Abstract: Linoleyl β-sitosterol was synthesized by sequential microwave and ultrasonic treatment. Qualitative and quantitative analysis of the synthetic product was carried out. Single factor and orthogonal array design experiments were conducted to examine the effect of molar ratio of acid to alcohol, microwave heating time, number of microwave heating cycles and ultrasound irradiation time on the esterification rate in order to optimize the four conditions. The synthetic product was purified by solvent extraction and was analyzed by high performance liquid chromatography (HPLC), infrared spectroscopy, an element analyzer and nuclear magnetic resonance (NMR), and its oil solubility was studied. The results showed that the optimum conditions were as follows: molar ratio of acid to alcohol 2.2:1, microwave heating time 5 min, and 4 microwave heating cycles with 90 s ultrasonic irradiation apart, giving an esterification rate of up to 89.56%. The synthesized substance was identified as linoleyl β-sitosterol with a purity of up to 98.36%. The solubility of the linoleyl β-sitosterol in tea seed oil at different temperatures (-5, 4, 25 and 40 ℃) was more than 25 times higher than that of β-sitosterol under the same conditions.

Key words: β-sitosterol, linoleic acid, ultrasound, microwave, esterification