| As a new functional food additive, phytosterol has the function of reducing the levels of cholesterol and preventing cardiovascular disease, become one of the hot spots and beenwidelyconcernedand appliedduringrecent years. Natural plant sterols are safe but they are easilyoxidized at high temperature to generate phytosterol oxidation products (POPs) which are considered as toxic. In thisstudy, phytosterol was firstlymodified to its esterification form and then added to lipid matrix.The influencing factors of sterol oxidation reaction under high temperature were investigated following.On this basis of thesterol oxidesare separated, purified and detected,the storage stability of phytosterols in different lipid matrix are discussed.(1) Using the plant sterols and oleic acid as raw materials, esterificing plant sterols and oleic acid by chemical methods. Esterification was investigated as indicators in the orthogonal experiments, method of synthesizing phytosterols oletate by direct esterification of phytosterols and oleic acid was researched. The optimal conditions obtained were as follows:sodium bisulfate wasused as catalyst(2%molar of phytosterols), reaction temperature was135℃, molar ratio of oleic acid to phytosterols was1.3:1and reaction time was7h. Under the best reaction conditions, the average yield of esterification reached85.07%by the three parallel tests, the purity of product was95.24%by further purification. The phytosterol esters catalyzed in the optimum condition were confirmed by gas chromatography-mass spectrometry (GC-MS), and thin-layer chromatography (TLC) analysis. The results of GC-MS analysis shows that the sample obtained from purification was phytosterol esters which mainly contain campestero estersl, stigmasterol esters, β-sitosterol esters and small amount of brassicasterol esters And results of the effect of different amount of sterols and sterol esters on the antioxidantion of phytosterol esters compound oil, shows that:With the increasing of the added amount, the radical scavenging rate significantly increased, indicating that antioxidant activity of phytosterol esters compound oil is significantly enhanced with the increasing of the added amount of phytosterol esters.(2) High temperature oxidation products of phytosterols in the lipid matrix were used as raw materials. The objectives of this study were to purify phytosterol oxidation products by saponification. Mass concentration of the phytosterols was used as an index. Based on the single factor experimental results, response surface experiments were used to optimize the saponification and establish a mathematic modle between the factors and the index. Results indicated that the optimal saponification parameters were as follows:mass concentration of KOH-ethanol3mol/L, amount of KOH-ethanol40mL/g, saponification temperature70℃, saponification time2h. Under this condition, the mass concentration of the phytosterols was up to0.1452mg/mL.(3) Solid phase extraction eluted sequentially as follows:Elution was performed first with n-hexane:ether (=9:1,V/V) mixture; followed with n-hexane: ether (=1:1, V/V) mixture elution; finally eluted with acetone. The were detected by GC-MS analysis the result showed tha tmain components in acetone eluate were phytosterol oxides such as the type of sterol oxides were7-Ketocamp,7-Ketosito, α-Epoxychol/β-Epoxychol, α-Epoxycamp/β-Epoxycamp and a-Epoxystigma/β-Epoxystigma.(4) Free phytosterols and phytosterol esters were used as model compounds and heated at different temperatures in different lipid matrices and for various periods of time. Factors contributing to the oxidative stability of phytosterols were studied. The results showed that both temperature and heating time, as well as sterol structure and lipid matrix composition, affect phytosterol oxidation. In particular, with the increase of temperature, time and amount, the chain length of the lipid matrix and degree of unsaturated matrix increase, the oxidation of the sterol enhances and retention rate reduces.(5) A quality concentration of5%phytosterols and phytosterols ester were added respectively into three kinds of vegetable oils (cooking oil, corn oil and rapeseed oil) stored at room temperature,36℃and60℃. Results showed that the total sterol concentration in sterol-rich corn oil, cooking oil and rapeseed oil slowly decreased with time in the process of low-temperature storage, andthat the vegetable oil presentsgood stability (or opaque bottle) while stored in dark. The differences sterol group and sterol ester group were compared to find out that there was not statistically significant (p>0.05). |
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