茶鲜叶萎凋过程中主要品质成分的动态变化

Changes on Major Quality Indices in Tea Leaves during Withering

选用10份茶树品种春茶新梢的1芽2、3叶为试验材料,控温控湿（20-22℃、RH35%-45%）条件下,探讨不同萎凋程度茶鲜叶的主要品质成分动态变化规律。结果表明,随着萎凋程度（鲜叶减重率）的加重,水浸出物、咖啡碱、游离氨基酸和可溶性糖含量变化呈现升高趋势,茶多酚含量变化呈现先升高后降低的趋势,各主要品质成分含量的变化并不是同步的。茶鲜叶萎凋减重15%内以水分散失为主,各主要品质成分的含量（以干物质质量100%计）变化均不显著;萎凋减重至30%-45%,各主要品质成分含量陆续呈现显著变化,可溶性糖与咖啡碱、水浸出物含量先后达到最高值;萎凋减重至60%,只有游离氨基酸含量继续升高;最终游离氨基酸、可溶性糖、咖啡碱含量变化较大,比茶鲜叶中分别升高了24.6%、13.8%、11.9%。相关分析表明,游离氨基酸、可溶性糖、水浸出物与咖啡碱含量变化与萎凋失水显著正相关（相关系数为0.413、0.386、0.692、0.479）,尤其是游离氨基酸,而茶多酚含量变化与萎凋失水没有明显相关性。

Fresh spring shoots （two or three leaves and a bud） harvested from 10 tea cultivars were used in this experimentation conducted at 20？22°Cand 35%？45% RH. Changes on the major chemical components in the tea leaves as indices for quality were monitored at various withering stages. The results showed that, with increasing weight loss on the fresh tea leaves, there appeared to be a continual increase on the contents of water extracts, caffeine, free amino acids, and water soluble sugars,while polyphenols increased initially and followed by a decline in the leaves. These changes were not parallel. For instance, when the water loss was less than 15% , no significant alternations were observed in regard to the contents of these components （on a dry matter basis）. However, as the weight loss approached 30% ~45 % during withering, the water soluble sugars and caffeine, as well as the water extracts,reached their maximums. As the weight loss increased to 60%, only the contents of free amino acids continued to increase. At end of the withering process, the most significant changes were found on the contents of free amino acids, water soluble sugars, and caffeine, with increases of 24. 6% , 13.8%, and 11. 9 % ,respectively.The correlation analysis showed that （1） the weight loss of tea leaves during withering significantly affected the contents of free amino acids, water soluble sugars, water extracts,and caffeine,with correlation coefficients of 0.413,0.386,0.692,and 0.479,respectively; （2） the change on free amino acids content was particularly significant; and, （3） no significant effect was observed on the content of polyphenols.