Study On The Judgment Method Of Optimum Fermentation Of Congou Black Tea

Congou black tea, the kind of black tea that peculiar to China and the very first-made black tea inthe world is a traditional export commodity in China. With the conversion of export and domestic sales,the production of congou black tea has increased steadily in recent years. Fermentation is the keyprocess in the manufacturing of the congou black tea and the most critical step to ensure its quality. Inorder to establish a decision tree model for detecting the optimum fermentation of congou black tea, theeffects of fermentation temperature and fermentation time on physical and electrochemical indicators,dominant enzyme activities, tea polyphenols and their oxidation products, and the sensory evaluationresults were studied.The experimental results were as follows:The effects of fermentation temperature and duration on physical and electrochemical indicators(pH, conductivity, color) were discussed. The relationship between the pH of tea infusions andfermentation time was similar to a quadratic function, and the coefficient of determination was morethan90%. The conductivity of hot-water soaking and cold-water soaking tea infusions did not changesignificantly. Values of L, b, and Hab were found to decrease with fermentation time, but the a valueincreased; the relationship between the Eab of tea infusions and fermentation time was similar to aquadratic function, and the coefficient of determination was more than90%.The effects of fermentation temperature and duration on dominant enzyme activities, teapolyphenols and their oxidation products were discussed. The activity of PPO and POD declined morequickly during the initial stages, followed by a steadily unchanged trend. During the congou black teafermentation, an enzymatic oxidation of tea polyphenols, especially tea catechins takes place, leading toformation of a series of coloured chemical compounds, such as theaflavins (TFs) and thearubigins (TRs),so the tea polyphenols declined with fermentation time; the theaflavins (TFs) and thearubigins (TRs)increased during the initial stages, followed by a steadily declining trend, whereas theabrown (TB) werefound to increase with fermentation time.In order to establish a decision tree model based on the values of EGCG and Hab for detecting theoptimum fermentation of congou black tea, the correlation analysis and stepwise regression analysisbetween the physical and electrochemical indicators, dominant enzyme activities, tea polyphenols andtheir oxidation products, and the sensory evaluation results were studied, and the classification modelprediction accuracy was92.3%. This decision tree model was applied to four different fermentationtemperature treatment, starting from the beginning of fermentation, first satisfied the EGCG percentagewas lower than1and Hab value less than1at the same time, was moderately fermented sample. Thuswe can predict the optimum fermentation times of processing1~4(fermentation temperature:24℃,26℃28℃,30℃) were4.0,3.5,3.0,2.5h.