Ultrasound pretreatment for lipase-catalyzed synthesis of stigmasteryl oleate and evaluation of its physicochemical properties

Stigmasterol is an important natural compound with the ability to lower cholesterol and prevent cardiovascular disease. It is often esterified with fatty acids to enhance its range of applications and improve its bioaccessibility. In this paper, stigmasteryl oleate was efficiently synthesized via lipase catalysis under optimized ultrasound pretreatment conditions, and the physicochemical properties of stigmasteryl oleate were investigated. The results showed that the stigmasterol conversion reached 91.37% with an ultrasound power of 200 W, ultrasound pretreatment time of 1 h, lipase dosage of 50 g/L, and ultrasound pretreatment temperature of 50 °C. The chemical structure of the final stigmasteryl oleate product was identified using Fourier transform infrared spectroscopy, mass spectrometry and nuclear magnetic resonance spectroscopy. The melting and crystallization temperatures of stigmasteryl oleate were significantly decreased to 22.8 and 12.9 °C, respectively, while its solubility in edible oil was more than 20 times higher than that of stigmasterol. The peroxide value of stigmasteryl oleate was much lower than that of oleic acid (27.53 and 41.39 mmol/kg). The product of stigmasteryl oleate with more favorable physicochemical properties greatly facilitates the widespread use of stigmasterol in oil-based foods.