Microwave-assisted synthesis of 4,4-dimethylsterol-conjugated linoleic acid ester and its lipid-lowering benefits evaluation

4,4-Dimethylsterol (RST), rich in rice bran oil, is often considered to have good lipid-lowering properties, and conjugated linoleic acid (CLA), a special fatty acid, is also considered to have similar properties, but the low solubility and poor oxidation stability limits their application in the food industry. Typically, sterol esters have better solubility after esterification. However, it is difficult to esterify 4,4-dimethylsterol for its additional methyl groups. Therefore, a microwave-assisted esterification of 4,4-dimethylsterol with CLA was developed in this study, and the lipid-lowering function of 4,4-dimethylsterol-CLA esters (RSE) was evaluated with a high-fat diet (HFD)-induced mice model. The results showed that when the reaction condition of the molar ratio of RST to CLA was 1:3 and catalyzed with 5% (mol%) p-toluene sulfonic acid and 25% (mol%) dodecyl benzene sulfonic acid, and maintained at a microwave reactor for 125 min at 100°C, the highest esterification rate of 93.63% was acquired. Furthermore, the results of HFD-induced mice experiments demonstrated that RSE could significantly reduce body weight, as well as serum and liver triglyceride (TG) levels, while also exert hepatoprotective properties compared to RST. Additionally, it was found that RSE could affect appetite and regulate the expression of lipid metabolism-related genes in mice. These findings suggest that RSE holds potential for application in the field of functional foods.