Production, characterization, and antifungal application of biosurfactant sophorolipids from Starmerella bombicola and Candida riodocensiss

Sophorolipids are biosurfactants composed of a disaccharide sophorose linked by a hydroxyl group of fatty acids. Due to their surface-active properties, sophorolipids have a great potential for using in various industrial applications. The aim of this study is to characterize the functional property and production of sophorolipids by yeasts using a combination of glucose and palm oil as a hydrophilic or hydrophobic substrate, respectively. Starmerella bombicola has been known as an attractive yeast species for biosurfactant production while Candida riodocensis has not been much explored. S. bombicola and C. riodocensis were used as a host for production of sophorolipids from vegetable oil which is generally consisted of C16-18 fatty acids and thus is ideal for sophorolipids production. Here, the results showed that C. riodocensis and S. bombicola produced biosurfactants with emulsification activity against kerosene at the highest activity of 54.62% and of 60.23% after 4 or 7 days of cultivation, respectively. According to oil displacement assay, S. bombicola displayed slightly better activity to displace oil (1.17 cm) when compared to C. riodocensis (1.08 cm). Then, characterization of extracted sophorolipids was determined by fourier transform infrared spectroscopy (FTIR) which is confirmed as sophorolipids containing both lactonic and acidic forms. Palm oil appeared to promote cell growth of yeast cells as apparent for C. riodocensis. Yields of sophorolipids was obtained for C. riodocensis (45.70 g/L) and S. bombicola (39.36 g/L). Lastly, treatment with sophorolipids at 15-30 µg/ml also inhibited Candida albicans hyphal growth; thereby demonstrating their potential application in biomedicals.