Bacterial cellulase production using grape pomace hydrolysate by shake-flask submerged fermentation

Grape pomace is a lignocellulosic waste of wine industry, which comprises high moisture content, cellulose, and hemicellulose, making it a viable substrate to microorganisms. Also, it is a potential substrate for bio-products such as enzymes and biofuels. Thus, the aim of the study was at the optimization of solid to liquid ratio (w/v), pH, and fermentation period for maximal cellulase of Bacillus subtilis natto DSM 17766 by the Box-Behnken response surface method (RSM) using grape pomace hydrolysate (GPH). The GPH was obtained by autoclaving the grape pomace slurry prepared with 3% (w/v) H2SO4, shown to be better than 5%, at 121.1 degrees C for 15 min and filtering after pH adjustment. Cellulase was assayed by the DNS method using filter paper as substrate. The maximum cellulase activity was predicted at 0.178 IU/mL with solid to liquid ratio of 15:100 (w/v), pH 6.0, and 7 days of fermentation according to the response surface model, which agreed well to its experimental counterpart (0.176 IU/mL). The results also confirm higher impact of fermentation period and pH in comparison to change in grape pomace amount. Thus, this study shows that Bacillus subtilis natto can be a good producer of cellulase using the grape pomace hydrolysate as a low-cost carbon source.