Food Processing By-Products and their Utilization

Food Processing By-Products and their Utilization

An in-depth look at the economic and environmental benefits that food companies can achieve—and the challenges and opportunities they may face—by utilizing food processing by-products

Food Processing By-Products and their Utilization is the first book dedicated to food processing by-products and their utilization in a broad spectrum. It provides a comprehensive overview on food processing by-products and their utilization as source of novel functional ingredients. It discusses food groups, including cereals, pulses, fruits, vegetables, meat, dairy, marine, sugarcane, winery, and plantation by-products; addresses processing challenges relevant to food by-products; and delivers insight into the current state of art and emerging technologies to extract valuable phytochemicals from food processing by-products.

Food Processing By-Products and their Utilization offers in-depth chapter coverage of fruit processing by-products; the application of food by-products in medical and pharmaceutical industries; prebiotics and dietary fibers from food processing by-products; bioactive compounds and their health effects from honey processing industries; advances in milk fractionation for value addition; seafood by-products in applications of biomedicine and cosmeticuals; food industry by-products as nutrient replacements in aquaculture diets and agricultural crops; regulatory and legislative issues for food waste utilization; and much more.

• The first reference text to bring together essential information on the processing technology and incorporation of by-products into various food applications
• Concentrates on the challenges and opportunities for utilizing by-products, including many novel and potential uses for the by-products and waste materials generated by food processing
• Focuses on the nutritional composition and biochemistry of by-products, which are key to establishing their functional health benefits as foods
• Part of the "IFST Advances in Food Science" series, co-published with the Institute of Food Science and Technology (UK) 

This bookserves as a comprehensive reference for students, educators, researchers, food processors, and industry personnel looking for up-to-date insight into the field. Additionally, the covered range of techniques for by-product utilization will provide engineers and scientists working in the food industry with a valuable resource for their work.

• Language: English
• Publisher: Wiley
• Release date: Oct 23, 2017
• ISBN: 9781118432891

Book preview

About the IFST Advances in Food Science Book Series

The Institute of Food Science and Technology (IFST) is the leading qualifying body for food professionals in Europe and the only professional organisation in the UK concerned with all aspects of food science and technology. Its qualifications are internationally recognised as a sign of proficiency and integrity in the industry. Competence, integrity, and serving the public benefit lie at the heart of the IFST philosophy. IFST values the many elements that contribute to the efficient and responsible supply, manufacture and distribution of safe, wholesome, nutritious and affordable foods, with due regard for the environment, animal welfare and the rights of consumers.

IFST Advances in Food Science is a series of books dedicated to the most important and popular topics in food science and technology, highlighting major developments across all sectors of the global food industry. Each volume is a detailed and in-depth edited work, featuring contributions by recognized international experts, and which focuses on new developments in the field. Taken together, the series forms a comprehensive library of the latest food science research and practice, and provides valuable insights into the food processing techniques that are essential to the understanding and development of this rapidly evolving industry.

The IFST Advances series is edited by Dr Brijesh Tiwari, who is Senior Research Officer at Teagasc Food Research Centre in Ireland.

Forthcoming titles in the IFST series

Herbs and Spices: Processing Technology and Health Benefits, edited by Mohammad B. Hossain, Nigel P. Brunton and Dilip K Rai

List of Contributors

Ali Akbar, Department of Microbiology, Faculty of Life Sciences, University of Balochistan Quetta, Pakistan

Imran Ali, Plant Biomass Utilization Research Unit, Department of Botany, Chulalongkorn University, Bangkok, Thailand and Institute of Biochemistry, Faculty of Life Sciences, University of Balochistan Quetta, Pakistan

Anil Kumar Anal, Food Engineering and Bioprocess Technology, Department of Food Agriculture and Bioresources, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand

Manisha Anand, Food Engineering and Bioprocess Technology, Department of Food Agriculture and Bioresources, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand

Gabriel Arome Ataguba, Aquaculture and Aquatic Resources Management (AARM), Department of Food Agriculture and Bioresources, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand and University of Agriculture, Makurdi, Nigeria

Dattatreya Banavara, Global Innovation, Firmenich Inc, Plainsboro, NJ, USA

Deepak Bhopatkar, Global Research and Development, Mead Johnson Nutrition, Evansville, IN, US

Arup Jyoti Das, Department of Food Engineering & Technology, Tezpur University, Napaam, Sonitpur, Assam, India

Avishek Datta, Agricultural Systems and Engineering, Department of Food Agriculture and Bioresources, Asian Institute of Technology, Pathumthani, Thailand

Sankar Chandra Deka, Department of Food Engineering & Technology, Tezpur University, Napaam, Sonitpur, Assam, India

Lavaraj Devkota, Department of Chemical Engineering, Monash University, Clayton, Australia

Damodar Dhakal, Food Engineering and Bioprocess Technology, Department of Food Agriculture and Bioresources, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand

Taslim Ersam, Department of Chemistry, Faculty of Mathematics and Science, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia

Zannatul Ferdous, Agricultural Systems and Engineering, Department of Food Agriculture and Bioresources, Asian Institute of Technology, Pathumthani, Thailand

Ganjyal Girish, School of Food Science, Washington State University, Pullman, WA, USA

Juan M. Gonzalez, Global Research and Development, PepsiCo. Barrington, IL, USA

Wan Rosli Bin Wan Ishak, School of Health Sciences, Universiti Sains Malaysia Health Campus, Kubang Kerian, Kota Bharu, Kelantan, Malaysia

Surangna Jain, Food Engineering and Bioprocess Technology, Department of Food Agriculture and Bioresources, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand

Manoj Tukaram Kamble, Aquaculture and Aquatic Resources Management (AARM), Department of Food Agriculture and Bioresources, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand

Mandeep Kaur, Amity Institute of Food Technology, Amity University, Noida, India

Prerna Khawas, Department of Food Engineering & Technology, Tezpur University, Napaam, Sonitpur, Assam, India

Maushmi S. Kumar, Department of Pharmaceutical Biotechnology, Shobhaben Pratapbhai Patel School of Pharmacy and Technology Management, SVKM'S NMIMS, Vile Parle West, Mumbai, India

Navneet Kumar, Department of Processing and Food Engineering, College of Agricultural Engineering & Technology, Anand Agricultural University, Godhra (Gujarat), India

Md. Abdul Matin, Farm Machinery and Postharvest Process Engineering Division, Bangladesh Agricultural Research Institute, Gazipur, Bangladesh

Seema Medhe, Food Engineering and Bioprocess Technology, Department of Food Agriculture and Bioresources, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand

Medina-Meza Ilce Gabriela, Department of Biosystems and Agricultural Engineering. Michigan State University, USA

Didier Montet, Food Safety Team Leader, UMR Qualisud, CIRAD, Montpellier, France

Taslima Ayesha Aktar Nasrin, Postharvest Technology Section, Horticulture Research Centre, Bangladesh Agricultural Research Institute, Gazipur, Bangladesh

Ngo Dang Nghia, Institute of Biotechnology and Environment, Nha Trang University, Vietnam

Zjahra Vianita Nugraheni, Department of Chemistry, Faculty of Mathematics and Science, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia

Muhammad Bilal Sadiq, Food Engineering and Bioprocess Technology, Department of Food Agriculture and Bioresources, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand

Krishna R. Salin, Aquaculture and Aquatic Resources Management (AARM), Department of Food Agriculture and Bioresources, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand

H.K. Sharma, Food Engineering and Technology Department, Sant Longowal Institute of Engineering and Technology, Sangrur, Punjab, India

Sajal Man Shrestha, Food Engineering and Bioprocess Technology, Department of Food Agriculture and Bioresources, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand

Rahul Shrivastava, Maulana Azad National Institute of Technology, Bhopal MP, India

Manisha Singh, Food Engineering and Bioprocess Technology, Department of Food Agriculture and Bioresources, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand

M.K. Tripathi, Agro Produce Processing Division, ICAR-CIAE, Nabi Bagh, Bhopal MP, India

Kittima Triratanasirichai, Food Engineering and Bioprocess Technology, Department of Food Agriculture and Bioresources, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand

Hayat Ullah, Agricultural Systems and Engineering, Department of Food Agriculture and Bioresources, Asian Institute of Technology, Pathumthani, Thailand

Santad Wichienchot, Interdisciplinary Graduate School of Nutraceutical and Functional Food, Prince of Songkla University, Hat Yai, Songkhla, Thailand

Preface

This is the first book dedicated to food processing by-products and their utilization in a broad spectrum. It covers all food groups including cereals, pulses, fruits, vegetables, meat, dairy, marine, sugarcane, winery and plantation by-products. It aims to address the functional components, nutritional values and processing challenges relevant to the food by-products. This book provides the first reference text to bring together essential information on the processing technology and incorporation of by-products into various food and feed applications. Finally, it also delivers an insight into the current state-of-the-art and emerging technologies to extract valuable bioactive chemicals from food processing by-products. Over the past few years, not only food by-products, but also a number of other agricultural wastes, have attracted considerable attention as potential sources of bioactive chemicals, which can be used for various purposes in the pharmaceutical, cosmetic and food industries.

Considering the challenges in this area of the food industry, efforts are to be made to optimise food-processing technology to minimize the amounts of by-product waste. The food industry is generating increasing amounts of by-products all along the chain of food production and transformation. However, such by-products could be generated before the production of the finished product. Environmental regulations and high waste discharge costs have forced food processors to find ways to better treat and utilize processing wastes. Environmental legislation agencies have significantly contributed to the introduction of sustainable waste management practices throughout the world.

Efficient utilization of food processing by-products is important for the profitability of the food industry. By-products and wastes of food processing, which represent a major disposal problem for the industry concerned, are very promising sources of value-added substances, with particular emphasis being given to the retrieval of bioactive compounds and technologically important secondary metabolites. This makes them extremely suitable as raw materials for the production of secondary metabolites of industrial significance. The nutritional composition of such food waste is rich in sugars, vitamins, minerals and various health beneficial bioactive chemicals (polyphenols, carotenoids, polyacetylenes, glucosinolates, sesquiterpene lactones, alkaloids, coumarins, terpenoids, proteins, peptides, dietary fibers, fatty acids, etc.). The current trend in the world today is to utilize and convert waste into useful products and to recycle waste products as a means of achieving sustainable development. Over the next few years, the area of food processing waste management will expand rapidly.

In the last few years, there have been numerous publications focusing on the utilization of food processing by-products in both food and non-food applications. Furthermore, numerous texts and reference books are available on waste utilization and mostly their emphasis is on waste treatment. However, none of those sources deal with the utilization of by-products from the range of foods in a comprehensive way. This book is structured into 22 chapters covering an overview of food processing by products, nutritional, chemical, biochemical and physicochemical properties of food waste. It also includes food by-products, value addition and nutraceutical applications.

This book serves as a comprehensive reference book for students, educators, researchers, food processors and industry personnel, as well as policy developers, providing an up-to-date insight. The range of techniques for by-product utilization covered provides engineers and scientists working in the food industry with valuable resources for their work. As this proposed text is the first dedicated reference of its kind, it is expected that it will have broad and significant market appeal.

Anil Kumar Anal, PhD

Editor

Biography of Editor

Anil Kumar Anal DVM PhD

Head, Department of Food Agriculture and Bioresources

Associate Professor, Food Engineering and Bioprocess Technology,

Asian Institute of Technology, Thailand

Phone: [phone] (Office)[phone] (Mobile)

[e-mail]

Dr Anil Kumar Anal is Head of Department of Food Agriculture and Bioresources and Associate Professor in Food Engineering and Bioprocess Technology at the Asian Institute of Technology (AIT), Thailand. His background expertise is in the Food and Nutrition Security, Food Safety, food processing and preservation, valorization, as well as bioprocessing of herbs, natural resources including Traditional and Fermented Foods, microorganisms, and Agro-industrial waste to fork and value addition, including its application in various food, feed, neutraceuticals, cosmetics and pharmaceutics. His research interests also include the formulation and delivery of cells and bioactives for human and veterinary applications, controlled release technologies, particulate systems, application of nanotechnology in food, agriculture and pharmaceutics, functional foods and food safety.

Dr Anil has authored 5 patents (US, World Patents, EU, Canadian and Indian), more than 100 referred international journal articles, 20 book chapters, 3 edited books and several articles in international conference proceedings. He has been invited as Keynote Speaker and Expert in various Food, Biotechnology, Agro-Industrial Processing and Veterinary as well as Life Sciences based conferences and workshops organized by national, regional and international agencies. Dr Anil has been serving as Advisory member, Associate Editor, and member of Editorial Boards of various regional and international peer-reviewed journal publications. He has experience in conducting numerous innovative research and product developments funded by various donor agencies, including the European Union, FAO, Ministry of Environment, Japan, and various food and biotech industries.

Chapter 1

Food Processing By-Products and their Utilization: Introduction

Anil Kumar Anal

Asian Institute of Technology, Klong Luang, Pathumthani, Thailand

1.1 Introduction

Food industries are growing rapidly to huge numbers due to globalization and population increase and are providing a wider range of food products to satisfy the needs of the consumers. The major food industries of the world include dairy, fruits and vegetables, meat and poultry, seafood and cereal. However, these industries generate huge amounts of by-products and wastes, which consist of high amounts of organic matter leading to problems regarding disposal, environmental pollution and sustainability (Russ and Pittroff, 2004). In addition, there is the loss of biomass and valuable nutrients that can be used for developing value-added products. Food industries are currently focusing on solving the problems of waste management and recycling by valorization, i.e. utilization of the by-products and discarded materials and developing new value-added products from them for commercial applications. Waste valorization is an interesting new concept that offers a range of alternatives for management of waste other than disposal or land-filling. Valorization allows exploration of the possibility of reusing nutrients in the production of main products, and thus highlights the potential gains that can be achieved. Traditional methods of waste utilization include their use as animal feed, fertilizer or disposal (Jayathilakan et al., 2012). However, their use has been limited due to legal restrictions, ecological problems and cost issues. Therefore, efficient, cheap and ecologically sound methods for utilization of wastes are being focused upon, which can minimize the quantities of wastes exposed to the environment and the subsequent health hazards.

Wastes from the food industries generally comprise of dietary fibers, proteins and peptides, lipids, fatty acids and phenolic compounds, depending on the nature of the product produced. For example, the wastes from meat and poultry industries comprise of proteins and lipids, while waste from fruit and vegetable processing industries and cereal industries comprise of phenolic compounds and dietary fibers. The recovery of these bioactive compounds is important for their commercialization, so that they can be utilized as nutraceuticals and pharmaceutical products.

1.2 Food Processing Wastes and By-Products for Industrial Applications

Food-processing wastes and by-products are generated during processing of the various food products by the industries, which have not already been used for other purposes and have not been recycled. Crude raw materials such as cereals, fruits, vegetables and animals are processed to final products with the production of large amounts of materials in the form of wastes (Ezejiofor et al., 2014). These wastes emerging from the food processing industries differ from one another, depending on the type of product being produced and the production technique used. Even the amount and concentrations of wastes differ and do not remain constant. For example, wastes from the fruit and vegetable processing industries comprise of high concentrations of polyphenols and dietary fibers, whereas wastes from meat processing industries comprise of high protein and fat content. The food processing wastes also possess characteristics, such as large amounts of organic materials in the form of lipids, proteins and carbohydrates and high chemical oxygen demand (COD) and biochemical oxygen demand (BOD) (Ezejiofor et al., 2014). Hence, they are harmful and affect the environment and human health. Appropriate technologies that focus on their reuse for creation of valuable products, whose costs exceed the costs of reprocessing, should be considered. The different types of wastes produced by the different food processing industries are listed in Table 1.1.

Table 1.1 Different food processing industries and their wastes (Ezejiofor et al., 2014)

1.3 By-Products from Cereal Processing Industries

Cereals are the edible seeds derived from plants, which are a good source of carbohydrates. They contribute to 60% of the total world food production (Krishna and Chandrasekaran, 2013), with the main seeds being maize and wheat. Wastes from cereal processing are produced during the harvesting period, post-harvesting and the production period. Presently, these by-products are used as animal feed. However, they need to be utilized more efficiently as they comprise of proteins, dietary fibers and small amounts of unsaturated fatty acids.

Rice bran is an important cereal industry by-product, which is generated during the production of white rice. It is generated during the milling process, where it is separated from the rice to produce white rice. The rice bran production is 60–66 million tonnes annually (Ryan, 2011) and it is mostly used as animal feed or in the production of edible cooking oil. Rice bran is a rich source of nutrients, proteins and peptides, with a wide range of nutritional and functional applications. Defatted rice bran is another by-product, which is produced after oil extraction from the rice bran, also a good source of proteins and dietary fibers (Anal, 2013a). It are currently being utilized in food supplements and in the production of bakery items.

1.4 Fruits and Vegetables By-Products

The world production of fruits and vegetables has increased rapidly. As crop production increases, there is a concomitant increase in the quantity of by-products generated (FAO, 2009). The fruit and vegetable processing by-products are regarded as waste and disposed of in the environment, which causes ecosystem problems as they are prone to microbial degradation. However, fruit and vegetable by-products and wastes are very good sources of bioactive compounds, such as dietary fibers and phenolic compounds with antibacterial, cardio-protective and antitumor activities (Khao and Chen, 2013). Efforts are being made to develop methods to reuse these wastes and by-products by obtaining bioactive compounds for health benefits, profit-making and allowing their environmental-friendly disposal.

The total worldwide production of citrus fruits was reported as 7.78 million tonnes in 2009 (FAO, 2009). These include oranges, lemons, grapefruits and limes They are commonly used forms are as fresh pulps or juice, but following their processing, the by-products such as peels, pulp and seeds remain that make up 50% of the fresh fruit weight (Khao and Chen, 2013). From these wastes, fibers, flavanoids, pectins and limonene can be produced. The major flavanoids found in the citrus peels and seeds include hesperidin, narirutin, naringin and eriocitrin (Mouly et al., 1994). These flavanoids have found to have antioxidant activities (Manthey et al., 2001). Limonin, nimolin and nomilinic acid are major limonoids found mainly in the peels, and demonstrate antibacterial, antiviral and antimicrobial activities (Djilas et al., 2009).

Banana is the largest growing tropical fruit following citrus fruits, contributing to 16% of total fruit production worldwide (Mohapatra et al., 2010). Waste from banana products includes the peels that represent about 40% of the total weight of the fresh bananas (Tchobanoglous et al., 1993). These peels are utilized in animal feed and the preparation of banana chips and banana powder. However, still huge amounts of the peels are being under-utilized and disposed of, resulting in environmental pollution. These banana wastes contain dietary fibers, proteins and different bioactive compounds such as phenolic compounds with reported antioxidant activities (Anal et al., 2014). Hence they need to be recycled so that they can be used for producing various valuable products.

Mango (Mangifera indica L., Anacardiaceae) is a common seasonal fruit, which is mainly processed to produce products such as juices, pickles, purees and canned products (Aslam et al., 2014). Recent researches have indicated that mango wastes, which mostly include the peels (7–24%) and the kernels (9–40%), are good sources of bioactive compounds. The mango peels comprise of functional compounds such as polyphenols, carotenoids, vitamins C and E, dietary fibers and natural antioxidants (Ajila et al., 2007), whereas the kernels are sources of essential amino acids like lysine, valine and leucine (Abdalla et al., 2007), phenolic compounds, edible oils and high amounts of unsaturated fatty acids. These wastes show huge potential to be used as valuable ingredients for the purpose of making functional foods.

Mangosteen (Garcinia mangostana L) is a popular fruit of several Asian countries. However, the increasing consumption of this fruit has led to the generation of ample abandoned mangosteen pericarps. It has been reported that 10 kg of harvested mangosteens lead to the generation of about 6 kg of pericarps (Mohammad et al., 2014). These pericarps are woody in texture, comprising of bitter substances such as xanthones, tannins and anthocyanins (Lim et al., 2013) that have medicinal properties and are being used as dietary supplements. The therapeutic benefits of these components include hypolipidemia, anti-inflammatory, anti-microbial and anti-carcinogenic properties (Zafra-Stone et al., 2007; Mishra et al., 2016). Another by-product from the processing of mangosteens is their seeds, which contain 21.18% oil (Ajayi et al., 2006) with essential and non-essential fatty acids. They have been reported to be safe for the heart and liver; hence they can be used as edible oils.

The apple processing wastes are termed apple pomace, which makes up 25–35% of the total apple wastes (Dijlas et al., 2009). The apple pomace includes the peels, seeds, stems, core and the soft tissues. They are good sources of polyphenols, which are mainly present in the peels such as catechin, quercetin, hydroxycinnamates, chlorogenic acid and epicatechins (Mamma et al., 2009) and pectins, proteins and vitamins. However, they are mainly utilized in the production of pectins, which can be co-precipitated out from the apple pomace. These pectins demonstrate good gelling properties, even better than citrus pectins.

Tomato is an important vegetable, with a world total production of 141 million tonnes in 2009 (FAO, 2009). The major products produced using tomatoes are soups, ketchup, juice and paste. Along with their high consumption, there is the generation of huge amounts of by-products and wastes accounting for 40% of the total fresh weight of the tomatoes. These include the seeds (33%), peels (27%) and the pulp (40%) (Encinar et al., 2008; Kaur et al., 2008). These wastes are good sources of proteins (35%) and fats (25%) (Anal et al., 2013a). In addition, they contain high amounts of unsaturated fatty acids due to which the tomato seed oil is used as edible oil. Lycopene, an important carotenoid, is also present in large amounts in tomato wastes.

Carrot processing, for the production of carrot juice, generates wastes in the form of peels and pomace (Chantaro et al., 2008). These wastes make up 12% of the fresh carrot weight and comprises of several valuable compounds such as carotenes, uronic acids and sugars, which are generally discarded or used in feeds and fertilizers. These compounds have important beneficial properties and hence can be utilized for value addition. The carrot waste also contains huge amounts of fibers, including cellulose, hemicelluloses, lignin and pectin (Nawirska and Kewasniewska, 2005). Studies are being done to recover these fibers from the carrot waste residues, as they have been reported to have cholesterol-lowering effects that can protect against coronary heart diseases. Also, various attempts are being made to incorporate the valuable compounds from carrot wastes into the production of functional foods and beverages.

The total world onion production in 2009 was reported to be 72 million tonnes (FAO, 2009). During the processing of onions, the major wastes that are generated are the peels and roots. They are a serious threat to environmental pollution, as they are not suitable for fodder because of their aroma or as fertilizers due to the fast development of phytogenetic agents, and also they contribute to toxicity in animals during digestion (Bello et al., 2013). Hence, new applications need to be found for these wastes, which contain high amounts of polyphenols and dietary fibers.

Cabbage is also a vegetable that has a high production yield; however, since it is consumed either in the raw form or the fresh form, wastes generated are very little. The main wastes are their outer leaves which are disposed off. These leaves can be used mainly for the production of biofuels by the anaerobic digestion process (Liu et al., 2006).

1.5 By-Products from the Meat and Poultry Processing Industries

Meat and poultry processing generates a number of organic by-products like bones, blood, feathers, head etc. (Lasekan et al., 2013). The majority of these by-products are produced during the slaughtering process. The slaughterhouse waste comprises of the portion that cannot be utilized or sold as meat. This includes bones, skin, blood and internal organs (Lasekan, et al., 2013). Currently, these wastes are under-utilized, discarded and disposed of in landfills. However, they must be dealt with efficiently, as the growth of these industries mainly depends on the management of their by-products (Jayathilakan et al., 2012). The disposal of these wastes can also be difficult, due to their high water content, susceptibility to oxidation and changes caused by enzymatic activity that results in serious environmental pollution and hazards. Hence, it is essential to find applications for these wastes, which are becoming a serious environmental issue.

Blood is the first and most inevitable by-product of the meat and the poultry industries, which is a major problem due to its high pollutant load. However, blood comprises of a number of compounds that have potential value and is a good source of proteins which makes it an important edible by-product (Jayathilakan et al., 2012). Blood from a healthy animal is generally sterile. It will be approved for use in food products, if it has been obtained from bleeding a healthy animal. Due to an increasing trend in worldwide protein deficiency, usage of animal blood as a source of protein should be investigated and further extraction of bioactive peptides can be carried out to allow for large-scale utilization of the blood.

A great amount of poultry feathers of about 1.8 million tones are generated every year in the form of wastes (Wang and Cao, 2012). These feathers are an important waste product and are used mainly as animal feed; however, research is being made into their new applications. Feathers are composed of 90% proteins with the main one being keratin (Wang and Cao, 2012). The remainder comprises of 1% lipids and 8% water. Keratins are the major structural proteins found in feathers and are characterized by high amounts of cysteine and hydroxyl amino acids such as serine.

Bones are not usually consumed and have no value for the meat and poultry processing industries; hence they are discarded. Approximately 16–45 million tons of bones are discarded worldwide (Dong et al., 2014). They can also be utilized in feed products, as they comprise of proteins, calcium, essential minerals and lipids, which are useful for bodily function. Therefore, studies about comprehensive utilization of bones are required for developing an effective way to utilize the huge amount of bones as potential protein sources.

Skin is also an important and valuable by-product obtained from animals. Just like bones, the skin also contains huge amounts of proteins such as collagen. Gelatin is also one important protein that can be obtained after the hydrolysis of collagen under controlled conditions (Jayathilakan et al., 2012). Both of these proteins have been reported to have various functional and biological properties.

Another product of the poultry industry, which is largely produced and consumed, is poultry eggs. Their high nutritional value and relative low cost has led to their increased production worldwide. According to the FAO, global egg production in 2012 was reported as 65 million tonnes (FAO, 2012), which includes all types of eggs, including hatching eggs. However, the egg processing industries generate huge amounts of wastes, of about 1.5 million tonnes annually, in the form of shell wastes (Wei et al., 2009), which are discarded and disposed of in landfills. This contributes to environmental pollution and hazards and loss of potential revenues. By-products of the egg-processing industries comprise of the eggshells and the eggshell membrane (ESM) that represents 11% of the total egg weight (Stadelman, 2000). The ESM mainly are a very good source of bioactive compounds such as proteins and polysaccharides, together with high amounts of polypeptides (Zhao and Chi, 2009; Jain and Anal, 2016). Collagen makes up 10% of the total proteins, whereas the rest (70–75%) comprises of the glycoproteins. Due to their high protein content, they can be used for production of proteins, and peptides from them can be used in a wide range of food and nutraceutical applications.

1.6 Seafood Processing By-Products

Marine organisms are an important food source for many countries and contain value-added compounds such as lipids, amino acids, proteins and polysaccharides, which are crucial for human health. Industrial processing of these marine organisms leads to the generation of huge amounts of waste that are either discarded or used as fertilizers and fish meals. By-products from seafood processing include viscera, heads, backbones, skin, tail, blood and shells, which comprise of important bioactive compounds that can be used in pharmaceutical and nutraceutical applications (Anal et al., 2013b). Some of the valuable components that can be obtained from seafood processing are the bioactive peptides, proteins such as collagen, polyunsaturated fatty acids and chitin (Suresh and Prabhu, 2013).

Collagen is a major protein obtained from seafood processing by-products, which are mainly obtained from the skin, bone, tendons etc. (Regenstein and Zhou, 2007). They have a wide range of applications, such as gel formation, water binding, formation of stable emulsions and formation of films (Gomez-Guillen et al., 2011). They are also a good source of bioactive peptides. Gelatin, another protein, can also be derived from collagen, which have many applications in food industries. They can be used as food additives for improving the texture and stability of food products such as meat, bakery goods etc. (Mariod and Fadul, 2013). They are also used in the pharmaceutical industries for making capsules and tablet coatings.

Proteins from seafood by-products can be used to recover protein hydrolysates and peptides, by using various methods such as chemical hydrolysis, enzymatic hydrolysis, microbial fermentation, microwave and ultrasonic irradiation (Anal et al., 2013b). These protein hydrolysates and peptides possess strong biological activities such as antioxidant, antimicrobial and antihypertensive.

Marine fishes are mainly very good sources of polyunsaturated fatty acids such as omega-3 fatty acids. The by-products of fish processing, such as viscera, stomach, liver etc. can be used to recover polyunsaturated fatty acids with nutraceutical and pharmaceutical applications (Analava et al., 2014). Fatty acids such as eicosapentenoic acid (EPA) and docosahexenoic acid (DHA) can be obtained by molecular distillation. These omega-3 fatty acids have remarkable health benefits, such as protective effects against cardiovascular diseases, nerve and brain disorders and anti-inflammatory effects in diseases like Crohn's disease and kidney diseases.

Processing of crustaceans, such as shrimp and crab, generate solid by-products from which chitin can be obtained. Chitin is a linear amino polysaccharide and the most abundant biopolymer (Tharanathan and Kittur, 2003). They can be extracted from the crustacean by-products by enzymatic methods and fermentation by lactic acid bacteria. They also have a wide range of biological applications such as in edible packing, as bio-preservatives, food additives and nutritional and functional ingredients.

1.7 By-Products from the Dairy Processing Industries

The dairy industries are also major food processing industries that generate large amounts of by-products and waste during the manufacturing of various dairy food products and milk processing. These wastes contain high amounts of proteins, lipids, vitamins etc. and their utilization for the purpose of value addition can greatly enhance the profit of the dairy industries. Whey is a major by-product generated during the manufacturing of cheese, cottage cheese etc. which can be subdivided into rennet whey and acid whey. The whey comprises of high amounts of lactose and proteins. The whey proteins are composed of a number of proteins with a very high biological value, more than that of casein and soy proteins (Mandal et al., 2013). Lactose, on the other hand, can be used for the production of organic acids such as citric acid, gluconic acid and lactic acid by the process of microbial fermentation.

1.8 Conclusion

The food processing industries will continue to grow throughout the world, along with the demands of the consumers. This will also result in the generation of huge quantities of by-products and wastes that are currently being under-utilized. However, due to the growing concerns regarding environmental conservation, intensive research needs to be carried out such that the food wastes can be utilized for the purpose of value addition and human consumption. This will lead to maximum benefits to the industries, environment and the consumers.

References

Abdalla, A.E.M., Darwish, S.M., Ayad, E.H.E. and El-Hamahmy, R.M. (2007) Egyptian mango by-product. 1: Compositional quality of mango seed kernel. Food Chemistry, 103: 1134–1140.

Ajayi, I.A., Oderinde, R.A., Ogunkoya, B.O., Egunyomi, A. and Taiwo, V.O. (2006) Chemical analysis and preliminary toxicological evaluation of Garcinia mangostana seeds and seed oil. Journal of Food Chemistry, 101: 999–1004.

Ajila, C.M., Naidu, K.A., Bhat, S.G. and Prasada Rao, U.J.S. (2007) Bioactive compounds and antioxidant potential of mango peel extract. Food Chemistry, 105: 982–988.

Anal, A.K. (2013a) Food processing by-products. In: Handbook of Plant Food Phytochemicals: Sources, stability and extraction, Chapter 8 (eds B. Tiwari, N.P. Brunton and C.S. Brennan). Wiley Science Publishers, Oxford, pp. 180–192.

Anal, A.K., Noomhorm, A. and Vongsawasdi, P. (2013b) Protein hydrolysates and bioactive peptides from seafood and crustacean waste: Their extraction, bioactive properties and industrial perspectives. In: Marine Proteins and Peptides: Biolgical activities and applications, Chapter 36 (ed. S.K. Kim). John Wiley & Sons, Chichester, UK, pp. 709–735.

Anal, A.K., Jaisanti, S. and Noomhorm, A. (2014) Enhanced yield of phenolic extracts from banana peels (Musa acuminata Colla AAA) and cinnamon barks (Cinnamomum varum) and their antioxidative potentials in fish oil. Journal of Food Science Technology, 51(10): 2632–2639.

Analava, M., Baishakhi, D. and Anindya, M. (2014) Recovery of omega-3 health boosters from fisheries and poultry wastes and their micro-delivery techniques. International Journal of Drug Delivery Science, 1(1): 1–13.

Aslam, H.K.W., Raheem, M.I.U., Ramzan, R., Shakeel, A., Shoaib, M. and Sakandar, H.A. (2014) Utilization of mango waste material (peel, kernel) to enhance dietary fiber content and antioxidant properties of biscuit. Journal of Global Innovation Agricultural Social Science, 2(2): 76–81.

Bello, M.O., Olabanji, I.O., Abdul-Hammad, M. and Okunade, T.D. (2013) Characterization of domestic onion wastes and bulb fatty acids and metal contents. International Food Research Journal, 20(5): 2153–2158.

Chantaro, P., Devhastin, S. and Chiewchan, N. (2008) Production of antioxidant high dietary fiber powder from carrot peels. LWT – Food Science and Technology, 41(10): 1987–1994.

Dijlas, S., Canadanovic, B.J. and Cetkovic, G. (2009) By-products of fruit processing as a source of phytochemicals. Chemical Industry and Chemical Engineering, 15: 191–202.

Dong, X.B., Li, X., Zhang, C.H., Wang, J.Z., Tang, C.H. et al. (2014) Development of a novel method for hot-pressure extraction of protein from chicken bone and the effect of enzymatic hydrolysis on the extracts. Food Chemistry, 157: 339–346.

Encinar, J.M., Gonzalez, J.F. and Martinez, G. (2008) Energetic use of the tomato plant waste. Fuel Processing Technology, 89: 1193–1200.

Ezejiofor, T.I.N., Enebaku, U.E. and Ogueke, C. (2014) Waste to wealth-value recovery from agro-food processing wastes using biotechnology: A review. British Biotechnology Journal, 4(4): 418–481.

FAO (2009) High Level Expert Forum – How to Feed the World in 2050. FAO, Rome.

Gómez-Guillén, M., Giménez, B., López-Caballero, M.A. and Montero, M. (2011) Functional and bioactive properties of collagen and gelatin from alternative sources: A review. Food Hydrocolloids, 25(8): 1813–1827.

Jain, S. and Anal, A. K. (2016) Optimization of extraction of functional protein hydrolysates from chicken Egg Shell Membrane (ESM) by Ultrasonic Assisted Extraction (UAE) and Enzymatic Hydrolysis. LWT – Food Science and Technology, 69: 295–302.

Jayathilakan, K., Sultana, K., Radhakrishna, K. and Bawa, A.S. (2012) Utilization of by-products and waste materials from meat, poultry and fish processing industries: A review. Journal of Food Science and Technology, 49(3): 278–293.

Kaur, D., Wani, A.A., Oberoi, D.P.S. and Sogi,D.S. (2008) Effect of extraction conditions on lycopene extractions from tomato processing waste skin using response surface methodology. Food Chemistry, 108: 711–718.

Khao, T.H. and Chen, B.H. (2013) Fruits and vegetables. In: Valorization of Food Processing By-Products, Chapter 18 (ed. M. Chandrasekaran). Taylor and Francis Group, Boca Raton, FL, pp. 517–557.

Krishna, J.G. and Chandrasekaran, M. (2013) Cereals. In: Valorization of Food Processing By-Products, Chapter 12 (ed. M. Chandrasekaran). Taylor and Francis Group, Boca Raton, FL, pp. 303–330.

Lasekan, A., Bakar, F.A. and Hashim, D. (2013) Potential of chicken by-products as sources of useful biological resources. Waste Management, 33: 552–565.

Lim, Y.S., Lee, S.S.H. and Tan, B.C. (2013) Antioxidant capacity and antibacterial activity of different parts of mangosteen (Garcinia mangostana Linn) extracts. Fruits, 68(6): 484–489.

Liu, D., Liu, D., Zeng, R.J. and Angelidaki, I. (2006) Hydrogen and methane production from household solid waste in the two-stage fermentation process. Water Resources, 40: 2230–2236.

Mamma, D., Topakas, E., Vafiadi, C. and Christakopoulos, P. (2009) Biotechnological potential of fruit processing industry residues. In: Biotechnology for Agro-Industrial Residue Utilization, Chapter 14 (eds P.S. Nigam and A. Pandey). Springer Press, Hiedelberg, pp. 273–291.

Mandal, S., Puniya, M., Sangu, K.P.S., Dagar, S.S., Singh, R. and Puniya, A.K. (2013) Dairy By-Products: Wastes or resources. In: Valorization of Food Processing By-Products, Chapter 21 (ed. M. Chandrasekaran). Taylor and Francis Group, Boca Raton, FL, pp. 617–648.

Manthey, J.A., Grohmann, K. and Guthrie, N. (2001) Biological properties of citrus flavanoids pertaining to cancer and inflammation. Current Medicinal Chemistry, 8(2): 135–153.

Mariod, A.A. and Fadul, H. (2013) Review: Gelatin, source, extraction and industrial applications. ACTA Scientiarum Polonorum Technologia Alimentaria, 12(2): 135–147.

Mishra, S., Kumar, M.S., Stanley H.R.C. and Anal, A.K. (2016) Modulation of digestive enzymes and lipoprotein metabolism by alpha mangosteen extracted from mangosteen (Garcinia Mangostana) fruit peels. Journal of Microbiology, Biotechnology and Food Sciences, 6(1): 717–721.

Mohammad, M.A., Shitu, A., Tadda, M.A. and Ngabura, M. (2014) Utilization of various agricultural waste materials in the treatment of industrial wastewater containing heavy metals: A review. International Research Journal of Environmental Sciences, 3(3): 62–71.

Mohapatra, D., Mishra, S. and Sutar, N. (2010) Banana and its by-product utilization: An overview. Journal of Scientific and Industrial Research, 69: 323–329.

Mouly, P.P., Arzouyan, C.R., Gaydou, E.M. and Estienne, J.M. (1994) Differentiation of citrus juices by factorial discriminant analysis using liquid chromatography of flavones glycosides. Journal of Agricultural Food Chemistry, 42: 70–79.

Nawirska, A. and Kwasniewska, M. (2005) Dietary fiber fractions from fruit and vegetable processing waste. Food Chemistry, 91: 221–225.

Regenstein, J.M. and Zhou, P. (2007) Collagen and gelatin from marine by-products. In: Maximising the Value of Marine By-Products, 1st edition (ed. F Shahidi). Woodhead Publishing Ltd, Cambridge, pp. 279–303.

Russ, W. and Pitroff, R. (2004) Utilizing waste products from the food production and processing industries. Critical Reviews in Food Science and Nutrition, 44(1): 57–62.

Ryan, P.E. (2011) Bioactive food components and health properties of rice bran. Journal of the American Veterinary Medical Association, 238(5): 593–600.

Stadelman, W.J. (2000) Eggs and egg products. In: Encylopaedia of Food Science and Technology (ed. F.J. Francis). John Wiley & Sons, New York, pp. 593–599.

Suresh, P.V. and Prabhu, N. (2013). Valorization of Food Processing By-Products (ed. M. Chandrasekaran). Taylor and Francis Group, Boca Raton, FL, pp. 687–736.

Tchobanoglous, G., Theisen, H.M. and Vigil, S.A. (1993) Integrated Solid Waste Management: Engineering principals and management issues. McGraw Hill, New York, pp. 3–22.

Tharanathan, R.N. and Kittur, F.S. (2003) Chitin – The undisputed biomolecules of great potential. Critical Reviews in Food Science and Nutrition, 43(1): 61–87.

Wang, Y.X. and Cao, X.J. (2012) Extracting keratin from chicken feathers by using a hydrophobic ionic liquid. Process Biochemistry: 47: 896–899.

Wei, Z., Xu, C. and Li, B. (2009) Application of waste eggshell as low-cost solid catalyst for biodiesel production. Bioresource Technology, 100(11): 2883–2885.

Zafra-Stone, S., Yasmin, T., Bagchi, M., Chatterjee, A., Vinson, J.A. and Bagchi, D. (2007) Berry anthocyanins as novel antioxidants in human health and disease prevention. Molecular Nutrition Food Research, 51: 675–583.

Zhao, Y.H. and Chi, Y.J. (2009) Characterization of collagen from eggshell membrane. Biotechnology, 8: 254–258.

Chapter 2

Fruit Processing By-Products: A Rich Source for Bioactive Compounds and Value Added Products

Medina-Meza Ilce Gabriela¹ and Ganjyal Girish²

¹Biosystems and Agricultural Engineering, Michigan State University, USA

²School of Food Science, Washington State University, USA

2.1 Introduction

The expansion of fruit-processing worldwide has generated huge quantities of fruit wastes (Ayala-Zavala et al., 2011). Fruits are processed into various fruit-based products, such as juices, jams, jellies, concentrates, alcoholic beverages, vinegar etc. Fruit pomace, consisting of peel, seeds, core, stems and exhausted soft tissue, is the left-over solid biomass obtained as a by-product during the processing of fruits. In the tropics, fruits such as mango, pineapple, passion fruit and papaya contribute to higher fruit pomace generation and in the sub-tropics, mainly apples, grapes, oranges and berries generate higher processing by-products as pomace. The chemical composition of fruit pomace varies according to the type of fruit. Fruit pomace possesses a high phytochemical content that can be recovered for secondary food and non-food applications (Djilas et al., 2009). Currently, this is used as a cattle feed and the potential use of various fruit pomace as functional foods has been evaluated in various studies (Nawirska and Kwasniewska, 2005; Sun-Waterhouse, 2011). On the other hand, the negative concerns of the consumer versus synthetic products, has led to the possibility of using such by-products as an alternative source of natural antioxidants, especially considering the higher demand of additives to prevent lipid oxidation and oxidative rancidity in meat products, as well as to retard development of off-flavors, and to improve color stability.

This chapter focuses on the presence of bioactive functional ingredients in fruit-processing by-products, mainly fruit pomaces, and presents an overview of their value-added qualities. In the first sections of this chapter, a brief and comprehensive view of the different bioactive compounds in fruit pomaces is presented. Then, several categories of agro-industry by-products are discussed, with a particular emphasis on their potential as sources of bioactive molecules. Finally, comments on future directions in the field are provided.

2.2 Phenolic Compounds as Functional foods

Phenolic compounds, or polyphenols, constitute one of the largest and widely-distributed groups of phytochemicals. More than 8000 phenolic structures are known and among them around 4000 flavonoids have been identified (Tsao, 2010). Polyphenols are secondary metabolites that are derivatives of the pentose phosphate, shikimate and phenylpropanoid pathways in plants (Boudet, 2007; Tsao, 2010). They comprise a wide variety of molecules that have a polyphenol structure (i.e. several hydroxyl groups on aromatic rings), but also molecules with one phenol ring such as phenolic acids and phenolic alcohols. Phenolics have considerable physiological and morphological importance for plants; they play an important role in plant pigmentation, reproductions, UV-light protection, antioxidative and anti-feedant effects, as well as providing protection against pathogens and predators (Treutter, 2006).

Currently, there is an enormous interest in this class of compounds, due to their capacity to improve public health through their intake, where preventative health care can be promoted through a diet rich in fruit and vegetables. Studies have shown that phenolic compounds exhibit an extensive range of physiological properties; they may prevent degenerative diseases, and cardiovascular and neurodegenerative diseases, as well as some types of cancers (Tsao, 2010). Their potent antioxidants properties and their effects in prevention of oxidative stress-associated diseases are also known (Scalbert et al., 2005). Fruits, vegetables, whole grains, tea, chocolate and wine are rich sources of polyphenols and natural antioxidants. The most relevant groups of phenolic compounds for human health are phenolic acids, flavonoids, tannins, stilbenes and lignans. Generally, one or more sugar residues are linked to hydroxyl groups. These sugars can be present as monosaccharides, disaccharides or oligosaccharides (Bravo, 1998), and may also occur as functional derivatives such as esters and methyl esters (Harborne and Baxter, 1999).

2.2.1 Phenolic Acids

Phenolic acids comprise about a one-third part of dietary phenols, which can be present in the plant kingdom as free and bounds forms (Robbins, 2003). Phenolic acids consist of two subgroups, i.e. the hydroxycinnamic acids and the hydroxybenzoic acids. Hydroxycinnamic acids include aromatic compounds with a three-carbon side chain (C6–C3), with caffeic, ferullic, p-coumaric and sinapic acids being the most representatives. On the other hand, hydroxybenzoic acids are p-hydroxybenzoic acids, protocatechuic acids, and vanillic, syringic and gallic acids, the latter being the most representative of this group, which have in common the C6–C1 structure (Bravo, 1998). While fruits and vegetables contain many free phenolic acids, in seeds and grains they are often presents in their bound form, especially in bran or hull (Shi et al., 2003). Bound phenolic acids can be released by alkaline or acid hydrolysis, or even by enzymatic catalysis.

2.2.2 Flavonoids

Flavonoids are the most-common and widely-distributed group of plant phenolics, with exception of the algae and fungi kingdoms. They are low molecular weight compounds, with a C6–C3–C6 general structural backbone in which two C6 units (Ring A and Ring B) are of a phenolic nature (Tsao, 2010). Flavonoids can be further divided into sub-groups such as flavonols (or catequins), flavan-2-ols, flavones, flavanones, isoflavones and anthocyanins (Bravo, 1998). Flavonoids rarely appear in plants as aglycones, as they usually exist as glycosides. Flavonoids are important antioxidants as a result of their high redox potential, which allows them to act as hydrogen donors, reducing agents and singlet oxygen quenchers. Beyond that, they also present a metal chelating potential (Tsao, 2010; Tsao et al., 2003).

2.2.2.1 Isoflavones

Isoflavones have structural similarities to estrogens, and like estradiol molecules, they have a ring B attached to the C3 position of ring C. These phytochemicals are found in many plants, mostly in the leguminous family. Genistein and daidzein are two main isoflavones found in soy beans, along with glycetein, biochanin A and formononetin; they are also found in red clovers (Tsao, 2010). The open ring chalcones can be found in fruits such as apples, and beverages as beers (Zhao et al., 2005).

2.2.2.2 Flavones, Flavanols, Flavanones, Flavonols and Flavanonols

Flavones and their 3-hydroxyl derivatives flavonols, including their glycosides, methoxides and acylated products on all three rings, form the largest subgroup among polyphenols. Flavanones, such as naringenin and hesperidin, are especially abundant in citrus foods and prunes. Taxifolin is a well-known flavanonol from citrus fruits (Grayer et al., 2006). On the other hand, flavanols (also called catechins) differ from other flavonoids, because there are no double bonds between C2 and C3, and no C4 carbonyl in ring C.

Catechin and epicatechin are monomeric flavanols, usually are found in fruits, especially in the skins of grapes, apples and blueberries (Awad et al., 2000; Määttä-Riihinen et al., 2005; Wolfe et al., 2003); their derivatives (i.e. gallocatechins) are the major flavonoids in tea leaves and cacao (Lee et al., 2003). These monomers can form polymers, which are usually referred to as proanthocyanidins, because an acid-catalyzed cleavage of the polymeric chains generates anthocyanidins (Tsao, 2010).

2.2.2.3 Anthocyanins

Anthocyanins (from Greek anthos = flower and kianos = blue) are the most important group of water soluble plant pigments and are responsible for the color of flowers, leaves, stems, roots and fruits. Anthocyanidin is the basic structure of these compounds, and when they are found in their glycoside form (bonded to a sugar moiety), they are called anthocyanins. They may appear pink, red, purple or blue, depending on pH. However, the isolated anthocyanins are highly instable and susceptible to degradation (Giusti and Wrolstad, 2003). Other factors, such as degree of hydroxylation or methylation arrangement of the aromatic rings, storage temperature, light, oxygen, solvents, enzymes, proteins and metallic ions, can also affect their color (Rein, 2005).

Anthocyanins can act as antioxidants by donating hydrogen to highly reactive radicals. Their antioxidant potential is dependent on the number and arrangement of the hydroxyl groups and structural conjugation, as well as the presence of electron-donating/withdrawing substitutions in the ring structure (Lapornik et al., 2005). Anthocyanins are potential substitutes for prohibited food dyes, providing additional health benefits during their intake.

2.2.3 Tannins

Tannins are compounds of intermediate to high molecular weight. Goldstein and Swain (1963) defined plant tannins as water-soluble phenolic compounds having a molecular weight. Tannins have been found in carob pods; they are highly hydroxylated molecules and can form insoluble complexes with carbohydrates and protein. This capacity is responsible for the astringency of tannin-rich food, due to the precipitation of salivary proteins (Bravo, 1998). Within this general character, tannins exhibit a number of various bioactivities, which are often related to their antioxidant activity. Tannins are classified into two major groups on the basis of their structure: the hydrolysable tannins and the condensed tannins. Plants are able to biosynthesize gallotannins, ellagitannins, or a mixture of both types of hydrolysable tannins. While condensed tannins are present in many species of higher plants, the presence of hydrolysable tannins is limited to Angiospermae and Dicotyledons (Koleckar et al., 2008).

2.2.3.1 Hydrolysable Tannins

Hydrolysable tannins are compounds containing a central core of glucose or another polyol esterified with gallic acid. As the name indicates, these compounds are easily hydrolyzed by acid alkali, hot water and enzymic action, which produce polyhydric alcohol and phenylcarboxylic acid. According to this, they are also called gallotannins, or with hexahydroxydiphenic acid, are called ellagitannins (Bravo, 1998). Gallotannins consist of a central molecule, such as glucose, surrounded by gallic acid units. Tannic acid is the best know hydrolysable tannin, consisting of a gallotanin with a pentagalloyl glucose molecule.

2.2.3.2 Condensed Tannins

Condensed tannins are a major group of oligomeric and polymeric dietary polyphenols made up of flavan-3-ol and flavan-3,4-diols widely-distributed in plant foods, where they affect sensory properties such as astringency, bitterness, aroma and color. They are also named as Proanthocyanidins, because they decompose to anthocyanidins in heated ethanol solutions. The most frequent basic units of condensed tannins are derivatives of flavan-3-ols: (+)-catechin, (-)-epicatechin, (+)-gallocatechin and major polyphenols of green tea: (–)-pigallocatechin and (–)-epigallocatehin gallate (Koleckar et al., 2008). Proanthocyanidins can occur as polymers with 50 degrees of polymerization and greater, having molecular weights of 5000 Da. Proanthocyanidins are classified according to their hydroxylation pattern into several subgroups, i.e. procyanidins and prodelphinidins (Cos et al., 2004).

Procyanidins of the B-type (dimeric) and C-type (trimeric) are characterized by single linked flavanyl units, usually between C-4 of the flavan-3-ol of the upper unit and C-6 or C-8 of the lower unit, while Proanthocyanidins of the A-type possess an additional ether linkage between C-2 of the upper unit and a 7- or 5-OH of the lower unit. (Koleckar et al., 2008). The largest group of proanthocyanidins is formed by procyanidins. Procyanidin B-1 is present in grapefruit, sorghum and cranberries, B-2 in apples, cocoa beans and cherries, B-3 in strawberries and hops, and B-4 in raspberries and blackberries (Xie and Dixon, 2005). Furthermore, red wine, green tea, cocoa and chocolate are well-known sources of dietary protoanthocyanidins (Scalbert et al., 2005).

2.2.4 Stilbenes and Lignans

These groups of compounds are less common in the human diet; however, they are considered important to human health. The most representative stilbene is resveratrol, that can appear in both cis and trans isomeric forms, mostly glycosylated forms (Delmas et al., 2011). It can be found in grapes and red wine (0.3–7 mg aglycones/L and 15 mg glycosides/L) (Vitrac et al., 2002). Due to its anticarcinogenic effects, shown during screening of medicinal plants, it has been extensively studied.

Lignans are produced by oxidative dimerization of two phenyl propane units; they usually exist in the free form, while their glycoside derivatives are only a minor form. The richest dietary source is linseed, which contains secoisolariciresinol (up to 3.7 g/kg dry wt) and low quantities of matairesinol (Mazur et al., 1998). Other cereals (triticale and wheat), grains (lentils), fruit (pears, prunes) and certain vegetables (garlic, asparagus, carrots) also contain traces of these lignans, but concentrations in linseed are approximately 1000 times as high as concentrations in these other food sources. The interest in lignans has increased due to its potential applications in cancer chemotherapy and other different pharmacological effects (Saleem et al., 2005).

2.3 Fruit By-Products Sources

2.3.1 Agro-Industrial By-Products

The processing of fruits, oilseeds and vegetables produce high amounts of waste materials such as pomace, peels, seeds and oilseed meals. These by-products are generally utilized as animal feed or fertilizer; however, they still contain a huge amount of phenolic compounds and are potential sources of antioxidants. Hence the interest on further exploitation of by-products to produce food additives or supplements with high nutritional value has increased, since their recovery may be economically attractive.

2.3.1.1 Citrus Fruit

Citrus is the largest fruit crop in the world. Its worldwide production is over 88 million tons and one-third is processed. Oranges, grapefruit, lemons and mandarins represent up to 98% of the entire industrialized crop. They are processed principally to obtain juice, jam and segments of mandarin for canning industry. The USA and Brazil are the major producers; they harvest and process around 60% and 85% of the world's oranges, respectively (Djilas et al., 2009).

The citrus fruit industry generates large amounts of peel (albedo and flaveldo), pulp and seed after juice extraction, which represents more than 50% of the yield (Lario et al., 2004). Albedo is a white, spongy and cellulosic tissue, which is the main citrus peel component. Due to its high fiber content, albedo is considered as a potential for fiber source (Fernandez-Gines et al., 2004).

The juice pulp from the finishing process and the essences recovered from juice processing, along with peel press liquor, add up to 5% of fresh fruit. The peels especially have been found to contain high quantities of phenolics. Oranges, lemons and grapefruit peels contain 15% more polyphenols than the edible portions (Gorinstein et al., 2001). Similarly, lemon has been reported to have high amounts of antioxidant compounds (Marin et al., 2002). In addition, peels of yellow and white nectarines contain at least twice more phenolic compounds than the flesh (Gil-Izquierdo et al., 2002). Citrus seeds represent 0.1–5% of the whole fruit, and depending on the variety, they can be used for oil extraction and terpenoids recovery (Djilas et al., 2009).

Flavonoids are the largest group of bioactive compounds in citrus fruit. The main flavonoids found are hesperidine, narirutin, naringin and eriocitrin (Schieber et al., 2001). Otherwise, lemon peels contain mainly hesperidin and erocitrin, while naringin and erocitrin predominate from liquid residues (Coll et al., 1998). It has been reported that bergamot peel contains large amounts of naringin (up to 1 mg/g) and neohesperidin (1 mg/g), among others (Mandalari et al., 2007). It is well known that flavonoids from citrus have potential antioxidative, anticancer and anti-inflammatory activities. In addition, ascorbic acid is present in citrus fruit in high amounts. Ascorbic acid content is higher in peel than in flesh, and also is higher in peeled oranges and lemons than in grapefruits and their peels (Gorinstein et al., 2001).

2.3.1.2 Grape

The grape is one of the largest fruit crops, with more than 68 million tons produced annually (FAOSTAT, 2012); 80% of the crop is used in the wine industry and around 12 million tons of grape pomace is produced within a few weeks of the harvest period. Grape juices and wine processing generates seeds, skin and pomace as principal by-products. The pomace represents around 20% in weight of fresh fruit. Grape and products such as wine, juice, jams and raisins are economically important for the industry.

Wine industry wastes, which consist mainly of solid by-products, include marcs, pomace and stems, and account on average for almost 30% (w/w) of the grapes used for wine production. Grape by-products have been utilized for animal feed, but the presence of lignin reduces digestibility due to inhibition of cellulolytic and proteolytic enzymes, as well as the rumen microbiota (Kammerer et al., 2004). Furthermore, the final solid residue from ethanol production is generally used as fertilizer, although the high polyphenols content inhibits seed germination (Fontana et al., 2013).

Grape pomace is rich in polyphenols, with catechin, epicatechin, procyanidin B1, quercetin and kaempferol being the most relevant (Lu and Foo, 1999). Good amounts of anthocyanins are also reported; several glycosylated forms of malvinidin, as well as cyanidin and peonidin were recovered from grape pomace from several Italian varieties (Ruberto et al., 2007). On the other hand, grape seeds form a considerable portion of the grape, ranging from 38–52% of dry weight basis (Schieber et al., 2002). The seed oil is notable for its high unsaturated fatty acid content (especially linoleic acid) and is a great source of phenolic compounds such as gallic acid, catechin and epicatechin; as well as proanthocyanidins. In certain varieties, the content of phenolic acids is 2- or 3-fold higher in seeds than in press residue, whereas flavonoids tend to be concentrated in press residue (Maier et al., 2009). Thus, grape by-products are considered a valuable source of phytochemicals as functional compounds for food industries.

2.3.1.3 Apple

Apple is the most selected and a widespread fruit in the world. World apple production is nearly 76 million tons, of which 4 million tons are produced in the USA (FAOSTAT, 2012). Around 70% of apples are consumed as fresh, the rest being processed into value products such as juice, apple cider, jams, jelly and purees, with wine, vermouth and dried apple products too. In large-scale apple processing, by-products can be classified into two categories. The first is the fruit discarded into the sorting belt due to its partially bruised/spoiled nature, usually known as belt rejection. The second is the apple pomace obtained after juice extraction. The belt rejection apples are also discharged along with apple pomace as waste (Shalini and Gupta, 2010). About 65% of processed apples are used for juice concentrate; then apple pomace represents 25–30% of the original fruit and is generated during fruit pressing (Schieber et al., 2003). Apple pomace has high water content and is mainly composed of insoluble carbohydrates such as cellulose, hemicellulose and lignin. Apple pomace contains up to 5–10 g/kg phenolics, being phloridzin, quercetin and epicatechin as the most representative (Lu and Foo, 1999; Schieber et al., 2001); proanthocyanidins, chlorogenic acid and phloretin are also present in considerable amounts.

However, apple pomace composition varies according to the apple variety and the type of process used for juice extraction, mainly on how many times the fruit is pressed (Cetkovic et al., 2008). Traditional apple juice processing results in a juice poor in phenolics, with around 3–10% of the antioxidant activity (van der Sluis et al., 2002). It is well known that the phenolic compounds content is larger in peels than in flesh. Flesh contains catechins, procyanidins, phloridzin, phloretin glycosides, caffeic acid and chlorogenic acid; while the peels contains flavonoids not found in the flesh, such as quercetin and cyaniding glycosides (Wolfe et al., 2003). Hence, the commercial exploitation of apple by-products for phenolic compounds recovery seems promising.

Pectin represents around 10–15% of apple pomace on a dry weight basis (Oreopoulou and Tzia, 2007) and generally is recovered by acid extraction followed by precipitation. In general, apple by-products are a good natural source of bioactive compounds, with different health benefits and applications that should be further explored.

2.3.1.4 Tropical Fruits

Tropical fruit consumption has increased in the international markets, because of their remarkable flavor and nutritional properties (Ayala-Zavala et al., 2011). Some tropical fruits are considered exotic fruits when grown outside their country of origin. There is a wide list of tropical fruit products, but the most common are banana, papaya, mango, avocado, pineapple and peach. Those fruits are usually consumed directly by humans in their own country, but storage and processing steps are required for exportation to other locations. Thus, separation of the desired value products from plant tissue involves different processing steps and by-products generation as a consequence. The most common bioactive compounds present in tropical fruits are vitamins C and E, carotenoids, phenolic compounds and dietary fiber (Gonzalez-Aguilar et al., 2008).

Peach (Prunus persica) has been used in the food industry for the production of peach slices, syrups, juices and jam. By-products after processing are the kernels and peels. They are mostly used to obtain dietary fibers and pectin. Peach fiber has been incorporated into muffins, improving texture and flavor (Grigelmo-Miguel et al., 2001). Likewise, Bitter apricot (Prunus armeniaca L., Rosaceae) seeds are by-products of the apricot processing industry, with the peeled seeds serving as a raw material for the production of persipan (Schieber et al., 2001).

Mango (Mangifera indica L., Anacardiaceae) is one of the most important tropical fruits and its consumption is widely increasing in the international market. Major wastes of mango processing are peels and stones, amounting to 35–60% of the total fruit weight (Larrauri et al., 1996). Mango seed kernels are a good source of natural antioxidants. The main antioxidant are phenolic compounds (gallic and ellagic acids, and gallates) and phospholipids (Puravankara et al., 2000). Also, gallotannins and condensed tannin-related polyphenols were reported in mango kernels (Arogba, 2000).

Banana (Musa paradisiaca L., Musaceae) is another important crop worldwide. Peels constitute up to 30% of the ripe fruit. About 1000 banana plants are estimated to yield 20–25 tons of pseudostems, providing about 5% edible starch (Anand and Maini, 1997). Furthermore, anthocyanin pigments from banana bracts have been evaluated for their potential application as natural food colorants. It was concluded that the bracts proved to be a good and abundant source of anthocyanins of attractive appearance, as well as being a useful tool in anthocyanin identification, since all six most common anthocyanidins (delphinidin, cyanidin, pelargonidin, peonidin, petunidin and malvidin) are present (Pazmino-Duran et al., 2001).

2.4 Dietary Fibers-Rich By-Products

In recent years, consumers are becoming more interested in a diet rich in fruits and vegetables for a healthy lifestyle. Thus dietary fiber intake has