Analytical Methods For Triacylglycerols And Oxidized Triacylglycerol Polymers

Triacylglycerols(TAGs),the most abundant compounds contained in nature edible oils,are esters formed by three fatty acids bonded to a glycerol molecule.Because of the different fatty acids in glycerol skeleton and the existing of isomers,the analysis of TAG compositions is a challenging task.The research of analysis method of TAGs is important for monitoring quality and to ensure the safety of edible oil.Oxidized triacylglycerol polymers(TGP),harmful to human health,is a kind of extremely complex advance oxidation products generated in the lipid oxidation process.The total amount of polar group(PC)is an objectively endogenous parameter for characterizing the degree of oil oxidation,as that continues to grow during the process of oil oxidation.PC include oxidized triglycerides oligomers(TGO),oxidized triglycerides dimer(TGD),oxidized triglycerides monomer(ox-TG)and diacylglycerol(DG),free fatty acid(FFA),where TGO and TGD are collectively referred to TGP.The increase of TGP content will have adverse effects on human health.In this article,analytical methods for TAGs and TGP are stuied.First of all,explores the non-aqueous reversed-phase liquid chromatographic analysis of the conditions of the vegetable triglycerides,set up the water reversed phase high performance liquid chromatography-mass spectrometry(NARP-HPLC-MS)analysis method,and 17 kinds of vegetable oil are analyzed.The peak number of vegetable oil chromatogram found in this study is 17 to 22,with the peak number of palmitic acid type vegetable oil for 8 to 10,the peak number of linolenic acid type vegetable oil for 13-22,the peak number of linoleic acid type vegetable oil for 10 to 18,the peak number of oleic acid type vegetable oil for 8 to 11.The number of vegetable triglycerides equivalent carbon number(ECN)is in the range of 36 to 56.The ECN number of palmitic acid type vegetable oil is in the range of 44-50,the ECN number of linolenic acid type vegetable oil is 36-50,the ECN number of linoleic acid type vegetable oil is 38 to 52,the ECN number of oleic acid type vegetable oil is in the range of 44-52 According to the degree of unsaturation,TAGs was divided into different kinds.Palmitic acid type of vegetable oil SSU and SUU triglycerides content is higher,a total of 94.42%;the other 16 kinds of vegetable oil detection are not saturated degree is higher,SUU and UUU triglycerides total content between 88.73 to 99.17%.Set up a silver ion liquid chromatography-mass spectrometry(Ag-HPLC-MS)method,and analysis TAG positional isomers of evening primrose oil,moringa seed oil and grape seed oil.By Ag-HPLC-MS analysis,Moringa seed oil,evening primrose oil and grape seed oil were identified in 9,12 and 7 group TAG isomers.Combined with the result of one-dimensional NARP-HPLC-MS,moringa seed oil were detected in 22 kinds of TAGs and isomers,evening primrose oil were detected in 37 kinds of TAGs and isomers,grape seed oil were detected in 26 kinds of TAGs and its isomers.Then,the analysis methods of TGP were studied.A rapid column chromatographyefficient size exclusion chromatography analysis method of the TGP was established,and the heating products of high purity triolein(OOO)and trilinolein(LLL)were analyzed.Through the analysis of oxidation products of different heating time of OOO and LLL,the content of polar compounds were increased rapidly after the growth rate slowed down.Because of the linoleic acid unsaturated degree is higher than oleic acid,the PC contents of LLL grow faster.The TGO and TGD content of OOO and LLL were low at the beginning of heating,which were below 10%,the content of ox-TG is in 40-50%;with the extension of heating time,the content of TGO increased,where the content of TGD showed a steady increase trend,ox-TG content first rapidly decreased and only moderate after 36 h.The average molecular weights of TGO,TGD,ox-TG and DG were calculated to be 3215,1787,and 605 respectively,by using the standard working curves drawn from different molecular weight polystyrene standard materials.This method is easy to operate and the result is accurate.At last,rapid column chromatography-high size exclusion chromatography-mass spectrometry(PFC-HPSEC-MS)was established for the analysis of TGP.The MS results show that OOO and LLL have a similar oxidation mechanism,and they pass through the heating oxidation produced epoxy hydroperoxides,epoxy epidioxides,and mono-epoxide,respectively.