Study On The Chemical-synthesis And Characteristics Of Phytostanyl Esters Of Fatty Acids

Phytostanyl esters of fatty acids have important and beneficial physiological functions. The enzymic synthesis of phytostanyl esters is expensive and could not be developed into the large industrical scale production, the traditional chemical methods have their own drawbacks such as high reaction temperature and tend to side effect. The objectif of this study is to find out high efficiency catalyst for the synthesis of phytostanyl esters of fatty acids.Sodium dodecyl sulfate and hydrochloric acid as an efficient br(?)nsted acid– surfactant– combined catalyst was applied in the synthesis of phytostanyl esters. The synthesis of phytostanyl laurate was taken as representative for the synthesis of esters of saturated fatty acids, the reactional parameters were: substrate molar ratio 3.17:1, dose of catalyst 4.01% of phytostanols, reaction time 4.1 h and temperature 119℃under N₂, and the degree of esterification was 93.31%. The synthesis of phytostanyl esters of unsaturated fatty acids was investigated using linoleic acid. The optimal conditions were: the molar ratio of linoleic to phytostanols 3:1, dose of catalyst 3%, reaction temperature 150℃, reaction time 5 h under N₂, and the 81.23% of degree of esterification was obtained.Thin-layer chromatography to determine the phytostanol fatty acid esters method was confirmed. Silica gel column was utilized to separated phytostanyl esters. The saturated fatty acid esters were used petroleum ether/ethyl acetate (9:1, v/v) as mobile phase; the unsaturated fatty acid esters were used cyclohexane/anhydrous ether (19:1, v/v) as mobile phase, silica gel (from 100-200 mesh) as column packing, column packed height 75 cm and the sample volume 3 g. The ananlysis results of product by HPLC, FT-IR and MS showed that new functional group-ester bond was generated.The kinetic of the esterification were investigated under different temperature, the reaction appears to be a second-order irreversible reaction. The activitation energy of the reaction of synthesis of phytostanyl laurate was about 27.261 kJ/mol, the reaction rate could be expressed as r=7.54×10⁴ cAcB exp(-27.261/RT); The activitation energy of the reaction of synthesis of phytostanyl linoleate was about 25.744 kJ/mol and the reaction rate could be expressed as r=1.003×10⁴ cAcB exp(-25.744/RT).The solubility of phytostanols and the phytostanyl esters in various solvents were studied, and the curves were plotted, and provided a basis for the separation of phytostanyl esters from the reaction mixture. The crystallization and melting temperature of phytostanyl esters were detected, the results showed that by increasing the alkyl chain length of fatty acids, the crystallization and melting temperature increase, and by the increasing in the number of alkyl double bond, the crystallization and melting temperature reduced.The crystallization characteristics of sunflower oil with different content of phytostanyl lautate and phytostanyl linoleate was evaluated. The results indicated that sunflower oil with less than 5% of phytostanyl laurate would not form crystals at ambient temperature, and the crystallization temperature of sunflower oil were rarely influenced; the sunflower oil with less than 20% of phytostanyl linoleate were similar to that of original oil.The oxidation stability of phytostanyl laurate and phytostanyl linoleate in sunflower oil was evaluated. The result showed that the acid value of the system increased with the increase of phytostanyl esters amount in sunflower oil, but the heating time have no significant impact on acid value. Phytostanyl laurate and phytostanyl linoleate both have a certain effect on the oxidation stability of sunflower oil.