Nutraceuticals and Functional Foods in Health Promotion and Disease Prevention

The effect of dietary factors on health status has been recognized since antiquity. Although some of the dietary phytochemicals and bioactives have traditionally been considered as “antinutrients”, their beneficial effects in human health promotion and disease prevention has recently been acknowledged. While nutraceuticals, sometimes referred to as natural health products, are often used in medicinal forms as tablets, capsules or liquid, functional foods are those that resemble the traditional food, as such, but confer benefits beyond their nutritional role. Among diseases of concern, cancer and coronary heart disease (CHD) are high on the list. In this respect, phenolics of plant origin, as an example, have been found to act as free radical scavengers, inhibitors of cholesterol oxidation and DNA breakage, among others, thus serving as potential cancer preventing agents. The type of phenolics involved depends on the species as well as other variables. On the other hand, marine foods have often been considered as “heart food” because of the role of their omega-3 fatty acid constituents in lowering of triacylglycerol and cholesterol levels and hence the incidence of CHD. This overview provides a detailed account of food phenolics and marine oils in human health and disease prevention. INTRODUCTION Epidemiological evidence has pointed to the benefits of increased consumption of fruits and vegetables as well as marine foods in human health promotion and disease prevention (Block et al., 1992; Shahidi and Ho, 2000). While plant foods contain a variety of bioactives that exert their health benefits through synergistic action of the many classes of compounds involved, marine lipids are known to influence health through their omega3 fatty acid constituents. While initial research had concentrated on examining the benefits of plant-based foods through research into their vitamin C, vitamin E and carotenoid components, more recent work has confirmed that correlations of benefits with individual compounds, such as β-carotene, may contradict their perceived effects if used in the pure form. Hence β-carotene, when used as such, was found to increase the incidence of cancer in smokers (Omenn et al., 1996). Thus, the effects are found to be related to the co-operative and synergistic action of the cocktail or soup of bioactives presents in source materials. These findings have created the foundation for exploration and development of functional foods and nutraceuticals. The terms nutraceuticals and functional foods have been used to describe extracts and whole foods that have the characteristics of providing protective, preventive and possibly curative effects in the pathogens of cancer and other chronic disease progression. While nutraceuticals refer to components/extracts of food and non-food commodities taken in the medicinal form of tablet, capsule, powder, liquid and potion, functional foods resemble the traditional foods in their look, but both nutraceuticals and functional food groups provide benefits beyond what is rendered by their nutrient components. There are many different classes of bioactives present in foods, herbal and medicinal plants, depending on the species under consideration. Phenolic and polyphenolic group of compounds constitute an important class with biological activity Proc. WOCMAP III, Vol.6: Traditional Medicine & Nutraceuticals Eds. U.R. Palaniswamy, L.E. Craker and Z.E. Gardner Acta Hort. 680, ISHS 2005 14 (Table 1). While these components exert their effects through an array of possible mechanisms, the antioxidative role (Halliwell, 1996) of such compounds may be exerted by scavenging and neutralizing of free radicals (Wettasinghe and Shahidi, 1999a, b) or chelating prooxidant metal ions (Wettasinghe and Shahidi, 2002). In case of marine oils, their omega-3 components are known to exert influence on health as well as through their influence on eicosanoids metabolism. Hence, epidemiological studies have indicated that highly unsaturated fatty acids (HUFA) in marine oils lower the level of triacylglycerols and possibly cholesterol, enhance immuneresponse and help relieve problems associated with rheumatoid arthritis and diabetes, among others. In fact docosahexaenoic acid (22:6n-3, DHA) constitutes a major fatty acid of the gray matter of the brain and the retina of the eye (Shahidi and Finley, 2001). The organs most influenced by the omega-3 fatty acids are those with electrical activity and in addition to the brain and eye, heart is another major organ affected. However, highly unsaturated fatty acids involved are prone to oxidation and require stabilization in order to protect consumers from deleterious affects of oxidation products. This overview provides an account of the phenolics of nutraceutical, functional foods and medicinal plants as well as the role of phenolics in stabilization of marine oils. The biosynthesis of phenolics and their function in plant resources is also provided. BIOSYNTHESIS, CLASSIFICATION AND NOMENCLATURE OF PHENOLICS Phenolics and polyphenolics in nutraceuticals, functional foods and herbal products when consumed are known to play an important role in the human body. They constitute, perhaps, the largest group of secondary metabolites originating from phenylalanine, and to a lesser extent, in some plants, from tyrosine (Shahidi and Naczk, 2004). The conversion proceeds via the action of phenylalanine ammonia lyase (PAL) or tyrosine ammonia lyase (TAL) to afford trans-cinnamic acid or p-coumaric acid, respectively. These and related carboxylic acids are known as phenylpropanoids and constitute a C6-C3 moiety. The related phenylpropanoids are produced via successive hydroxylation and methylation to other C6-C3 compounds and these may in turn be reduced to alcohols, which serve as precursors in lignin synthesis, or may lose a C2 moiety to afford benzoic acid derivatives; it is also possible that acids involved lose a CO2 molecule to produce simple phenols. Fig. 1 illustrates a variety of C6-C3, C6-C1 and C6 compounds produced in plants (Shahidi, 2000a, b). The C6-C3 compounds, as their CoA adduct, may react with 4 molecules of malonyl CoA to afford stilbenes or chalcones via the action of stilbene synthase or chalcone synthase, respectively. The chalcones involved may subsequently cyclize to produce a wide range of C6-C3-C6 compounds, collectively known as flavonoids. The individual classes of compounds involved include flavones, flavonols, favonones, favononols, flavan-3-ols, anthocyanidins, catechins and isoflavones, among others. Fig. 2 illustrates the variety of flavonoids present in nutraceutical, functional foods and medicinal products. In addition to the above classes of compounds, lignans could be produced by the addition of two molecules of C6-C3 while coumarins, cutins and suberins may result from combination and/or transformation of C6-C3 compounds. Meanwhile, condensation of gallic acid with sugars leads to the production of hydrolyzable tannins and that of flavan3-ols with one another affords condensed tannins (Fig. 3). ISOLATION, CHARACTERIZATION AND ANTIOXIDANT POTENCY OF PHENOLICS AND POLYPHENOLICS Phenolic compounds in different source materials may be extracted into a suitable solvent following removal of their lipid constituents. Solvents often used for this purpose include acetone, ethanol, methanol and water, depending on the nature of phenolics involved and the type of source material under investigation. Therefore, catechins are extracted from green tea into water, while oilseeds, herbals and medicinal plants may be extracted using organic solvents usually containing 5-20% water. Following extraction,