Simultaneous production of amylases and proteases by Bacillus subtilis in brewery wastes

The simultaneous production of amylase (AA) and protease (PA) activity by Bacillus subtilis UO-01 in brewery wastes was studied by combining the response surface methodology with the kinetic study of the process. The optimum conditions (T = 36.0 °C and pH = 6.8) for high biomass production (0.92 g/L) were similar to the conditions (T = 36.8 °C and pH = 6.6) for high AA synthesis (9.26 EU/mL). However, the maximum PA level (9.77 EU/mL) was obtained at pH 7.1 and 37.8 °C. Under these conditions, a considerably high reduction (between 69.9 and 77.8%) of the initial chemical oxygen demand of the waste was achieved. In verification experiments under the optimized conditions for production of each enzyme, the AA and PA obtained after 15 h of incubation were, respectively, 9.35 and 9.87 EU/mL. By using the Luedeking and Piret model, both enzymes were classified as growth-associated metabolites. Protease production delay seemed to be related to the consumption of non-protein and protein nitrogen. These results indicate that the brewery waste could be successfully used for a high scale production of amylases and proteases at a low cost.