Comparative Analysis And Evaluation Of Dark Tea Quality From Different Origins

Dark tea belongs to one of the six major tea groups,and is a post-fermented tea,named because of the black appearance of the finished tea,with the main production areas distributed in Guangxi,Sichuan,Yunnan,Hubei,Hunan,Shaanxi and other places.In recent years,as the public’s awareness of the health properties of dark tea has deepened,more and more consumers and operators have begun to pay attention to dark tea,and research on dark tea has become an important direction.Although there are many studies on dark tea,the current studies are mostly limited to a single variety or comparing dark tea with other tea types,and the studies comparing the quality of dark tea from different origins for analysis are still insufficient.Based on this,this study was conducted with 34 dark tea samples from five provinces to determine the content of various biochemical components such as water extracts,tea polyphenols,amino acids,soluble sugars,tea pigments(theaflavins,thearubigins and teabrownins),catechins,and flavonols through sensory evaluation,biochemical analysis,and aroma discrimination,using electronic nose technology to determine the aroma characteristics of tea broth,and using principal component analysis,Cluster analysis and partial least squares discriminant analysis were used to evaluate the comprehensive quality of dark tea of different origins and to investigate the differences between dark teas of different origins in depth.The main findings of the study are as follows:Evaluation of sensory quality of dark tea from different origins: in general,the dry dark tea is flaky in shape,the soup color is mainly yellow,with coarse and old leaf smell,and the leaf base is well-proportioned;the soup color of Yunnan Pu’er ripe tea,Guangxi Liubao tea,and Sichuan side tea is mainly red and thick,red and brown,with pure aroma and aging fragrance,and the taste is mellow or slightly less mellow;the soup color of Hunan Anhua dark tea is mostly orange and orange-red,dominated by orange,and the aroma is pure,and the taste is mellow or still mellow;Shaanxi Fu tea leaf bottom is brown,showing golden flowers,with floral and fruit aroma.The PCA results showed that the content and composition characteristics of biochemical components of dark tea from different origins differed greatly;the OPLS-DA results showed that the 34 tea samples were mainly gathered in six different regions according to the origin,indicating that the quality components of dark tea from different origins were similar,but the quality components of dark tea from different origins differed significantly;the mean content of tea polyphenols and flavonoids of Anhua dark tea was low,and the content of thearubigins was high.The mean content of soluble sugars and catechins in Liubao tea was low and the content of teabrownins was high;the mean content of teabrownins in Shaanxi Fu tea was low and the mean content of tea polyphenols,soluble sugars,theaflavins and catechins was high;the mean content of amino acids,soluble sugars,caffeine,flavonoids,theaflavins,thearubigins and catechins in Sichuan side tea was low;Yunnan Pu’er tea had low contents of tea polyphenols and amino acids,and high contents of caffeine,flavonol compounds,theaflavins,teabrownins,thearubigins and ester-type catechins;black hair tea had low contents of caffeine,theaflavins and teabrownins,and high contents of amino acids and non-ester-type catechins.The results of cluster analysis showed that the clustering results of 34 tea samples were approximately the same as the results of tea samples grouped by origin,except for Yu Cheng Tibetan tea and Black Mao tea 2010,which were copolymerized into 6 major categories,among which Guangxi Liubao tea,Hunan Anhua dark tea,Sichuan side tea,Yunnan Pu’er ripe tea,Black Mao tea and Shaanxi Fu tea were clustered into one category,indicating that there were obvious characteristics and differences in the quality components content of dark tea of different origins.The results of electronic nose technology showed that the contribution of principal components of PCA analysis was higher than that of LDA analysis,but the differentiation of LDA analysis was significantly better than that of PCA,and could distinguish the differences of aroma characteristics of tea samples from different origins;in a word,both PCA and LDA could only distinguish some tea samples,but not all tea samples;The sensor R7(W1W)corresponding to the sulfide class contributed the most to the first principal component,followed by the R2(W5S)nitrogen oxide class;R2(W5S)nitrogen oxide contributed the most to the second principal component,followed by the R10(W3S)long-chain alkane class.The relative content patterns of methyl group,alcohol,aldehyde and ketone aroma substances in the tea samples of each dark tea of different origins were similar,but the relative content patterns of nitrogen oxides,sulfide group and aromatic components organic sulfide were different.The experimental results showed that the quality of dark tea from different origins showed differences due to the differences in raw materials and stacking conditions,etc.Caffeine and flavonols are richer in Pu-erh ripe tea,which is made from Yunnan large-leaf species sun-blue maocha;black maocha and Liubao tea with short stacking time have less polyphenol and amino acid conversion,while Pu-erh ripe tea has high content of teabrownins and caffeine due to long stacking time.The results of multivariate statistical analysis showed that the content and composition characteristics of biochemical components of dark tea varied greatly among different regions.The aroma discrimination results showed that the aroma characteristics of Yunnan Pu-erh ripe tea were closer and differed significantly from those of dark tea from other regions,but dark tea from other regions could not be effectively distinguished;dark tea from the same region was more easily clustered together,and its quality had certain similarities and commonalities.The research results have certain theoretical and promotional application value for operators and consumers to correctly understand and publicize the quality characteristics of dark tea of different origins and promote the scientific and orderly development of dark tea industry.