Molar ratio of (-)-epicatechin and (-)-epigallocatechin gallate determined their enzymatic oxidation products and color characteristics

Catechins are the primary polyphenols in tea. Enzymatic oxidation models of (-)-epicatechin (EC) and (-)-epigallocatechin gallate (EGCG) with different proportions were established to investigate the formation mechanism of oxidation products and their relationship to color characteristics. Their oxidation products were analyzed by liquid chromatography tandem mass spectrometry (LC-MS) combined with UV-visible spectrometry. These products were quantified by LC-MS and performed correlation coefficient analysis of color. The results indicated that single oxidation of EGCG dominated the whole reaction when EGCG had high proportions in the reaction mixture, promoting the formation of red pigments such as dehydrotheasinensin AQ and theacitrinin B. When EC with high ratios, the oxidation pathways preferred utilizing both EC and EGCG, promoting the formation of yellow pigments such as theaflavin and theadibenzotropolone A. This study provided the detailed oxidation mechanism of EC and EGCG mixture, suggesting that the proportions of catechol-type and pyrogallol-type catechins markedly affected the direction of enzymatic oxidation reaction and further influenced the color formation.