Production of Gallic Acid by Immobilized Aspergillus niger Using Polyurethane Foam as Solid Support

The present study was aimed at finding the optimal conditions for maximum gallic acid production using polyurethane-immobilized Aspergillus niger cells and determining the operational stability of recycled cells for gallic acid production. Maximum gallic acid (142 µg/ml) was produced with 1% tannic acid at 40°C, pH 5.0, with polyurethane foam size of 1.5 cm3 cubes after 48 h under submerged fermentation at 220 rpm, as compared to free cells, which produced 72 µg /ml gallic acid in 72 h at 37°C and pH 5.0. Continuous production of gallic acid by recycling of the immobilized cells resulted in maximum gallic acid production of 199 µg/ml after the fourth cycle, and thereafter remained stable till the seventh cycle and could be continued till the tenth cycle. Pyrogallol, a degradation product of gallic acid and gallic acid decarboxylase (GADC), was also monitored under static and aerobic states and showed comparable values, in contrast to bacteria where aeration caused inhibition. However, 72.73% inhibition of GADC activity by oxidizing agents with simultaneous increase in gallic acid production was observed. This is the first report of gallic acid production by immobilized A. niger cells, producing higher amounts of gallic acid in a shorter cultivation time.