Impact of enzymatic fermentation on taste, chemical compositions and in vitro antioxidant activities in Chinese teas using E-tongue, HPLC and amino acid analyzer

Green, white and black teas showed different degrees in enzymatic fermentation through relevant processing procedures. To reveal the impact of enzymatic fermentation in tea-leaves, 44 chemical components including 17 phenolic compounds, 3 purine alkaloids, 19 free amino acids and γ-aminobutyric acid (GABA) in 27 various tea samples were determined by HPLC and amino acid analyzer, respectively. Additionally, E-tongue and 5 various assays were developed for taste evaluation and in vitro antioxidant activities analysis. Multivariate statistical analyses, such as PCA, HCA and PLS-DA (R2X = 1.000, R2Y = 0.932, Q2 = 0.908, respectively) divided theses teas into green, white and black tea categories, indicating the profound impact of enzymatic fermentation on tastes and chemical compositions. The enzymatic fermentation highly significantly (p < 0.001) promoted the decreases of 5 catechins (i.e. C, EC, GC, ECG and EGCG), gallic acid, rutin and 6 free amino acids, and the accumulations of 4 flavonoids (i.e. taxifolin, myricetin, queretin and luteolin), ellagic acid and 4 free amino acids in tea-leaves. The bivariate correlation analysis confirmed that 7 catechins, GG and 7 free amino acids might impress bitterness, umami and astringency, which also contributed to the antioxidant activities in tea-leaves. This study advanced the knowledge about enzymatic fermentation in tea-leaves processing.