Elucidation of formation mechanism of oolong tea polyphenol: Oolongtheanins

2014 Fiscal Year Final Research Report

• Project/Area Number: 24780123
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Food science
• Research Institution: Gifu University
• Principal Investigator: YANASE Emiko 岐阜大学, 応用生物科学部, 准教授 (60313912)
• Research Collaborator: NAGAOKA Satoshi 岐阜大学, 応用生物科学部, 教授 (50202221)
• Project Period (FY): 2012-04-01 – 2015-03-31
• Keywords: ウーロン茶ポリフェノール / ウーロンテアニン / カテキン / 酸化反応 / 反応機構 / コレステロール吸収阻害

Outline of Final Research Achievements

Oolongtheanins are the catechin dimers found in oolong tea leaves. To clarify the formation mechanism, the oxidation of EGC was investigated. As a result, the formation mechanism was proposed on the basis of isolated three intermediates. 1) After one pyrogallol type catechin was oxidized to form o-quinone, another pyrogallol type catechin attacked on o-quinone. 2) Resulting dimer is oxidative cyclized, then hydrated, generating bicyclo type intermediate I (dehydrotheasinensins). 3) Transformation of I to lactone type intermediate II (pro-oolongtheanins) by dehydration and rearrangement reaction. 4) Generation of intermediate III by hydrolysis of lactone moiety and recyclization. 5) Oolongtheanins are formed by decarboxylation and oxidation. Effective synthetic method of oolongtheanins was investigated based on this mechanism. In addition, the micellar solubility of cholesterol with them were measured in vitro, and Oolongtheanin-3’-O-gallate showed a strong inhibitory ability.

Free Research Field

天然物化学