Research On Enzymatic Synthesis Of Phytosterol Esters

Phytosterols are proved beneficial in lowering the risk factors for obesity-relateddiseases such as cholesterol-lowering activity and prevention of cardiovascular diseases.However, poor water soluble and fat-soluble of phytosterols have limited their applications infood and pharmaceutical industry. Modified phytosterol via esterification is used to increaseits solubility in fat, which would greatly extend its applicability. Currently, phytosterol estersare mainly synthesized by two ways: chemistry and enzyme method. Compared withchemical methods, enzymatic Synthesis has the advantages of mild reaction conditions, lowenergy consumption, Eco-product and so on. Preparation technology, separation methods andProperties of phytosterol esters were investigated systematically in this dissertation.First, phytosterol esters were detected by gas chromatography mass spectrometry(GC-MS) and gas chromatography (GC). The results showed that esters were successfullysynthesized. The reaction products were detected by GC.In order to synthesize phytosterol esters, an organic system and a ionic liquidmicroemulsion system were designed. The influences of different factors in both systemswere investigated. In n-hexane system, lipase AYS was selected for further experiments,molar ratio of myristic acid to phytosterol3:1,lipase AYS load10%(on the basis of thesubstrate mass),reaction temperature50℃, the yield of esterification can reach69.93%after72h. In the ionic liquid microemulsion system, lipase AY30was selected as biocatalyst,water content(w0)5.4,surfactant concentration300mmol/L, enzyme load10%, PH7.4,reactiontemperature50℃,the yield can reach87.80%after24h. The conversion of phytosterol estersstill retained82.50%after7cycles of the system reuse.Thin-layer chromatography (TLC), column chromatography and extraction wereinvestigated. The composite solvents n-hexane/isopropyl alcohol was used for extractingreaction products based on different solubility of phytosterol and phytosterol esters indifferent organic solvents. We can gain a purity of95.17%,96.64%and recovery of92.35%,90.11%of phytosterol myristate and phytosterol laurate, respectively.The physicochemical properties and solubility in oils of phytosterol esters were also studied. Phytosterol esters are white powers, with no smell, light flavor, the density is slightlyless than water, insoluble in water, ethanol, isopropyl alcohol, soluble in n-hexane, n-heptane,a melting point of about85℃.Acid values are lower than5mgKOH/g, and peroxide valuesare less than1meq/kg. The solubilities of esters in oils are about3-7times of phytosterols’.