fungal laccase‐catalyzed oxidation of EGCG and the characterization of its products

BACKGROUND: Fungal laccase (EC 1.10.3.2) is an important enzyme for catalyzing the oxidation of tea polyphenols during the fermentation of tea. (−)‐Epigallocatechin gallate (EGCG) is the main ingredient of tea polyphenols. To a certain extent, the oxidation degree of EGCG reflects the fermentation degree of tea. This study preliminarily optimized the conditions for catalytically oxidizing EGCG by Aspergillus sp. trijbl1112 laccase and systematically analyzed the components and contents of the EGCG oxidation products. RESULTS: Aspergillus sp. trijbl1112 laccase oxidized EGCG into free catechins, ester catechins, gallic acid and tea pigments. The reaction conditions had a significant impact on the oxidation rate, types and concentrations of the products. At natural pH, 69.29% of EGCG was oxidized when 1 mL of EGCG (1 mmol L⁻¹) was catalyzed by 10 µg of fungal laccase for 150 min at 70 °C. When the EGCG oxidation rate was 69.27%, free catechins ((+)‐catechin and (−)‐epigallocatechin) and tea pigments (mainly thearubigin and theabrownin) constituted 48.42 and 38.87% of the oxidation products respectively. CONCLUSION: The results may provide a theoretical basis for the application of EGCG oxidation using laccase and provide a novel technique for obtaining high production of tea pigments. © 2014 Society of Chemical Industry