Biosurfactant production by a novel yeast Cyberlindnera fabianii MIAU-1: process optimization, structural...

Biosurfactant production by a novel Cyberlindnera fabianii MIAU-1 isolate was achieved using co-carbon substrates glucose and sunflower oil, in addition to yeast extract and urea as nitrogen sources. The surface tension of the fermentation medium, consisting of optimal concentrations of glucose (10%), sunflower oil (10%), yeast extract (3 g/L) and urea (3 g/L), was reduced to 36.39 mN/m. This strain produced 39.85 g/L of biosurfactant after 48 h of fermentation under bioreactor conditions. This indicates a 6.78% increase over the 37.32 g/L biosurfactant produced using shake flask after 72 h. The biosurfactant was purified and then characterized using FT-IR and NMR. The crude (CBS) and purified (PBS) biosurfactants were determined to have glycolipid (sophorolipid) structure. The degradation temperatures of CBS and PBS were determined to be 255 °C and 275 °C, respectively, following thermogravimetric analysis. CBS reduced the surface tension of distilled water to about 40 mN/m at 43.63 mg/L its critical micelle concentration (CMC); and PBS reduced it to about 50 mN/m at 1290.91 mg/L CMC. CBS maintained stable surface activity over the range of pH, salinity, temperature, and heating time. Additionally, CBS used at various concentrations exhibited antibacterial activity and inhibited the growth of Listeria monocytogenes, Salmonella Enteritidis and Escherichia coli O157:H7. CBS also showed anti-adhesive activity to prevent biofilm formation of Staphylococcus aureus and L. monocytogenes.