Antibacterial activity of emulsions containing unsaturated fatty acid ergosterol esters synthesized by lipase-mediated transesterification

Ergosterol, like cholesterol, has many beneficial physiological activities, and because it has no adverse clinical problem with cholesterol, it is a substance that can be used as a biomaterial in the food and cosmetics industry. However, ergosterol has low oil solubility and is easily crystallized, which is problematic for its direct use in the industry. This problem can be solved by combining fatty acids with ergosterol. In this study, ergosterol derivatives with unsaturated fatty acids were synthesized from ergosterol and various plant oils. Specifically, ergosterol oleate (EO), ergosterol linoleate (EL), and ergosterol linolenate (ELn) were synthesized using Proteus vulgaris K80 lipase. To effectively synthesize these unsaturated fatty acid ergosterol esters (FAEEs), 25 mM ergosterol and 40 mM plant oil were added into hexane solvent, and transesterification reaction was performed at 40 °C. Proteus vulgaris K80 lipase showed higher conversion yield than other commercial lipases, due to its high affinity to ergosterol and broad substrate specificity. Rapeseed oil, sunflower seed oil, and linseed oil were used to synthesize EO, EL, and ELn, respectively. The FAEEs were purified, and their purity was confirmed by FT-IR and LC-MS. The solubility of the FAEEs in a tricaprylin solvent was increased 11-16 times, compared to that of ergosterol. We found that EL- and ELn-containing emulsions had strong growth inhibitory activity against some dairy and cosmetic spoilage bacteria.

Keywords: Antibacterial activity; Emulsion; Ergosterol; Fatty acid ergosterol ester; K80 lipase; Transesterification.