Research On The Change Pattern Of Taste Quality Of Spring Congou Black Tea And Its Improvement Process

In order to find out the evolution pattern of the taste quality of spring Congou black tea and improve the taste quality,sensory evaluation,electronic tongue taste analysis and sweetness quantification were used to evaluate the taste quality of spring Congou black tea.High-performance liquid chromatography,non-targeted metabolomics and other technologies were used to analyze the key compounds in the taste quality difference of spring Congou black tea.Moreover,the expression of key compounds in the anabolic pathway genes was analyzed,and the processing technology of spring black tea was explored.The main findings are as follows:(1)From 2018 to 2020,the fresh leaves of the same grade and different periods of the main planted tea tree varieties in Hunan(Baojing huangjincha No.1,Zhuyeqi and Bixiangzao)were used as raw materials to be made into Congou black tea by the same process.The sensory evaluation results of Congou black tea made in different periods showed that the taste quality in the early spring was better than that in the late period,and it was more sweet,mellow and umami.The taste analysis of the electronic tongue further showed that the Congou black tea in different periods of spring was effectively distinguished by PCA and cluster analysis,and the umami electrode intensity showed a decreasing trend.At the same time,the quantitative analysis of sweetness based on the sucrose reference solution also showed that the sweetness score of early black tea was significantly higher than that of late black tea.(2)Correlation analysis was carried out between the sensory evaluation results and the quantitative detection results of the main taste compounds,and it was found that with the passage of spring,the contents of tea polyphenols,total flavonoids and catechins,which were negatively correlated with taste quality,showed an increasing trend.The positively correlated amino acid and sugar contents showed a decreasing trend.Tea polyphenols,EGCG,ECG,ester catechins,total catechins,and theanine content were significantly correlated with sensory evaluation taste scores,electronic tongue umami intensity and sweetness quantification intensity.The multivariate stepwise regression analysis based on taste substances showed that the compounds that existed the greatest impact on the taste score of sensory evaluation was the total content of flavonoids.(3)UHPLC-Q-TOF/MS was used to detect non-volatile metabolites in dry tea and fresh leaves in different periods of spring,and 49 main differential metabolites affecting the taste quality of Congou black tea in early,middle and late spring were obtained.Among them,catechins,amino acids and flavonoid-O-glycosides are highly correlated with taste sensory scores,and EGCG,theanine and quercetin-O-glycosides account for a large proportion,indicating that the three are potential key differential metabolites for quality evolution.In addition,the difference of EGCG in black tea and its fresh leaf raw materials in different periods of spring was significantly correlated with the enzyme activity of PPO,and the evolution law of theanine and quercetin-O-glycoside in both was highly correlated,indicating that the factors affects the taste quality of black tea in spring mainly come from fresh leaf raw materials.(4)The correlation analysis between the relative content of theanine and flavonol glycosides and the RT-qPCR results of their synthesis pathway gene showed that the correlation coefficient between the expression of theanine synthesis and metabolism genes and the relative content of theanine was low and not significant.The expression level of F3’H,F3 Glc T and quercetin-O-glycosides were highly positively correlated,and the correlation coefficient between the relative content of quercetin-O-glycosides and the expression level of F3 Glc T was greater than the correlation coefficient with the expression level of F3 Gal T,indicating that the content of quercetin-O-glycosides is mainly affected by the expression levels of F3’H and F3 Glc T genes.(5)By analyzing the processing technology of Congou black tea and the influence of each process on the formation of flavor substances,it was found that the process of Congou black tea mainly affected the amino acid biosynthesis and metabolism pathway from fresh leaves to tea.The withering process had the greatest impact on the total amount of amino acids,accounting for 375% of the total change;the fermentation process had a greater impact on the contents of flavonoids,catechins and amino acids.The temperature-controlled withering at 22°C to 25°C or variable-temperature fermentation at a higher temperature(40°C for 1 h+30°C for 2 h)can improve the taste quality of spring Congou black tea.