Chemistry of Secondary Polyphenols Produced during Processing of Tea and Selected Foods

Abstract

This review will discuss recent progress in the chemistry of secondary polyphenols produced during food processing. The production mechanism of the secondary polyphenols in black tea, whisky, cinnamon, and persimmon fruits will be introduced. In the process of black tea production, tea leaf catechins are enzymatically oxidized to yield a complex mixture of oxidation products, including theaflavins and thearubigins. Despite the importance of the beverage, most of the chemical constituents have not yet been confirmed due to the complexity of the mixture. However, the reaction mechanisms at the initial stages of catechin oxidation are explained by simple quinone–phenol coupling reactions. In vitro model experiments indicated the presence of interesting regio- and stereoselective reactions. Recent results on the reaction mechanisms will be introduced. During the aging of whisky in oak wood barrels, ellagitannins originating from oak wood are oxidized and react with ethanol to give characteristic secondary ellagitannins. The major part of the cinnamon procyanidins is polymerized by copolymerization with cinnamaldehyde. In addition, anthocyanidin structural units are generated in the polymer molecules by oxidation which accounts for the reddish coloration of the cinnamon extract. This reaction is related to the insolubilization of proanthocyanidins in persimmon fruits by condensation with acetaldehyde. In addition to oxidation, the reaction of polyphenols with aldehydes may be important in food processing.

A new catechin oxidation product and polymeric polyphenols of post-fermented tea

“…Elemental composition and infra-red absorptions of the oxidation products were similar to those observed for the polymers of post-fermented tea. In the 13 C NMR spectrum of the polymer of 3, the pyrogallol-type B-ring signals are significantly reduced compared with that of 3, because oxidation and the subsequent coupling reactions are primarily taking place at the B-rings (Tanaka, et al, 2010). In contrast, the spectrum of the polymers of post-fermented tea exhibited the signals attributable to the B-ring carbons (δ 108, 128135 and 145).…”

“…However, recent studies suggest some beneficial effects of post-fermented tea (Chiang, Weng, Lin-Shiau, Kuo, Tsai, & Lin, 2006;Duh, Yen, Yen, Wang, & Chang, 2004;Kuo, Weng, Chang, Tsai, Lin-Shiau, & Lin, 2005;Noguchi, Hamauzu, & Yasui, 2008;Oyaizu, Hotsumi, Takagi, Matsumoto, Fujita, Matsuzaki, & Yamashita, 2005;Oyaizu, Hotsumi, Takagi, Matsuzaki, Yamashita, Takenaga, & Itho, 2006). Black and oolong tea production includes a process called "tea fermentation", in which constituents of fresh tea leaves are chemically altered by enzymes originally contained in the leaves (Roberts, 1962;Tanaka, Matsuo, & Kouno, 2010). In contrast, the post-fermented teas are produced by 4 aerobic or anaerobic microbial fermentation of heat-processed green tea leaves (Gong, Watanabe, Yagi, Etoh, Sakata, Ina, & Liu, 1993;Okada, Takahashi, Ohara, Uchimura, & Kozaki, 1996).…”

Biomimetic One-Pot Preparation of a Black Tea Polyphenol Theasinensin A from Epigallocatechin Gallate by Treatment with Copper(II) Chloride and Ascorbic Acid

“…A large part of black tea polyphenols remain to be chemically identified due to difficulty in purification. 22,23) These byproducts are probably related to the unknown black tea polyphenols and chemical characterization is now in progress.…”

Catechin oxidation products: mechanistic aspects and kinetics

“…The oxidation products are the oxidation dimers. The dimers are linked either by C6 → C8 or C 6→ C6 interflavan linkages and are classified as B-type dehydrodicatechins, resulting from the repeated condensation reactions between the A-ring of the lower unit and the B-ring of the upper unit through a mechanism of so-called 'head to tail' polymerization [3] or they contain additional C-O-C ether-type interflavan linkages and are classified as A-type dehydrodicatechins [4].…”