Biosurfactant production by Lactobacillus spp. strains isolated from Romanian traditional fermented food products

Biosurfactants are surface-active molecules produced by different microorganisms, including Lactobacillus spp. strains, with emulsifying properties. For their emulsifying activities as well as for the inhibition of some pathogenic microorganisms, biosurfactants produced by lactobacilli could find important applications in food industry. The aim of this study was to screen for biosurfactant production in several lactic acid bacteria (LAB) strains. Ten LAB strains selected previously for antifungal activities were used in experiments. The biosurfactant production was evaluated both in supernatant and in cells cultivated in Man-Sharp-Rogosa (MRS) broth. Oil spreading test, emulsification activity, and drop collapse methods were used for evaluation the biosurfactant production. Antimicrobial action of biosurfactants against Escherichia coli, Bacillus cereus, Staphylococcus aureus, Candida parapsilopsis and mycotoxigenic fungi was also examined. Molecular analyses were performed for characterization of selected bacteria. Three out of ten tested LAB strains exhibited clear biosurfactant production. The emulsifying action of kerosene was detected both in extracts from supernatants and from cells. For the strains L26 and L35, the level of cell-bound biosurfactant production was higher than the excreted one; for L61 the emulsifying activity was higher in supernatant, mainly against edible oils. The antimicrobial action of extracted biosurfactants suggests that these compounds could be involved in the inhibitory action of LAB. This study demonstrates that two strains of L. plantarum (L26 and L35) and one strain of L. brevis (L61) were able to produce cell-bound and excreted biosurfactants. High emulsifying activity was detected on edible oils, giving stable emulsions, suggesting the possible use of these biosurfactants in food industry.