连续慢速做青过程中乌龙茶主要化学成分的变化

Changes in the Major Chemical Constituents of Oolong Tea under Continuous Low-Speed Green-making Process

本研究采用一种新型全自动做青工艺,通过缓慢、连续地滚动或振动对茶叶造成机械损伤,使茶叶发生各种生化反应并逐渐形成其独特品质风味,以期从源头解决做青工艺复杂、劳动强度大等问题,测定五次传统做青(每次摇青4 min,晾青1.5 h)及采用滚筒长径比为1.5 m/0.7 m的摇青机缓慢连续(1.84 r/min)进行摇青7.5 h(每隔1.5 h取一次样品)的白叶单丛主要化学成分和品质差异。结果表明:相同做青次数下,连续慢速做青下乌龙茶感官品质优于传统做青;水浸出物含量随做青次数增加而减少,其在晒青后出现峰值25.33%;传统做青茶多酚含量先增加后减少,其峰值出现在第四次做青(CT4),为19.71%,连续慢速做青茶样则先减少后增加,峰值为17.92%,出现在摇青1.5 h(LX1);传统做青游离氨基酸总量在第三次做青(CT3)达到峰值2.42%,而连续慢速做青下氨基酸峰值在做青3 h(LX2),为2.61%;两种工艺下儿茶素总量在晾青和摇青前期增加,摇青后期降低;两种工艺下乌龙茶香气物质有较大差异,传统做青第一次做青(CT1)和第二次做青(CT2)萜烯醇类香气物质较高;而连续慢速做青6 h(LX4)茶样杂环类香气物质较高;两种工艺下多酚氧化酶和β-葡萄糖苷酶相关基因的表达量呈现出不同的变化趋势,6个基因的表达量在连续慢速做青6 h(LX4)最高。结合感官评价的结果,表明连续慢速做青是一种适用于乌龙茶加工的新技术。

In order to solve the problems of complicated greening process and high labor intensity at source,a new fully automatic greening process was adopted in this study,which caused mechanical damage to tea leaves by slowly and continuously rolling or vibrating the tea leaves at a low speed,resulting in various biochemical reactions and gradually forming its unique quality and flavor.We determined the major chemical constituents and quality differences of Baiye dancong from five traditional green-making sessions(4 min per rotating and 1.5 h of setting)and 7.5 h of low-speed greenmaking(1.84 r/min)using a rotating machine with a drum length/diameter ratio of 1.5 m/0.7 m(sampling every 1.5 h).The results showed that:In the same number of green-making,the sensory quality of oolong tea under low-speed green-making was better than that of CT.The peak of water extract content was 25.33%,it occurred after withering and decreased with the increasing of the number of green-making.During the traditional greening process,the content of tea polyphenols increased first and then decreased,with a peak of 19.71% at CT4.On the contrary,the peak occurd at LX1 with 17.92%.The free amino acid content of traditional greening reached a peak of 2.42% in CT3 and 2.61% in LX2.The total amount of catechin increased in the early stage of withering and shaking in both processes and decreases in the later stage of shaking.The aroma substances of oolong tea differed greatly under the two processes,with higher aroma substances of terpene alcohols in CT1 and CT2,while the heterocyclic aroma substances were higher in LX4 tea sample under the new process.The expression of PPO and β-G related genes showed different trends under the two processes,with the highest expression of six genes at LX4.Combined with the results of sensory evaluation,it showed that continuous low-speed green-making would be a new technology for oolong tea processing.