Phenolics in Food and Natural Health Products: An Overview

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1 Chapter 1 Phenolics in Food and Natural Health Products: An Overview Downloaded via on November 2, 2018 at 10:51:33 (UTC). See for options on how to legitimately share published articles. Fereidoon Shahidi 1 and Chi-Tang Ho 2 1 Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3X9, Canada 2 Department of Food Science, Rutgers, The State University of New Jersey, 65 Dudley Road, New Brunswick, NJ Phenolic and polyphenols compounds occur in food as secondary metabolites. Different classes of phenolics are often encountered in foods and these exert beneficial health effects related to their antioxidant activity, chemopreventive effect and anticarcinogenic potential, among others. These activities are often governed by the structural characteristics of the bioactive components present. In addition, processing of foods might affect the chemical and activity of the compounds involved. Introduction Phenolic compounds in foods and natural health products originate from one of the main classes of secondary metabolites in plants derived from phenylalanine or tyrosine (/). The term 'phenolic' or 'polyphenol' can be defined as a substance which possesses an aromatic ring bearing one or more hydroxyl substituents, including functional derivatives (esters, methyl ethers, glycosides etc.) (2). Most phenolics have two or more hydroxyl groups and are bioactive substances occurring widely in foods American Chemical Society 1

2 2 Occurrence of Phenolics The phenolics which occur commonly in foods and natural health products may be classified into simple phenols, hydroxybenzoic acid and hydroxycinnamic acid derivatives, flavonoids, stilbenes, lignans and hydrolyzable as well as condensed tannins. The Simple Phenols and Phenolic Acids The simple phenols include monophenols such as p-cresol isolated from several fruits and diphenols. Diphenols such as hydroquinones are probably the most widespread simple phenols (3). There are two classes of phenolic acids, hydroxybenzoic acids and hydroxycinnamic acids. Except in certain red fruits and onions, the content of hydroxybenzoic acids in edible plants is usually very low (/). Tea can be an important source of gallic acid which is 3,4,5-trihydroxybenzoic acid (4). Gallic acid usually occur in plants in souble form as catechin esters, quinic acid ester or hydrolyzable tannins. The hydroxycinnamic acids and their derivatives are more common than are the hydroxybenzoic acids in foods. Hydroxycinnamic acids and their derivatives are almost exclusively derived from p-coumaric acid, caffeic acid, and ferulic acid whereas sinapic acid is, in general, less encountered. The occurrence of hydroxycinnamic acids in food has been reviewed by Herrmann (J). Caffeic acid and its esterified derivatives are the most abundant hydroxycinnamic acids in a variety of fruits. On the other hand, ferulic acid and its derivatives are the most abundant hydroxycinnamic acids found in cereal grain (6). Flavonoids Flavonoids are ubiquitous in plants; almost all plant tissues are able to synthesize flavonoids. There are also a wide variety of types - at least 2000 naturally occurring flavonoids. Flavonoids are present in edible fruits, leafy vegetables, roots, tubers bulbs, herbs, spices, legumes, tea, coffee, and red wine (1,2,7). They can be classified into seven groups: flavones, flavanones, flavonols, flavanonols, isoflavones, flavanols (catechins), and anthocyanidins. The structures of these flavonoids are given in Figure 1. Examples of common flavonoids in foods are listed in Table I. In general, the leaves, flowers, and fruits or the plant contain flavonoid glycosides; woody tissues contain aglycones, and seeds may contain both.

3 3 Flavanol (catechin) Anthrocyanidin Figure 1. Sturctures of flavonoids.

4 4 Table I. Different Classes of Flavonoids, Their Substitution patterns and Dietary Sources Class Name Substitution Dietary Source Flavone Apigenin 5,7-OH Parsley, celery Rutin 5,7,3',4'-OH, Buckwheat, citrus 3-O-rutinose, Tangeretin 4,5,6,7,4'- Citrus OCH 3 Flavanone Naringin 5,4' - OH Citrus Naringenin 5,7,4' - OH Orange peel Flavonol Kaempferol 3,5,7,4' - OH Broccoli, tea Quereetin 3,5,7,3',4'-OH Onion, broccoli, apples, berries Flavononol Taxifolin 3,5,7,3',4' -OH fruits Isoflavone Genistein 5,7,4' - OH Soybean Daidzein 4' - OH, 7-0- Soybean glucose Puerarin 7,4'-OH, 8- Kudzu C-glucose Flavanol (-)-Epicatechin 3,5,7, 3',4' -OH Tea (catechin) (-)-epigallocatechin 3,5,7, 3',4',5'- Tea OH (-)-epigallocatechin 5,7, 3',4',5'- Tea gallate OH, 3-gallate Anthocyanidin Cyanidin 3,5,7,3',4'-OH Cherry, strawberry Delphinidin 3,5,7, 3',4',5'- Dark fruits OH As a result of their ubiquity in plants, flavonoids are an integral part of the human diet. It is estimated (<S) that the average American's daily intake of flavonoids is close to 1 g per person. However, this estimated daily intake of flavonoids may be too high when compared to the results of the Zutphen Elderly Study by Hertog et al. (Ρ). They measured the content of selected flavonoids,

5 namely quercetin, kaempferol, myricetin, apigenin, and luteolin in various foods most commonly consumed in The Netherlands. By assessing the flavonoid intake of 805 men aged years, they found that the mean baseline flavonoid intake was 25.9 mg daily. Hertog et al. (10) also found that the major sources of flavonoid intake were tea (61%), onion (13%), and apple (10%). Certain later studies provided more precise individual data concerning the intake of various classes offlavonoids.for example, the consumpstion of flavonols for American has been estimated at mg/d (//). 5 Stilbenes Stilbenes are phenolic compounds which contain two benzene rings separated by an ethane bridge. They are widely distributed in higher plants and their main physiological roles relate to their action as phytoalexins and growth regulators (12). Stilbenes had not caught the attention of food and nutritionists until one of its family members, resveratrol (3,5,4'-trihydroxystilbene) was reported to demonstrate a preventing effect on cancer (13,14). Lignans Lignans are dimers of phenylpropanoid units linked by the central carbons of their side chains. In plants, lignans and their higher oligomers act as defensive substances (/). Lignan-rich plant products were found to be active ingredients in the treatment of disease in Chinese folk medicine. Unfortunately, many of the active ingredients of these plant products have not been scientifically tested as therapeutic agents (15). However, flax and sesame lignans have been considered as important components with health benefits (16,17). Tannins Depending on their structures, tannins are defined as hydrolyzable or condensed. Hydrolyzable tannins are glycosylated gallic acids (7). Condensed tannins also known as proanthocyanidins and are linear polymers of flavan-3-ol (catechin and gallocatechin), andflavan-3,4-diolunits. The consecutive units of condensed tannins are linked through the interflavonoid bond between C-4 and C-8 or C-6 (18). Tannins occur widely in different foods and are often concentrated in the skin of fruits and seed coats, among others.

6 6 Antioxidant Properties of Phenolics Antioxidants are added to fats and oils, or foods containing fats, to prevent the formation of various off-flavors and other undesirable compounds that result from the oxidation of lipids. The most widely used synthetic antioxidants, BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene) and TBHQ (tertiary-butylhydroquinone) are all phenolics. Antioxidants not only protect the quality of lipid-containing foods, but in living systems dietary antioxidants may also be effective in protecting in vivo lipid peroxidation and combating carcinogenesis, heart disease and aging. Although dietary essential antioxidant nutrients such as tocopherols and ascorbic acid have the ability to inhibit lipid peroxidation in vivo, numerous other nonessential antioxidants are consumed daily, often at concentrations far exceeding those of nutrient antioxidant (19). Flavonoids are the most important among these nonessential dietary antioxidants. Flavonoids are known antioxidants and act as free radical acceptors and chain breakers. Many of the flavonoids have shown marked antioxidant characteristics. Flavonols are known to chelate metal ions at the 3-hydroxy-4- keto group, 5-hydroxy-4-keto group, or both. An ortho-diphenolic group on the B-ring can also demonstrate metal chelating activity (20). A recent review compared the antioxidant activity of a large number of food phenolics (21). Phenolics and Disease Prevention Almost all phenolics possess several common biological and chemical properties: (a) antioxidant activity, (b) the ability to scavenge active oxygen species, (c) the ability to scavenge electrophiles, (d) the ability to inhibit nitrosation, (e) the ability to chelate metals, (f) the potential to producing hydrogen peroxide in the presence of certain metals, and (g) the capability to modulate certain cellular enzyme activities. Rencetly, phenolics, particularly flavonoids have been intensively investigated because of these broad potential pharmacological activities (22). It appears that diets in rich in phenolics may protect against cardiovascular diseases, neurodegenerative disorders, and some forms of cancer (23,24). Several phenolics have been recognized as active chemopreventive agents. Epigallocatechin 3-gallate (EGCG) from green tea and theaflavins from black tea exert strong inhibitory effects on diverse cellular events asocociated with multistage carcinogenesis. Several chapters in this volume provide recent studies on tea polyphenols and cancer. Curcumin, a yellow ingredient from tumeric (Curcuma longae L.) has also been extensively investigated for its cancer preventive potential (25). A similar compound, 6-gingerol grom ginger

7 (Zingiber officinale Roscoe) also has antitumer promotional effects. The molecular mechanisms explaining the anticancer effects of 6-gingerol has been discussed in detail in this volume. Many of the beneficial health effects are known to be linked to the antioxidant activity of the components involved althugh this is not always the case. 7 References 1. Shahidi, F.; Naczk, M. Phenolics in Food and Nutraceuticals. CRC Press, Boca Raton, FL Harborne, J.B. In Methods in Plant Biochemistry, Vol. 1: Plant Phenolics; Harborne, J.B., Ed.; Academic Press: London, UK, 1989, pp Van Sumere, C. F. In Methods in Plant Biochemistry, Vol. 1: Plant Phenolics; Harborne, J.B., Ed.; Academic Press: London, UK, 1989, pp Tomas-Barberan, F. Α.; Clifford, M. N. J. Sci. Food Agric. 2000, 80, Herrmann, K. CRC Crit. Rev. Food Sci. Nutr. 1989, 28, Monach, C.; Scalbert, Α.; Morand, C. R.; Jiménez, L. Am. J. Clin. Nutr. 2004, 79, Ho. C.-T. In Food Factors for Cancer Prevention; Ohigashi, H.; Osawa, T.; Terao, J.; Watanabe, S.; Yoshikawa, T., Eds.; Spinger: Tokyo, Japan, 1993, pp Kuhnau, J. World Rev. Nutr. Diet. 1976, 24, Hertog, M. G. L.; Feskens, E. J. M.; Hollman, P. C. H.; Katan, M. B.; Kromhout, D. Lancet 1993a, 342, Hertog, M. G. L.; Hollman, P. C. H.; Katan, M. B.; Kromhout, D. Nutr. Cancer 1993b, 20, Manach, C.; Scalbert, Α.; Morand, C.; Ramesy, C.; Jimenez, L. Am. J. Clin. Nutr. 2004, 79, Gotham, J. In Methods in Plant Biochemistry, Vol. 1: Plant Phenolics; Harborne, J.B., Ed.; Academic Press: London, UK, 1989, pp Jang, M.; Cai, L.; Udeani, G. O.; Slowing, Κ. V.; Thomas, C. F.; Beecher, C. W. W.; Fong, H. H. S.; Farnsworth, N. R.; Kinghorn, A. D.; Mehta, R. G.; Moon, R. C.; Pezzuto, J. M. Science 1997, 275, Savouret, J. F.; Quesne, M. Biomed. Pharmacother. 2002, 22, Ayres, D. C.; Loike, J. D. Lingans: Chemcial, Biological and Clinical Properites; Cambridge Univeristy Press: Cambridge, UK, Kang, M-H.; Naito, M., Tsujihara, N.; Osawa, T. J. Nutr. 1998, 128,

8 8 17. Spence, J.D.; Thornton, T.; Muir, A.D.; Westcott, N.D. J. Am. College Nutr. 2003, 22, Hemingway, R. W. In Chemistry and Significance of Condensed Tannin, Hemingway, R. W.; Karchesy, J.J., Eds., Plenum Press: New York, 1989, pp Decker, E. A. Nutr. Rev. 1995, 10, Ho, C-T. In Food Factors for Cancer Prevention. Ohigashi, H.; Osawa, T.; Terao, J.; Walanabe, S.; Yoshikawa, T., Eds.; Springer: Tokyo, Japan. 1993, pp Kim, D. O.; Lee, C. Y. CRC Crit. Rev. Food Sci. Nutr. 2004, 44, Huang, M. T.; Ferraro, T. In Phenolic Compounds in Food and Their Effects on Health II: Antioxidants & Cancer Prevention; Huang, M. T.; Ho, C.-T.; Lee, C. Y., Eds., American Chemical Society: Washington, D.C., 1882, pp. 8-34, 23. Hertog, M. G. L.; Hollman, P. C. H.; Katan, M. B. J. Agric. Food Chem. 1992, 40, Block, G. Nutr. Rev. 1992, 50, Lin, J. K. In Phytochemicals: Mechanisms of Action, Meskin, M. S.; Bidlack, W. R.; Davies, A. J.; Lewis, D. S.; Randolph, R. K., Eds., CRC Press: Boca Raton, FL, 2004, pp