Catalyst‐free synthesis of phytosterol diacid monoesters and their competitive effect on the solubilization of cholesterol in model bile mixed micelles

Impact of molecular interactions between hydrophilic phytosterol glycosyl derivatives and bile salts on the micellar solubility of cholesterol

Hydrophilic phytosterol glycosyl derivatives are synthetic phytosterol analogues by coupling with the glycosyl moiety to improve the water solubility and bioaccessibility of free phytosterols. The aim of this study is to clarify the molecular interaction of phytosterol glycosyl derivatives with bile salts and the consequent impact on cholesterol solubilization. Sharp nonlinear decrease in the micellar solubility of cholesterol and accompanying changes in particle size, zeta potential and microtopography of mixed micelles were observed when phytosterol glycosyl derivatives were introduced in cholesterol-loaded bile salt micelles. These results suggested that β-sitosterol glycosyl derivatives molecules indeed participated in the formation of mixed micelles. Further, nuclear magnetic resonance showed that the structural change of mixed micelles was caused by the insertion of β-sitosterol glycosyl derivatives via hydrogen bonds with sodium taurocholate, which resulted in the low cholesterol solubilization. Moreover, the hydrogen-bond interactions were apparently influenced by the glycosyl moiety of β-sitosterol glycosyl derivatives. These molecular mechanisms may contribute to the development of cholesterol-absorption inhibitors.

Synthesis, Physical Properties, and In Vitro-Simulated Gastrointestinal Digestion of Hydrophilic β-Sitosterol Sugar Esters

Hydrophilic β-sitosterol sugar esters were synthesized by a two-step biocatalytic approach using β-sitosterol vinyl adipate as an intermediate. The maximum conversion (above 90%) of β-sitosterol vinyl adipate was achieved using the saccharides glucose, sucrose, and raffinose. The chemical structure of the synthesized esters was confirmed by various techniques. The investigation of physical properties revealed that β-sitosterol sugar esters had enhanced water solubility (3.0-8.0 mM at 35 °C), reduced crystallinity, and high wettability. Their lyotropic liquid crystal properties were observed by polarized light microscopy. Furthermore, β-sitosterol sugar esters could be hydrolyzed into β-sitosterol adipate under simulated intestinal conditions at a low rate (2.83-18.14%). Most β-sitosterol sugar esters probably entered into intestinal bile salt micelles with ester bonds intact and showed up to 10-fold higher in vitro bioaccessibility than free β-sitosterol in non-fat systems. The excellent physical and functional characteristics of β-sitosterol sugar esters suggested their great potential application in the food industry.