Characterisation, surface properties and biological activity of a biosurfactant produced from industrial waste by Candida sphaerica UCP0995 for application in the petroleum industry

The development of less toxic, biodegradable, surfactants, such as biosurfactants, is a key strategy for acquiring environmentally friendly compounds. The aim of the present study was to employ an optimised medium containing 9% ground nut oil refinery residue and 9% corn steep liquor for the production of a biosurfactant by Candida sphaerica. Fermentation was carried out at 28 °C and 200 rpm for 144 h. Biosurfactant yield was 9 g/l. The biosurfactant reduced the surface tension of the medium to 25 mN/m, with a critical micelle concentration of 0.025%. The product demonstrated stability with regard to surface tension reduction and emulsification in a range of temperatures (5–120 °C) and pH values (2–12) as well as tolerance to high concentrations of NaCl (2–10%). Hydrophobicity tests indicate two possible insoluble substrate uptake mechanisms: direct interfacial uptake and biosurfactant-mediated transfer (cell contact with emulsified or solubilised hydrocarbons). The biosurfactant was characterised as an anionic glycolipid consisting of 70% lipids and 15% carbohydrates and demonstrated no toxicity to the microcrustacean Artemia salina or the vegetables Brassica oleracea, Solanum gilo, Lactuca sativa L. and Brassica oleracea L. The biosurfactant recovered 95% of motor oil adsorbed to a sand sample, demonstrating considerable potential for use in bioremediation processes, especially in the petroleum industry.

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► A low-cost glycolipidic biosurfactant was produced by the yeast Candida sphaerica.
► The biosurfactant showed a surface tension of 25 mN/m and a CMC of 0.025%.
► The biosurfactant was stable under extreme environmental conditions.
► The biosurfactant did not exhibit toxicity against vegetal seeds or brine shrimp.
► The biosurfactant recovered 95% of motor oil adsorbed in sand.