ABSTRACT
It is well known that tea contains catechins besides caffeine. Although catechins are widely distributed in the plant kingdom, the catechin monomers in many plants coexist with larger amounts of dimeric to polymeric proanthocyanidins, which are comprised of catechin units connected by C-C bonds.2 However, the polyphenol composition of C. sinensis is unique, and mainly comprised of four monomeric catechins-(–)-epicatechin (1), (–)-epigallocatechin (2) and their galloyl esters,
5.1 Introduction ..................................................................................................... 59 5.2 Model Fermentation Experiments .................................................................. 61 5.3 Production and Oxidation of Theaavins ....................................................... 62 5.4 Oxidation of Catechol-Type Catechins ...........................................................64 5.5 Oxidation of Pyrogallol-Type Catechins and Formation of Theasinensins ....66 5.6 Polyphenol with a Theanine Strecker Aldehyde Moiety ................................68 5.7 Another Pathway for Benzotropolone Formation ........................................... 70 5.8 Why Are Black Tea Polyphenols So Complex? .............................................. 71 References ................................................................................................................ 73
(–)-epicatechin gallate (3) and (–)-epigallocatechin gallate (4) (gure 5.1)—and the concentration of proanthocyanidins is much lower than that of the monomers.3,4 In addition, an abundance of the catechins with pyrogallol-type B-rings and their galloyl esters is also characteristic of tea leaves.5,6 These catechins are responsible for the characteristic bitterness and astringent taste of green tea.
