Antibacterial Activity of a Linolenic Acid Stigmasterol Ester Produced by Lipase-Mediated Transesterification

Phytosterols are naturally found in lipid-rich plant foods and oils. These compounds exhibit various pharmacological effects, including anti-inflammatory, antimicrobial, antioxidant, and cholesterol-lowering properties. However, their industrial application has been limited due to their high melting points and poor solubility in both water and oil. Some unsaturated fatty acids can enhance phytosterols' oil solubility while exhibiting antimicrobial activities against various bacterial strains. In this study, we synthesized a linolenic acid stigmasterol ester (LASE) to improve oil and emulsion solubility of stigmasterol, a phytosterol known for its beneficial physiological effects in humans. LASE was synthesized with Candida antarctica lipase A through a transesterification reaction using stigmasterol and α-linolenic acid-rich linseed oil as substrates. The reaction was conducted at 50°C in isooctane with 20 mM of both stigmasterol and linseed oil. Following synthesis, LASE was purified using preparative liquid chromatography. The purified LASE demonstrated a 20-fold improvement in solubility in tricaprylin (TCN) compared to stigmasterol. Additionally, its antibacterial activities against specific food spoilage bacteria were confirmed using a TCN-based emulsion system.