Physicochemical characterization of tensio-active produced by Geobacillus stearothermophilus isolated from petroleum-contaminated soil

Abstract

Biosurfactants are surface-active agents of microbial origin, and have a property of lowering the interfacial tension between two liquids. They act on the interface and are amphiphathic molecules; in with both hydrophilic and hydrophobic portions are present in the same molecule. However, the economics of producing biosurfactant has limited its commercial applications, and the costs can be reduced using cheap substrates or industrial waste. The present study showed the biosurfactant production using corn steep liquor and palm oil as carbon and nitrogen sources for reduction the costs of production. The biosurfactant production by Geobacillus stearothermophilus UCP 986 was carried out using optimized culture medium constituted by palm oil (7.5%) and corn steep liquor (4.5%) using Bioflo fermentor, at temperature of 45°C, during 32h and agitation of 300rpm. The biosurfactant showed a reduction of the water surface tension of 72–31mN/m and interfacial tension of 0.3mN/m. The biosurfactant was obtained from the net metabolic liquid by acetone precipitation corresponding to the yield of 2.3g/L. The isolate biosurfactant showed a CMC of 2.5% and non-ionic profile. The best emulsification index (E24) obtained was 87% using motor oil burned. The biosurfactant solution (2.5%) used in oil spreading test increases the viscosity of engine burning oil of 149.2% and 138.2% to vegetable fat post-frying, respectively. The gas chromatography–mass spectrometer indicated at 29.52min a molecular weight of 207Da and eight peaks by FT-IR identified the chemical structure of the biosurfactant produced by G. stearothermophilus.