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

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 green-making (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.