Production of biosurfactants by foodborne yeasts and investigation of their functional properties

In this study, firstly the biosurfactant production capacities of 142 food originated indogenous yeast strains were investigated. At this stage, Cyberlindnera fabianii MIAU-1 strain was selected as the biosurfactant producer strain based on the reducing of the surface tension parameter as well as the preliminary screening tests. In experiments searching the effects of different types and concentrations of carbon and nitrogen sources on the biosurfactant production of this strain, the surface tension of the medium was reduced to 28.25 mN/m at the optimum level when glucose (10%), sunflower oil (10%), yeast extract (3 g/L) and urea (3 g/L) were used together. In addition, the highest reduction in the surface tension of medium was achieved to be 24.46 mN/m by the biosurfactant produced in the medium prepared by using the food industrial wastes (olive mill wastewater, 20% and waste frying oil, 10%). In studies where biosurfactant production was carried out under bioreactor conditions using optimum defined and waste-based media, it was found that 37.3235 and 6.262 g/L crude biosurfactant were produced, respectively. For the biochemical characterization of the crude and also purified biosurfactants from the yeast, FT-IR and NMR methods were used and it was determined that these biosurfactants had a sophorolipid structure. The critical micelle concentrations of the crude biosurfactants produced in defined and waste-based media were found to be 42.68 and 423.99 mg/L and also these concentrations of the purified biosurfactants were 1290.27 and 1813.80 mg/L, respectively. When the functional properties of the crude biosurfactant produced in a defined medium were examined, it was determined that this biosurfactant generally maintained its stability by reducing the surface tension of water under different ambient (pH, salt concentration and temperature) conditions. In addition, the produced biosurfactant had antibacterial activity against the pathogens of Listeria monocytogenes (89.23-92.03), Salmonella Enteritidis (62.23-76.66%) and Escherichia coli (45.83-58.34); and also anti adhesion effect to prevent biofilm formations of Staphylococcus aureus and L. monocytogenes by the highest rates of approximately 67% and 55.50%, respectively.