Tanaka Takashi
Graduate School of Biomedical Sciences, Division of Natural Product Chemistry, Nagasaki University, Nagasaki, Japan.
Yakugaku Zasshi. 2008 Aug;128(8):1119-31. doi: 10.1248/yakushi.128.1119.
Recent biological and pharmacological studies strongly suggested that plant polyphenols in foods, beverages and crude drugs have various health benefits. However, still there are chemically uncharacterized polyphenols, especially those with large molecular weights. The typical example is black tea polyphenols. Four tea catechins of fresh tea leaves are enzymatically oxidized in tea fermentation process of black tea manufacture to give a complex mixture of the oxidation products. Despite many efforts since 1950's, major part of the black tea polyphenols has not been clarified yet. We have investigated the oxidation mechanism of each catechin by employing a newly developed in vitro model fermentation system. The oxidation was initiated by enzymatic dehydrogenation of catechins, and subsequent intermolecular quinone-phenol coupling reactions followed by cascade-type degradation of the unstable products resulted in the formation of complex black tea polyphenols. Besides black tea polyphenols, this review introduces the chemistry of insolubilization of persimmon proanthocyanidins, wood polyphenols in connection with whisky polyphenols, and co-polymerization of cinnamaldehyde and proanthocyanidins in cinnamon bark.
近期的生物学和药理学研究有力地表明，食品、饮料和天然药物中的植物多酚具有多种健康益处。然而，仍存在化学性质未明确的多酚，尤其是那些分子量较大的多酚。典型的例子是红茶多酚。在红茶制造的茶叶发酵过程中，新鲜茶叶中的四种儿茶素会被酶促氧化，生成氧化产物的复杂混合物。自20世纪50年代以来，尽管人们付出了诸多努力，但红茶多酚的主要成分仍未得到阐明。我们通过采用新开发的体外模型发酵系统，研究了每种儿茶素的氧化机制。儿茶素的酶促脱氢引发氧化反应，随后分子间醌-酚偶联反应以及不稳定产物的级联式降解导致了复杂红茶多酚的形成。除了红茶多酚，本综述还介绍了柿子原花青素的不溶性化学、与威士忌多酚相关的木材多酚，以及桂皮醛和桂皮原花青素在肉桂树皮中的共聚反应。
