α-linolenic acid and phytosterol both have blood lipids-reducing, cholesterol-lowering activity and prevention of cardiovascular diseases. However, the weak oxidative stability ofα-linolenic acid and the poor fat-solubility of phytosterol have limited their application in food and pharmaceutical industry. These disadvantages could be solved by esterification. In this paper, according to the inadequate reaearch about chemical synthesis process of phytosterol estrs of polyunsaturated fatty acid, such as unclear reaction kinetics, no obvious advantage of edible products and more by-products, the green synthesis techniques of edible phytosterolα-linolenate was studied systematically by response surface methodology, the mathematical model of synthesizing phytosterolα-linolenate using direct-esterification without solvents was set up, the synthesis mechanism and reaction kinetics of phytosterolα-linolenate were discussed. Bassed on the purification and structure identification of phytosterolα-linolenate, the further studies about physiochemical properties and its antioxidant in plant oils were carried out. The main conclusions were obtained as follows:1. Direct-esterification of phytosterolα-linolenate without solventsThrough the catalysts screening, the sodium bisulfate was selected as a high efficient, green chemical catalyst for synthesis of phytosterolα-linolenate. The effect of each parameter of direct-esterification without solvents on the degree of esterification （DE） was investigated systematically by single factor experiment and Box-Benhnken design method. The results showed that the importance sequence of parameters was that: reaction temperature > catalyst amount > reaction time; the regressing model of direct-esterification of phytosterolα-linolenate without solvents was established by SAS analysis: Y=98.473333-1.953750X1+0.508750X2-3.060000X3-1.962917X12-1.857500 X1X2-4.922917X22-1.340000X1X3-3.800000X2X3-4.985417X32, X1=catalyst amount; X2= reaction time; X3= reaction temperature. Combined with the monitoring of peroxide value （POV） and conjugated diene value （CD）, a safety, green and pollution-free synthesis technology was obtained. The concrete conditions are as follows: vacuum 0.030.04Mpa, material molar ratio 3:1, catalyst amount 2%,reaction time 8h, reaction temperature 130℃. Under these conditions, the DE was 87%, the POV and CD value of product were 2.0098 meq/kg and 4.04mmol/kg oil, respectively.2. Reaction kinetics ofα-linolenate without solventsKinetic parameters were determined by studying the concentration of generated phytosterolα-linolenate Cc in the reaction process under different conditions and reaction equilibrium constant under different reaction temperature. A kinetic equation was received, it could give a precise description of the concentration of generated phytosterolα-linolenate changed with reaction time in the reaction process changed with reaction time when the reaction temperatures were 120℃～160℃. Namely, when the molar ratio of phytosterol andα-linolenic acid was 1:3, the amount of sodium bisulfate was 2%, the activation energy Ea was 44.44kJ/mol, the pre exponential factor k0 was 2.65×104 L2·mol-2·h-1, the kinetic rate equation was: r=2.65×104e-44.44/（RT）CACB.3. Purification and analysis of phytosterolα-linolenate The TLC results showed that successful separation of phytosterol,α-linolenic acid and phytosterolα-linolenate was performed by using petroleum ether（60-90）/anhydrous ether/acetic acid （90:10:1,v/v/v）as the developer. The conditions of silica gel column chromatography were as follows: silica gel （from 80～100 mesh） as column packing, petroleum ether（60-90）/anhydrous ether/acetic acid （90:10:1,v/v/v）as eluent, eluent flow rate 1.5mL/min, column temperature 30℃, column packed height 70cm （column 1000mm×30mm i.d）. Under these conditions, the purification recovery and purity of product were above 90% and 97%.The ananlysis result of product by GC, UV, FTIR and NMR showed that there were no carboxylic acid and organic acid, new functional group-ester bond was generated. It is proved the sample from purification was phytosterolα-linolenate.4. Physiochemical properties and antioxidant activity of phytosterolα-linolenateThe phytosterolα-linolenate was light yellow viscous liquid with inherent flavour of phytosterolα-linolenate. Acid value （AV） 2.20mgKOH/goil,POV 0.96meq/kg, the content of trans fatty acid（TFA） was lower than 0.1%, specific gravity 0.93, melting point 6.01℃, viscosity 53.66mm2/s, refractive index 1.5263, crystallization temperature -20.233℃.The physicochemical indexes reached the quality standard of similar products in the market.Take phytosterol as control sample, the antioxidation of phytosterolα-linolenate in plant oils （or simultaneous addition of other antioxidations） were evaluated by Schaal oven test （40℃、80℃） and Rancimat inductive time accelerating oxidation process（110℃）. The results showed that phytosterol and phytosterolα-linolenate both could improve the antioxidation of plant oils. Under the same concentration, the antioxidation of phytosterolα-linolenate was superior to phytosterol in plant oils. There was a dose-effect relationship between the antioxidation and the addition of phytosterol or phytosterolα-linolenate both. Further study showed that the antioxidation of phytosterol and phytosterolα-linolenate both could increased significantly when combined with VE, BHT, TBHQ and 40% tea-polyphenol.
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