Chemical And Instrumental Assessment Of Tea Quality

Sensory assessment is the major method for identification and evaluation of tea. However, it is completely experiential and is affected by the psychological and physiological status of the tea tasters. It is a common aspiration of the researchers, producers and managers to search for chemical and instrumental methods for evaluation of tea quality. Though progresses were made in this field, some of the technologies are still to be consummated and some them are difficult to be used in practice because of expensive equipment or complicated operations. HLPC, GC, color difference technologies and principal component analysis (PCA) method were used to construct mathematical models for estimation of tea quality so as to get useful information for developing equipments for evaluation of teas.Chemical composition, color difference of black tea infusions and their relationship with sensory quality assessed by tea tasters were analyzed. There was significant correlation between the individual quality attributes. Content of caffeine, nitrogen, amino acids, polyphenols, gallocatechin (GC), epigallocatechin (EGC), catechin (C), epicatechin (EC), epicatechin gallate (ECG), catechin gallate (CG), total catechins, theaflavin (TF) and theaflavin-3'-gallate (TF3'G) and infusion colour indicator ofΔL,Δa,Δb andΔE were significantly correlated to total quality score (TQS). The parameters correlated significantly with the TQS were classified into 4 groups. Group 1 is compounds with nitrogen element; group 2 phenol compounds; group 3 tea pigments and group 4 infusion color indicators. Four principal components were screened from the 4 groups as independent variables for constructing regression equations for estimation of black tea quality by principal component analysis. The regression of the TQS upon the principal components gives a highly significant relationship.Parameters of liquor color difference, taste related constituents and aroma related volatiles in 23 Chinese green tea (Camellia sinensis) samples were analyzed by color difference meter, high performance liquid and gas chromatographs respectively. Seven variables were extracted by principal component analysis from the data sets corresponding to the liquor color, taste and aroma and linear regression of total quality score (TQS) upon the 7 extracted variables produced a significant relationship: TQS=105.82-0.56 (AE)-0.15 (total catechins)+0.32 (geraniol) +0.53 (GCG) +0.44 (linalool oxide I) -0.54 (ascorbic acid)+0.24 (n-valeraldehyde) (p=0.003, standard error of the estimation =2.97). The regressive relationship simplifies the process of chemical and instrumental assessment of sensory quality of green tea and could be used for green tea quality assessment.Infusion chemical composition, color difference indicators and volatile constituents of seventeen jasmine scented tea samples and their correlation to sensory total quality score given by tea tasting panel were studied by techniques of high performance liquid chromatograph (HPLC), color difference metre and gas chromatograph. Spearman's linear correlation analysis showed that concentration of nitrogen, caffeine, catechin (C), epicatechin (EC), catechin gallate (CG), total catechins, terpineol, nerol and infusion light-black indicator AL, yellow-blue indicatorΔb, total color difference indicatorΔE were significantly correlated to sensory total quality score, respectively. Ten regression equations of the total quality score upon 12 components extracted from 36 tested indicators by principal component analysis (PCA) were obtained and they could properly estimate total quality score of jasmine scented teas.Based on the above results, chemical and color difference analysis together with PCA were used to identify and classify 10 Chinese green teas and 10 Korean green teas by 3-D plot. The results showed that the Chinese and Korean teas were partially identified and classified by the method.