Study On Preparation And Cholesterol-lowering Effect Of Hydrophilic Phytosterol Derivatives

Phytosterols are a kind of natural component with a variety of physiological functions,such as cholesterol-lowering,anti-cancer,anti-inflammatory property and so on.Phytosterols have the characteristics of insolubility in water and poor solubility in oil,high melting point and low bioavailability,which limits their various applications in food industries.In order to broaden the application of phytosterols in water-based food,the present study aimed to synthesize hydrophilic phytosterol derivatives with polyethylene glycol?PEG?and ionic liquid as hydrophilic modifiers and catalyst,respectively,to improve their water solubility.On this basis,the cholesterol-lowering effect of hydrophilic phytosterol derivatives and their potential cholesterol-lowering mechanism were explored.Firstly,the intermediate phytosteryl hemisuccinate?PSHS?was synthesized and separated.The target product,hydrophilic phytosterol derivatives?phytosteryl polyethylene glycol succinate,PPGS?was further synthesized with purified PSHS as the reaction material.The chemical structure of the products was characterized by thin layer chromatography?TLC?,fourier transform infrared spectroscopy?FT-IR?,mass spectroscopy?MS?,and nuclear magnetic resonance spectroscopy?NMR?.These present results proved that the intermediate product and target product were successfully synthesized.The water-solubility of PPGS was siginificantly higher than that of phytosterols.Secondly,the synthetic conditions of PSHS and PPGS were explored.According to the single factor experiment,the mass conversion of PSHS could reach above 94.0%under the optimum conditions:tuluene,4%?w/w?[BSO₃HMim][HSO₄]as a catalyst,1:1.5 as the molar ratio of succinic anhydride to phytosterols,100?,75mmol/L as the concentration of reactant and 2 hours.PPGS was successfully synthesized in solvent-free system and the mass and molar conversion of PPGS could reach above97.2%and 88.0%under the optimum conditions:6%?w/w?[BSO₃HMim][HSO₄]as a catalyst,1:1.25 molar ratio of PSHS to PEG 2000,110?,and 1 hour.Furthermore,one-pot esterification route was attempted to synthesize PPGS to simplify the steps of separation and purification by directly adding PEG 2000 and[BSO₃HMim][HSO₄]into the reaction system of PSHS.The mass and molar conversion of PPGS could achieve above 97.8%and 90.3%.Thridly,three kinds of hydrophilic phytosterol derivatives?PPGS-600,PPGS-1000,PPGS-2000?were prepared with PEG 600,PEG 1000 and PEG 2000 as hydrophilic modifiers.Subsequently,the effects of PPGS-600,PPGS-1000 and PPGS-2000 on lipid levels of serum,liver and feces were investigated in SD-rats fed a high-fat diet by oral administration for 8 weeks.The results showed that PPGS had a certain inhibitory effect on the body weight of high-fat diet rats.They reduced serum total cholesterol?TC?levels in different degrees,serum low-density lipoprotein cholesterol?LDL-C?levels,LDL-C/HDL-C values,liver cholesterol levels,and increased fecal bile acid content.Meanwhile,PPGS-600,PPGS-1000 and PPGS-2000increased the mRNA levels of liver LDLR,SREBP-2 and CYP7A1,indicating that hydrophilic phytosterol esters reduced cholesterol by affecting the expression of cholesterol metabolism-related receptors,proteins,or enzymes in the liver.