Pomegranate peel is a low-cost substrate for the production of tannase by Bacillus velezensis TA3 under solid state fermentation

Abstract

Tannase production from Bacillus velezensis TA3 was optimized by sequential statistical approach using pomegranate as a solid substrate. Easily available and low-cost substrates such as cow dung, coffee husk, apple peel and pomegranate peel were initially screened. Among these substrates, pomegranate peel was found to enhance tannase activity. Further, pomegranate peel was used as the substrate to optimize the factors by traditional methods. In one-variable-at-a-time approach optimum process conditions were, 48 h incubation (1.92 U/g), 0.3% tannic acid (1.33 U/g), 0.08% minerals (2.3 U/g) with 55% initial moisture content (2.7 U/g). To screen the impact of variables such as fermentation period, moisture content, sodium chloride level, tannic acid concentration and required minerals on tannase production under solid state fermentation, a two-level full factorial design was used. Among these factors, incubation time, moisture and tannic acid concentrations were found to have significant influence on tannase production (p < 0.001). The optimum concentration of these three significant factors was further evaluated by central composite design (CCD) and response surface methodology (RSM). The optimum concentration of these variables was determined as 57 h incubation, 72.5% moisture and 0.68% tannic acid. Under optimized conditions, the experimental result of 32 U/g substrate was very close with predicted value (33.1 U/g substrate) which validated the experimental design. RSM mediated statistical approach showed 9-fold enzyme activity than unoptimized medium.