homophilically or heterophilically (Antoni et al., 2014). In addition, the intercellular subunits interact with scaffolding proteins, including zonulae occludens (ZO) and cingulin, to connect to the actomyosin ring. This allows the cellular cytoskeleton to alter and modulate the barrier to health (Fasano, 2011). Maintaining a healthy and integral barrier function is important to prevent infectious diseases (Natividad & Verdu, 2013). Increased permeability leads to increased bacterial translocation, which in turn promotes intestinal inflammation (Natividad & Verdu, 2013). Possible interactions between transferred bacteria and the host immune cells may promote autoimmune diseases such as multiple sclerosis and rheumatoid arthritis (Groschwitz & Hogan, 2009). In addition, impaired barrier function was associated with a systemic immune activation that may develop chronic viral infections and metabolic diseases (Groschwitz & Hogan, 2009). To avoid disease, it is critical to broadening the knowledge of IECs barrier function, specifically the tight junctions regulated at the transcriptional and post-transcriptional levels (De Santis et al., 2015). Nutrient sensing by IECs could be an approach to achieve better barrier function and avoid diseases.

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Regulation of Tight Junctions by Dietary Components

The dynamic nature of tight junctions explains their sensitivity to food components in the intestinal lumen (De Santis et al., 2015). Different nutrients’ regulation of intestinal barrier function was reported either by increasing or decreasing its permeability (De Santis et al., 2015; Lerner & Matthias, 2015). Amino acids such as glutamine and tryptophan have been shown to increase intestinal barrier function and reduce permeability (Rapin & Wiernsperger, 2010). Vitamin D and polyphenols such as quercetin and kaempferol enhance the expression of tight junctions and inhibit the dissociation of tight junction proteins after exposure to oxidative stress (Peterson & Artis, 2014). In contrast, compounds such as gliadin have been shown to reduce the barrier function dramatically. This effect is associated with the development of celiac disease (De Santis et al., 2015). In addition, Chitosan was reported to adversely regulate barrier function by altering tight junction distribution (Peng et al., 2009). Although butyrate enhances tight junction assembly, the influence of components such as medium-chain fatty acids is still controversial (Lerner & Matthias, 2015; Peng et al., 2009). Mechanisms through which these nutrients alter tight junction permeability include signal transduction pathways and regulatory cytokines (De Santis et al., 2015).

2.3

Carbohydrates and Intestinal Barrier Function

Few studies correlate the modulation of the epithelial barrier with dietary carbohydrates. Carbohydrates are a large group of molecules that differ in structure, digestibility, and physical and physiological effects on the GI tract. They account for 45–65% of the daily total calorie intake (Slavin & Carlson, 2014). Carbohydrates were first reported for their potential in barrier function protection by clinical groups questioning the efficiency of preoperative fasting, a procedure that had been practiced for a long time with elective surgeries (Diks et al., 2005). Although the procedure was amended by the late 1980s to allow drinking clear fluids up to 2 h before operations, preoperative fasting was not the best metabolic state for patients to face operation stress (Ljungqvist, 2004). Preoperative consumption of a carbohydrate-rich solution recovered impaired intestinal barrier function in rats undergoing major abdominal surgeries, indicated by reduced Horseradish peroxidase (HRP) flux from the mucosal to the serosal side epithelium (Bouritius et al., 2008; van Hoorn et al., 2005). In addition, reduced bacterial translocation to distal organs such as liver, kidney, and mesenteric lymph nodes was observed (Van Middelaar-Voskuilen et al., 2003). This is in accordance with the reduction of bacterial adherence to the intestinal wall in the presence of nutrients compared to in the fasting state (Nettelbladt et al., 1996). Although the correlation test did not show the dependency of bacterial translocation on barrier permeability to HRP (Van Middelaar-Voskuilen et al., 2003), these results suggest the role of carbohydrates in

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improving the intestinal barrier to both molecules and bacteria. Lower barrier permeability of molecules reduced endotoxins and lipopolysaccharides (LPS) transport and reduced the levels of downstream inflammatory agents such as tumor necrosis factor-alpha (TNF-α) and interleukin (IL)-2, IL-4, and IL-6 (Macintire & Bellhorn, 2002). Although these studies provide important information, less is known about the mechanisms by which carbohydrates with varying structures may improve the epithelial barrier.

2.3.1

Non-digestible Polysaccharides

Polysaccharides, as an important dietary component known as fibers, have been found to improve physiological and metabolic conditions such as hepatotoxicity, colitis, and obesity (Fan et al., 2013; Macintire & Bellhorn, 2002; Yang et al., 2014; Yue et al., 2014) and to have bioactive activities such as antioxidant, anticoagulant and anti-inflammatory activity (Fitton et al., 2015; Ramberg et al., 2010). However, few recent studies correlate polysaccharides with intestinal epithelial barrier integrity. The immunomodulatory and anti-inflammatory effects of Acanthopanax senticosus (also known as Siberian Ginseng) polysaccharides (ASPS) were extensively reported (Chen et al., 2011; Fang et al., 1985; Han et al., 2003). Han et al. (2016) were the first to report the regulatory influences of ASPS on intestinal barrier function. A well-optimized mouse model was used to model intestinal damage following injection by E. coli LPS. The model showed disrupted mucosal barrier function, distorted morphology, and defective digestive function by LPS. Pre-treatment with ASPS improved intestine morphology, increased the expression of tight junction proteins, and increased the number of goblet cells (Han et al., 2016). The mechanisms behind this effect are not fully understood, although an important role of the anti-inflammatory potentials of ASPS to downregulate inflammatory cytokines is proposed (Han et al., 2014). Another fucose-enriched sulfated polysaccharide known as fucoidan was reported to protect against hydrogen peroxide (H2O2)-induced intestinal barrier damage (Iraha et al., 2013). Fucoidan improved transepithelial electrical resistance (TEER) values in Caco-2 monolayers that were fully polarized, indicating that the promotion of epithelial cell proliferation is not the key factor of fucoidan effects. Instead, fucoidan may promote the expression and assembly of tight junction proteins. In addition, pre-incubation of Caco-2 monolayers with fucoidan prevented H2O2-induced injury of the cells’ H2O2-induced injury by reducing paracellular permeability and upregulation of claudin1 and claudin2. In another study, polysaccharides from squid ink of Ommastrephes bartrami (OBPS) were recommended as a potent bioactive polysaccharide that protects intestinal barrier function from oxidative stress-induced intestinal injury (Zuo et al., 2015). Mice that consumed OBPS for 25 days by oral gavage were more resistant to intestinal damage by intraperitoneally injected cyclophosphamide (Zuo et al., 2015), a commonly used therapeutic drug for cancer treatment (Emadi et al., 2009). OBPS induced

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Fig. 2.1 Wild jujube polysaccharides are protective against TNBS-induced colitis in the rat (Yue et al., 2015)

upregulation of myosin II expression, which is known to form a thick protein ring encompassing epithelial cells at the level of tight junctions and adherens junctions (Shen et al., 2006). In addition, claudin2, ZO1, E-cadherin, and many tight junction effector proteins were highly upregulated after OBPS pre-treatment. Polysaccharides from wild jujube, Ziziphus jujube (WJPS), showed potential to ameliorate intestinal barrier permeability in Caco-2 monolayers as well as in rats characterized with 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced ulcerative colitis (Yue et al., 2015). TNBS-induced colitis, which is similar to Crohn’s disease, showed lowered expression levels of claudin1, claudin4, occludin, and ZO1. However, the expression of these proteins was significantly increased to almost normal levels after administration of 80 mg kg 1 of WJPS for 10 days following colitis induction. As a result, the intestine morphology and function were significantly improved (Fig. 2.1). In addition, WJPS mitigated the adverse effects of TNF-α, an important mediator of Crohn’s disease, on Caco-2 monolayer barrier function.

2.3.2

Non-digestible Oligosaccharides

Non-digestible oligosaccharides are short polymers of simple sugars, usually between three to ten units long, and are considered natural components of the fiber portion of several foods. Recent studies (Cobb & Kasper, 2005; Vos et al., 2007) revealed the bioactive and biological capabilities of dietary non-digestible oligosaccharides such as human milk oligosaccharides (HMOS), broadly acknowledged for its immunomodulatory effects, as well as fructans [including inulin and fructooligosaccharides (FOS)] and galactooligosaccharides (GOS). Non-digestible oligosaccharides are consumed in the colon by commensal microbiota that ferments them, producing SCFAs, which are absorbed by the colon to provide energy and confer physiological benefits (Cobb & Kasper, 2005). In addition to their role in fermentation, cholesterol reduction, and bile acid release, these oligosaccharides

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induce anti-inflammatory, anti-tumor, and antioxidant activities (Cobb & Kasper, 2005; van Kooyk & Rabinovich, 2008). Except for few recent studies, the protective influences of non-digestible oligosaccharides on intestinal barrier function were not studied. The prebiotic effects (producing SCFAs through fermentation) of these oligosaccharides are the most extensively proposed mechanism to explain its ability to improve the intestinal barrier function. However, the use of cell culture systems, which use a microbial-free environment, to study the effect of GOS and FOS on intestinal permeability shed light on different fermentation-independent mechanisms, including cell sensation and its downstream signaling pathways. HMOS was found to interact with lectin proteins and specific intercellular cell adhesion molecules and affect T cells in vitro (Eiwegger et al., 2004; Naarding et al., 2005; Schumacher et al., 2006). Additionally, Shirai et al. (2013) demonstrated that different molecular structures of FOS affect intestinal barrier function differently. Kestose, a prebiotic FOS component composed of glucose-fructose-fructose, dosed at 1% (w/v) reduced intestinal permeability and stimulated restoration and reassembly of tight junction proteins in Caco-2 monolayers following a calcium switch assay (Shirai et al., 2013). Weaker effects by nystose, composed of glucosefructose-fructose-fructose, were observed, indicating the presence of an accurate level of cell sensing. It was proposed that the myosin-light chain dephosphorylation pathway drove kestose influences, indicating the existence of apical Caco-2 sensing machinery for kestose. Interestingly, kestose also significantly increased stimulation of bifidobacteria growth more than nystose both in vitro and in vivo using gnotobiotic mice (Suzuki et al., 2006). Akbari et al. (2015) showed a preventive effect of GOS on distorted intestinal epithelium barrier due to exposure to the fungal mycotoxin, deoxynivalenol. They reported that 2% GOS in cell culture media accelerated the recovery of Caco-2 monolayers and reduced the paracellular flux following a calcium switch assay. This quick recovery was shown to be due to a faster rate of tight junction protein assembly, specifically improved cellular localization of claudin3 in the cellular membrane. In addition, 2% GOS in mice diets improved the epithelium barrier and ameliorated the defects in the intestinal morphology observed after deoxynivalenol toxicity (Fig. 2.2). Results from the studies outlined above strongly suggest that oligosaccharides may be sensed at the intestinal epithelium to stimulate direct receptor-mediated effects that protect intestinal barrier function (Akbari et al., 2015).

2.4

Mediterranean Fruit Biowaste Sources for Increased Gut Health

As described in previous sections, non-digestible carbohydrates are showing great potentials for gut health applications. Some of the non-Mediterranean well-known sources that had been investigated, such as Siberian Ginseng and Wild Jujube are

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Fig. 2.2 Galactooligosaccharides prohibit deoxynivalenol-induced overexpression of claudin3 and maintain its normal distribution in the mouse intestine. Immunofluorescence photomicrographs of mouse distal small intestine stained for claudin3 (Akbari et al., 2015)

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reviewed. Less research was performed on Mediterranean fruits as a source of ingredients beneficial for gut health. The large amount of biowaste produced from different Mediterranean fruit industries drives the need for research investigating possible useful applications to valorize these biowastes. One of the major valorization strategies is the extraction and purification of phytochemicals from Mediterranean fruit biowaste. On the other hand, the bioactivity of the dietary fiber content in Mediterranean fruit biowaste is still underestimated, although few recent studies turned the attention toward it. Here, we shed light on three biowaste candidates that could be prolific sources for dietary fiber with functional attributes in food for gut health applications.

2.4.1

Apple Pomace

Apple is always linked with good health indicators. For example, it is known for its high potentials in reducing the risk of cancer and its cholesterol-lowering benefits. Although different studies reported that these health benefits conferred by apple consumption are attributed to its high phenolic content (Nagasako-Akazome et al., 2005; Nagasako-Akazome et al., 2007; Ravn-Haren et al., 2013; Ravn-Haren et al., 2018) indicated that the effective dose used in Nagasako-Akazomeet et al. studies are far above the realistic human intake of polyphenols through apple consumption. In the same context, Skinner et al., 2019 showed that apple pomace reduced dietinduced non-alcoholic steatohepatitis (NASH) in growing female Sprague-Dawley rats (Skinner et al., 2019). Therefore, it is recommended that health benefits related to modulating plasma cholesterol and lipid metabolism are more likely to be attributed to the fiber content in apples, with apple pomace as an excellent source for these fibers. In the apple juicing and cider pressing industry, the generated wet pomace represent up to 25% of the fresh fruit weight (Waldbauer et al., 2017). In addition, the pomace is fecund with bioactive compounds known for its health benefits. Of these compounds, dietary fibers represent the largest part per weight of dry apple pomace. Sato et al. (2011) averaged the dietary fiber content of apple pomace from 11 different apple cultivars to be around 43.6% (Sato et al., 2011). In a recent study, Dufourny et al., 2021 evaluated the incorporation of apple pomace into piglets postweaning diet. They showed that 4% apple pomace in the diet is a promising weaning strategy to maintain a healthy gut. In addition, intestinal morphology was significantly improved in piglets receiving 4% apple pomace and showed a higher ileal ratio villus length/crypt depth compared to piglets receiving 0% and 2% apple pomace. Moreover, 4% apple pomace increased the gut microbial richness and the bacterial profile (Dufourny et al., 2021). Fiber fermentation by the commensal colonic microbiota is an important mechanism through which apple pomace fibers could modulate gut health. Ravn-Haren et al., 2018 reported that apple pomace improved gut health in Fisher rats through

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higher production of SCFAs, indicating elevated caecal fermentation (Ravn-Haren et al., 2018). The three major SCFAs (acetate, propionate, and butyrate) increased with pomace consumption. In addition, apple pomace promoted a statistically significant increase in butyrate production, indicating microbial switch toward butyrate-producing populations. Butyrogenic bacteria were previously reported to be enriched by apple pectin consumption in rats (Licht et al., 2010). In addition, butyrate production by fermentation is directly linked to improved gut health as SCFAs are the main energy sources of colon epithelium cells (Roediger, 1982).

2.4.2

Olive Pomace

Although the fact that the largely produced quantities of olive pomace were considered an environmental problem (Khdair, 2020). Potentials and opportunities of using it as a rich source of bioactive materials are quickly expanding. Different extraction processes of phytochemicals from olive pomace were recently optimized (Cea Paze et al., 2019; Chanioti et al., 2021; Gómez-Cruz et al., 2020; Macedo et al., 2021). These phytochemicals can improve dietary overall nutritional value when added as a supplementary ingredient. However, targeting the bioactive dietary fiber content of olive pomace for health applications is not extensively studied. Ribeiro et al. (2021) used an in vitro simulated gastrointestinal digestion approach to evaluate the potential effects of olive pomace on gut health. Data showed that both olive pomace powder-derived fractions, liquid-enriched powder (rich in phenolics), and pulp-enriched powder (rich in insoluble fiber) induced higher short-chain fatty acid production after 48 h fecal fermentation. In addition, the fiber-rich fraction showed significant inhibition against pathogenic mucin-adhesion, specifically against Listeria monocytogenes (20%) and Bacillus cereus (22%) (Ribeiro et al., 2021). Regarding intestinal permeability, a recent study investigated the effect of supplementing the young chicken diet with olive pomace extract on improving intestinal barrier function. It was shown that short-term fasting of young broiler chickens could induce leaky gut and significant downregulation of Claudin-1 and increased levels of inflammatory biomarkers through the TLR4 pathway. However, supplementation with 500 ppm olive pomace extract ameliorated these adverse effects (Herrero-Encinas et al., 2020). In addition, bioactive compounds of olive pomace have shown immunomodulatory effects in broiler chickens, pigs, calves, and fish by reducing the production of pro-inflammatory cytokines and increasing the anti-inflammatory cytokines (Gisbert et al., 2017; Herrero-Encinas et al., 2019; Liehr et al., 2017; Morrison et al., 2018).

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Pomegranate Peel

Pomegranate fruits contain up to 60% of their weight as peels (Ismail et al., 2012). Pomegranate peels are popular fruit biowastes popular for their benefits ranging from fighting ache and pimples (Karray et al., 2021) to fighting cancer (Ahmadiankia et al., 2018; Bagheri et al., 2018). Recently, pomegranate has provided favorable therapeutic properties in various gastrointestinal diseases, making it an increasingly attractive source of bioactive components (Parisio et al., 2020). Most of the available studies investigating pomegranate peel health benefits attribute it to the antioxidant and anti-inflammatory effects of its content of phenolic compounds (Gullón et al., 2020). However, pomegranate peels are a rich source for bioactive polysaccharides, with pectin considered to be the major polysaccharide accounting for up to 25% (Talekar et al., 2018). Furthermore, Wu et al. (2019) showed that pomegranate peels polysaccharides confer immunomodulatory effects in immunosuppressed mice, making it possible valuable adjacent immune-potentiating therapy as well as possible immunostimulant food additive (Wu et al., 2019). In a recent study of the antiparasitic effect of pomegranate peels extract, El-Kady et al. (2021) showed that pomegranate peels extract effectively protects against intestinal Giardia lamblia infection in rats, restores villi structure, and halts the apoptotic cell death program in treated intestinal cells (El-Kady et al., 2021). In addition, Eid et al. (2021) reported that including 4% of pomegranate peel powder in the diet of laying hens significantly reduced the impact of oxidative stress induced by dexamethasone on the body weight and egg production (Eid et al., 2021). Moreover, pomegranate peel flour ferment by colonic microbiota promotes SCFAs release, suggesting another mechanism in promoting health benefits (Gullon et al., 2015). Taken together, different mechanisms are linked to the observed bioactivity of pomegranate peels. However, the role of its fiber content in general and pectin, particularly in modulating gut health, needs to be investigated.

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Part II

Olive Bio-wastes: Chemistry, Functionality and Technological Applications

Chapter 3

Olive Fruit by-Products: From Waste Streams into a Promising Source of Value-Added Products Trabelsi Najla, Mariem Habibi, Maryem Hadj Ammar, Leila Abazza, and Ridha Mhamdi

Abbreviations DMF OF OMWW OP OSks OSts POC

3.1

multi-phase decanters Olive Fruit Olive Mill waste water Olive Pomace Olive Skins Olive Stones Patè Olive Cake

Olive oil Industry and Olive Biomass Residue

The major olive items are tabled olives and olive oil, which are essential ingredients in healthy nutrition, and the Mediterranean diet. The phenolic compounds, which display antioxidant activity, make olive oil a key ingredient in human consumption. Tyrosol, oleuropine, caffeic acid, vanillic acid, and hydroxytyrosol are the most common phenolics found in olive oil (Sygouni et al., 2019). Due to the rising T. Najla (*) · L. Abazza · R. Mhamdi Laboratory of Olive Biotechnology, Center of Biotechnology of Borj-Cédria, Hammam-Lif, Tunisia e-mail: [email protected] M. Habibi · M. H. Ammar Laboratory of Olive Biotechnology, Center of Biotechnology of Borj-Cédria, Hammam-Lif, Tunisia Faculty of Sciences of Bizerte, University of Carthage, Zarzouna, Tunisia © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 M. F. Ramadan, M. A. Farag (eds.), Mediterranean Fruits Bio-wastes, https://doi.org/10.1007/978-3-030-84436-3_3

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demand for olive oil worldwide due to its nutritional, antioxidant, cardiovascular, and cosmetic properties, olive oil production has steadily increased over the last few decades. This increase caused an undesired side-effect; in fact, the quantities of the by-products of the olive oil industry have also increased significantly, mainly due to the modification of the old batch press system for modern olive oil production processes based on continuous centrifugation (Gómez-Caravaca et al., 2017).

3.1.1

Kinds of Olive Oil Industry Machines

The extraction of olive oil separates and extracts the oil in the olive drupes from the other fruit contents. It requires various steps, such as removing leaves, olive washing, grinding, pounding, and oil separation. Olive crushing, malaxing of the resulting paste, and isolation of the oily phase is the mechanical processes used to extract olive oil from the olive fruit. Three different systems are commonly used in the most recent one: the traditional discontinuous press process, the three-phase, and the two-phase decanter centrifugal methods where olive should be crushed to a fine paste with different types of crusher. The amount and physicochemical properties of the waste and effluent produced depend on the extraction method used (Perri et al., 2012; Servili et al., 2012; Souilem et al., 2017). 3.1.1.1

Discontinuous Pressing Process

Nearly until around 30 years ago, all olive oil was obtained by the discontinuous pressing processes (Fig. 3.1). This traditional olive-presses is essentially composed of a large, cylindrical millstone fixed with an upper milling-stone used to crunch the olive fruit. After grinding, the olive paste is spread onto fiber discs, which are stacked on top of each other and then put in the press. To compress the solid fraction of the olive paste and percolate the liquid fraction, pressure is exerted on the discs (oil and vegetation water). To easily separate the oil from the other phases, a small amount of water is applied. A solid residue called olive pomace (olive cake) and an emulsion containing olive oil, separated by decantation from the remaining

Recepon of olives

Crushing using cylindrical millstone

Olive paste is spread onto fiber discs

Pressure extracon

Olive pomace

Seling

OMWW

Olive Oil

Fig. 3.1 Different steps of discontinuous pressing process of olive oil extraction

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OMWW, are obtained by the press extraction process. This process, from which OP and OMWW are developed as by-products, offers inexpensive equipment and technological simplicity. A small volume of OMWW (40–60 L/100 kg olive) is created because a small amount of water is added. However, it also has drawbacks, such as process discontinuity, which exposes the olive paste to oxygen and light, in addition to the elevated labor costs (Skaltsounis et al., 2015). Over the years, the olive oil extraction method has experienced profound changes due to discontinuous production and high management costs (Caponio et al., 2018).

3.1.1.2

The Continuous Centrifugation Process

The continuous extraction methods replaced the conventional pressing process progressively in the 1970s, which have been done mainly for economic and realistic purposes. To isolate all the steps by centrifugation, the continuous olive oil extraction process uses a horizontal centrifuge (decanter). The variations in the olive paste constituents’ density are dependent on (olive oil, water, and insoluble solids). Decanters may act either as three-phase or two-phase systems, with minor modifications.

Continuous Three-Phase Decanter At the centrifugation phase, the continuous three-phase decanter process (Fig. 3.2) includes the addition of warm water (1.25–1.75 times more compared to the press extraction), yielding a greater volume of OMWW (80–120 L/100 kg olive). Much like the pressing system, the three-phase system produces three fractions: a solid residue (OP, 30%) and two liquid phases (oil, 20%, and OMWW, 50%). The extraction is carried out in two steps. The first one consists of a separation of the Addion of water

Recepon of olives

Preliminary treatment

Crushing

Kneading

3-phase centrifuge extracon

Oil

Dried

pomace

Olive mill

waste waters

Fig. 3.2 The continuous extraction systems of olive oil with three-phase centrifugation

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solid (pomace)/liquid phases (pomace/oil and wastewater), which are carried out by centrifugation with a horizontal axis. The second step is to separate the liquid/liquid phases (oil/wastewater) by centrifugation with a vertical axis. The products resulting from this process are oil, wastewater, and pomace. The three-phase method of olive mills is an intensive water process that generates an enormous quantity of polluted effluents commonly referred to as OMWW (di Lecce et al., 2014). This system provides numerous benefits, such as full automation, improved oil quality, and smaller areas, but requires more costly installation, higher water and energy usage, and higher outputs from OMWW. The triphase system is still the most commonly used method for producing virgin olive oil despite its high water consumption, particularly in countries where significant amounts of olives are produced in a short time. The continuous extraction system with three-phase centrifugation whose three phases are oil, wastewater, and pomace.

The Two-Phase Extraction In the 1990s, the two-phase extraction method (decanter) was developed to decrease OMWW volume and reduce phenol washing (Fig. 3.3). The olive paste is separated into two phases using this technology: olive oil and pomace. The semi-solid by-product (a mixture of olive husk and OMWW) can be reprocessed to increase olive oil extraction yields the olive pomace developed using this method. Due to the reduction of water use, two-phase systems have been described as environmentally friendly. Due to the high concentration of their pollutant load, however, the resultant oil pomace (10 L/100 kg olive) is hard to control (Skaltsounis et al., 2015). During the production of olive oil using a two-phase method, semi-solid waste (65% moisture) is made, which is called a solid waste olive mill or "two-phase olive pomace" or “alperujo”. The treatment of waste from two-phase systems, on the other hand, poses major problems due to moisture (65%, w/w) and carbohydrate concentrations characterizing this type of waste (Sygouni et al., 2019).

recepon of olives

Preliminary treatment

kneading

Crushing

leaf removal wash

2-phase centrifuge extracon

Olive Oil

Wet pomace

Fig. 3.3 The continuous extraction systems of olive oil with two-phase centrifugation

3 Olive Fruit by-Products: From Waste Streams into a Promising Source. . . Recepon of olives

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Preliminary treatment

Malaxage

Crushing

Separaon of oil using Mul-phase decanters (DMF)

Olive Oil

Wet Pomace (Pâté) without stone

Dried Pomace with stone

Fig. 3.4 Multi-phase decanters (DMF) extraction system of olive oil

The Multi-Phase Decanters (DMF) In the oil field, a new feature of the centrifugal extraction method is the multi-phase decanters (DMF) that operate without adding water for processes and with the advantage that a dried pomace and a by-product called ‘pâté’ (Fig. 3.4) are recovered without traces of stone, made from pulp and vegetation water (Lanza et al., 2020). The revolutionary two-phase decanter, called Leopard, has recently been produced by the Pieralisi Group S.p.A. It also separates the paste (pulp) from the husk after the malaxation stage, thereby reducing the oxidation process. This husk is also dehydrated, similarly to one obtained from three-phase decanters (Cecchi et al., 2019; Cedola et al., 2017; Lanza et al., 2020).

3.1.2

Olive Biomass Residue

3.1.2.1

Olive Wood and Leaves

Large amounts of waste, including leaves and olive tree wood, are produced at the initial steps of the olive oil production process. Olive leaves are agricultural by-products collected during the process of processing fruit (Şahin & Bilgin, 2017). Since ancient times, olive tree leaves have been used for various purposes, especially to promote health and preservation. Antioxidant, anti-hypertensive, antiinflammatory, hypoglycemic, and hypocholesterolemic properties are defined. Most of these properties are due to their high bioactive compound content (Roselló-Soto et al., 2015). Also, olive wood is an interesting and abundant source of antioxidants, especially polyphenols that can be used as food additives and/or nutraceuticals for the food and pharmaceutical industries (Ghanbari et al., 2012).

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Olive Fruit Bio-Waste

The olive fruit (OF) is composed of three parts: epicarp (skin), mesocarp (pulp), and endocarp (stone). The olive skin is covered with wax; during the growth phase, the skin color changes from light green to purple and black. The pulp accounts for between 84% and 90% of the total fruit mass. The stone may differ from 13 to 30% of fruit weight and contains 2–4 g oil/100 g. Olive fruit weight varied from 2 to 12 g, though some varieties can weigh as much as 20 g (Ghanbari et al., 2012). The mean composition of OF is constituted of 50% water, 1.6% protein, 22% oil, 19% carbohydrate, 5.8% cellulose, 1.5% inorganic substances, and 1–3% phenolic compounds. Other important compounds present in olive fruit are pectin, organic acids, and pigments (Ghanbari et al., 2012). The extraction of olive oil is done exclusively by mechanical techniques that consist of crushing the fruit to allow the oil release. As a result of olive processing, a vast quantity of olive by-products are produced.

Olive Skins (OSks) Olive skins are obtained from dry pomace and corresponding to the light fraction, rich in oligosaccharides, mannitol, phenols, and triterpene acid (mainly oleanolic and maslinic acids). Pentacyclic triterpenes present in olive skins presented several biological activities such as antiproliferative, anti-inflammatory, antiarthritic, antidiabetic, antiparasitic, antimicrobial, antiviral, anti-cancer, and hepatoprotective (Fernandez-pastor et al., 2017).

Olive Stones (OSts) Olive stones are lignocellulosic materials obtained as by-products of both the olive oil industry (crushed pits) and table olive industry (whole pits), representing about 10% of the weight of the olive fruits and seeds (Gullón et al., 2020). OSs are a good source of proteins, lipids, phenols, free sugars, and phenolics. In fact, OSs are mainly composed by cellulose (28.1–40.4%), hemicelluloses (18.5–32.2%) and lignin (25.3–27.2%), in addition to salidroside (tyrosol-glucose), nuezhenide (glucoseelenolic acid-glucose-tyrosol) and nuezhenide-oleoside. These by-products also contained polyunsaturated fatty acid (PUFA, mainly linoleic acid), oligosaccharides, fermentative sugars, and phenolics (Gullón et al., 2020).

Olive Pomace (OP) OP is a semi-solid paste and heterogeneous biomass with high moisture and oil content, depending on the cultivation area and the extraction method. It is the most important waste produced by agro-industry due to the production of the continuous

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phase of olive oil. The high content of phenolic compounds in OP pomace (phytotoxic) is reported as an environmental threat (Antónia Nunes et al., 2019; Nunes et al., 2016). This by-product is composed of a fibrous portion of the fruit, stone, 5% residual oil, and a quantity of water ranging from 25 to 30% using a pressure oil extraction device (traditional method), 50–55%, 55–70%, and 50% using a "threephase," "two-phase" and "water-saving" centrifugation system, respectively (Regni et al., 2017). In addition to water, OP contained different inorganic compounds and has a median pH of 4.8–5.2. The composition depends on the fruit’s intrinsic factors, such as variety and maturation stage (M’Sadak et al., 2015). Besides, OPs obtained from the 3- and 2-phase systems differ significantly by their percentage of humidity, residual oil, and bio-phenolic. These parameters are in the following range for the three-phase pomace: humidity 45–55%, oil 3.5–4.5%, and phenolic compounds 200–300 mg/100 g, while the ranges in the two-phase pomace are: humidity 65–75%, oil 3–4%, and phenolic compounds 400–600 mg/100 g (Milczarek et al., 2019). Concerning total phenolic content, the amounts obtained by the three-phase method was higher (24% w/w on a dry basis) than those obtained by the two-phase (20.4% w/w on a dry basis). In terms of mineral content, OP is mainly constituted by potassium (P), calcium (Ca), and sodium (Na) (Paulo & Santos, 2020). Besides, PO water is an excellent source of high added value compounds such as phenolics, carbohydrates, and proteins. The main phenolic compounds in the OP are hydroxytyrosol, oleuropein, tyrosol, caffeic acid, p-coumaric acid, vanillic acid, verbascoside, elenolic acid, catechol, and rutin (Ghanbari et al., 2012). Besides, OP provides a typical composition of lignocellulose biomass, including ligni6n (30.0–41.6%), cell wall polysaccharides (35.3–49.0%) as cellulose, pectic polymers, and hemicelluloses (xylans, glucoroxylans, xyloglucans, and manans) (Gullón et al., 2020). After centrifugation, the residual paste is still rich in oil (approximately 12–15% of total oil), which is removed through the second centrifugation method (Gullón et al., 2020; Mateos et al., 2019). This oil, along with that obtained by extracting hexane from a paste-like by-product called "alpeorujo" or "alperujo," corresponds to the crude oil of olive pomace (OPO). To extract compounds responsible for undesirable colors and flavors and compounds affecting oil stability, raw olive-pomace oils need chemical refining. Refined olive pomace oil obtained by refining crude olive pomace oil is blended with a sufficient amount of virgin olive oil (approximately 10%), resulting in commercially available olive pomace oil (Clodoveo et al., 2015). With its high nonounsaturated fatty acids (MUFA), OPO is recommended to be an exciting alternative to reach the recommendation to consume 20% of total dietary energy in the form of MUFA, with the total fat intake representing up to 35% of the total caloric value of the diet. Besides, OPO contains an important of minor bioactive molecules exhibiting health potentials such as pentacyclic triterpenes, aliphatic fatty alcohols, sterols, Tocopherol, squalene, and phenolic compounds (Fig.3.5) (Mateos et al., 2019).

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(1) Hydroxytyrosol

(2) Tyrosol

(4) Oleuropein

(6) Apigenin

(3) Oleocanthal

(5) Verbascoside

(7) Oleanolic acid

(9) Squalene

(11) Oleic acid

Fig. 3.5 Main bioactive compounds of olive bio-wastes

(8) Maslinic acid

(10) Tocopherol

(12) Linoleic acid

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Olive Mill Waste Water (OMWW) OMWW is generated in the form of a liquid of dark red to black color from threephase extraction systems characterized by an acidic pH between 4.2 and 5.9, saline toxicity translated by high electrical conductivity, and a large load of organic pollutants (Skaltsounis et al., 2015). OMWW may use starch, phenolic, polyalcohol, lipids, and pectin to contain various bio-compounds that inhibit bacterial activity and make it phytotoxic (Nunes et al., 2016). It also contains organic substances, including olive pulp, carbs, mutyles, lignin, tannins, lipids, and inorganic and other suspended components in a reasonably stable emulsion. OMWW contains a high level of carbohydrates, proteins, fatty acids, carotenoids, tocopherols, pectins, mucilage, lignin, tannins, lipids, and inorganic substances. Remarkably, this residue has a high phenolic content (up to 53% of the phenolic content in olive fruit) due to the high solubility of these compounds in water. Their concentrations vary between 0.5 and 2.4 g/L. During oil extraction, hydrolytic enzymes of olive secoiridoids, oleuropin, and ligstrosides allowed to obtain many of these phenolic compounds. Most of them are hydrophilic and therefore remain in the water when served during olive oil processing (Milczarek et al., 2019; Sedej et al., 2016). On the other hand, the sediment that settles at the bottom of the olive oil tanks during the oil storage before commercialization is another by-product generated in the olive oil mills. It consists mainly of fat and water and intended to refrain or make soap (Romero et al., 2017).

Olive Paste: Patè Olive Cake (POC) POC obtained with the multi-phase decanters (DMF) consists of a semi-solid olive cake with the pulp of olive, olive skin, and wastewater of the olive mill. The POC contains fatty acids (palmitic acid, oleic acid, and PUFA) because of the remaining olive oil (8–12%). It also includes triterpenic acids (principal oleanolic acid) and other phenolic compounds, including hydroxytyrosol, tyrosol, derivatives of secoiridoids, verbascoside, and other phenolic acids (Fig.3.5). Carotenoids and lignans in POC are also found (Tufariello et al., 2019). Olive paste is known to be a potentially cost-effective starting material rich in phenolic compounds, which can be extracted and used for food and pharmaceutical applications (Cedola et al., 2017). It is potentially ideal for multiple applications, including animal feeding, and in the form of food supplements or food additives for human consumption (Cecchi et al., 2019). Oversaw the setting, management, and disposal of OP and OWW throughout the years, several Olive Oil By-Products uses, namely its integration in low organic matter soils or feeds, were considered to resolve this problem. The recovery of phenolic compounds from such waste has significant potential as antioxidants for food and/or the nutraceutical industries (Araújo et al., 2015). The use and recycling of olive biomass as new resources can motivate a circular and sustainable economy.

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This requires knowledge regarding residue characteristics and properties for different applications (Romero et al., 2017).

3.2 3.2.1

Olive Bio-wastes Applications Food Applications of Olive Wastes

Natural antioxidants extracted from agri-food wastes are more demanding than synthetic ones. With the availability of modern green technologies, researchers have been established new concepts, allowing for effective utilization of bio-wastes of the agri-food sector towards creating value-added products (Ben-Othman et al., 2020). In this context, some studies have been led to extract bioactive molecules from olive by-products. These antioxidant molecules will be added to vegetable oils to increase their shelf life because it is well known that oils rich in unsaturated fatty acids are more susceptible to oxidation (Difonzo et al., 2020). Orozco-Solano et al. (2011) have tested the oxidative stability of edible vegetable oils: a high oleic sunflower oil (HOSO) with added phenolics extracted from olive pomace in comparison with the same oil, not enriched or enriched with dimethylsiloxane and with extra virgin olive oil (EVOO), with 400 μg mL 1 of phenolics naturally present. They found that the enriched HOSO was more resistant to oxidation even than EVOO. Indeed, during the heating process, the degradation curve of hydroxytyrosol and secoiridoid derivatives was more marked in EVOO. Abd-ElGhany et al. (2010) confirmed these findings and showed a significant decrease in sunflower oil deterioration enriched with olive waste cake extract during the forced heating process at 180  C. Romeo et al. (2020) studied the enrichment of sunflower oil with phenolic extracts from OMWW containing hydroxytyrosol, tyrosol, verbascoside, apigenin, oleuropein, p-cumaric acid, vanillic acid, cafeic acid, chlorogenic acid, and luteolin. This addition allowed the production of an improved oil with higher bio-phenol contents and antioxidant properties for up to 90 days of storage at two tested temperatures. As compared to the control, this result displayed an enhancement of 50% of the enriched oil’s oxidative stability. Thereby, olive pomace and waste water’s suitability as raw material to extract bioactive compounds offers an excellent alternative to using olive-tree materials different from the leaves. The enrichment of refined edible oils with natural antioxidants from olive bio-wastes is a sustainable strategy to benefit from this residue (Abd-ElGhany et al., 2010; Orozco-Solano et al., 2011; Romeo et al., 2020). Today, the consumer is more demanding, selective, and strategic in the choice of his diet. Thus, consumers increasingly demand foods rich in natural antioxidants. In this context, researches were being carried out to study the use of olive pomace or its phenolic extracts to develop potential applications as food antioxidants. Recently, a new by-product Patè Olive Cake (POC) obtained by multi-phase decanter with DMF technology was used to study the possibility to add it in some food products (Cecchi et al., 2019; Cedola et al., 2017; Tufariello et al., 2019). POC is essentially composed

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of water, olive pulp, and olive skin and is rich in valuable bioactive compounds. Moreover, it still contains about 8-12% residual olive oil. Cedola et al. (2017) have enriched fish burgers with dry olive pomace flour (DOPF) characterized by the high total content of phenolics, flavonoids, and consequently high antioxidant capacity. The results showed improved fish burger quality with the DOPF enrichment and proved the decrease in the sensory attribute. For this reason, to reduce the bitter defect of phenolic compounds, a pretreatment of DOPF with water or milk was considered before their addition to the burger’s formulation. This pre-treating signs amended the burger sensory quality by reducing the concentration of bitter components. On the other hand, POC was used to fortify pasta, bread, and a granola bar. The descriptive analysis showed that the appearance of pasta was strongly affected. Indeed, the color and evenness of the color of enriched pasta differed from the control. Besides, a decrease of ‘eggy’ flavor and increase of olive oil, earthy, and wheat flavors were underlined. The presence of bio-phenols had especially no significant effect on bitterness and a very low impact on taste attributes. The texture was also changed, and, except for stickiness, fortification has increased astringency, dryness, and firmness. Regarding the effect of POC addition on bread and granola bar, the intensity of aroma and flavor attributes was slightly increased by pâté, with earthy as the most discriminating attribute. Nevertheless, color, color intensity, and bitterness were the most affected attributes by the presence of pâté. Despite this change, about 30% of consumers choose the fortified sample over each food control. Besides, 50% were willing to pay more for the fortified products (Cecchi et al., 2019). Worldwide, yogurt is an important dairy food product, which is the most popular functional drink. Aliakbarian et al. (2014) added phenolic compounds extracted from olive pomace into fermented milk using co-culture Streptococcus thermophilus and Lactobacillus acidophilus to obtain a probiotic food. The results showed that the enriched yogurt contained higher total phenolic content and exhibited an important antioxidant activity than the control one. Polyphenols did not interfere with the fabrication process and slightly reduced during storage. The number of viable, functional microorganisms showed a similar tendency in both fermented milks until 28 days.

3.2.2

Feed Uses of Olive Bio-Wastes

The consumption of an enriched diet with meat-producing animals can influence fresh meat’s oxidative status and stability during storage. These compounds, particularly hydroxytyrosol, are effective free radical scavengers in humans and they may retard lipid oxidation in meat products (Branciari et al., 2016; King et al., 2014; Munekata et al., 2020; Roila et al., 2018). Roila et al. (2018) found that OMWW bio-phenols used in chicken diets could delay meat lipid and protein oxidation without influencing its color stability. However, to better clarify these compounds’

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role in the shelf life of chicken meat packaged with different systems, further studies are needed. It is also necessary to define the most suitable concentration of bio-phenols to be used in animal diets to exert their best activity (Roila et al., 2018). Branciari et al. (2016) investigated OMWW polyphenolic extract’s dietary effect and dehydrated olive cake (DOC) on Campylobacter spp. in broiler chickens. Both OMWPE groups showed a lower prevalence of Campylobacter spp. in the flock than the control group and, consequently, meat. Fish oil is considered the principal dietary constituent in fish feeds due to its high digestibility and essential fatty acid content, especially omega-3 (highly unsaturated fatty acids). Researches have illustrated vegetable by-products’ valorization as an alternative and sustainable lipid source to replace fish oil (FO) in fish feed. Considering the capacity of OP to prevent atherogenesis and, therefore, the onset of CVDs, researchers focused on using OP in fish feeds (Nasopoulou et al., 2011, 2014a, 2014b; Sioriki et al., 2016). In the study of Nasopoulou and coauthors (2011), they have given to gilthead sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax) two experimental diets: olive pomace diet and olive pomace oil diet. This was to examine if the replacement of fish oil by the olive oil by-product in fish feeds affects growth performance, fatty acid composition, and cardio-protective properties of fish. The both experimental diets showed satisfactory growth performance factors on gilthead sea bream but not on sea bass. Indeed, the olive pomace diet induced a decrease of fatty acid levels in total lipids of gilthead sea bream while exhibited the most potent biological activity against platelet aggregation induced by Platelet Activating Factor. These findings indicate the possibility of substituting fish oil with olive pomace in fish feed, improving its cardioprotective properties (Nasopoulou et al., 2011). Sioriki et al. (2016) confirmed these previous findings. They showed that OP could be vaporized in aquafeeds production and improve the cardioprotective properties of the final product (sea bream) by enriching the fish lipid profile with specific cardioprotective lipid compounds of plant origin.

3.2.3

Olive by-Product in Food Packaging

Edible films, thin polymer layers, attracted more attention and used in food products to improve their preservation, distribution, and marketing as environmentally friendly alternatives to synthetic films (Galus & Kadzińska, 2015). Recently, some natural additives extracted from plants and agriculture bio-waste are incorporated into edible films, particularly molecules with antioxidant and/or antimicrobial compounds, which are getting much interest in the food industry (Valdés García et al., 2020). Among these bio-wastes, olive by-products contain pulp, oil, vegetative waters, and bioactive such as hydroxytyrosol that has extensively reported its in vitro and in vivo antioxidant and antimicrobial properties. Nevertheless, no literature information illustrated the uses of cornstarch-based films incorporating an olive fruit by-products extract. Basing on antioxidant and antimicrobial activity, Valdés García and coauthors (2020) developed new active edible films, using corn

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starch with the addition of an olive by-products extract (OE), to be used for food packaging applications. The incorporation of OE enhanced the antioxidant potential and antimicrobial effect of these novel active films against E. coli and S. aureus, being noticeable for films added with 0.2% wt OE. Besides, a clear thermo-oxidative stability improvement has been underlined with OE incorporation. This developmental approach allows reducing the use of synthetic additives and the production of food wastes, contributing to a circular economy (Valdés García et al., 2020).

3.2.4

Production of Energy, Biochars, and Agriculture Applications of Olive Waste

Olive by-products are well used for energy production. For example, the analysis of Andalusian by-product shows that 80% of waste olive biomass is exploited for energy generation with 47% of electricity generation and 33% for thermal energy. Nevertheless, this direct combustion of olive biomass has not reported in many research papers as it already represents a well-established industry. In fact, in olive oil-producing regions, the use of olive stone as a biofuel for heating is widely widespread, particularly in agro-industries, livestock farms, greenhouses, and domestic heating systems (Berbel & Posadillo, 2018). The treatment of olive biomass by pyrolysis, anaerobic thermal decomposition at high temperatures, leads to solid products (chars). “Biochars" obtained from olive wastes are applied as a soil amendment to improve productivity, protect carbon reserves, or filter percolating soil water (Dutournié et al., 2019; El-bassi et al., 2020; Gámiz et al., 2016; Haddad et al., 2021; Hmid et al., 2014; Madžarić et al., 2018; Manolikaki et al., 2016; Marks et al., 2020; Marra et al., 2018; Pellera et al., 2012). Marra et al. (2018) characterized the physicochemical and morphological biochars obtained from two-phase solid OMW at different pyrolysis temperatures (PT from 300 to 1000  C). Besides, they studied the effect of biochar water extracts on the growth of different plants (Lepidium sativum L. and Brassica rapa L. subsp. oleifera), nematode (Meloidogyne incognita), and fungal species (Aspergillus niger, Fusarium oxysporum, Rhizoctonia solani). The results showed that temperature reduces the alkyl C fractions coupled to the enrichment in aromatic C products. The thermal treatment also influenced several compounds present in the organic feedstock (fatty acids, phenolic compounds, triterpene acids), which reduced at 300  C or completely disappeared at 500  C in biochars as compared to untreated OMW. Also, the surface morphology of biochars was affected by increasing porosity and heterogeneity of pore size as a function of PT. Water extracts of untreated OMW had an inhibitory effect on the two studied plants and the nematode M. incognita but stimulated the fungal growth. Nevertheless, the pyrolysis induced a decrease of degradable carbon sources and an increase of aromatic fractions, which may be associated with plant and nematode growth and inhibit most of the tested fungal species.

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Haddad et al. (2021) research consists of biochars’ characterization derived from raw cypress sawdust and impregnated with KCl or OMWW, using different techniques (TGA, XRF, SEM, CO2 adsorption). They considered the elaborated biochar could be a highly effective, attractive, and promising organic fertilizer. The biochars with OMW and KCL are rich in potassium, phosphorus, nitrogen, and sodium. The authors confirmed in this study the significant improvement of potassium bioavailability by biochars addition to soil. They also confirmed that these biochars’ use allowed the suppression of various pathogens and improve soil fertility. On the other hand, some researchers exploited different olive solid waste to create efficient adsorbents for removing various aquatic pollutants while applying different physicochemical treatment methods and the processing conditions (Bhatnagar et al., 2014; Pellera et al., 2012). Several parameters can influence the absorptive properties of developing adsorbents from olive wastes, such as the precursor’s nature, the type of activation. For example, in the comparative study of Pellera et al. (2012), the copper solution’s adsorption potential of raw hydrothermally treated and pyrolyzed rice husks, olive pomace, orange waste, and compost was evaluated. Cu (II) adsorption dependent on various parameters, such as adsorbent dose, pH, contact time, and initial Cu(II) concentration. Regardless of the materials, the optimum Cu (II) adsorption conditions were determined in the range of 5–12.5 g/L for the adsorbent dose, 5–6 for the pH, and 2–4 h reaction time. Concerning the adsorption kinetics and all the tested materials, the experimental data is best appropriate to the pseudo-second-order model, while the adsorption equilibrium was best described by the linear and the Freundlich isotherms. Generally, rice husks and olive pomace biochars achieved by the 300  C pyrolysis present the highest Cu(II) adsorption capacity. In contrast, pyrolysis at 600  C negatively affects the adsorption capacity for all the materials. This could be attributed to this process’s high temperature, which affects the number of active sites on the material’s surface. To improve the α-glucan content in the edible fungus Pleurotus eryngii, Avni et al. (2017) have enriched the cultivation substrate with olive mill solid waste (OMSW) from three-phase olive mills. This study showed that higher total glucan concentrations were enhanced up to twice when the growth substrate was enriched with 80% of OMSW compared to no enriched substrate. Thus, these findings prove that the studied mushroom Pleurotus eryngii can be a potentially rich source of glucans for nutritional and medicinal applications. The application of OMSW into the cultivation substrate allowed to enrich the glucan content in fruiting mushroom bodies (Avni et al., 2017).

3.2.5

Olive Wastes for Human Health Uses

Some biophenols such as hydroxytyrosol (HyT), oleuropein (OLE), oleocanthal (OLC) are found in olive by-products (pomace and water waste) and associated with beneficial effects that include the metabolic compartment. Recent research focused on a phenolics-rich purified extract from OMWW, termed A009, obtained

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by microfiltration and reverse osmosis. A009 extract was mostly rich in hydroxytyrosol (Baci et al., 2019; Bassani et al., 2016; Rossi et al., 2015). This purified extract exerted strong anti-angiogenic effects on endothelial cells in vitro and in an angiogenesis model in vivo (Rossi et al., 2015). Further, Bassani et al. (2016) proved that A009 rich in HyT inhibited proliferation, migration, invasion, adhesion, sprouting of colon cancer cells, and release of angiogenic, pro-inflammatory cytokines (VEGF, IL-8). Baci et al. (2019) investigated the effects of A009 on human prostate cancer (PCa). They found that this purified extract inhibited PCa cell proliferation, adhesion, migration, and invasion. Besides, olive pomace’s polar lipids can inhibit or antagonize Platelet-activating factor (PAF) with a mode of action similar to that of virgin olive oil. To approve the bioactivity of the compounds under in vivo conditions, researchers proceeded to supply with OP’s polar lipids the induced hypercholesterolemic diet of rabbits (Karantonis et al., 2006; Nasopoulou et al. 2014a, 2014b). For that purpose, they have isolated polar lipids from OP and tested their antagonistic and inhibitory activities against PAF. The studied extracts inhibited PAF activity toward washed rabbit platelet aggregation and its specific binding on its receptor on rabbit platelets. The in vivo dietary intervention caused a diminution in rabbits’ platelet sensitivity that consumed olive pomace’s polar lipids, determined by their increased EC50 values for PAF induced aggregation in their platelet-rich plasma. Up on atherogenesis, PAF blood levels augmented in all groups. As a protective mechanism countervailing, increased activity of plasma PAF-AH accompanied this increase of the Blood PAF level in all groups. As regards the morphometric assessment concerning early atherosclerosis lesions, the results showed that consumption of polar lipids allows to reduce the development of these lesions as compared to the control group consuming only an atherogenic diet, thus confirming their beneficial effects against the development of inflammatory disease (Karantonis et al., 2008; Nasopoulou et al. 2014a, 2014b). A recent study was performed conjointly by researchers from Fondazione Edmund Mach (San Michele all’Adige, Italy), OlioCru s.r.l (Arco, Italy), and the study center was the Casa di Cura Eremo di Arco s.r.l. (Italy), a private specialist clinic specialized in treating cardiovascular disease (CVD) (Conterno et al., 2017). During this study, olive pomace-enriched biscuit (olive-enriched product, OEP) or an isoenergetic control (CTRL) have been randomly given to human subjects for 8 weeks. Microbiota, metabolites, and some clinical parameters have been measured from fasted blood samples, 24-h urine and fecal samples collected before and after dietary intervention. This investigation showed that the ingestion of olive pomace extract-enriched biscuits provoked small changes in the composition of the gut microbiota. The OEP biscuits induced a significant increment in the excretion of small phenolic acids in urine, indicating up-regulation of microbial polyphenol biotransformation in the intestine. OEP also led to a significant augmentation in homovanillic acid and DOPAC in fasted plasma samples, indicating related clearance of these compounds from the blood or extended-release and uptake from the intestine (Conterno et al., 2017).

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The work of Lanza et al. (2020) consists of studying the olive pâté obtained by multi-phase decanter (DMF) as a potential source of bioactive compounds. The pâté contains a high amount of phenolic compounds, mainly represented by secoiridoids and verbascoside. The authors investigated the efficacy of two different ways of debittering of DMF pâté using sequential filtrations and spontaneous fermentation to make the pâté edible. Besides, they evaluated the effect of its phenolic bioactive extracts on pathogenic bacteria and colon cancer cell model. Daily filtrations of pâté are more efficient in phenolic degradation. The indigenous microflora activity takes a long time to degrade bio-phenols and, therefore, de-bitter them. None of the pâtés displayed antibacterial activity on multidrug-resistant bacteria in the tested concentration range. Concerning the colorimetric assay, MTS for cell viability and metabolic activity tested on colon cancer cells Caco-2 and HCT116 suggest a potential beneficial effect of the dried extracts probably related to the modulation of gene expression under these treatments (Lanza et al., 2020).

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Chapter 4

Anaerobic Digestion Technology of Solid and Liquid Forms of Olive Wastes in the Mediterranean Region Ouahid El Asri, Soufiane Fadlaoui, and Mohamed Ramdani

Abbreviations AD FAO OMWW OP

4.1

Anaerobic digestion Food and Agriculture Organization Olive Mill Wastewater Olive Pomace

Introduction

The olive tree grows naturally in the Mediterranean country owing to its optimal climatic conditions for its cultivation. Moroccan olive tree populations are about 37 million trees growing over 400,000 hectares (Essadki et al., 2006). Jordan has 25 million olive trees, which produce around 220,000 tons of olive fruit per year (Khdair et al., 2019). Spain has 2.57 million hectares of olive trees (Pleguezuelo et al., 2018). So, Spain’s agricultural area dedicated to olive trees is more than 80% of the Spanish agricultural field (Fernández-Lobato et al., 2021). Generally, the Mediterranean basin has more than 750 million olive trees extended over ten million hectares, equal to 95% of olive world culture (Aguilera et al., 2015). Therefore, the countries which surround the Mediterranean Sea are the major olive producers worldwide. The olive tree combines several economic, social, and cultural approaches for Mediterranean citizens attributed to its oil and fruit (Loumou & Giourga, 2003). These final products play a crucial contribution to Mediterranean people’s diet, O. El Asri (*) Plant Biotechnology Laboratory, Faculty of Science, Ibn Zohr University, Agadir, Morocco e-mail: © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 M. F. Ramadan, M. A. Farag (eds.), Mediterranean Fruits Bio-wastes, https://doi.org/10.1007/978-3-030-84436-3_4

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habits, health, and religion. About 90% of the olive tree’s economic benefit is primarily acquired from olive oil production (Oteros et al., 2013). Therefore, the Mediterranean interest in cultivating and developing the olive tree is mainly for olive oil production. The olive fruit’s transformation into olive oil is domesticated about 6000 years ago in the Mediterranean region (Grigg, 2001). The Mediterranean countries produce more than 95% of the olive oil world production (Calabriso et al., 2015; de Graaff & Eppink, 1999). Significant production of organic wastes accompanies this large Mediterranean olive oil production. During 2 months of olive oil production, one ton of olive fruits produces ca. 1–2 tons of liquid olive waste called olive mill wastewater (OMWW), and 800 kg of solid olive waste called olive pomace (OP) (Medouni-Haroune et al., 2018; Paraskeva & Diamadopoulos, 2006). The Mediterranean region produces a significant volume of OMWW (30 million m3) (Barbera et al., 2013). Only at Spain’s level generates more than four million tons of OP (Borja et al., 2005; Tekin & Dalgıç, 2000). This large amount of organic wastes has a wide organic and mineral load and phenolic compounds. This composition makes this liquid and solid waste as well highly toxic towards ecosystems. Consequently, OP and OMWW generated by olive oil production present a significant threat to the environment and economic issues. We are faced with the need to treat, manage, and valorize these olive oil production wastes. Several techniques (Landfill, natural evaporation, incineration, composting, and anaerobic digestion) are reported for the management of olive fruit wastes. Several researchers have recommended using anaerobic digestion (AD) to achieve the last decade’s previous goal (Elasri & Afilal, 2016). The AD is a multistage microbial decomposition of organic matter that comprises four phases (hydrolysis, acidogenesis, acetogenesis, and methanogenesis). AD is a management and treatment technique and a method of producing renewable energy in methane gas (Angelidaki et al., 2011; El Asri & Hafidi, 2015). The AD of OMWW can generate 25 m3of methane (CH4) per ton of olives that converted to immense heat potential (1 GJ/ton olives) (Gelegenis et al., 2007). Thus, the AD of olive mill waste can play an efficient role in removing the high organic, mineral, phenolic load, protecting the environment, and generating energy. This chapter is designed to provide the suitable application of anaerobic digestion technology in the treatment, management, and energy conversion of solid and liquid waste products during the Mediterranean region’s olive oil production. The chapter is divided into three axes. Firstly, an update of the olive fruit’s current situation and its industry in the Mediterranean area was presented. In the second part, we have highlighted the main steps necessary to transform olive fruit into olive oil in the Mediterranean mill and the organic wastes produced during the industrialization. Finally, we discussed the anaerobic digestion technology of solid and liquid olive waste. Some new applications for improving this process to generate a large amount of energy, eliminate its toxic load, protect the environment, and produce fertilizer are also highlighted.

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4.2

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Current Situation of Olive Crops in the Mediterranean Region

The olive tree in the Mediterranean basin covers more than ten million hectares (Aguilera et al., 2015; Nieto et al., 2013). The cultivated olive called Olea europaea is a species indigenous to the Mediterranean region (Murphy, 2014). This olive tree is an evergreen plant, and it has long-lived that can arrive at more than 500 years, in some country such as Spain that has 4400 trees with 700–1000 years old (PérezRodrigo & Aranceta, 2016). Olea europaea is a famous tree in the Mediterranean region, and it can provide several therapeutic molecules. We have grouped and classified these molecules in Table 4.1 with their useful role in the human body. So, the fruit and oil of Olea europaea can be considered a useful therapeutic agent in human diseases. The production and consumption of olive fruit and oil are substantial crops in the Mediterranean region (Roselli et al., 2016). Comparing the annual olive output of the 21 Mediterranean countries in the FAO databases, we noted that Spain is the first olive producing country in the Mediterranean basin with a production exceeding nine million tons (Mt). Italy occupies second place (1.87 Mt), followed by Morocco in the third position with 1.56 Mt. Turkey and Greece successively occupy fourth (1.5 Mt) and fifth (1.07 Mt). Other Mediterranean countries do not exceed one million tons (Fig. 4.1). Pérez-Rodrigo and Aranceta (2016) reported that Spanish olive production exceeds 50% of total world production. Researchers confirm that Spain is the world’s leading producer and exporter of olive oil (Folgado-Fernández et al., 2019; Pleguezuelo et al., 2018). This place is for some reasons: (i) Spain has the highest olive tree area harvested (2.57 Million hectares), (ii) good production efficiency ranging from 2270 to 5356 kg ha 1 (Pleguezuelo et al., 2018), (iii) the large concentration of olive trees (91% of the cultivated land) in some of its regions (Rodríguez Sousa et al., 2019), (iv) growth of the European organic market by 7.6% in 2014 with 26.2 billion € generated (Pleguezuelo et al., 2018), (v) the national consumption is the second largest olive oil consumer in the world (Roselli et al., 2016), Spanish citizens are growingly aware of the impact of olive oil on health. Italy’s second place is due to 150 million olive trees in 907,197 olive farms, and with Italian citizens as the first consumer of olive oil in the world (Roselli et al., 2016; Valenti et al., 2017).

4.3

Characterization of Mediterranean Olive Fruit

Mediterranean olive fruit is an oval drupe with a weight that can reach 12 g. The pulp or mesocarp is the principal constituent of this fruit (65–75%) (Gharbi & Hammami, 2019). Calabriso and al. stated that olives’ pulp could reach up to 80% of the whole fruit’s weight (Calabriso et al., 2015). The endocarp (pit or stone) represents 25–35% of the fruit (Gharbi & Hammami, 2019). The pit contains the seed; it means 2.5–4%

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Table 4.1 Health benefits of active components and ingredients of olive oil Chemical components Unsaturated fatty acids

Saturated fatty acids

Polyphenols

Active ingredients Oleic acid; Linoleic acid; Omega-3

Palmitic acid; Stearic acid; Myristic; Arachidic Heptadecanoic; Behenic and lignoceric acid Tyrosol; Hydroxytyrosol Lignans; Secoiridoids. Hydroxybenzoic acids and Hydroxycinnamic acids

Hydrocarbons

Squalene and Beta-carotene

Sterols

4α-desmethylsterols; 4-Methylsterols; Triterpene dialcohols

Tocopherols

E vitamins

Health benefits + Reduced blood pressure by regulating the activity of the adrenergic receptors + Improved endothelial function, vascular reactivity, and cardiac electrophysiology, as well as potent antiplatelet and antiinflammatory effects + Stabilized postprandial or plasma concentrations and improved inflammatory activity + Reduced incidence of risk factors for coronary heart disease + Improved the intracellular antioxidant defense systems (immunomodulatory) + Inhibited skin, breast, colon, and lung cancer cell growth + They are an antidote to reduce accidental druginduced toxicities (cytoprotectant) It is a potent quencher of singlet oxygen + Improving prevention conditions, such as macular degeneration, cataract, eyesight, skin, and nails + The decreased tumorigenesis process as colon, lung, and skin cancers + Improving hypocholesterolemia, antiinflammatory, and anticarcinogenic effects + They are the most potent fat-soluble antioxidant known in nature + Play a putative role in the prevention of Alzheimer’s disease + Strong substrate for chemotherapeutic strategies for inducing apoptosis and

References Lopez-Huertas (2010), Teres et al. (2008)

Voon et al. (2011)

Di Benedetto et al. (2007), Owen et al. (2000)

Senthilkumar et al. (2006), Smith (2000), Starek et al. (2015)

Lukić et al. (2017)

Tucker and Townsend (2005)

(continued)

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Table 4.1 (continued) Chemical components

Pigments

Active ingredients

Triterpene Acids

Chlorophylls mainly pheophytin; Carotenoids; Xanthophylls such as antheraxanthin, betacryptoxanthin, luteoxanthin, mutatoxanthin, neoxanthin, and violaxanthin Oleanolic and maslinic acids

Aliphatic and Aromatic Alcohols

Docosanol; tetracosanol; hexacosanol; octacosanol, and geranylgeraniol

Health benefits

References

impact the expression of oncogenes Improved the inhibition of foodborne pathogens and stimulation of the growth of beneficial gut microbiota

Gavahian et al. (2019)

Improved endothelial function Anti-cancer, antiinflammatory, and antioxidant activities as well as being cardioprotective Decreased nitric oxide production by macrophages cells. Reduced TNF-α and prostaglandin E2 production Reduced thromboxane A2 production Reduction of eicosanoid release by the inhibition of phospholipase A2 enzyme activity So, reduce the release of different inflammatory mediators

de la Torre et al. (2020)

(FernándezArche et al., 2009)

of the fruit’s weight (Calabriso et al., 2015). The olive seed weighs 3 g with the dimensions (length of 21 mm and width of 17 mm) (Al-Bachir, 2017). The Mediterranean region’s olive fruit contains 25 to 32% oil; water quantity is 40 to 55%, and olive pit with vegetal residues from 23 to 35% (Pérez-Rodrigo & Aranceta, 2016). The principal amount of oil, 70%, comes from the mesocarp, and 30% produced by the endocarp (Calabriso et al., 2015). In mesocarp cells, specifically in the vacuoles, the oil is present as small drops, but in endocarp cells, the oil is in the cytoplasm’s colloidal system (Cerri & Reale, 2020).

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Annual Production (tonnes)

10000000 9000000 8000000 7000000 6000000 5000000 4000000 3000000 2000000 1000000 0

Fig. 4.1 The annual olive production in Mediterranean countries

4.4

How Is Olive Oil Produced from Olive Fruit in the Mediterranean Region?

The Mediterranean countries produce more than 95% of the olive oil world production (Calabriso et al., 2015; de Graaff & Eppink, 1999). Olive oil is the juice of the olive tree fruit; it is obtained through a series of processes. Five kilograms of olive fruit can produce one liter of oil (Kapellakis et al., 2008). Previously, Mediterranean producers started with the olive fruit’s crushing, and then it was placed in the pressure process. It was divided from the water by decantation, where it was collected from the tank’s surface. This traditional separation has significant time, energy, and lower oil yield (Mwaurah et al., 2020). After the progress of technological inventions in the oil extraction field, distinguished extraction systems that are the most widespread in the Mediterranean region (hydraulic pressing systems, selective filtration, and centrifugation process) were developed. The Mediterranean countries can currently produce annually 2.5 million metric tons per year (Valenti et al., 2017). In the following section, we will decorticate the principal vital steps necessary to produce this immense amount of olive oil in the Mediterranean region.

4.4.1

Collection, Leaf Removal, and Washing

After collecting olive fruit from their trees by hand or mechanical devices such as olive shakers, the producers remove branches, wood material, and the leaves that are

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still attached to them. The existence of leaves increases the green color and leads to bitter savor with an organoleptic sensation of the oil (Di Giovacchino et al., 2002). The olive fruit’s washing step is fundamental to eliminate all foreign matter that contaminates the oil and destroys the machinery (Guardia-Rubio et al., 2007).

4.4.2

Crushing and Malaxation

Crushing is assured by two types of machines, stone mills with three or two heavy wheels revolved for crushing the olive fruit or stainless steel hammer mills (Gharbi & Hammami, 2019; Polari & Wang, 2020) (Fig. 4.2). This step is essential and rips the mesocarp and endocarp cells’ parenchyma cells to ease the oil’s output.The mixing of the paste product is for easing the isolation of the oil and water phases; its purpose is to break oil/water emulsion drops. Stillitano et al. described this step as the promoter of oil drops coalescence, i.e., it is the passage from little drops into significant drops of oil (Stillitano et al., 2019). The approach in Mediterranean producers of olive oil extraction is currently to use the heat malaxator (Esposto et al., 2013). Finally, the olive oil has three forms: entirely free, droplets with microgels, or emulsified in the water warranting for another step (extraction) to increase the free fraction.

4.4.3

Extraction

The extraction step consists of separating the oil from the tissue cell, the pit’s debris, and fruit water. This step presents different concepts such as pressure, centrifugation, and selective filtration process or combinations of these methods.

Fig. 4.2 The crushing stage in Moroccan mill, (a): Stone mills two heavy wheels, (b): The paste production

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Fig. 4.3 The extraction process in Moroccan mill, (a): Olive paste between filters and metal disks, (b): Pressure machine

The pressure process consists of exerting pressure on olive paste between filters and metal disks to get out olive juice (Fig. 4.3a). In practice, the paste is placed in oil diaphragms, set under a hydraulic pressure unit (Di Giovacchino, 2013). Under pressure conditions, the oil runs per the olive paste. The majority of olive mills in Morocco are pressure-based for extracting olive oil (Di Giovacchino et al., 2002) (Fig. 4.3b). The selective filtration process or the percolation method is also called Sinolea (Clodoveo et al., 2014). This process has not used any pressure to the paste (Gharbi & Hammami, 2019). The principle is that the oil alone adheres to the metal due to its lower interfacial tension than water with the steel blade (Di Giovacchino, 2013). So, the adhering oil is separated from the pomace and water. Centrifugation is a new process compared to last techniques. In Spain, this process is widespread. Di Giovacchino et al. (2002) counted more than 1.7 thousand mills with centrifugation systems. It can separate the olive oil fraction by the density of each paste constituent in a rotary system. Horizontal (or decanter) and vertical centrifugation are distinguished. Horizontal centrifugation has two type systems, which are three-phase or two-phase. The 2-phase characterize the olive mills in Greece, but the Spanish olive mills mainly have 3-phase (Di Giovacchino et al., 2002). The three-phase centrifugation divides the olive paste into the dry residual matter called olive pomace, water, and oil. Still, in two-phase centrifugation, the olive pomace and water exist together (Clodoveo et al., 2014). Also, the 3-phase technology requires warm water, but for the 2-phase technology, water is not needed for separating the oil (Calabriso et al., 2015). The vertical centrifugation is considered the last extraction step of olive oil (Masella et al., 2009).

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Olive Mill Waste: Types, Characteristics, and Environmental Impacts

Three types of waste during the transformation of fruit to olive oil are distinguished, including olive pomace, wood material (mainly leaves), and the olive oil mill wastewater. The significant amount of phenolic compounds (98%) in olive fruit is located inside the wastes (Obied et al., 2005). Barbera et al. (2013) estimated the Mediterranean OMWW to be over 30 million m3 in 2 months of olive oil production. The yearly output of OP in Spain is between 2 and four million tons, but Turkey fluctuates between 100 and 120 thousand tons (Borja et al., 2005; Tekin & Dalgıç, 2000). Some researchers have mentioned that 100 kg of processed olives can get from 3 to 10 kg of olive leaves (De Leonardis et al., 2008; Malheiro et al., 2013). Thus, a large quantity of organic waste resulting from olives’ transformation into oil is recovered. The olive leaves are used in the phytotherapy field or animal feed. The OP is a semi-solid or semi-liquid waste. It is regrouping the crushed constituents of the olive fruit (pulp, pit, and skin), water (25–80%), and residual olive oil from 2 to 3% (Medouni-Haroune et al., 2018; Rodrigues et al., 2015). The OP contains a high amount of cellulose (55 g) and lignin (21 g) in 100 g of total solids (El Achkar et al., 2018). These characteristics are mainly depending on the types of extraction technology used (Francik et al., 2018). The 2-phase centrifugation produces OP with high water content (56.6–74.5%) (Diacono & Montemurro, 2019). However, the 3-phase centrifugation makes OP with very low moisture. Medouni et al.(2018) stated that one ton of olive could produce 400–800 kg of OP with humidity that varies from 35 to 60% (Medouni-Haroune et al., 2018). A large part of hydroxytyrosol and its derivatives phenolic (98%) stay with OP (Antónia Nunes et al., 2019). Thus, the OP has phytotoxic and antimicrobial activity thanks to phenolics content and high salinity. The OMWW is the red-brown to black-colored mills effluent (Zarkadas et al., 2019). It is a stable emulsion with 83–94% water, 0.4–2.5% minerals, and high chemical oxygen demands (COD) (30–320 g L 1) (Dermeche et al., 2013; Magdich et al., 2020). This olive waste is rich in phenolic substances, mainly three elements (Tyrosol, hydroxytyrosol, and oleuropein) (Abu-Lafi et al., 2017). The treatment of 1 m3 OMWW with ethyl acetate could produce 0.247 kg hydroxytyrosol, 0.062 kg tyrosol, and 3.44 kg of total phenols(Kalogerakis et al., 2013). Peri and Proietti (2014) stated that the phenol component’s content is between 4–10 g L 1. D’Antuono et al. (2014) demonstrated that the phenolic content is more significant in OMWW (24 g L 1) of Italy and Greece. Therefore, the phenol content shows qualitative variation different from country to country. The Rodis et al., 2002 noted that the phenolic amount in OMWW (53%) is more critical than OP (45%)(Rodis et al., 2002). The volume of OMWW produced depends on the region of the Mediterranean basin, species variety, cultivation methods, and extraction technology types (Aviani et al., 2012; Dermeche et al., 2013). For example, the same quantity of olives (100 kg) can produce different volumes of OMWW, in the pressure process (40–60 L), compared with the 2-phase centrifugation (10 L) and in 3-phase systems

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Fig. 4.4 Negative impacts of OMWW on the soil’s biological and physicochemical properties

(80–120 L)(Ahmed et al., 2019). The water in OMWW is produced by vegetation water, washing, and the processes described above. McNamara et al. (2008) simulated that ten million m3 of OMWW generated by 3 phase extraction are similar to the wastewater produced by 20 million citizens (McNamara et al., 2008). Thus, we have a large volume of OMWW rich in organic substances, and phenolic compounds, which makes this liquid waste highly toxic towards some beneficial bacteria, earthly and aquatic organisms, and crops (Magdich et al., 2020; Niaounakis & Halvadakis, 2006). It can also destruct soil and plant growth by its phytotoxic effect on seed germination. In Fig. 4.4, the negative impacts of OMWW on the soil’s biological and physicochemical quality are summarized. So, the olive mill waste presents a real danger to ecosystems (fresh and coastal waters, land, streams, and rivers) in Mediterranean countries.

4.6

Anaerobic Digestion (AD) of Olive Pomace

In the last decades, organic wasteis used as an anaerobic digestion treatment before energy recovery (Elasri & Afilal, 2016; Nguyen et al., 2007). The OP has taken growing attention from the moment that researchers have confirmed its transformation into biogas by AD (Borja et al., 2005; Gianico et al., 2013). Tekin and Dalgıç (2000) estimated a high quantity of renewable energy (4.108 MJ) produced by the

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conversion of 107 m3 of methane issued alone for the annual production of OP in Turkey (Tekin & Dalgıç, 2000). Italian researchers have estimated a volume of 1.9 million m3 biogas produced from a yearly amount of OP (Valenti et al., 2017). Thus, the energetic valorization of OP by AD could be used for green energy generation and reduce pollution. We can also see that the recovery of this waste is different from one Mediterranean country to another. This finding shows that each country has different anaerobic digestion conditions. The un-pretreated and mono-digestion of OP produces lower energy because it presents some constraints. This observation is confirmed by studies such as Amirante et al. (2018) and Aylin Alagöz et al. (2015). The constraints that could cause this reduction in conversion to methane are: (i) the high concentration of phenolics, (ii) fast acidification in the digester, (iii) high level of volatile fatty acids, (iv) a large amount of casein in OP inhibits microbes (Milanese et al., 2014), (v) the organic components limit the hydrolysis step is not readily soluble, and (vi) the OP is characteristically lignocellulosic materials often recalcitrant to biodegradation (El Achkar et al., 2018). However, researchers have stated that using OP as an alone substrate of AD is not advisable (Fernández-Rodríguez et al., 2014). So, the enhancement of methane yield produced by the AD of OP needs to raise these constraints and improve this process’s phases. In the next part of the chapter, we will present the different techniques, which allow the optimization of this treatment.

4.6.1

The Necessity of Pretreatment

Pretreatment became necessary to preconditioning of OP to facilitate the AD process. Several types of pretreatment are distinguished. Ultrasound is a successful technology for enhancing OP’s AD (Gianico et al., 2013). Some researchers have confirmed that this pretreatment is mostly used before the AD of OP (Dinc & Yel, 2020; Rincón et al., 2014). This technology generates sinusoidal acoustic waves that break down significant material such as lignin and cellulose within OP into smaller molecules. Rincón et al. (2014) confirmed that ultrasound pretreatment of OP at 24 kHz frequency for 90 min could increase the solubilization of this material and methane yield (5.6%) compared to the control. Ruggeri et al. (2015) demonstrated that this treatment increases biogas production by 61-fold using a dose (8000 kJ L 1). Basic pretreatment is mixed with the OP and some alkali reagents characterized by high delignification capacity, including sodium hydroxide (NaOH), potassium hydroxide (KOH) or ammonium hydroxide (NH4OH) (Pellera et al., 2016). These chemical agents increase the solubility and degradation of organic matter by breaking chemical bonds within lignin and polyphenol in OP (Zhen et al., 2017). Thus, it contributes to the hydrolysis of OP, allowing its transformation from the solid to the liquid phase. The alkali reagents can also neutralize various acidic products, prevent the pH from falling too much during the acidogenesis phases, and induce lipids’ saponification in olive pomace (Elalami et al., 2020; Hendriks & Zeeman, 2009).

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Fig. 4.5 Biogas plant proposal for the valorization of olive pomace in the Mediterranean region

Pellera et al. (2016) confirmed that NaOH pretreatment is an effective way for improving the biodegradability of OP to obtain energy recovery (242 mL CH4 g VS 1). Elalami et al. (2020) demonstrated that the basic pretreatment influences lignin and hemicellulose hydrolysis, methane produced volume reaches a maximum of 280 mLCH4 g VS 1 and removed 96% of initial lipids from OP. Salt pretreatment is the addition of particles such as CaCO3, FeCl3, and ZnO in OP (Amirante et al., 2018; Ruggeri et al., 2015). These particles have several roles, including the formation of biofilm and microbial aggregates on the lignocellulosic part of the OP and increasing pH in the digester. Ruggeri et al. (2015) confirmed that CaCO3 addition is useful for AD of OP; it can produce a large amount of methane (748 mL CH4 g VS 1). This result is obtained using 5 g/L of calcium carbonate in the digester; it improves the production of biofilm on lignocellulosic materials of OP, growth of certain strains of methanogens, and the reaction medium through a buffering action that can impede the acidification and the time of the lag phase. Amirante et al. (2018) used the ZnO to increase methanogenesis bacteria growth kinetics at the beginning of OP treatment so that this particle can reduce the lag phase of AD. The pretreatment is necessary for the successful AD of OP into methane generation. The selection of an effective pretreatment depends on the OP composition, type of extraction, energy consumption, and treatment budget. For example, combining pretreatments with salt pretreatments leads to more unsatisfactory performance than when performing the pretreatments separately. For this, we recommend carrying out the pretreatment of OP individually, i.e., in separate tanks (Fig. 4.5).

4.6.2

Anaerobic Co-digestion

The co-digestion process improves the degradation activity owing to the synergistic impact of the organic matters characterized by appropriate nitrogen or carbon amount. So, we must ensure an optimal C/N ratio for this process’s proper conduct; this C/N ratio for AD is in the range of 20–30 (El Asri et al., 2020). Aylin Alagöz

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Table 4.2 Different techniques for improving AD of OP Pretreatment type. Untreated Untreated Ultrasound Ultrasound Salt pretreatment Basic pretreatment Basic pretreatment Codigestion: Apple pulp and OP Codigestion with Scenedesmus quadricauda Codigestion with Dunaliella salina

Methane yield (mL CH4/ g VS 1) 6.67 17 393 537 748 242 280 216 461 330

References Ruggeri et al. (2015) Azbar et al. (2008) Rincón et al. (2014) Ruggeri et al. (2015) Ruggeri et al. (2015) Pellera et al. (2016) Elalami et al. (2020) Riggio et al. (2015) Fernández-Rodríguez et al. (2019) Fernández-Rodríguez et al. (2014)

et al. (2015) confirmed that co-digestion of OP with wastewater sludge could increase the methane yield from 0.16 to 0.21 LCH4 g VS 1. Riggio et al. (2015) demonstrated that the use of a co-digestion between cow slurry (85%), apple pulp (5%), and OP (10%), is economically favorable. This mixture produces 400 L kg VS 1 of biogas that can produce 2.2 KWh t 1 (Riggio et al., 2015). Some researchers are currently using a particular substrate for anaerobic co-digestion of OP, such as algae species (Dunaliella salina, Scenedesmus quadricauda). The use of a mixture of 25% S. quadricauda and 75% of OP can improve the methane yield to 25% generated from the single substrate (Fernández-Rodríguez et al., 2019). The same proportion of mixture, but with other algae (Dunaliella salina), obtains 330 mL CH4 g VS 1 (Fernández-Rodríguez et al., 2014) (Table 4.2). The anaerobic co-digestion enhances the C/N ratio, methanogenic bacteria activity, and limited ammonium inhibition, which increases the OP conversion to green energy.

4.7

Anaerobic Digestion of Olive Mill Wastewater

The OMWW is 150-fold more strongly charged with pollutants than usual household wastewater (Sabbah et al., 2004). Typically, a high organic load produces more biogas (El Asri & Afilal, 2017). In Turkey, the OMWW can produce 42 million cubic meters of biogas (Ulusoy & Ulukardesler, 2017). In general, the AD of OMWW can generate 25 m3 CH4 t 1 of olives converted to great heat potential (1 GJ per ton olives) (Gelegenis et al., 2007). Thus, the AD of OMWW can produce a high amount of energy. Researchers confirmed that AD of OMWW is not satisfactory and not recommended (Hamdi, 1996). It was already shown their toxic nature towards microbes, making methanogens bacteria sensitive to large organic load, lipids, and phenolic compounds. It is also characterized by weak alkalinity. It has a very low

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nitrogen amount, which is needed for microbial growth, and a higher C/N ratio. Therefore, reducing this toxicity is considered a primary goal of allowing microbial processes’ success. For this, we have regrouped several hopeful and alternative ways that can remove the toxicity of OMWW over the next sections.

4.7.1

Dilution

The methane production decreases when the digester’s organic matter concentration increases (Elasri et al., 2018). The methanogenic bacteria are remarkably inhibited by pH drops, the high concentration of phenolic compounds, and volatile acid products during the AD of OMWW (Hamdi, 1996; Wang et al., 1989). The dilution of OMWW is the oldest treatment; at the beginning of AD, researchers always use large dilutions to reduce the inhibition process (Marques, 2001). The dilution could decrease the concentration of lipids and phenolics, leading to an increase in methane production. Researchers recommended using a dilute (1/4) for this lipid-rich wastewater (Fang Lou et al., 2012; Koutrouli et al., 2009). Gharsallah (1994) demonstrated that methane production by AD of OMWW with a small organic amount (20 gCOD L 1) had a much higher organic charge (200 gCOD L 1). Ruggeri et al. (2015) recommended diluting OMWW with tap water to increase both biogas and methane production. They obtained 13.5 L/L of biogas with a large quantity of methane (74%). The water dilution allowed to increase the production of methane by more than 36-fold compared to the test without dilution and pretreatment. Beccari et al. (1996) confirmed that enough dilution (10 gCOD L 1) could reach a high concentration of methane (80%). Therefore, the dilution of OMWW in the AD process can eliminate its toxicity to the methanogenic bacteria, reducing inhibition risk; consequently, methane production increases. Hamdi (1996) reported that the dilution equally reduces the digester’s volumetric capacity. Thus dilution is a straightforward and less expensive method; it only requires choosing the suitable concentration (1/4) and a large digester for significant energy recovery.

4.7.2

Pretreatment Process

It has been already reported that the pretreatment is necessary for the AD of OP. This step is essential in the AD of OMWW to increase the conversion to methane. Among the chemical pretreatments of OMWW is the employing of some coagulation agents such as Al2SO4, FeSO4, and FeCl3. These coagulants’ addition allows improving AD of OMWW for obtaining 80% methane production, higher than the untreated OMWW (Ahmed et al., 2019). Researchers have recommended the use of bentonite. It is a nontoxic clay mineral with high adsorption characteristics and cation exchange capacity (Al-Essa, 2018). The bentonite can play two roles; it adsorbs lipids and can output them slowly during the AD process (Beccari et al., 2002). Beccari et al.

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(2002) recommended the combination of Ca(OH)2 and bentonite to eliminate a significant quantity of lipids (99.5%) and phenolic drivers (45%) before the AD process of OMWW. Currently, Fenton pretreatment takes up space in the AD of OMWW. This process is a non-selective way of degradation; it consists of generating a strong oxidant called hydroxyl radicals in the presence of Fe2+ ions by catalytic oxidation of H2O2. This Fe2+/H2O2 system can enhance the delignification and hemicellulose degradation into OMWW (Maamir et al., 2017). It can also destroy polyphenols by anodic oxidation by producing hydroxyl radicals (Khoufi et al., 2006). Maamir et al. (2017) recommended Fenton pretreatment to ameliorate their conversion into biogas and reach 24% compared to untreated. Khoufi et al. (2006) have confirmed that this process reduces the OMWW toxicity from 100% to 66.9% using some conditions. Firstly, the decreasing phenolic (65%) and ortho-diphenols (74.5%) compounds, and secondly, the increasing pH from 4 to 7.6 (Khoufi et al., 2006). Amor et al. (2015) recommended using the Fenton technique for OMWW after an AD process to better yield. Thus, the combination of Fenton pretreatment and the AD process can be a successful solution for the treatment and management of OMWW. The applications of microbial additives as biological pretreatment stage in the AD process of OMWW is necessary, it can improved the methane production. Borja et al. (1995b) noticed that the addition of Azotobacter Chroococcum and Aspergillus terreus allows to reach significant production 315 and 350 mL CH4 g 1 COD, respectively, against the 260 mL CH4 g 1 COD obtained for the untreated OMWW (Borja et al., 2005).

4.7.3

Anaerobic Co-digestion

The digestion process needs selecting suitable matter to have an excellent synergistic balance and reduce the negative impact of toxicity of OMWW. Researchers have used certain organic materials, such as agricultural residues and organic wastes, to succeed in this process. Athanasoulia et al. (2012) recommended using a mixture of 70% waste-activated sludge and 30% OMWW to enhance the methane production and remove 72% organic loading rates. Gelegenis et al. (2007) recommended using diluted poultry manure for improving the AD of OMWW. Dareioti et al. (2009) used other organic mixtures (5% cheese waste, 40% cow manure, and 55% OMWW) to produce 1.3 L CH4 L 1. Therefore, a regrouping of the previous processes independently in a single plant with two separate bioreactors makes it possible to maximize the biogas generation. This renewable energy produced can ensure the olive mill’s energy satisfaction and the treatment station’s liquid waste progress. Therefore, we can conclude that constructing a biogas plant that combines these methods of improving anaerobic digestion makes it possible to recover energy from this waste (Fig. 4.6).

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Fig. 4.6 Strategy proposal for the valorization of olive mill wastewater in the Mediterranean region

4.8

Conclusions and Future Directions

Every year, olive oil production increases by increasing the demand for cooking, kitchen, therapy, and medicine. This continuous production of olive oil is accompanied by a progressive production of OP and OMWW, leading to the increased risk of destruction of our planet’s natural ecosystems. The conversion of olive wastes into methane by AD has become a necessity. Few adjustments such as the dilution, pretreatments, and anaerobic co-digestion of these olive mill wastes before or during this anaerobic treatment process are needed. In this chapter, we have shown that AD, with some modifications, makes it possible to recover this waste by enhancing clean energy and reducing their volume production and their impact on the environment. The solid and liquid olive mill wastes are not waste but a renewable deposit of energy and fertilizer for Mediterranean countries. So, the AD process of olive waste in the Mediterranean region is an efficient means for treating, managing, and producing sustainable energy. It has a lot of advantages, it is a simple technology whit a high applicable COD and polyphenols, it is no use of fossil fuels for treatment and chemicals, the reactors can be operated during the harvesting seasons only, it also contributes to the economic viability of olive mills by keeping costs and financial benefits, and it has a high degree of compliance with many Mediterranean national waste strategies. The separation of pretreatment and the AD phases, such as pretreatment tank, hydrolytic-acidogenic reactor, and methanogenic digester, in three completely independent reactors, can be used as a strategy to enhance the AD digestion of solid and liquid forms of olive wastes in the Mediterranean region. Currently, the application of nanotechnology in the form of chips and sensory systems in the AD of OP or OMWW process can afford an innovative way of controlling, monitoring, and correcting the inhibition produce by different parameters.

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Chapter 5

Agronomic Olive Bio-waste Management: Combination of Olive Mill Wastewater Spreading and Compost Amendment – Effects on Soil Properties and Olive Tree Performance Salwa Magdich and Emna Ammar

Abbreviations BOD COD DM Gs OMW Pn

5.1

Biological oxygen demand Chemical oxygen demand Dry matter Stomatal conductance Olive mill wastewater Photosynthesis

Olive Sector

The olive tree was introduced in the Mediterranean basin about 6000 years ago. It is considered one of the oldest known cultivated trees in the world (COI, 1998). The tree belonging to the botanic family of the Oleaceae may reach 8–15 m height, its trunk is typically gnarled and twisted, and it could produce olives for more than a hundred years. The olive leaves are oblong silvery green, measuring 40–100 mm long and 10–30 mm wide. The fruit is 5–10 mm long, thinner-fleshed, and smaller in

S. Magdich Laboratory of Environmental Sciences and Sustainable Development, University of Sfax, Preparatory Institute of Engineering Studies of Sfax, Sfax, Tunisia E. Ammar (*) Laboratory of Environmental Sciences and Sustainable Development, University of Sfax, Preparatory Institute of Engineering Studies of Sfax, Sfax, Tunisia National Engineering School of Sfax, Sfax, Tunisia © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 M. F. Ramadan, M. A. Farag (eds.), Mediterranean Fruits Bio-wastes, https://doi.org/10.1007/978-3-030-84436-3_5

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wild plants than in orchard cultivars. Olive fruit is harvested green to the purple color stage during the autumn season (Abu Hanieh et al., 2020). Since the end of the last century, to reduce costs, the cultivation systems have changed from traditional plant systems to intensive ones (Miglietta et al., 2019; Romero-Gámez et al., 2017). At the same time, other countries have introduced olive production, and new cultivars were used (Dabbou et al., 2009). At present, the worldwide production area involved in olive growing includes more than ten million hectares; the world production has increased thanks to the development of modern olive groves. Indeed, traditional olive groves intensification and new production area expansion are noted in the last years, improving the olive oil world production (Cappelletti et al., 2017). The Mediterranean basin is the traditional and main area of olive cultivation, including 97% of the world olive orchards (Belaqziz et al., 2016; Galanakis & Kotsiou, 2017; Hamimed et al., 2021; Sáez et al., 2021). In Tunisia, the olive (Olea europaea L.) tree is the most important evergreen tree, with 90 million olive trees covering 1.8 million hectares of land and growing traditionally in rain-fed conditions. This is the case of the Sfax region, where more than 25% of national olive oil is produced (COI, 1998; Rouina et al., 2020). The mean plantation density is 35 trees per hectare, with a minimum value of 22 and a maximum of 100–150, respectively, in semi-arid conditions and irrigated systems. Furthermore, noticeable olive tree expansion occurs with the controlled irrigation culture system practice (Ben Ahmed et al., 2007; Miglietta et al., 2019). In the Mediterranean countries where edaphic and climatic conditions are suitable for olive tree cultivation, olive oil is the main source of food vegetable oil, and the olive oil industry is the most important economic sector, especially in Spain, Greece, Italy, and Tunisia (Bargougui et al., 2019; Hamimed et al., 2021). From 2009 to 2015, the average world production of olive oil was about 2.9 million tonnes, and more than two million tons were produced in the European Union, with about 63% in Spain, 20% in Italy, 14% in Greece, and 7% in Tunisia (International Olive Oil Council, 2016). Besides these main countries followed by Syria, Morocco, and Turkey, many other countries in the Middle East, the USA, Australia, Argentina, and China have started improving their olive oil production by increasing the olive tree implantation (Hamimed et al., 2021; Hanieh et al., 2020; Roig et al., 2006; Souilem et al., 2017).

5.2

Olive Processing and Biomass Residues from the Olive Oil Industry

Olive oil extraction involves different successive processes, starting with leaf removal, olive washing, followed by grinding, malaxing, and finally oil separation (Fig. 5.1). The oil yield and the amount, as well as the physicochemical properties of the produced wastes and effluents, depend on the olive oil extraction method used to

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Olives

Reception and storage

Defoliation and washing Olive washing wastewater

Crushing

Leaves, branches

Malaxation (ambiant temperature 25-30 °C)

Water

Extraction (Pressure/Centifugation)

Olive oil

Olive mill wastewater

Evaporation

Spreading

Olives Pomace

Treatment

OMW Paste

Co-composting

Compost

Fig. 5.1 Olive oil extraction process and valorisation of olive mill wastewater (OMW) perspectives

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directly transform the fruit of the fresh olive into a natural fruit juice, i.e., virgin olive oil, using only mechanical methods, in order to preserve its authentic organoleptic characteristics, according to the European Commission Regulation No. 1513/2001 (COI, 1998; Official Journal of European Community, 2001). Olive fruits must be processed as quickly as possible after harvesting; this step would minimize oxidation and give low oil acidity. The diverse/multiple processes used to extract olive oil are mechanical with the malaxation of the resulting paste and the separation of the oily phase by pressure or centrifugation. These processes are generally achieved with three systems commonly used, i.e., the traditional discontinuous press process, the three-phase, and the two-phase decanter centrifuge methods (Boskou, 1996; JICA, 1993; Souilem et al., 2017). Consequently, the water volume consumed for the extraction depends on the extraction system. Indeed, the extraction of 100 kg olives needs 40–60 L of water for classical pressure, 100 L for continuous centrifugation process, and only 2–3 L for a two-phase ecological system (Ammar et al., 2005; Boskou, 1996; Caputo et al., 2003). Considering the olive drupe, which includes the epicarp (2.0–2.5% DM), the mesocarp (70–80% DM), the endocarp (18–25% DM), and the kernel (2–5% DM), the olive oil is located in the mesocarp, and the cellulosic matter is predominant in the endocarp (74% DM) (JICA, 1993). The residual bio-wastes issued from olive processing are olive leaves rich in extractives compounds (36.5% DM), a source of phenolics, and antioxidants. Indeed, phenolic compounds present as a residual mixture include monomeric aromatics and polymerized heterogeneous pigments that vary from 0.5 to 24 g/L in the OMW (Galanakis & Kotsiou, 2017; JICA, 1993; Skaltsounis et al., 2015; Zagklis et al., 2013). After olive washing and leaves separation, the oil extraction leads to a main solid phase: olive pomace made up of crushed olive stones, a part of the process water, and all the non-oil material from the olive fruit. It is rich in lignin (24–40% DM), cellulose and hemicellulose (24–40% to 11–16%), ash (8–14% DM), and extractives compounds (20–34% DM) such as tyrosol, hydroxytyrosol, oleuropein and others promoting this bio-waste. According to the olive process used, a residual fatty material percentage could be found in the pomace extracted in refinery industries (JICA 1996; Negro et al., 2017). The effluent from olive oil production named olive mill wastewater (OMW) or olive vegetation water, “Alpechin” or “Jamilia” in Spain, “Aqua di vegetazioni” in Italy, or “Katsigaros” in Greece and “Margines” in Tunisia, has attracted scientific attention during the three last decades.

5.3

Olive Mill Wastewater (OMW) Characterizations

Despite the economic interest and the agricultural importance of olive growing, it is undoubtful that the olive oil extraction process generates considerable quantities of agro-industrial wastes (Al-Imoor et al., 2017). In addition to its main product, the olive oil industry generates enormous amounts of bio-wastes (Al-Imoor et al., 2017),

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mainly effluent: the olive mill wastewater and a solid olive pomace (Buchmann et al., 2015). The OMW annual amount generated worldwide was estimated to be about 30 million m3 in the Mediterranean basin (Haddad et al., 2021). Considering its most important characteristics’, OMW is an aqueous, dark, foulsmelling, and stable emulsion (Hamimed et al., 2021; Kavvadias et al., 2014). Its disposal is one of the most severe environmental issues in the Mediterranean basin countries producing olive oil. More specifically, OMW is characterized by high pollutant load, salinity, and phytotoxic levels of phenolics representing 98% of the olive fruit (Sáez et al., 2021; Souilem et al., 2017). It includes relatively high organic compounds and mineral nutrients concentrations (JICA 1996; Chtourou et al., 2004; Jarboui et al., 2010; Chatzistathis & Koutsos, 2017). Besides the severe environmental problem raised, OMW offers precious fertilizing value attributed to its rich nutrient resources (Jarboui et al., 2012; Skaltsounis et al., 2015; Souilem et al., 2017). This effluent consists typically of 83–94% water, 4–16% organic compounds, and 0.4–2.5% minerals (Ammar et al., 2005; Dermeche et al., 2013; Hamimed et al., 2021). Furthermore, OMW is characterized by a high potassium concentration and exceptional levels of nitrogen, phosphorus, calcium, magnesium, and iron (Barbera et al., 2013; Jarboui et al., 2008, 2012; Magdich et al., 2020). Its organic fraction includes sugars, tannins, polyphenols, polyalcohols, pectins, lipids, and proteins; these are valuable resource compounds representing a stock for recovery and/or valorisation perspectives (Galanakis & Kotsiou, 2017; Piotrowska et al., 2011). The effluent average physicochemical characteristics are presented in Table 5.1. It should be mentioned that the OMW chemical composition may vary according to many factors; these are the olive tree variety, climatic and agronomic conditions, the olive ripeness, the fruit storage conditions, and the extraction process used (Ammar et al., 2005; Boskou, 1996; Hamimed et al., 2021; Jarboui et al., 2008; Negro et al., 2017). Table 5.1 Physico-chemical characterization of the raw OMW spread Parameter pH Electrical conductivity (mS cm 1) COD (g L 1) BOD (g L 1) Organic matter (g L 1) N (g L 1) Total phenols (g L 1) P (g L 1) K (g L 1) Na (g L 1) Cl (g L 1) Ca (g L 1) Mg (g L 1)

Piotrowska et al. (2011) 4.90  0.22 11.6  0.66

Jarboui et al. (2012) 4.87  0.10 14.1  0.20

Magdich et al. (2020) 4.17  0.38 11.4  0.74

187  1.23 38.4  1.13 47.5  1.56 1.70  0.22 3.31  0.10 0.06  0.02 3.47  0.64 0.04  0.10 1.00  0.12 0.03  0.10 0.02  0.01

125  0.80 31.8  0.66 56.4  1.98 1.40  0.08 4.00  0.09 1.02  0.02 4.27  0.32 1.20  0.12 0.47  0.13 1.36  0.05 0.58  0.24

128  1.56 48.2  1.22 50.4  1.11 1.87  0.39 0.99  0.12 0.58  0.20 5.89  0.76 1.36  0.24 0.86  0.17 1.20  0.11 0.46  0.10

Standard deviations represent analytical procedure variability

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Therefore, because of the effluent high organic load, its seasonal operation, high territorial scattering, and the presence of recalcitrant compounds (phenolic compounds), the development of adapted technologies and strategies for this liquid effluent management has been urgently stressed these last decades. Consequently, in the literature, several treatment methods have been recently developed and reported. These could be grouped into four principal types: natural evaporation (disposal), physicochemical (adsorption, coagulation, flocculation, electrocoagulation), biological (aerobic, anaerobic, integrated approaches), and oxidation and advanced oxidation method, as well as the various hybrid technologies (Ammar et al., 2005; Bargaoui et al., 2020; Dermeche et al., 2013; Jarboui et al., 2008, 2010; Mekki et al., 2006a, 2006b, 2008; Zagklis et al., 2013). Nevertheless, a benchmarking of all of these techniques could be established considering the treatment effectiveness in terms of chemical oxygen demand (COD) and phenolic content reduction reflecting ecotoxicity, CO2 emissions expressing energy consumption, and economic viability based on the treatment cost and the possible profit-making from the process by-products’ produced (Lee et al., 2019; Zagklis et al., 2013).

5.4

Olive Mill Wastewater Agronomic Valorisation

Low organic matter content is a common feature of Mediterranean soils. It causes deterioration of workability and limits fertility and productivity (Chehab et al., 2019). Moreover, in arable soils, the long-term continuous decomposition of organic matter may lead to soil degradation with its consequent inability to ensure sustainable production (Hemmat et al., 2010). The soil acts as a filter that retains suspended solids and clay, humus, and newly formed organic colloids fixed to the mineral salts (Di Bene et al., 2013). In some cases, soil microorganisms may enhance the rapid organic constituents’ decomposition, such as lipids and phenols present in OMW (Jarboui et al., 2012; Riolfatti, 1983). Indeed, when spread in the soil, the phenols degradation is boosted by their exposure to light and air; consequently, after 1–4 months, their levels in the soil would be reduced to reach normal values (Potenz et al., 1980; Saadi et al., 2007). Furthermore, in the soil, the phenolic compounds are the precursors of humic substances which represent the most active fraction of the soil organic matter; they play an important role in soil fertility and protect plant growth from contaminants like pesticides and heavy metals (Toscano & Montemurro, 2012). Finally, following OMW spreading, the unpleasant odour released is scaled-down and remains less offensive than other waste materials (Proietti et al., 1995). Therefore, agricultural practices based on OMW spreading are strongly recommended for Mediterranean agroecosystems, especially in Tunisia, where the effluent production may reach about 7  105 m3 year 1, a vast volume generated during few months between November and February (Mekki et al., 2018). In agricultural land, OMW application is a simple and relatively inexpensive disposal

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method that may contribute to sustainable agriculture development, particularly under the severe climatic conditions that affect olive oil-producing countries (Sierra et al., 2007). For these reasons, more attention was given to better managing OMW spreading the practice, and to improve olive production with low cost while considering the product quality and the environment preservation results based on a benchmarking study (Zagklis et al., 2013).

5.4.1

OMW Spreading in an Olive Field

The recycling of the olive mill effluent through its spreading in the olive field would have two main impacts, firstly on the soil physicochemical and microbiological characteristics and secondly on the tree that would use the OMW as fertilizer. Both of these effects will be developed in this session. 5.4.1.1

Olive Extraction Effluent Effects on Soil Properties

In a sandy olive field, the application of OMW at three doses: 50, 100, and 200 m3 ha 1 year 1 over three successive years in the South of Tunisia (Fig. 5.2) revealed that the electrical conductivity, organic matter, total nitrogen, sodium, and potassium soil contents increased proportionally to the OMW concentration and application frequency in the soil OMW-treated layers, i.e., 0–20, 20–40, 40–60 and 60–80 (Fig. 5.3) (Magdich et al., 2013). In addition, aerobic bacteria and fungi increased in proportion with the OMW spreading rates. Following OMW application, all the soil enzyme activities tested (dehydrogenase, β-glucosidase, and urease) were enhanced in the OMW-amended soils compared to the control, especially in the superficial horizon (0–20 cm) (Magdich et al., 2020). Indeed, Piotrowska et al. (2006) reported increases in dehydrogenase, fluorescein diacetate hydrolase, urease activities, and decreases of nitrate reductase and phosphatase soil enzyme activities after OMW application. The OMW agronomic valorisation by its spreading in the olive field improved the soil chemical and microbial properties; these have beneficial effects on soil fertility and seem to stimulate soil enzymatic activities by increasing the organic matter, nutrients, and microbial activity. Nevertheless, the addition of 200 m3 ha 1 could increase the salinity of the soil after long-term and frequent applications of OMW, which negatively impacts the soil’s chemical properties (Magdich et al., 2012, 2013, 2020). Similarly, Ben Rouina et al. (2006) found that the annual application of OMW in a sandy soil olive orchard, at a rate of 100 m3 ha 1, for 10 years markedly improved soil fertility. Nutrients availability was significantly increased, especially in the surface soil layers, after OMW application, with a particular increase of inorganic N, extractable P, exchangeable K, and Mg and available micronutrient concentrations (Chaari et al., 2014; Kavvadias et al., 2014).

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OMW evaporation pond

Impact on physiological and biochemical responses of olive trees

OMW doses agronomic application (50, 100, and 200 m3 ha-1 year-1)

Effects on chemical and microbial soil properties

Fig. 5.2 Olive mill wastewater management and spreading in olive field

More recently, Belaqziz et al. (2016) found that after spreading untreated OMW in soil, the nutrients rates increased by 81% for N, 66% for P, and 88% for K. Particularly, the soil K level increase could be considered as the most exciting effect of OMW application on soil chemical properties (Ayoub et al., 2014; Chartzoulakis et al., 2006). Generally, soil fertility is thoroughly enhanced, and no serious adverse effects on soil chemical properties have been reported (Chartzoulakis et al., 2010; Hamimed et al., 2021). Furthermore, the amendment of sandy-soil by different OMW doses (25, 50, 75, and 100 m3 ha 1) has strongly enhanced its physicochemical properties in organic matter, nitrogen, and potassium (Bargougui et al., 2019). These authors affirmed significant proliferations of the soil microbiological activities, in parallel to the OMW doses applied increase, and the soil respirometric activity monitoring revealed that the OMW addition at a dose of 50 m3 ha 1 has significantly improved its biological activity; this fact is correlated with the soil enrichment with organic matter improving microflora growth.

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Total nitrogen (mg kg-1)

500

(A)

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First year

450

Second year

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Third year

350 300 250 200 150 100 50 0 0-20 20-40 40-60 60-80 0-20 20-40 40-60 60-80 0-20 20-40 40-60 60-80 0-20 20-40 40-60 60-80 Control

Exchangeable potassium (mg kg-1

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First year

(B)

Second year

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Third year

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0 0-20 20-40 40-60 60-80 0-20 20-40 40-60 60-80 0-20 20-40 40-60 60-80 0-20 20-40 40-60 60-80 Control

50

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200

Fig. 5.3 Total nitrogen (a) and exchangeable potassium (b) contents at the different layers in the experimented field after three successive years of OMW application at different doses (control: 0 m3 ha 1, 50 m3 ha 1, 100 m3 ha 1 and 200 m3 ha 1). Values represent the means of three samples (SE)

OMW spreading leads to soil polyphenols content increase following the yearly numbers, and the quantity applied. However, at 50 m3 ha 1 and after six successive years of spraying, no difference was noticed while comparing the treated soil to the control one (Magdich et al., 2012). In the same perspective, Meftah et al. (2019) affirmed that the irrigation of sandy olive soils by two different OMW doses: 50 m3 ha 1 and 200 m3 ha 1 has strongly influenced the soil physicochemical and microbiological characteristics. A remarkable richness in organic matter and concentration rise of the different mineral elements has been revealed. In addition, the dynamics of the phenolic compound exhibited the migration of these compounds, which have been detected beyond 120 cm soil depth, correlating with the sandy and highly permeable grain size of the studied soil (Jarboui et al., 2010).

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At a rate of 80 m3 ha 1, OMW spreading in the olive field showed that, despite long-lasting repeated applications, no residual effects or negative trends were observed in the soil chemical and biochemical parameters (Di Bene et al., 2013). Similarly, Mekki et al. (2013) did not identify any adverse effect on initial soil pH after OMW addition, but its electrical conductivity was increased. Moreover, Chaari et al. (2015) reported that the soil pH, electrical conductivity, organic matter, total nitrogen, phosphorus, sodium, and potassium contents increased with the OMW rate spread in the olive grove. Recently, when spreading a large amount of OMW (500 m3 ha 1), a dose higher than the limit value (80 m3 ha 1) established by the Italian Law (574/1996), Lanza et al. (2020) noticed chemical and microbiological soil properties improvement. According to these authors, the OMW spread significantly enhanced the soil characteristics by increasing the organic-reducing substances content and humic-like properties. In addition, the spreading of 100 m3 OMW ha 1, an amount 1.25 times that established by the Italian law, reduced the soil chemical fertilization and its productivity compared to the untreated control soil. Finally, in the OMW-treated parcels with different doses, it was ascertained that the soil microorganisms’ respiratory activity was higher than that of the control parcels in the short, medium period (2–8 months). The OMW application to the soil surface of an olive orchard (Olea europaea L.) during the wintertime for three consecutive years, at a maximum annual rate of 420 m3 ha 1, exhibited the most important effects on soil composition, including significant enhancement of soil fertility, and an increase of phenolic compounds content in the OMW-treated soil. However, phenols decomposed rapidly, and no accumulation trend was observed after subsequent applications (Chartzoulakis et al., 2010). The same authors did not notice any alteration in drainage water composition at a 2 m depth following OMW applications for 3 consecutive years (364 m3 ha 1 year 1) in a 20-year-old olive grove planted on a medium texture fluvisol. In the olive orchards, the OMW successive spreading on sandy soils with doses below 200 m3 ha 1 did not negatively affect and induced a soil conglomeration thanks to its high organic matter content. Moreover, it was noticed that the organic matter rate increases the soil aggregates cementation. Therefore, the structural stability was improved, and wind erosion was reduced (Abichou et al., 2009). In particular, OMW spreading may initially decrease the water infiltration due to the water repellency of the fatty particles adsorbed in the soil surface layers. However, this action was attenuated after these substances decomposition in a short time. Subsequently, the porosity was improved, while air and water dynamics soil were increased and surface soil crust formation reduced. These facts lead to erosion reduction in the sloping land and waterlogging at the plain (Mahmoud et al., 2010). Considering telluric microbial flora, changes in bacterial communities were observed by Paredes et al. (1987) and later by Karpouzas et al. (2010) as a consequence of soil OMW application. The first authors reported an initial decrease in spore-forming bacteria that was followed by an increase. They also observed the

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enhancement of acidophilic, nitrogen, and phosphate cycles. Mekki et al. (2006a) found a significant reduction in the number of soil nitrifying bacteria at the highest OMW dose applied (400 m3 ha 1). Based on a biochemical approach, Mechri et al. (2007) observed that the addition of more than 30 m3 OMW ha 1 generated an increase of soil fungi, Gram-negative bacteria, and actinomycetes, while Grampositive bacteria decreased significantly after 1 year. Kotsou et al. (2004) reported that OMW application resulted in a shift of the bacterial community toward copiotrophic bacteria, which comprise the first colonizers of newly added organic matter. Interestingly, the OMW amendment caused minor long-term effects on soil microflora, whereas there was no evidence of any inhibitory effect on the soil microorganisms’ growth. Mechri et al. (2010) revealed that OMW agronomic application has essential effects on the soil microbial community. Bacteria were relatively more reduced by OMW application than fungi and actinomycetes, as demonstrated by an increased index of fungal/bacterial and actinomycetes/bacterial. These soil microbial modifications were higher in the OMW amended soil than in control, especially at the high OMW rate. El Hassani et al. (2010) observed a slight increase in yeast, actinomycetes, nitrogen aerobe, and cellulolytic abundances when the OMW spread dose was equivalent to 160 m3 ha 1, compared to the 80 m3 ha 1 standard dose. Thus, high OMW concentrations were toxic for these microbial groups. This antimicrobial activity was principally caused by phenolic compounds (Ammar et al., 2005; Jarboui et al., 2012; Ramos-Cormenzana et al., 1996). Barbera et al. (2013) reported that OMW exerts two contrasting actions on soil microflora its stimulated soil microflora development by temporarily soil carbon enrichment and inhibited some microorganisms and phytopathogenic agents by phenolic compounds. According to Casacchia et al. (2012), soil amendment using OMW can be an important agricultural practice for supporting and stimulating soil microorganisms in sustainable olive orchards. 5.4.1.2

Olive Tree Performances Improvement by OMW Spreading

The impacts of OMW spreading on olive tree production performances and olive oil quality are considered to apprehend better the fertilizing effects of OMW spread in olive tree orchard, respecting a circular economic approach.

Olive Tree Performance After 6 years of OMW application in the olive grove, the olive-trees (Olea europaea L., variety Chemlali) production was increased by 30% and the optimum rate used was exceeding 50 m3 ha 1 year 1, but the yield increase was limited to around 1% when the OMW amendment volume was doubled (Magdich et al., 2012). Moreover, spreading 100 m3 resulted in the highest olive yield. These results reflected the

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continuous improvement of olive yield up to the spreading rate of 100 m3 ha 1 year 1 and the overall OMW beneficial fertilizing effect of olive trees. The olive productivity improvements could be related to the effluent richness in easily assimilated available substances, providing carbon, phosphorus, potassium, and energy to soil microflora (Lozano-García et al., 2011). On the other hand, the OMW applied doses include about 86% water (Table 5.1). The positive effect of the OMW amendment on olive growth and productivity has also been demonstrated previously by Altieri and Esposito (2008) in olive orchard amended over 5 years with experimental olive mill waste. Furthermore, Nasini et al. (2013) confirmed the enhancement of olive productivity in orchards treated with solid olive mill waste. Concerning physiological and biochemical olive tree parameters, significant raises of net photosynthesis (Pn) and stomatal conductance (Gs) in OMW treated olive trees by 50, and 100 m3 ha 1 were noted. The lowest Pn and Gs rates were recorded for the highest OMW dose (200 m3 ha 1) spread. In addition, olive plants amended with 200 m3 ha 1 exhibited a significant decrease of both chlorophylls (a + b) and carotenoid contents, while olive trees that received 50 and 100 m3 ha 1 of OMW showed higher photosynthetic pigments contents compared to the untreated control olive trees (Magdich et al., 2016). In the olive tree leaves irrigated with 200 m3 ha 1, the photosynthetic performance and the total chlorophyll and carotenoid concentration reductions could represent an adaptive mechanism for the olive tree to cope with an excessive OMW dose than merely a negative consequence of it. In this perspective, OMW-treated plants had similar or even higher photosynthetic rates than control plants. The stomatal conductance and maximum quantum yield were not affected by the raw OMW application, giving similar values to control olive trees during the experimental period (Chartzoulakis et al., 2010). In addition, the application of limited OMW doses of 10 and 20 L m 2 is recommended to improve olive plant performances. Indeed, significant increases in shoot growth, photosynthesis, fruit set, and fruit yield were suggested (Ayoub et al., 2014). The OMW spread at 50, and 100 m3 ha 1 significantly increased the olive leaves mineral contents (N, P, K, Ca, and Mg). Nevertheless, the highest OMW application (200 m3 ha 1) was associated with a significant reduction of olive leaf nutrient concentrations (Magdich et al., 2016), confirming that olive tree responses depended on the OMW dose applied. However, olive trees amended with 200 m3 ha 1 showed significant leaf nutrient concentrations decrease compared to the control plants. This result would be attributed to soil nutrient depletion since the highest OMW application reduced the olives mineral uptake significantly, as previously reported by Mechri et al. (2011). In this context, Chartzoulakis et al. (2010) exhibited that the raw OMW application did not affect the leaf N, P, Ca, Mg, and Na concentration of olive trees. This mineral content rise was attributed to the soil chemical properties improvement beneficial for soil fertility, offering the opportunity to recycle the various effluent minerals input. When studying the effects of OMW application (30, 60, 100, and 150 m3 ha 1) on the physiology and mineral nutrient contents of olive trees, Mechri et al. (2011) supported that at the highest application rate (150 m3 ha 1), the olive trees uptake reduction of N, P, K, Ca, Mg, Fe, Cu, Mn and Zn occurred. In addition, the olive

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trees amended with the same dose exhibited a decrease in photosynthetic rate, as well as reduction of quantum yield and photosystem II photochemical efficiency, together with depressed electron transport rate. The OMW toxic impacts on young olive trees growing in pots after irrigating with five OMW doses (0, 2, 4, 6, and 8 L pot 1) were observed by Ammar and Ben Rouina (1999), who noticed high toxicity effects that resulted in plant death, occurring at the highest doses (6 and 8 L pot 1). In an open field test, Ferri et al. (2002) did not report any significant changes in olive tree production when provided with 50 m3 of OMW that were extracted by the pressure extraction method. However, the OMW application improved soil chemical properties by increasing the exchangeable K in loamy clay soil and P in a “red soil”.

Olive Oil Quality The OMW long term is spreading effect on olive oil characteristics, after 6 yearly successive spreadings was investigated by Magdich et al. (2015), considering the free acidity, peroxide values, as well as K232 and K270 coefficients; the olive oil extracted from the control parcel and that of the OMW treated-parcels met the European Union requirements of an extra virgin olive oil category (Table 5.2). Therefore, the OMW agronomic application did not affect the oil quality indices since no statistically significant difference ( p > 0.05) was recorded between the control and the different OMW doses used for soil amendment after 6 years of spreading. Furthermore, the oil phenols contents showed an increase of 10% in oil samples issued from OMW treated plants. This result is of great interest since phenolics are associated with the nutritional and sensory olive oil qualities and play a beneficial role in human health by their anticarcinogenic, antiatherogenic, antimicrobial, and antioxidant activities (Ben Youssef et al., 2012; Galanakis & Kotsiou, 2017). Indeed, phenolics are in the olive fruit (28%), but 2% are extracted in the oil phase. In the OMW, more than 40 relevant bioactive phenolics were identified, such as phenolic acids ( p-coumaric, benzoic, ferulic, protocatechuic, gallic), phenolic alcohols (tyrosol and hydroxytyrosol present at 25% of OMW DM). Moreover, OMW includes oleuropein, dimethyl-oleuropein, verbascoside, secoiridoid derivatives, and flavonoids (apigenin, anthocyanin, flavone, and quercetin). In this context, Ayoub et al. (2014) claimed that OMW application in the olive orchard (cv. Nabali Muhassan) for three seasons had no adverse effect on oil quality parameters (acidity, peroxide value, and UV absorbance at 232 nm, 270 nm) since all the oil samples analyzed were within the limits of the olive oil standard, classified as extra virgin olive oil. Indeed, Proietti et al. (2015) reported that solid oil mill waste and its derived-compost application to the soil for three consecutive years in an olive grove did not negatively impact oil quality and improved its phenolic contents. In addition, α-tocopherol content increased significantly ( p > 0.05) for the different OMW treatments compared to the control after six consecutive spreading years (Table 5.2). The increase of this antioxidant would have a positive effect on the

Total oil content (% FW) 28.6  1.47 29.4  2.32 28.9  1.63 28.2  1.14 –

Free acidity (%) 0.36  0.01 0.37  0.12 0.36  0.05 0.39  0.04 0.80

Peroxide value (meq O2 kg 1) 4.10  0.26 4.20  0.14 4.80  0.06 4.60  0.42 20 K232 2.00  0.02 2.34  0.01 2.18  0.18 2.02  0.03 2.50 K270 4.10  0.26 4.20  0.14 4.80  0.06 4.60  0.42 20

Extinction coefficients

Values represent the means of three samples (SE); FW fresh weight

OMW spread dose (m3 ha 1 year 1) Control 50 100 200 Standard values (International Olive Oil Council, 2016)

Total chlorophylls (mg kg 1) 0.32  0.05 0.34  0.06 0.38  0.02 0.34  0.02 – Carotenoids (mg kg 1) 1.76  0.02 1.80  0.01 1.76  0.05 1.79  0.06 –

α-Tocopherol (mg kg 1) 418.3  3.44 543.2  4.27 542.1  3.17 483.3  4.30 –

Total phenols (mg kg 1) 154.5  3.42 170.4  1.23 171.2  1.86 165.5  1.44 –

Table 5.2 Total oil content, free acidity, peroxide value, extinction coefficients, total chlorophylls, carotenoids, α-tocopherol and total phenols contents in the olive oil sampled after the sixth spreading of OMW at different doses: control (0 m3 ha 1), 50 m3 ha 1, 100 m3 ha 1 and 200 m3 ha 1

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commercial oil quality. Moreover, oil from olives submitted to OMW spreading would be nutritionally and healthy better than that obtained in the control treatment. Previous works carried out in Tunisia consisted of studying the effects of different OMW doses spreading on the soil and the plant and the dose optimization to be spread in an olive orchard. Considering the impacts on the soil, the olive tree production, and the oil quality, the results found enhanced the implementation of a national regulation allowing the spread of the effluent, like in other olive oil-producing countries such as Italy. The Tunisian decree authorizes this practice to appear, which authorizes 50 m3 ha 1 dose spreading once every 2 years in the same plot (JORT, 2013).

5.4.2

OMW Co-composting and Compost Amendment for Agricultural Land

Composting, a natural biological recycling process, has gained appeal in recent decades as agricultural soils continue to lose their fertility and the soil amendments necessary to replenish organic matter and nutrient content. The intensive agricultural production generally practiced leads to soil fertility loss, soil erosion, water contamination, soil compaction, and organic matter content reduction. Low organic matter rate is a common feature of Mediterranean soils, highly correlated to their fertility and productivity potential due to their direct impact on physical, chemical, and biological properties (Alburquerque et al., 2007; Masmoudi et al., 2020). Three successive phases can characterize the composting process: the initial short activation phase followed by a thermophilic phase where microbial activity is too intense, decomposing the bio-waste organic matter and the temperature remains above 45  C for 6 months. Finally, the maturation phase is lanced when temperature drops (Akratos et al., 2017; Chowdhury et al., 2013; Hachicha et al., 2006). OMW composting has proved to be an efficient valorization method as its final product was characterized as an excellent soil amendment. This process transforms the hazardous waste into an excellent quality final-product, increasing the income and viability of small-scale olive mill plants (Akratos et al., 2017; Hachicha et al., 2009). Therefore, the use of OMW as compost in agricultural land could increase soil organic content, and as a result, composting can play a vital role in modern sustainable agricultural practices (Chowdhury et al., 2013). Many researchers have proposed the direct application of OMW for agronomic purposes to take advantage of its high nutrients concentration and its soil ions mobilizing potential. In contrast, adverse effects are associated with its high mineral salt content, acidic pH, and the presence of phenolic compounds (Belaqziz et al., 2016). To overcome the phytotoxic effects of soil OMW spreading, its co-composting with other agro-industrial bio-wastes has been suggested (Fig. 5.4) (Akratos et al., 2017; Hachicha et al., 2009; Majbar et al., 2018; Zagklis et al., 2013). Composting is one of the main efficient technologies for OMW recycling that

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Turned mechanically

OMW Humidification

Olive's pomace and OMW solid dehydrated Poultry manure

Fig. 5.4 Co-composting of OMW with other agro-industrial wastes, including its dehydrated solid residue

transforms the effluent into fertilizer and provides efficient soil amendment that may complement and/or substitute chemicals (fertilizing and pesticides). This process allows the return of nutrients to cropland, avoiding the adverse effects often observed when applying these bio-wastes directly to the soil. The OMW could be absorbed in a solid substrate (lignocellulosic wastes or manures) before composting (Rigane & Medhioub, 2011). When OMW was composted with wheat straw, the end product presented a degree of humification of 78% and residual lignin content of 30%. Indeed, lignin fraction solubilized by the thermophilic flora decreased during the compost maturation stage. No phenols or phytotoxicity was detected in the end product. In addition, pot and field experiments performed on maize, rye grass, potato, and horticultural plants indicated that OMW co-composting was able to support partially or the nutritional culture’s needs and to improve soil properties (Hachicha et al., 2006, 2009; Tomati et al., 1996). During composting, the humidification of the processed bio-waste with OMW improved the compost quality. Consequently, the olive mill extraction effluent did not hinder the process (Hachicha et al., 2006). Indeed, the harmful phenolic compounds were widely decomposed during composting stages, and the minor remaining part would be degraded while applying the organic conditioner into the soil. As a result, the prepared composts were similar to an organic conditioner of vegetal compost. In terms of fertilizing value, such composts did not negatively impact soil phenols, pH, and electrical conductivity at different depths. The analyzed parameter concentrations were almost the same as those of the cattle manure. In this perspective, after 7 months of OMW composting with sesame bark, all of the phenolic compounds disappeared, and the phytotoxic effluent effects decreased during the composting, while assessed by the plant germination index that reached 80% after 210 days (Hachicha et al., 2009). This trend was confirmed by the

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correlation between physicochemical and toxic parameters. The results obtained confirmed the stability of the compost prepared from OMW with sesame bark and indicated gradual detoxification as the compost gets mature; such compost has been proved to be a good soil fertilizer improving its agronomic characteristics. Co-composting of OMW with poultry manure showed a significant phenols content decrease (99%) with a noticeable transformation of the low molecular weight fraction to a higher one during composting (Rigane et al., 2015). The same authors found that OMW-compost application improved the chemical and physicochemical soil properties, mainly fertilizing elements, such as calcium, magnesium, nitrogen, potassium, and phosphorus. In this context, olive mill by-products (olive mill solid husk, olive mill pomace, OMW, and leaves) were co-composted with poultry manure for up to 6 months. The produced compost was well disinfected due to the high temperatures achieved, characterized by a C/N ratio close to 10, a neutral pH, and richness in mineral nutrients (Bargaoui et al., 2020). These results confirmed the feasibility of the co-composting process to reduce OMW environmental pollution impact as well as their valorisation into valuable organic fertilizers with high nutrient values. In this perspective, Regni et al. (2017) showed that the long-term amendment with fresh and composted solid olive mill waste represents an efficient strategy to increase both soil fertility and carbon sequestration efficiency. Sáez et al. (2021) found that the composting method assisted with the earthworms enhanced phenolic compounds depletion and OMW ecotoxicity reduction more efficiently than composting alone, especially during the maturation stage. Moreover, vermicomposting was more effective in the OMW salinity reduction. The same authors mentioned that the final compost showed a photostimulation effect. Therefore, these in situ bioremediation strategies can be considered potential tools for decontamination and recovery of long-term OMW stored in evaporation ponds, which still poses an unsolved environmental problem. In the same way, MartínezGallardo et al. (2020) proved that composting is a sustainable way to recycle OMW along with organic wastes, simultaneously solving their negative environmental impact. The use of a fungal consortium for the bioaugmentation of composting process improves the bioremediation efficacy of the technique by speeding up the decrease of phytotoxicity and ecotoxicity and enhancing the phytostimulant produced compost properties (Chtourou et al., 2004; Jarboui et al., 2012). The valorisation of OMW and the wine by-products is a promising strategy for OMW sustainable management, allowing environmental threats to transform into valuable products. Indeed, the produced composts for soil amendment significantly improved soil fertility since field experiments showed an increase in radish yield by 10%. Moreover, the produced composts were harmless and did not have any phytotoxic effect on radish growth (Majbar et al., 2018). Galliou et al. (2018) produced an organic fertilizer (57% organic carbon) rich in nutrients (3.5% N, 1% P, 6.5% K) and with low phenolic content (2.9 g/kg), following OMW treatment combining solar drying and composting. These authors noticed that the composting process of the dried OMW with grape marc biowaste produced an excellent amendment for pepper plant cultivation, which approved its fertilizing effect similar to commercial NPK fertilizers.

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Conclusion

OMW exacerbates environmental problems in Mediterranean countries. This effluent is phytotoxic and contains phenolic compounds, organic acids, and lipids. It also includes high percentages of organic matter and notable potassium, nitrogen, phosphorus, calcium, and magnesium levels, which could be reused as fertilizers for sustainable agricultural practices. Indeed, the reuse of OMW by spreading or co-composting leads to a decrease in these pollutant bio-wastes. It improves the chemical, biological, and physical soil properties and can enhance crop yields, especially olive tree yield, by physiological and biochemical characteristics. The OMW application at defined doses is a solution to improve soil fertility when soil organic matter content falls below 1%, especially in semi-arid Mediterranean regions. The strengths of the OMW reuse as a soil amendment are the availability of the law regulating the spreading process in different countries, its timely disposal, simple equipment and technology required with low cost, and agronomic and environmental advantages. Consequently, the OMW controlled spreading on agricultural soil can be considered an alternative technique to chemical fertilizers since it provides soil with fertilizing substances. Finally, the co-composting of OMW is a feasible method of producing mature, pathogen-free compost, rich in nutrients and with low phenol content ensuring maximum benefit for crop production.

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Chapter 6

Olive Waste as a Promising Approach to Produce Antioxidants, Biofertilizers and Biogas Ayoub Haouas, Anas Tallou, Amin Shavandi, Mounir El Achaby, Khalid Aziz, Ayoub El Ghadraoui, and Faissal Aziz

6.1

Introduction

Olive fruits are used as table olives or for the production of olive oil; both are produced from different olive cultivars. Overall, the consumption of olive oil reaches 3.300,000 tons per year (IOOC, 2018). Olives are the leading tree crop, which is currently an important sector of Mediterranean countries such as Spain, Italy, Tunisia, and Morocco, accounting for 97% of world production (Oteros, 2014).

A. Haouas · A. Tallou Laboratoire Polyvalent en Recherche et Développement, Faculty of Science and Techniques, Sultan Moulay Slimane University, Beni Mellal, Morocco A. Shavandi BioMatter-Biomass transformation Lab (BTL), Université Libre de Bruxelles, Brussels, Belgium M. El Achaby Materials Science and Nano-Engineering (MSN) Department, Mohammed VI Polytechnic University (UM6P), Benguerir, Morocco K. Aziz Materials, Catalysis, and Valorization of Natural Resources, Faculty of Sciences, Ibn Zohr University, Agadir, Morocco A. El Ghadraoui Department of Chemistry “Ugo Schiff”, University of Florence, Florence, Italy F. Aziz (*) Laboratory of Water, Biodiversity & Climate Change, Semlalia Faculty of Sciences, Cadi Ayyad University, Marrakech, Morocco National Centre for Research and Study on Water and Energy (CNEREE), Cadi Ayyad University, Marrakech, Morocco e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 M. F. Ramadan, M. A. Farag (eds.), Mediterranean Fruits Bio-wastes, https://doi.org/10.1007/978-3-030-84436-3_6

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The three-phase olive oil extraction process generated a large wastewater volume, consisting of a mixture of olive juice and added water and containing residual oil. Several studies have shown that olive mill wastewater (OMWW) is a notorious high phytotoxicity pollutant with a negative impact on the environment, especially soil and water (Caporaso et al., 2018). The composition of OMWW contains a considerable amount of free phenolic compounds such as gallic acid, veratric acid, cinnamic acid, vanillic acid, caffeic acid, and tyrosol. These compounds have been reported to have antimicrobial action and phytotoxic effects, partially or totally inhibit the germination of seeds and plants and microorganisms’ growth (Ntougias et al., 2013). High concentrations of phenolic compounds can damage membranes and denature cellular proteins. They interfere with enzyme activity and promote the precipitation of healthy proteins. The free fatty acids, which are also present, exacerbate the inhibitory action of phenolics. During the last years, massive production of OMWW was stated, which must be treated before release into the environment (Azaizeh et al., 2020). The spreading of the waste from the olive oil mill, namely OMWW, in the surrounding land poses serious environmental problems. OMWW contains a wide range of valuable resources, such as a high proportion of organic and inorganic nutrients that could be recycled (Abu Tayeh et al., 2020). Many valorizing strategies have been proposed, including composting and soil applications (Haouas et al., 2020a, 2020b; Majbar et al., 2018; Muscolo et al., 2018), livestock feed (Shabtay et al., 2009), biogas production (Tallou et al., 2020b), recovery of phenolic compounds (Lissaneddine et al., 2021; Gullón et al., 2020) and biochar production (Abdelhadi et al., 2017). Other techniques have been used by the food and chemical industries to valorize the OMWW, particularly the production of natural antioxidants, disinfectants, biopolymers, and biogas (Ntougias et al., 2013). Nevertheless, to date, none of them has been adopted a real valorization of OMWW at an industrial scale. This chapter reports the most viable technologies to recycle OMWW to produce valuable products and a successful example of valorization, reducing the gap between lab-scale research and the actual applications at the industrial level.

6.2

OMWW Composition and Toxicity

The chemical composition of OMWW is highly variable, both qualitatively and quantitatively. It depends on many factors such as climatic conditions, cultivar type, fruit maturity, and olive oil extraction method (Khdair et al., 2019). Generally, OMWW contains soft tissues of the olive fruit in the form of soluble organic compounds and a large fraction of water (around 80%) used in the various stages of the oil extraction processing (Dutournié et al., 2019; Gullón et al., 2020). It is characterized by undesirable color and odor, acidic pH (between 3.0 and 5.9), and

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Fig. 6.1 OMWW’s mean composition

salt minerals (0.4–2.5%). Typically, OMWW consists of 2–15% of the total polyphenolics content 0.03–1.1% lipids, and 4–16% organic compounds (Fig. 6.1), such as carbohydrates (2–8 g/100 g), pectin, lignin, and tannins (Rahmanian et al., 2014). This aqueous waste represents a crucial environmental problem and has been the most polluting waste produced by olive mills in the Mediterranean region over the years (Gullón et al., 2020; Roig et al., 2006). OMWW is often disposed of in evaporation ponds or various environmental receptors that cause strong odors, soil infertility, plant growth inhibition, pollution of natural streams, and severe effects on groundwater, aquatic fauna, and ecological status (Dutournié et al., 2019). Phenolic compounds are the leading cause of toxicity presented in OMWW due to their low molecular weight (Fiorentino et al., 2003). Only 1–2% of the total phenolic compounds produced during the grinding of olive pulp remain in the oil phase. In comparison, approximately 98% is lost in the OMWW, which agrees with phenols’ hydrophilic nature and their high solubility in the water phase (Babić et al., 2019; Caporaso et al., 2018). Soluble phenolics in OMWW contain cinnamic acid derivatives (e.g., caffeic, coumaric, and ferulic acid), benzoic acid derivatives (e.g., protocatechuic, hydrobenzoic, vanillic, and gallic acid), and tyrosol derivatives such as p-hydroxytyrosol and 4-hydroxyphenyl acetic acid. However, the list continues with other problem molecules such as caffeoylglucose, apigenin, quercetin, cyanidin, etc. (Justino et al., 2012). The high concentration of polymeric phenols has antimicrobial and phytotoxic effects due to their ability to combine with other organic components (e.g., proteins), thereby altering cell membrane permeability and intercellular transfer mechanisms (Peri & Proietti, 2014; Regni et al., 2017). These compounds may also cause narcotic effects on seeds and early plants due to non-covalent membrane interactions. The

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availability of phenolics has led to a significant shift in soil microbial communities during the OMWW application in arable lands, affecting both the prokaryotic and eucaryotic physiological systems. Phenolic compounds, such as p-coumaric acid and ferulic acid, are reported to decrease the phosphorylation efficacy of mitochondria, likely due to structural changes in the inner mitochondrial membrane (Ntougias et al., 2013). Several studies demonstrated that the reduction of short polymeric chains of phenolics cannot necessarily lead to mitigation of toxicity and that other factors contribute to OMWW acute toxicity. The phytotoxicity of OMWW could be related to high salinity (high presence of Na+ and Cl ) that resulted in osmotic stress, which reduced cell turgidity and inhibition of root and sprout elongation. Likewise, the presence of high-reduced sugars can stimulate microbial growth, increasing respiration and lower dissolved oxygen concentrations in water (McNamara et al., 2008). Souilem et al. (2017) and Babić et al. (2019) highlighted the high chemical oxygen demand (COD) and biological oxygen demand (BOD) values in OMWW ranging from 80 to 200 g/L. These values are higher than the pollution indexes of municipal water, ranging from 12 to 63 g/L. As a result of this pollution index, the discharge of OMWW into water streams is prohibited as it may result in significant damage to aquatic flora and fauna. For agricultural use, effluents of good quality should be characterized by much lower BOD and COD values, respectively, 10–20 and 30–60 mg/L. Besides, extended OMWW dose applications can increase the abundance of the soil denitrifying communities. However, the nitrifying population is suppressed as a result of the reducing power of OMWW phenolics. In particular, ammonia-oxidizing bacteria are highly suppressed in the presence of OMWW. Simultaneously, members of cluster 3 of Nitrosospira are proliferated (Ntougias et al., 2013). Consequently, the inhibition of the nitrification process due to OMWW soil applications affects the soil nitrogen cycle. Moreover, OMWW has a low biodegradability since the BOD/COD ratio ranges from 0.25 to 0.30 due to organic substances that are not biologically degradable in short times (Souilem et al., 2017). Microbial communities in OMWW may also be directly involved in acute toxicity, mainly against aquatic biota. Venieri et al. (2010) reported that specific indigenous microbial taxa, Aeromonas hydrophila, and Enterobacter cloacae harmed the aquatic crustacean Thamnocephalus platyurus, linking the microbial activity of specific OMWW indigenous microbiota to the toxicity on aquatic organisms (Ntougias et al., 2013).

6.3

Biotreatments of OMWW and the Valuable Products

Due to the high organic loads, salts, and pH of OMWW, careful management is needed. On the other hand, high amounts of phosphorus, potassium, and organic matter could contribute to the fertilization of Mediterranean soils that are deficient in organic matter and nutrients (Regni et al., 2017). Many processes have been

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proposed to convert OMWW to valuable material, including physical, chemical, physicochemical, and biological treatments or a combination of these. However, they still encounter some difficulties related to their high organic loads, which are hard to biodegrade, seasonal operation of olive mills, regional scattering, and the high treatment cost, particularly for small-middle-sized enterprises. In the last decade, several physicochemical processes have been studied to treat OMWW, such as microfiltration, ultrafiltration, nanofiltration, coagulationflocculation, ion exchange, electrocoagulation, and reverse osmosis. Besides, chemical processes are used, including electrolytic oxidation, Fenton oxidation, neutralization with lime, and combustion. Of them all, the solar drying of OMWW in ponds and the subsequent discharge of remaining solids in landfills is by far the most applied method for the management of OMWW. This process significantly reduces OMWW volume but creates significant odor problems in the area. Also, the organic content and toxicity of OMWW are not reduced to acceptable levels. However, these methods faced a lack of sustainability and cost-efficiency and other environmental issues (forming more toxic by-products) (Khdair & Abu-Rumman, 2020). Membrane extraction techniques, composting, and anaerobic digestion could be a possible solution for OMWW valorization, especially for reducing its toxicity first and obtaining valuable products (Fig. 6.2).

Fig. 6.2 Scheme of OMWW biotreatments and the resulted products

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Extraction and Valorization of Bioactive Compounds

The OMWW contains many bioactive compounds with many biological properties such as antioxidant and antimicrobial activities of bioactive additives in food products and cosmetics (Galanakis & Kotsiou, 2017). Antioxidant molecules of OMWW are well known for their unique antioxidant properties for human health that promise their reutilisation in pharmacy applications (Galanakis & Kotsiou, 2017). Regarding the specific aromatic compounds, verbascosides derivatives, coumaric acid, caffeic acid, tyrosol, and hydroxyl-tyrosol are the essential phenolic molecules described in OMWW as possible food antioxidants and antimicrobial agents (Table 6.1). Therefore, OMWW is considered a potential agent to confer antimicrobial activity to nanocomposites (Table 6.1), with a significant added value of decreasing the environmental impact of an offensive food stream (Sisti et al., 2019). Several studies have reported the antimicrobial effect of olive polyphenols against Staphylococcus aureus, Bacillus subtilis, Bacillus cinerea, Escherichia coli, and Pseudomonas aeruginosa (Yangui et al., 2010). The extracted bioactive molecules were tested in the nanocomposite formulation used as a bioplastic for food packaging purposes. There is a growing interest for edible food packaging development by using phenolic compounds from OMWW. Different studies focused on evaluating the feasibility and economical processes for recovering essential phenolic compounds from OMWW due to their high aromatic content (polyphenols and phenolic compounds). Membrane extraction technology has been primarily developed and considered the most efficient alternative to classical separation techniques to extract phenolic compounds from OMWW (Khdair & Abu-Rumman, 2020). Table 6.1 OMWW bioactive compounds and their main properties and applications Bioactive compounds Protocatechuic acid, vanellic acid, and ferulic acid

Main properties Antimicrobial activity

Natural OMWW phenolic extract Hydroxytyrosol and tyrosol alcohols and caffeic acid, and p-coumaric acids Hydroxytyrosol and tyrosol Raw OMWW

Retarding lipid oxidation

Hydroxytyrosol and tyrosol

Neuroprotective effect against oxidative stress and mitochondrial dysfunction Antibacterial and antifungal activity Reducing lipid and protein oxidation in blood and several vital organs in lambs Antioxidant and antibacterial activities

Applications Multifunctional biopolymer composites for antibacterial packaging Food industry byproducts Pharmaceutical industries

References Sisti et al. (2019)

Medical and nutritional use Animal feed

Abu-Lafi et al. (2017) Makri et al. (2018)

Food, cosmetic or pharmaceutical applications

Belaqziz et al. (2017)

Caporaso et al. (2018) Giacomazza et al. (2018)

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Membranes are barriers between two fluid phases (source and receiving phases), allowing selective permeation of solutes from one side of the barrier to the other. The membrane technology is a new cost-effective system for the complete exploitation of OMWW, which allows the obtaining of concentrate fractions (bioactive molecules) and water. The obtained water was characterized as nutrients rich solution due to dissolved nutritive minerals with no phytotoxic properties on plants. In this context, it could be considered for use in irrigation or reuse in the milling process (Paraskeva et al., 2007).

6.5

Composting is an Eco-Friendly Valorization Technic’s of OMWW.

Intensive agricultural production generally leads to soil fertility loss, soil erosion, water contamination, soil compaction, and organic matter content reduction. Low organic matter content is a common characteristic of Mediterranean soils. It is highly correlated with their potential productivity and fertility due to its direct impact on the physical, chemical, and biological properties of soils (Alburquerque et al., 2009). Therefore, the use of organic waste as compost on agricultural land could increase soil organic content, and composting can play a vital role in modern sustainable agricultural practices (Chowdhury et al., 2013). Because of the high organic load and the substantial amounts of plant nutrients (N, P, K, Ca, Mg, and Fe) available in OMWW sludge, their conversion to organic fertilizers by composting is a real opportunity. The composting of OMWW from the 3-phase method has been documented in the literature as an appropriate solution for organic fertilizer production. The compost produced from these olive mill wastes could be used in agriculture as an environmentally friendly, good quality soil amender and fertilizer. Olive mill wastes can be composted either pure or mixed with other wastes that act as bulking agents (Atif et al., 2020). Several authors have studied the co-composting of olive mill by-products with other agricultural wastes. Some suitable materials used as bulking agents were wheat straw (Madejon et al., 1998), cotton waste (Cegarra et al., 2000), poultry manure, and poplar sawdust with bark chips (Filippi et al., 2002). Recently, phosphate residues were used as a co-substrate during composting (Atif et al., 2020; Haouas et al., 2020a, 2020b). In all cases, the final product showed a high degree of humification, no phytotoxic effect, and improved content of the mineral nutrients. The high-value product of composting was lack of toxicity, which was ascertained by criteria such as phenolic content and the germination index. Besides, OMWW enriched compost was mature, pathogen-free compost, ensuring maximum benefit for crop production. However, some instructions must be considered to obtain the desired result from OMWW composting, including reducing concentrations of stable organic compounds (e.g., lipids, polyphenols, lignins, cellulose, hemicellulose, and pectin) by combining composting with other pre-treatments

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methods such as solar drying. Also, ensuring a small surface area and particle size of starting materials to provide suitable aeration and additives can mitigate nitrogen loss. Composting is also a suitable technology economically feasible for small or medium-sized olive mills, such as those found throughout Mediterranean countries (Haouas et al., 2020b). The OMWW composting is an essential and promising solution providing an added income to the agro-industries. However, this technology has not handled large quantities of OMWW due to its high moisture content, limiting its use as raw material, mainly in open-air pile composting. As a result, anaerobic digestion followed by composting of the produced digestate proved to be more efficient in treating OMWW, which could reuse much more of this waste and turn it into hygienic beneficial by-products such as biogas and compost (Table 6.1).

6.6

Anaerobic Digestion of OMWW

Treatment of OMWW was investigated by different authors using different technologies (reverse osmosis, coagulation-flocculation, advanced oxidation process, aerobic treatment or composting, and anaerobic digestion process). However, many of these techniques are still limited in terms of efficiency provided high-cost requirements and complexity. Various methods of organic waste treatment are available. Still, anaerobic digestion seems to be the best option due to the efficiency provided, low cost, energy production, and valorization of the by-product rich in essential elements important to the plants (Breitenmoser et al., 2019; Calabrò et al., 2018; Hamdi, 1996; Masebinu et al., 2019). Anaerobic digestion is a succession of three different metabolic reactions (hydrolysis, acidogenesis, and methanogenesis); some authors add acetogenesis before methanogenesis (Breitenmoser et al., 2019). Furthermore, the biogas produced during the anaerobic digestion process is considered cleaner than fossil fuels, while various organic wastes are transformed into energy instead of using limited resources (Bona et al., 2020; Lanzini et al., 2017). Anaerobic digestion has several economic, social, and environmental benefits, such as low-cost requirement, effectiveness in pathogen removal after the process, production of bio-fertilizers rich in essential elements, and less biomass sludge (Chuka-ogwude et al., 2020; Seyedin et al., 2020). The biogas obtained from the anaerobic digestion of various organic waste is composed of 48–65% of CH4 (methane), 36–41% of CO2 (carbon dioxide), up to 17% of N2 (nitrogen),