Oxidation characteristics of catechins in suspended fermentation of different varieties’ tea leaves

This study focused on the efficiency of enzymatic synthesis for theaflavins (TFs) and SII types of thearubigins (SII-TRs) in suspended fermentation of different varieties of tea leaves. The results showed that the content of catechins in tea variety-Xiaoxianghong 21-3 (XXH21-3) was the highest among the five kinds of fresh tea leaves, and it had the strongest ability of transforming catechins to TFs and SII-TRs. The total amount of catechins for XXH 21-3 decreased rapidly and the conversion ratio of TFs reached the highest level of 13.96% after 20   min, the residual catechins was the lowest (3.08%) and the conversion rate of SII-TRs was the highest (13.02%) after 120   min during the suspended fermentation of five varieties tea leaves. Among the six catechin types, epicatechin gallate (ECG), epigallocatechin gallate (EGCG) and epigallocatechin (EGC) were consumed in large quantities, and the residues were all less than 5% in the final stage of fermentation, of which ECG consumption was the fastest, followed by EGCG. These results demonstrated that the concentration of catechins and PPO activities were positively correlated with the formation of TFs and SII-TRs, POD activity was positive correlation with synthesis of SII-TRs and negative correlation with TFs.