Phenolic Compounds in Agri-Food By-Products, Their Bioavailability and Health Effects
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Journal of International Society for Food Bioactives Nutraceuticals and Functional Foods Review J. Food Bioact. 2019;5:57–119 Phenolic compounds in agri-food by-products, their bioavailability and health effects Fereidoon Shahidi*, Varatharajan Vamadevan†, Won Young Oh and Han Peng Department of Biochemistry, Memorial University of Newfoundland, St. John’s, NL, A1B 3X9, Canada †Present address: Cargill, 14800 28th Avenue N., Plymouth, MN 55447, USA. *Corresponding author: Fereidoon Shahidi, Department of Biochemistry, Memorial University of Newfoundland, St. John’s, NL, A1B 3X9, Canada. Tel: 709-864-8552; Fax: 709-864-2422; E-mail: [email protected] DOI: 10.31665/JFB.2019.5178 Received: February 01, 2019; Revised received & accepted: March 01, 2019 Citation: Shahidi, F., Vamadevan, V., Oh, W.Y., and Peng, H. (2019). Phenolic compounds in agri-food by-products, their bioavailability and health effects. J. Food Bioact. 5: 57–119. Abstract Phenolic compounds constitute a large and diverse group of secondary metabolites derived from phenylalanine and tyrosine and are widely distributed throughout the plant kingdom. They could be divided into different class- es such as simple phenol, phenyl acetic acid, hydroxybenzoic acid, hydroxycinnamic acid, and other phenylpro- panoids as well as condensed tannins (proanthocyanidins) and hydrolysable tannins, among others, depending on their basic carbon skeleton structure. Phenolic compounds in plant-based foods have been suggested to have a number of beneficial health effects including prevention of cancer, cardiovascular disease, diabetes, immune disorders, neurogenerative disease and others. These properties are largely attributable to the antioxidant -activ ity of the phenolic compounds as well as other mechanisms of action. Therefore, nutraceuticals of plant origin may evolve to be considered a vital aspect of dietary-disease preventive food components. Agri-food industries generate substantial quantities of phenolic rich by-products, which could serve as an attractive and commercially viable source of nutraceuticals. This contribution mainly summarizes the occurrence of phenolic compounds and some other bioactives in various Agri-food by-products, their bioavailability and health benefits. Keywords: By-products; Bioactive compounds; Phenolics; Nutraceuticals; Health benefits; Bioavailability. 1. Introduction of terpenoids, phenolic compounds, and alkaloids as well as other nitrogen containing plant constituents (Harborn, 1999). Apart from Plants produce a great variety of organic compounds that comprise this classification, the main bioactive phytochemicals in foods in- both major types of chemicals such as carbohydrate, protein, lipid clude polyphenols, terpenoids, glucosinolates and other sulphur- and nucleic acids as well as non-nutritive phytochemicals. Though containing compounds (Espín et al., 2007; Tomás-Barberán et al., phytochemicals, by the strictest definition, are chemicals that are 2004). Phenolic compounds constitute a very large group of phy- produced by the plants, currently the term is being only used for tochemicals that are widely distributed in higher plants (Macheix non-nutritive (not considered as essential nutrients), biologically et al., 1990). The general break down of non-nutritive plant-base active, chemically derived compounds found in plants (Alasalvar natural products is shown in Figure 1. and Shahidi, 2009). Many of the phytochemicals have the capac- Phenolics are secondary metabolites synthesized by plants both ity to alter enzymatic and chemical reactions, and therefore may during normal development (Harborne, 1982; Pridham, 1960; Sha- impact human health both positively and negatively (Thompson, hidi and Naczk, 2004, Shahidi and Peng, 2018) and in response 1993). to stress conditions such as infection by pathogens and parasites, Most phytochemicals can be classified into three major groups wounding, air pollution, exposure to extreme temperatures and UV Copyright: © 2019 International Society for Nutraceuticals and Functional Foods. 57 All rights reserved. Phenolic Compounds in agri-food by-products Shahidi et al. Figure 1. General breakdown of non-nutritive plant-base natural products. radiation (Beckman, 2000; Nicholson and Hammerschmidt, 1992; 2008; Peng et al., 2018). Zobel 1997; Shahidi and Yeo, 2016). They are commonly found in This contribution aims to provide an overview of the findings both edible and non-edible plant parts and may act as phytoalex- related to the phenolic profiles of various by-products, their bioa- ins, antifeedants, attractants for pollinators, contributors to plant vailability and health benefits. Other nutraceuticals in by-products pigmentation, antioxidants and protective agents against UV light. particularly referred to carotenoids and betalains also have been In addition, phenolics may contribute to the bitterness, astringency, reviewed in this work, but to a lesser extent. color, flavor, odour, and oxidative stability of food (Shahidi and Naczk, 2004). Phenolic compounds exhibit a wide range of physiological 2. Dietary phenolics and nutraceuticals: overview properties, such as anti-allergenic, anti-artherogenic, anti-inflam- matory, anti-microbial, antioxidant, anti-thrombotic, cardiopro- Phenolics are a group of organic compounds with one or more tective and vasodilatory effects (Benavente-Garcia et al., 1997; hydroxyl groups on the aromatic ring(s). They range from simple Manach et al., 2005; Middleton et al., 2000; Puupponen-Pimiä et phenols, which are relatively rare (either absent or comprise only al., 2001; Samman et al., 1998, Shahidi and Peng, 2018). There- a small proportion) in their natural distribution (Cowan, 1999) to fore, consumption of plant-based foods is instrumental in health complex compounds known as polyphenols (Bravo 1998). These promotion and disease risk reduction. Furthermore, consumers are diversified groups of phytochemicals are derived from phenylala- increasingly aware of diet related health problems, therefore de- nine and tyrosine (Harborne, 1982; Morello et al., 2002; Shahidi, manding natural ingredients, which are expected to be safe and 2000; Shahidi and Naczk, 2004; Shahidi and Yeo, 2018; Shahidi health promoting (Schieber et al., 2001b). and Peng, 2018). Most naturally occurring phenolic compounds The agri-food industry produces large volumes of wastes, both are present as conjugates with mono- and polysaccharides, linked solids and liquid, resulting from the production, preparation and to one or more of the phenolic groups and may also occur as func- consumption of food. In addition to food wastes, food industry tional derivatives such as methyl and other esters (Harborne, 1989; uses a large amount of water and proportion of water used may Harborne et al., 1999; Shahidi and Naczk, 1995). Flavonoids, phe- leave as part of the products (blanching water, olive mill waste- nolic acids, and tannins are the most important dietary phenolics water, etc.). In many cases, by-products from agri-food indus- (King and Young, 1999). try are being increasingly recognized as a good and inexpensive source for obtaining bioactive compounds including high-phenolic products (Peng et al., 2018; Shahidi, 2009; Schieber et al., 2001b; 2.1. Flavonoids Tomás-Barberán et al., 2004). Thus, a number of studies to exam- ine the occurrence of phenolic compounds in various by-products/ The largest group of polyphenols is the flavonoids, which account residuals of agri-food industry and their antioxidant activity have for 60% of the total dietary phenolic compounds (Harborne and increased considerably in recent years and the major/selected by- Williams, 2000; Nichenametla et al., 2006; Shahidi and Naczk, products of processing industry have been summarized and re- 2004) and there are an estimated 4,000 known flavonoids (Wrol- viewed as a source of antioxidant (Balasundram et al., 2006; Dimi- stad, 2005). Flavonoids are C15 compounds all of which have the trios, 2006; Moure et al., 2001; Schieber et al., 2001b; Shahidi, structure C6-C3-C6 (Harborne and Simmonds, 1964). They gener- 58 Journal of Food Bioactives | www.isnff-jfb.com Shahidi et al. Phenolic Compounds in agri-food by-products Figure 2. Major classes of flavonoids and its some individual compounds. ally consist of two aromatic rings, each containing at least one hy- Apart from various vegetables and fruits, flavonoids are found in droxyl, which are connected through a three-carbon “bridge” and seeds, nuts, grains, spices, and different medicinal plants as well in become part of a six-member heterocyclic ring. beverages, such as wine, tea and beer (Shahidi and Naczk, 1995; The flavonoids are further divided into subclasses based on the Yeo and Shahidi, 2017). connection of an aromatic ring to the heterocyclic ring, as well as the oxidation state and functional groups of the heterocyclic 2.2. Phenolic acids ring. Within each subclass, individual compounds are character- ized by specific hydroxylation and conjugation patterns (Merken and Beecher, 2000). Figures 2 and 3 show the major classes of Phenolic acids, in the form of substituted derivatives of hydroxy- flavonoids and their generic structures, respectively. Among the benzoic and hydroxycinnamic acids, are the predominant pheno- major classes of flavonoids, flavones and flavonols are the most lics in food from plant sources, manly grains, legumes and oil- widely occurring and structurally diverse compounds (Harborne seeds. These derivatives differ in the pattern of their hydroxylation et al.,