Synthesis of Theaflavin from Epicatechin and Epigallocatechin by Plant Homogenates and Role of Epicatechin Quinone in the Synthesis and Degradation of Theaflavin

Abstract

Oxidation products of (-)-epicatechin and (-)-epigallocatechin by treatment with homogenates of 62 plants belonging to 49 families were compared. Forty-six plants were capable of synthesizing theaflavin, a black tea pigment, regardless of whether they contained catechins. Loquat, Japanese pear, and blueberry had activities higher than that of fresh tea leaves after 5 h of treatment; furthermore, these plants oxidized theaflavin to theanaphthoquinone. An additional new metabolite, dehydrotheasinensin, was generated on treatment with fresh tea leaves, eggplant, and unripened Japanese orange. Evidence for the oxidation of epigallocatechin and theaflavin by electron transfer to epicatechin quinone was demonstrated in a time course study using bananas and trapping the quinone intermediates as glutathione conjugates.

Oxidation of Tea Catechins: Chemical Structures and Reaction Mechanism

“…In this mechanism, 1 appeared to be oxidized very slowly compared to 2 because 1 was regenerated by reduction of 1a. Its rapid oxidation-reduction turnover was chemically proved by a similar experiment in the presence of glutathione, in which 1 was completely converted to glutathione adducts of 1a and, in contrast, about 70% of 2 was unchanged (Tanaka et al, 2002a). This coupled oxidation mechanism can be explained by higher enzyme specificity to 1 and the lower oxidation-reduction potential of 2 (Roberts, 1957a).…”

“…2). The structure of this yellow pigment was established by two-dimensional NMR spectroscopic analysis and the chemical derivatization (Tanaka et al, 2000), and the oxidation mechanism of the formation of 7 from 5 was deduced as shown in Fig 3. In this mechanism, the epicatechin quinone (1a) was responsible for the initial oxidation of the benzotropolone ring of 5 (Tanaka et al, 2002a). In addition, two new oxidation products of 5, bistheaflavin A (8) (Tanaka et al, 2001) and dehydrotheaflavin (9) (Tanaka et al, 2002b) were isolated in similar model fermentation experiments using banana and tea leaf homogenates, respectively.…”

“…Besides tea, many plants including loquat, Japanese pear, apple and banana are capable of synthesizing theaflavins when epicatechin and epigallocatechin are added, and it was suggested that their mechanism of theaflavin production was similar to that in tea fermentation (Tanaka et al, 2002a). Especially, the homogenates of banana and Japanese pear can be used as excellent enzyme sources for a model fermentation system applicable to large-scale experiments, because these fruits show strong enzyme activities, and practically no oxidation products of their own were detected on HPLC analysis.…”

Oxidation mechanism of black tea pigment theaflavin by peroxidase

“…Our previous study showed that theanaphthoquinone (7) is produced from 3 by polyphenol oxidase in the presence of epicatechin; however, the oxidation reaction of 7 has not been observed. 12,21 This study revealed that 7 is oxidized by peroxidase to afford 8. The production of 8 from 3 via 7 by peroxidase is assumed to occur during the process of black tea production.…”

Alternative pathway implicated as an influencing factor in the synthesis of theaflavin

“…These plants include loquat, banana, apple and Japanese pear, of which banana and Japanese pear were identified as excellent enzyme sources. This is based on strong enzymatic activity with practically no oxidation products of their own detected during HPLC analysis [37,38]. Japanese pear and loquat homogenates were reported to have a much larger theaflavin synthesis capacity in comparison to fresh tea leaves and were also the highest among 62 plants belonging to 49 families [38].…”