Immobilization of tannase from Rhizopus oryzae and its efficiency to produce gallic acid from tannin rich agro-residues

Abstract

Different tannin rich agro-residues, like sal seed (21% tannin), fruit of myrobalan (37.6% tannin) and tea-leaf (14.1% tannin) were selected for enzymatic conversion of their tannin content to gallic acid. These tannin rich substrates were used as carbon source in Czapek-dox medium for the production of tannase (E.C. 3.1.1.20, tannin acyl hydrolase) from Rhizopus oryzae (RO IIT RB-13, NRRL-21498). The maximum enzyme production of 17.7 U/mL was obtained in sal seed powder incubated for 48 h at 30ºC. The enzymatic conversion of these agro-residues was carried out using immobilized tannase. Substrate concentrations of 8% sal seed, 7% myrobalan and 6% tea leaf (w/v) were found to be the optimum for maximum bioconversion. The maximum bioconversion (90 and 87%, respectively) was achieved with sal seed and tea leaf as substrate at 40ºC and initial pH 4.5. In case of myrobalan, the maximum bioconversion was 90.2% at 50ºC and initial pH 5.0. Moreover, optimization of the pH and temperature largely reduced the incubation time to 36 h. The immobilized tannase was stable for 7 cycles. The kinetic properties of immobilized enzyme revealed that there was a decrease in maximal reaction velocity (Vmax) and increase in Michaelis constant (Km) when compared to its free native counterpart.