Research On Yellowing Process Of Huoshan Bud Yellow Tea

Huoshan bud yellow tea is produced in Huoshan County,Lu’an City,Anhui Province,Dabie Mountain hinterland,and is one of the most tender yellow teas,with high market value.However,in recent years,in order to cater the famous green tea market,many local tea factories gradually omitted the yellowing process,which is the "yellow to green".The tea has lost its unique characteristics of "yellow leaves,yellow infusion,sweet and mellow taste",which are characteristic of Huoshan bud yellow tea.This is seriously misleading the consumer’s perception of bud yellow tea.In the long run,the traditional Huoshan bud yellow tea will disappear in the Chinese tea market.In order to bring Huoshan bud yellow tea back to the tea market with the quality characteristics of yellow tea,we used one bud and one leaf to two leaves of fresh leaves(C.sinensis Jinjizhong),and firstly,based on the evaluation of the finished tea color and taste,we obtained the optimal parameters of yellowing process(number of yellowing times,water content of yellowing leaves and yellowing temperature).Then,we investigated the dynamic effects of the yellowing process on the quality and key chemical components in leaf production based on metabolomics.It aims to find the best yellowing process and reveal the mechanism of the influence of yellowing process on the quality of yellow bud tea.The results are as follows.(1)We have found a set of parameters for the optimal yellowing of Huoshan bud yellow Tea.Firstly,after two times of yellowing,the color of the dried tea and tea infusion was yellow and bright,and the bitterness and astringency of taste were reduced and the sweetness increased.Meanwhile,the content of ester catechins was the lowest.The results showed that the two times of yellowing was beneficial to the quality of Huoshan bud yellow tea.Then,we explored the optimal water content of the leaves in the second yellowing process at the same temperature,and found that when the water content of the leaves was 40%,the color of the tea infusion was yellow and bright,and the taste of sweetness was most obvious;the content of ester catechins decreased significantly,and the content of soluble sugars and free amino acids accumulated.Finally,we compared the effect of different temperatures on the quality of yellow tea when the water content of the leaves was 40% in the second yellowing process.The results showed that when the smothering temperature was 40℃,the finished tea had the highest sweetness,and the brightness and yellowness of the tea infusion were moderate,which conformed to the characteristic of "yellow leaf,yellow infusion,sweet and mellow taste" of yellow tea.In word,Huoshan bud yellow tea needs to go through two times yellowing.And in the second yellowing process,the temperature is controlled at about 40℃,and the water content of the leaves is about 40% is appropriate.(2)The dynamic changes in the quality and chemical composition of Huoshan bud yellow tea under the optimal yellowing conditions were revealed.The results showed that,under 40℃,the yellowing time was 12～18 h,and the yellow color,sweetness,umami and richness of the tea samples reached a high level,and the overall quality was high.However,The color and taste quality of the leaves deteriorated significantly after 24 h of yellowing.Meanwhile,the content of most amino acids,catechins,GBVs,and phenolic acids was high at 18 h before yellowing,but decreased significantly after 18 h.The content of phaeophorbides increased significantly after 30 h,which may be the main reason for the browning in leaf production.Combining the PLS regression results,we deduced that the improvement of sweetness and richness in the first 18 h of yellowing was closely related to the high levels of most amino acids and sucrose,and the decrease of many differential metabolites related to taste was the main reason for the overall decrease of taste richness in the later stage of yellowing.