Tannase production by Aspergillus species and some properties of immobilized tannase from a potent Aspergillus carneus strain

摘要

Eight species of aspergilli, which grew on tannic acid as a sole carbon source were tested for their tannase activity. A. carneus was selected as the best producer of tannase. Maximum tannase yield was detected after 2 days of fermentation in mediumcontaining 1.0% tannic acid. The maximum production occurred when the pH was controlled at 5.0 during fermentation. Among the various carbon sources investigated, tannic acid (1.5%, w/v) yielded maximal production of tannase. The NaNO_3 was the most favorable nitrogen source for tannase production. Incorporation of CaCl_2 (0.1mg/l) stimulated tannase production. Tannase immobilized by covalent binding had high activity, particularly on chitosan beads through glutaraldehyde. The immobilized tannase retained 88% of the initial catalytic activity, even after being used ten times. The optimum pH of the immobilized tannase was shifted from pH 5.0 for the free to lower pH (4.0) for immobilized tannase. Enhanced pH stability was found for immobilized tannase. The optimum reaction temperature of the immobilized tannase was shiftyed from 40 deg c to 50 deg c. Little thermoinactivation was found for immobilized tannase. A linear relationship was observed between gallic acid production by two was very rapidly increased with bound tannase, whilst reducing sugars were only slowly released in case of free tannase, suggesting some change in mode of action of the two enzymes.