Biotransformation of tea catechins using Aspergillus niger tannase prepared by solid state fermentation on tea byproduct

A tannase that was prepared from Aspergillus niger by a solid-state fermentation on tea byproducts was investigated to transform the catechins in tea infusion. The tannase could effectively hydrolyze epigallocatechin gallate (EGCG), gallocatechin gallate (GCG) and epicatechin gallate (ECG) of tea infusion, which showed pH values ranged from 4.8 to 5.3 during the tannase treatment. The enzyme was active and stable within pH 3.0–7.0 and 4–60 °C. The enzyme had Kms of 14.89 mmol/L, 16.13 mmol/L and 3.57 mmol/L for EGCG, GCG and ECG, respectively in pure solutions. However, the hydrolysis of individual EGCG, GCG and ECG in the tea infusion showed different kinetic parameters from those in pure solutions. The transformation of EGCG was the dominant reaction in tea infusion. After the tannase treatment, tea infusion was detected to have significant increases in the clarity and activities for scavenging 2, 2′-azino-bis (3-ethylbenzothiazoline-6-sulfonate) (ABTS) radical, 2, 2-diphenyl-1-picryl-hydrazyl (DPPH) radical and hydroxyl radical. The results indicated the tannase was effective to transform the catechins, which could be possibly used for commercial extraction of catechins. In addition, the results suggested it is more desirable to follow the dynamic model to control the tannase treatment of tea infusion for a better processing.