Source: Refs. 10 and 11.

Source: Refs. 10 and 11.

The tea flavanols are water-soluble, colorless, astringent substances that oxidize rapidly, especially in an alkaline environment. They occur in the cytoplasmic vacuoles of the leaf cells. They form complexes with many other substances (13). Epigallocatechin gallate constitutes a high proportion of fresh-leaf weight. Tea beverage quality is correlated with fresh-leaf flavanol content, especially with the gallated compounds that decrease in quantity as the leaf ages on the growing plant. They are the most important components in the black-tea manufacturing process.

Catechins are notable antioxidants, a property also exhibited by their oxidation products present in black tea and by other flavonoid compounds (14). This is demonstrated by their ability to scavenge free radicals generated in many in vitro systems. The physiological significance of this property will be discussed later in this article.

Other Polyphenols

Other polyphenols include gallic acid (7) and quinic acid; flavonols, such as kaemferol (11), quercitin (12), myricetin (13), and their glycosides; a group of chalcan-flavan di-mers; proanthocyanidins; a group of flavone-C-glycosides (10); and a group of bisflavanols also known as theasinen-sins (12). Depsides present include chlorogenic acid (8),p-coumarylquinic acid (9), and theogallin (3-galloylquinic acid) (10), which is unique to tea (Fig. 2). It occurs at relatively high concentrations (1% of dry weight) and is said to correlate with quality. Most of the polyphenols participate in the important reactions that occur during manufacture.

Caffeine and Other Xanthines

Tea flush contains 2 to 4.5% caffeine and much smaller amounts of theobromine. Theophylline may be present but in small quantities. Caffeine is responsible for the mild stimulatory properties of tea beverage and is generally

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