Sophorolipids from Candida bombicola using mixed hydrophilic substrates: production, purification and characterization.

Sophorolipids (SLs) are glycolipids type of biosurfactants and are produced by the yeast Candida bombicola. Medium containing mixed hydrophilic substrate (deproteinized whey and glucose), yeast extract and oleic acid was investigated in this study for SLs production from the yeast. The produced SL was also purified and characterized in the study. At an optimum combination of the medium constituents, the yeast C. bombicola produced maximum 23.29+/-0.54 g/l, 25.54+/-1.01 g/l and 33.32+/-0.83 g/l of the biosurfactant when fermentation was carried out in batch shake flasks, in bioreactor without pH control and in bioreactor with pH control, respectively. Produced SL was purified by silica gel column chromatography and was characterized using FTIR, (1)H NMR and LC-MS whose results revealed it to be (17-hydroxyoctadecenoic)-1'4''-lactone-6'6''-diacetate SL. Further, its critical micelle concentration and minimum surface tension against water were found to be 27.17 mg/l and 34.18 mN/m, respectively. Results of interfacial tension obtained using the SLs between water and either n-hexane, sunflower oil or olive oil proved its ability to solubilize non-aqueous phase liquids in water. Further, the biosurfactant was found to be stable at wide range of pHs, temperature and salt concentrations. The results of emulsifying activity and stability of the product against the tested organic solvents and oils together with its ability to solubilize fat and oil confirmed the potential of the biosurfactant in environmental applications.