| Phytosterol is a kind of active molecule that is widespread in nature with various important physiological functions such as hypolipidemic,anti-inflammation,anti-cancer,anti-oxidation properties and so on.The special chemical structure of phytosterols leads to their low oil solubility and water insolubility,limiting their applications in foods.The aim of this study was to synthesize phytosteryl lipoate efficiently by enzymatic and chemical methods,which helps produce phytosterol derivatives with ideal physicochemical properties,good safety as well as multi-functions.The physicochemical properties of phytosteryl lipoate and the oxidation stability of soybean oil supplemented with phytosteryl lipoate were also explored.In this paper,phytosteryl lipoate was successfully synthesized using Candida rugosa as the catalyst.By single factor experiments,the optimum conditions for the synthesis of phytosteryl lipoate in enzymatic route were obtained.The maximum conversion of 71.2%could be achieved when the following conditions were employed:150 mmol/L phytosterol,1:2.5 molar ratio of phytosterol to lipoic acid,10 g/L 4?molecular sieves,60 g/L Candida rugosa in 2-methyl-2-butanol/n-hexane?1:1,v/v?,55oC,96 h and 150 r/min.Compared with enzymatic modification,chemical route has the advantages of low cost and high efficiency.Therefore,this paper has further explored the esterification of lipoic acid and phytosterol in chemical route.EDC/DMAP/Et3N composite catalyst was selected as the optimal catalyst for the synthesis of phytosteryl lipoate.The optimum reaction conditions were obtained as follows:75 mmol/L phytosterol,1:2.5 molar ratio of phytosterol to lipoic acid,1:1.6:1.6:2.4molar ratio of lipoic acid to EDC,DMAP and Et3N.Using the method of batch feeding,EDC and Et3N were firstly dissolved in the solvent,then DMAP and lipoic acid were added,and the reaction was stirred for 1 h at room temperature;finally,phytosterol was added to continue the reaction for 23 h.The highest esterification rate could reach 90.9%under the selected conditions.Phytosteryl lipoate was traced by thin-layer chromatography and purified by silica gel column chromatography.The developing solvent and eluent were petroleum ether?60-90oC?/ethyl acetate/formic acid?15/1/0.02,v/v/v?.High performance liquid chromatography was used to determine the esterification rate of the reaction and the purity of the product with 100%methanol solution used as the mobile phase.The purified stigmasteryl lipoate was then structurally identified and characterized by fourier transform infrared spectroscopy,mass spectrometry and nuclear magnetic resonance spectroscopy.The oil solubility,melting and crystallization characteristics,thermal stability,oxidation resistance and bioavailability in vitro of phytosteryl lipoate were investigated.The results showed that the solubility of phytosteryl lipoate were twice higher than that of phytosterol in soybean oil.The melting and crystallization temperature of phytosteryl lipoate were lower than those of phytosterol.The thermal stability of phytosteryl lipoate was greatly improved comparing with lipoic acid.Hence their chemical structure would not be affected during common heat processing.Both phytosterol and phytosteryl lipoate had antioxidant effects,and the ability of the esterified phytosterol to eliminate DPPH·free radicals was stronger.By in vitro digestion experiments,the bioavailability of phytosteryl lipoate was measured as1.2%.Although it might not be well absorbed by the upper gastrointestinal tract,the experimental results also indicated that it would be hydrolyzed into free phytosterols and lipoic acid instead,which could exert their cholesterol-lowering and anti-oxidant functions together.The oxidative stability of soybean oil supplemented with phytosteryl lipoate was studied.The results showed that when 0.2 g/kg phytosteryl lipoate were added in soybean oil,regardless of high temperature or room temperature storage,the oxidation stability of soybean oil were highly improved. |
PDF Full Text Request