86(P-89) 茶葉発酵時におけるカテキン類酸化過程の化学的解析(ポスター発表の部)

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Theaflavins and thearubigins are major pigments of black tea and it is generally accepted that these are produced by oxidadtion of flavan-3-ols (catechin) during tea fermentation. Although structures and biogenesis of theaflavins were well studied, little has been known about thearubigins. The purpose of our study is to clarify the oxidation mechanism of flavan-3-ols and characterization of thearubigins, In the present study, we first showed production of theaflavin (3) from epicatechin (1) and epigallocatechin (2) by treatment with various plant homogenates including blueberry, eggplant, loquat, Japanese apricot, apple, grape, and banana. In banana fruit homogenate, 1 was oxidized to give a new trimeric product (4), and 2 was oxidized to a monomeric product (5). When a mixture of 1 and 2 was treated with banana fruit homogenate, a new product 6 having naphthoquinone moiety and theaflavin dimer 7 were produced. Their structures were established on the basis of spectroscopic evidence. The product 6 was probably formed by oxidation of 3 with an aid of polyphenol oxidase, while 7 was generated by oxidative coupling of 3 catalyzed by peroxidase-H_2O_2. Treatment of a mixture of 1 and 2 with polyphenol-free homogenate of fresh tea leaves afforded a new dimeric pigment 11 together with 3, 6, oolongtheanin(10), and theasinensins C and E (8 and 9). In this oxidation, 2 was consumed faster than 1. The pigment 11 showed large absorption band at 395nm in UV-VIS spectrum and it seems to be related to that of thearubigin. It was deduced that 11 was formed by oxidation of biphenyl moiety of theasinensins (8, 9) which formed by oxidative coupling between two B rings of 2. The observation suggested the occurrence of chromophores similar to that of 11 in thearubigins of black tea.
天然有機化合物討論会の論文
2000-10-01

86(P-89) 茶葉発酵時におけるカテキン類酸化過程の化学的解析(ポスター発表の部)

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