Highly Efficient Synthesis of Phytosterol Linolenate Catalyzed by Candida Rugosa Lipase through Transesterification

Abstract

In recent years, phytosterols and their fatty acid esters have attracted much attention due to their beneficial effects on human health, while the latter showed excellent advantage in oil solubility. In this study, a novel method was developed for highly efficient synthesis of phytosterol linolenate through lipase-catalyzed transesterification of phytosterols with ethyl linolenate. The effects of lipase, and of solvents with different Log P values on the transesterification of phytosterols were investigated. And the solubility of phytosterols and residual activities of lipase after exposure to different solvents were also considered. Results showed that the conversion was positive correlated with the Log P values of the solvent. Candida rugosa lipase and iso-octane was the most suitable biocatalyst and solvent, respectively. The effects of other reaction parameters, including lipase load, reaction temperature, substrate concentration, substrate molar ratio and reaction time on the conversion of phytosterols to phytosterol linolenate were investigated. And the highest yield (95.9 ± 0.8%) of phytosterol linolenate was obtained in short reaction time (2 h) under the selected conditions: 75 mmol/L phytosterols, 1:1.75 molar ratio of phytosterols to ethyl linoenate, 120 g/L 3 Å molecular sieves and 20 g/L Candida rugosa lipase in iso-octane, 150 r/min and 40°C, suggesting that Candida rugosa lipase–catalyzed transesterification of phytosterols was an efficient route for phytosterols esters synthesis. The solubility of phytosterols and its linolenate in vegetable oil was also compared and results showed that the oil solubility of phytosterols was significantly improved by transesterification with ethyl linolenate, facilitating the incorporation into a variety of oil- or fat-based foods.