Abstract

The production and properties of biosurfactants synthesized by Candidaguilliermondii NRRL Y-2075 and Bacillus subtilis NRRL B-94 using soy processing waste (okara) as substrate were investigated under different fermentation techniques. Higher oil displacement activities for the isolated biosurfactants were achieved by using submerged fermentation technique (SMF) for both organisms. Preliminary chemical characterization and IR spectroscopy for C. guilliermondii biosurfactant revealed that, it is mainly a glycolipid complex, while that of B. subtilis biosurfactant was found to be a complex mixture of lipoprotein and glycolipid. Both biosurfactants formed stable water-in-oil emulsions with motor oil and sunflower oil, while soybean oil was only emulsified by C. guilliermondii biosurfactant. The surface tension of water was reduced to 51 mN/m by C. guilliermondii biosurfactant at a critical micelle dilution (CMD) of 8% concentration, while B. subtilis biosurfactant showed a minimum surface tension of 48 mN/m at CMD value of 10% concentration. Both biosurfactants exhibited good antimicrobial activity against the tested bacteria and yeast strains with different values of minimum inhibitory concentrations (MIC).

Key words: Surfactant, Candida guilliermondii, Bacillus subtilis, soy processing waste, submerged fermentation.