Lipase-catalyzed Synthesis Of Phytosterol Esters And Their Lipid Metabolic Effects On Hyperlipidemia Rats

Phytosterols (plant sterols) are one of important minor compounds naturallyoccurring in plants. They may interfere with the intestinal cholesterol absorption byinhibiting cholesterol incorporation into micelles in the lumen of the intestine.However, practical applications of free phytosterol in foods are limited because oftheir poor solubility and low bioactivity. Esterification of phytosterols with fattyacids or oil and fats can increase their lipid solubility and thus facilitates the in-corporation into a variety of foods.Phytosteryl esters are presently synthesized bychemical and enzymatic esterification. Enzymatic synthesis using lipase had anadvantage over Chemical synthesis, due to its high activity, selectivity, and mod-erate conditions in which it operate. Phytosterol esters were synthesized by lipasefrom Candida rugosa, and then their metabolic effects were detected using animaltests. The main conclusions were obtained as follows:(1) The synthesis of phytosterol oleic acid esters catalyzed by lipase fromCandida rugosa in the organic medium was investigated. The reaction conditionswere optimized using response surface methods (RSM) measured by the degree ofesterification (DE). A quadratic response regression equation of esterification rateon independent variables of temperature, reaction time, substrate molar ratio (oleicacid: phytosterol) and catalyst amount was established. The results demonstratedthat the optimum conditions were temperature of41℃, reaction time of19h, sub-strate molar ratio (oleic acid: phytosterol) of2.4:1and catalyst amount of7%. Un-der the optimized reaction conditions, the DE of phytosterol with oleic acid reached77.43%. The purity of the sterol esters in the product was91.2%after separationand purification.(2) Then the phytosterol esters catalyzed in the optimum condition confirmedby gas chromatography-mass spectrometry (GC-MS), ultraviolet–visible spectros-copy (UV-VIS), thin-layer chromatography (TLC) and infrared spectrometry (FT-IR)analysis．The analysis results of product by FT-IR, UV-VIS and TLC showed thatthere were almost no phytosterols and new functional group-ester bond were gen-erated. It was proved that the sample from purification was phytosterol esters con-taining campestero estersl, stigmasterol esters, β-sitosterol esters mainly and bras- sicasterol esters minorly through GC-MS analysis.(3) Effect of phytosterol oleate ester and phytosterol linoleyl ester on the me-tabolism of lipids were studied and compared. The hyperlipidemia models ofSprague-Drawly (SD) rats were established by feeding high-fat diet and then werefed by phytosterol ester-contained diet. The results demonstrated that six weekslater, the two kinds of phytosterol esters could reduce blood lipid, including reducetotal cholesterol (TC), low density lipoprotein-cholesterol (LDL-C), ApoproteinsB(ApoB) and increase high density lipoprotein-cholesterol (HDL-C) and Apopro-teinsAⅠ (ApoAⅠ), especially phytosterol linoleyl ester has much better choles-terol-lowering effect than phytosterol oleate ester. The results also showed twokinds of phytosterol esters was able to scavenge free radical and decrease lipid pe-roxide content of the malondialdehyde (MDA), thus they could ease significantlyhyperlipidemia.