Catalytic properties of immobilized tannase produced from Aspergillus aculeatus compared with the free enzyme

Abstract

Aspergillus aculeatus tannase was immobilized on several carriers by entrapment and covalent binding with cross-linking. Tannase immobilized on gelatin with cross-linking agent showed the highest activity and immobilization yield. The optimum pH of the immobilized enzyme was shifted to a more acidic range compared with the free enzyme (from pH 5.5 to pH 5.0). The optimum temperature of the reaction was determined to be 50°C for the free enzyme and 60°C for the immobilized form. The thermal stability, as well as stability over a wide range of pH, was significantly improved by the immobilization process. The calculated Km of the immobilized tannase (11.8 mg ml-1) is higher than that of the free tannase (6.5 mg ml-1), while Vmax of the immobilized enzyme (0.32 U (μg protein) -1) is lower than that of the free tannase (2.7 U (μg protein)-1). The immobilized enzyme was able to retain 84 % of the initial catalytic activity after 5.0 cycles.