Chitosan Activated with Genipin: A Nontoxic Natural Carrier for Tannase Immobilization and Its Application in Enhancing Biological Activities of Tea Extract.

In this work, a non-toxic chitosan-based carrier was constructed via genipin activation and applied for the immobilization of tannase. The immobilization carriers and immobilized tannase were characterized using Fourier transform infrared spectroscopy and thermogravimetric analysis. Activation conditions (genipin concentration, activation temperature, activation pH and activation time) and immobilizations conditions (enzyme amount, immobilization time, immobilization temperature, immobilization pH, and shaking speed) were optimized. The activity and activity recovery rate of the immobilized tannase prepared using optimal activation and immobilization conditions reached 29.2 U/g and 53.6%, respectively. The immobilized tannase exhibited better environmental adaptability and stability. The immobilized tannase retained 20.1% of the initial activity after 12 cycles and retained 81.12% of residual activity after 30 days storage. The catechins composition analysis of tea extract indicated that the concentration of non-ester-type catechins, EGC and EC, were increased by 1758% and 807% after enzymatic treatment. Biological activity studies of tea extract revealed that tea extract treated with the immobilized tannase possessed higher antioxidant activity, higher inhibitory effect on α-amylase, and lower inhibitory effect on α-glucosidase. Our results demonstrate that chitosan activated with genipin could be an effective non-toxic carrier for tannase immobilization and enhancing biological activities of tea extract.