Study On The Synthesis And Properties Of D-isoascorbyl Oleate

L-ascorbic acid,also known as Vitamin C(Vc),is a kind of natural antioxidant with extensive sources and high antioxidation capacity.However,its weak hydrophobicity leads to the limited application in oils and fats.In order to increase the hydrophobicity of Vc,it is necessary to make an appropriate modification for the structure of Vc that induces a fatty acid with the hydrophobicity onto the side chain to synthesize the fatty acid ester of L-ascorbic acid.D-isoascorbic acid(IA)is an optical isomer of Vc.Compared with Vc,IA possesses a stronger antioxidant activity and cheaper price.Furthermore,the unsaturated fatty acid is more beneficial to human health than the saturated fatty acid,and the fatty acid ester of ascorbic acid prepared with IA and unsaturated fatty acid as raw materials has a lower melting point and is therefore a more suitable antioxidant used in edible oil.Accordingly,this research selected oleic acid and IA as the raw material to prepare the D-isoascorbyl oleate(IAO),a new oil-soluble antioxidant,mainly consisting of the optimization of synthetic technology condition,structural characterization,and performance assessment.The detailed research contents and results were presented as follows:First,IAO was synthesized via using lipizyme 435 as biocatalyst and oleic acid as acyl donor,and it was quantified and qunlitatived by high performance liquid chromatography(HPLC).The purity of IAO purified by the solvent extraction and column chromatography methods was up to 89.23%.Based on the structural characterization of the product by ESI-MS,FT-IR,1H and 13 C NMR,it was well proved that oleic oil was induced onto the hydroxy at position sn-6 of IA,and the prepared IAO was D-isoascorbic acid-6-oleic acid ester.Second,the effects of different reaction conditions on IAO yield were ascertained by single factor experiment,and the Box-Behnken model between IAO yield and screened factors(reaction time,temperature,and molecular sieve amounts)was developed using JMP software to optimize the reaction conditions for the synthesis of IAO.The results showed that,under the optimal conditions,namely a molar ratio of D-isoascorbyl acid and oleic acid of 1:3,lipase amount of 3%,oleic acid concentration of 0.6 mol/L,reaction temperature of 53.3 °C,molecular sieve amount of 150 g/L,reaction time of 21.3 h,the tested IAO yield was 74.65 ± 1.50%,which was closed to the predicted yield of 78.40%.Finally,the melting points of IAO,L-ascorbyl oleate(AO),and L-ascorbyl palmitate(AP)were determined by DSC.2,2-Diphenyl-1-picrylhydrazyl(DPPH)radical scavenging activity,superoxide radical scavenging activity,and hydroxyl radical scavenging activity were assessed in order to evaluate the antioxidant effect of IAO,also compared with AP,Vc,IA,BHT,TBHQ,and VE of commercial grade.Additionally,these antioxidants were used in rapeseed oil and soybean oil,and the antioxidant effects were analyzed by Rancimat and DSC.The results showed that the melting point of prepared IAO was 28.73 °C,which was lower than that of AO(52.79 °C)and AP(70.44 °C),and IAO had a stronger DPPH· and ·OH scavenging activity than BHT and VE.The antioxidant effect in different vegetable oils ranked as TBHQ>IAO>AP>BHT>VE,in which the antioxidant activity of IAO was slightly lower than TBHQ,but significantly higher than BHT and VE.Therefore,IAO is a promising substitute of artificially synthesized antioxidant used in oil and oil-based food.