Differential activities of fungi-derived tannases on biotransformation and substrate inhibition in green tea extract

Tannases are important enzymes in the antioxidant potential of tea leaves. In this study, we evaluated the effect of two tannases (T1 and T2) on biotransformation of tea polyphenols and antioxidative activities from catechins in green tea extract (GTE). The T1 tannase-catalyzed reaction was inhibited by the addition of >2.0% GTE substrate, whereas the T2-catalyzed reaction was not inhibited, even by addition of 5.0% GTE. Furthermore, the T1 tannase-catalyzed reaction was inhibited by addition of 10mgmL^-1 EGCG, whereas the T2 tannase-catalyzed reaction did not display any inhibitory effect. These results indicate that T2 tannase was more tolerant than T1 tannase to substrate inhibition in degallation reactions. Specifically, the substrate EGCG (90,687.1μgmL^-1) was transformed into gallic acid (50,242.9μgmL^-1) and EGC (92,598.3μgmL^-1) after 1-h treatment with T2 tannase (500Ug^-1). The tannase-mediated product displayed higher in vitro radical-scavenging activity than the control. IC₅₀ value of GTE on ABTS and DPPH radicals (46.1μgmL^-1 and 18.4μgmL^-1, respectively) decreased markedly after T2 tannase treatment (to 35.8μgmL^-1 and 15.1μgmL^-1, respectively). These results indicate that T2 tannase treatment of GTE enhanced its radical-scavenging activity, an increase that was also observed in the reaction using EGCG substrate. Taken together, our results revealed that T2 tannase is more suitable for biotransformation of catechins in GTE than T1 tannase, and T2 treatment provides an enhanced radical-scavenging effect.