茶树群体品种常见的紫色芽叶所制成的绿茶苦涩味明显。分离测定了茶树紫色芽叶主要苦涩味特征成分,用苦涩味阈值和苦涩味指数定量评价了各成分的呈味特征。结果表明,茶树紫色芽叶花青素含量高达1.14%,紫色芽叶中花青素和儿茶素的含量分别是绿色芽叶的57倍和1.13倍,花青素和儿茶素含量较高是其苦涩味较强的主要原因。茶叶苦涩味成分阈值的大小顺序为：咖啡碱(0.30)<花青素(0.40)<儿茶素(0.80);以苦涩味指数评价成分对紫色芽叶苦涩味实际影响大小顺序为：儿茶素(3.32)>咖啡碱(2.13)>花青素(0.57)。研究还表明,在紫色芽叶加工绿茶的过程中,添加约0.2%的酪蛋白具有降低苦涩味的作用,可使品质得到改善,使茶汤中多酚类浓度降低19.5%,苦涩味指数由3.70降至2.98,由此提供了一种降低紫色芽叶苦涩味的技术途径。采用多酚-蛋白复合反应模型,提出了用相对沉淀率(R_A)作为酪蛋白对多酚类物质的苦涩味抑制能力的评价指标。

The quality of the green tea made from purple tea leaf, which is common in tea production, is not so good for its evident bitterness and astringency. In this paper, the main bitterness and astringency characteristic components of purple tea leaf were separated and determined, and the taste characteristics of those components were quantitatively evaluated by the threshold and index of bitterness and astringency. The results showed that the content of anthocyanidins was as high as 1.14%, and the contents of anthocyanidins and catechins of purple tea leaf were 57 and 1.13 times to those of green tea leaf, their higher content was mainly responsible to the bitterness and astringency of purple tea leaves. The order of threshold of those components was caffeine (0.30) < anthocyanidins (0.40) < catechins (0.80), and the order of bitterness and astringency index was catechins (3.32) > caffeine (2.13) > anthocyanidins (0.57), which was also used to evaluate the effect of components on the taste of tea. Furthermore, adding 0.2% casein into purple tea leaf during green tea processing could reduce the bitterness and astringency, the quality could be promoted, the concentration of tea polyphenols in tea infusion could reduce 19.5%, and the bitterness and astringency index decreased from 3.70 to 2.98. The research provided a technological method to reduce the bitterness and astringency of purple tea leaves. By using the polyphenol-protein complex reaction model, the relative precipitation rate (R_A) was used as the index to evaluate the inhibiting ability of casein to the bitterness and astringency of polyphenols.