Biosurfactant production by Bacillus subtilis UFPEDA 86 using papaya (Carica papaya L.) waste as substrate: Viability studies and pH influence of the culture medium

Biosurfactants are surface-active compounds derived from microorganisms and offer several advantages over chemical surfactants, such as low toxicity, good biodegradability and ecological acceptability. Even though interest in biosurfactants is increasing, these bioproducts do not compete economically with synthetic surfactants due to the overall costs of the bioprocess. The use of inexpensive raw materials is an important approach to reduce these costs since the substrate price account for 10 to 30% of the final product expenses. In this study, papaya (Carica papaya L.) waste was used as a substrate to produce biosurfactant by Bacillus subtilis UFPEDA 86 strain. In addition, culture medium pH was corrected from 5.25 to 6.8 in order to analyze the influence of this variable on the biosurfactant production. The submerged fermentation was carried out on a shaker incubator at 37°C, 200 rpm for 96 h. Biomass and substrate concentration, surface tension, emulsification index and critical micelle concentration were analyzed. The strain was well adapted to both substrates studied, without and with pH correction. Using the broth without pH correction (pH=5.25), a maximum cell concentration of 1.07 g L-1 at 36 h a 25.5% surface tension reduction, emulsification index of around 61% and critical micelle concentration of about 35 mg L-1 was obtained. Using the broth with pH correction to 6.8, better results; maximum cell concentration of 1.14 g L-1 at 24 h, a 32.5% surface tension reduction, emulsification index of around 66% and critical micelle concentration at about 35 mg L-1 was obtained. The papaya waste proved to be an effective substrate in the biosurfactant production by B. subtilis UFPEDA 86 and the pH variable proved to be of great importance in the yield of this process.   Key words: Biosurfactant, submerged fermentation, papaya waste, Bacillus subtilis.