ABSTRACT
Polyphenols are plant metabolites that feature multiple phenolic hydroxyl groups, and which are widely distributed in the plant kingdom (Giannasi, 1988). Many angiosperms, gymnosperms, ferns, and even algae (Markham, 1988; Niemann, 1988; Targett and Arnold, 1998) contain polyphenols, and in some cases the polyphenols are accumulated in very high concentrations (from a few percent to 30% of the dried material) (Nutrient Data Laboratory Beltsville Human Nutrition Research Center Agricultural Research Service, 2004). Although there are other subtypes with different molecular skeletons and biosynthetic origins, catechins and proanthocyanidins are the most
2.1 Introduction 19 2.2 Structure of Catechins and the Polyphenol Composition of
Green Tea 20 2.3 Extraction, Separation, and Analysis of Tea Catechins 24 2.4 Polyphenols of Oolong Tea, Postfermented Tea, and Black Tea 25 2.5 Chemical Reactivity of Tea Catechins 27 2.6 Hydrophobic Interactions with Coexisting Compounds 33 2.7 Conclusion 35 References 35
important polyphenols found in foods (Figure 2.1), being widely distributed in fruits, vegetables, spices, and herbs. Catechins may also be called flavan-3-ols, which represent a relatively small group of the flavonoid class of natural products, while proanthocyanidins are defined as oligomers and polymers of catechins, in which catechin units are connected through carbon-to-carbon linkages. Catechin monomers and proanthocyanidin oligomers are closely related biosynthetically and coexist in many plants, such as grapes, apples, pine, and blueberries. Bananas (Tanaka et al., 2000) and persimmons (Tanaka et al., 1994) are unusual fruits, as they contain only polymeric proanthocyanidins. In contrast, the tea plant, Camellia sinensis (L.) O. Kuntze (eaceae), is also unusual, as it contains almost exclusively catechin monomers (Hashimoto et al., 1992). is chapter first introduces the chemical compositions of tea polyphenols. en, extraction, separation, and analytical methods are also briefly introduced. Finally, the physicochemical characteristics of polyphenols as they relate to their biological functions are discussed.
