喝茶回甘的分子機制

Molecular Mechanisms Responsible for the Umami Sensation of Teas

鍾澤裕(Tse-Yu Chung) ； 曾志正(Jason T. C. Tzen)

《農林學報》 63卷2期 (2014/09) Pp. 91-97

https://doi.org/10.30089/JAF.201409_63(2).0003

摘要

回甘主要是透過舌頭味蕾細胞上的甘味接受器辨認到適當的啟動分子（例如，胺基酸），導致其結構改變而活化，並進而將訊息傳至大腦，讓人產生鮮美甘甜的滋味。當啟動分子活化甘味接受器時，若能搭配合適的增強分子（例如，核苷酸）共同作用，其引發的回甘效果就可以大大提升數倍。茶的回甘滋味乃決定茶湯品質高低的重要因素之一。綠茶及烏龍茶的回甘分子機制，基本上是以其茶湯內豐富的游離胺基酸（主要是谷胺酸與茶胺酸）為啟動分子，搭配茶倍素（或作用稍弱的沒食子酸）當增強分子，共同活化甘味接受器而引發回甘滋味。經過反覆烘培及陳放精煉而得的熷烏龍茶，雖其游離胺基酸於製程中裂解或反應殆盡，但其茶湯更具回甘滋味；而其回甘分子機制有別於原來的烏龍茶，乃以楊梅黃酮（或作用稍弱的槲皮素）為啟動分子，並搭配沒食子酸當增強分子，更緊密結合地活化甘味接受器，引發更強的回甘效果。

關鍵字

烏龍茶 ； 谷胺酸（味精） ； 回甘滋味

並列摘要

Umami sensation is a pleasant savory taste stimulated by the umami receptor inside taste bud cells via its conformation change induced by proper activators, such as amino acids, leading to a series of signal transductions to brain cells. The stimulation of umami sensation by activators is greatly (in general, several folds) elevated by suitable enhancers, such as ribonucleotides. One of the most important factors to evaluate qualities of teas is the umami taste of their infusion. On the basis of the above molecular mechanism for umami sensation, abundant free amino acids (mainly glutamate and theanine) and theogallin (or gallic acid with a weaker effect) are regarded as activators and an enhancer to be responsible for the umami sensation of green and oolong tea infusions. The infusion of Tzen oolong tea refined by baking and aging periodically possesses a higher umami taste though free amino acids are completely degraded after the tea conversion from oolong tea. In contrast, myricetin (or quercetin with a weaker effect) and gallic acid are found in the infusion of Tzen oolong tea, and regarded as an activator and an enhancer to bind tightly to the umami receptor, leading to a relatively strong umami sensation.

並列關鍵字

Glutamate ； oolong tea ； umami sensation