Estimation of black tea quality by analysis of chemical composition and colour difference of tea infusions

Chemical composition, colour differences of black tea infusions and their relationships with sensory quality assessed by tea tasters were analysed. There were significant correlations 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 indicators of ΔL, Δa, Δb and ΔE were significantly correlated to total quality score (TQS). The parameters correlating significantly with the TQS were classified into four groups. Group 1 was compounds containing nitrogen, group 2 phenol compounds, group 3 tea pigments and group 4 infusion colour indicators. Four principal components were screened from the four 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.