Optimization of biosurfactant production by Bacillus Subtilis N3-1P using the brewery waste as the carbon source

Biosurfactants are biologically produced by microorganisms and therefore biodegradable, making ideal substitutes to chemical surfactants for various applications. Large scale production of biosurfactants is limited because of the high cost. The production cost could be reduced by optimizing cultural conditions and using wastes as substrates. In this work, the response surface methodology (RSM) was used to optimize biosurfactant production by Bacillus subtilis N3-1P strain using brewery waste as the sole carbon source. Five independent variables were varied; carbon and nitrogen concentration, agitation speed, temperature and initial pH. Surface tension and emulsification index were used to measure biosurfactant production. Results indicated that the 'best' surface tension and emulsification index were 27.31 mN m^-1 and 63.11%, respectively, under optimized cultural conditions (7% (v v^-1) brewery waste, 6.22 g L^-1 ammonium nitrate, initial pH of 6.41, 150 rpm, and 27°C). The predicted responses were validated experimentally under the 'optimum' conditions, and 657 mg L^-1 of biosurfactant was produced with a critical micelle concentration of 107 mg L^-1.