Chemical Synthesis And Antioxidant Activity Of Phytosteryl Esters

Currently, there are two methods to synthesize physterol esters: chemical synthesis and enzymic synthesis. But the enzymic synthesis could not be developed into the large scale production in industry due to its high cost. The chemical methods are simple, economical and high in yields. However, they have their own drawbacks such as high temperature and prolonged reaction time. Thus, it is desired to find out catalysis with high efficiency for the synthesis of physterol esters.Cupric dodecyl sulfate as an efficient micelle-catalyst was utilized in the synthesis of phytosterol ester. The synthetic procedure of phytosteryl laurate representative of phytosterol saturated fatty acid ester was studied. The effect of the ratio of FA to phytosterol, amount of catalyst, reaction temperature and reaction time on reaction was investigated. By single factor test and orthogonal design experiment, the optimum parameters of preparation of phytosteryl laurate were obtained. The optimal reaction conditions were as follows: ratio of FA to phytosterol 1.3 : 1, amount of catalyst 1.0 mol % of phytosterol, reaction temperature 120℃, and reaction time 4 hours under N2. And the 92.1% of rate of esterification was acquired.The synthesis of phytosteryl unsaturated fatty acid ester was studied using conjugated linoleic acid. Sadium dodecyl sulfate was sorted out as catalyst under comprehensive consideration of the rate of esterification and the degree of oxidization evaluate by p-anisidine value of the system. Similarly, the influence of the ratio of CLA to phytosterol, amount of catalyst, reaction temperature and reaction time on reaction was investigated. The optimal conditions were: the ratio of CLA to phytosterol 1.2 : 1, amount of catalyst 2.0 mol %, temperature 110℃, and time 3 hours under N₂, and the rate of esterification was 77.1% in optimum conditions.Silica gel column was applied to separate phytosteryl esters. And cyclohexane: diethyl ether (19:1, v/v) was used as mobile phase. The flow rate was 25 mL/h. The separated product was identified as phytosteryl ester by TLC, HPLC, IR and GC - MS.The solubility of phytosterol, phytosteryl laurate and phytosteryl palmitate in various solvents were determined by gravimetric analysis. Their curves were plotted. And the separation and purification methods of physterly ester from the reaction mixture were studied.The reaction kinetics ofβ-sitosterol with lauric acid using SDS-HCl as a catalyst were studied. The reaction met the second 2 order reaction. And the activitation energy of the reaction was about 88.03 kJ/mol. And kinetic constants at different temperatures were calculated. The experimental results show that rate equation of esterification forβ-sitosterol with lauric acid could be expressed as r = 1.1595×10¹² exp[88.03/(RT)]_cAcB.The solubility of phytosterol, phytosteryl laurate, phytosteryl palmitate, phytosteryl oleate, and phytosteryl conjugated linoleate in fish oil at 50℃were 1.0 %, 8.7 %, 4.9 %, 42.0 % and 46.2 %, respectively.The antioxidation activity of phytosteryl esters in fish oil at 50℃was studied by the determination of POV of the fish oil system. Their optimum concentration was 0.05‰. Under this condition the order of antioxidation ability from high to low was: phytosterly laurate, phytosteryl oleate, phytosteryl conjugated linoleate and phytosterly palmitate. And there were synergy effects on antioxidant ability between physteryl ester and Vitamin E.