Study On Characteristics Of Triacylglycerols In Edible Oils By Using HPLC

Triacylglycerols(TAGs) are the main components in oils which the content is up to 95%. If it had n kinds of FAs, it may be composed of n3 kinds of TAGs, except for enantiomers, it also had(n3+n2)/2 kinds of TAGs. Compared to FAs, it is more complicated and hard to analyze. The study and exploration of the distribution of TAGs has always been the direction of the efforts of the oil chemists. In this study, we analyzed TAGs and regioisomers by different chromatographic methods, in order to provide more information and basis of TAGs for further study on edible oils.Firstly, FAs on sn-1,2,3 in 44 kinds of edible oils were analyzed by pancreatic lipase hydrolysis combined with GC. Results revealed that, except for tropical woody plant oil(coconut, palm kernel and palm oils etc.), in vegetable oils, PUFAs were more easily connected on sn-2 of glycerol skelton, while SFAs were more easily connected on the sn-1(3), MUFAs were equally distributed on glycerol skelton; In animal oils, SFAs were more easily connected on sn-2 of glycerol skelton, while MUFAs and PUFAs were more easily connected on the sn-1(3). Compared with the FAs composition, this method can provided more information of FAs distribution on the glycerol skelton, but it could not reflect the distribution of TAGs directly.Secondly, non-aqueous reversed phase high performance liquid chromatography(NARP-HPLC) had been used to analyze TAG profiles distribution in 44 edible oils. In these oils, 5-20 peaks were shown on the chromatograms, and equivlant carbon numbers(ECNs) were from 30 to 52. Oils abundant in lauric acid had 17-20 peaks, and ECNs were from 30 to 48; oils abundant in palmtic aicd had 8-10 peaks and and ECNs were from 44 to 50; Oils abundanr in oleic acid had 7-11 peaks, ECNs were from 42 to 50; Oils abundant in oleic and linoleic aicd had 5-15 peaks, ECNs were from 38-50; Oils abundant in linolenic acid had 15-19 peaks, ECNs were from 36-48. This method can directly provide TAG distribution, but it had fewer TAGs compared to the theoretical, which indicating that single chromatographic peaks on the chromatogram may not represent one TAG, it may contain two or more TAGs, LC-MS also had proved this point. Results showed that, oils abundant in lauric acid(coconut oil and palm kernel oil) may be expressed as “SSS”; oils abundant in palmtic acid(palm oil, palm stearin etc.) can be expressed as “SSU” and “SUU”; other vegetable oils abundant in oleic, linoleic and linolenic acids can be expressed as “UUU”, which contained large amounts of OOO, OOL, OLL, LLL, Ln LL, Ln Ln L etc.Finally, by adjusting the type and proportion of mobile phases, the separation effect of TAG regioisomers on Ag+-HPLC was improved. Off-line two-dimensional LC was adopted to analyze TAGs and its regioisomers in oils, which selected NARP-HPLC in combination with Ag+-HPLC. Taking evening primrose and pine nut oils as examples, different components of evening primrose(8 fractions) and pine nut(13 fractions) oils were prepared, and then, all these components were further analyzed by Ag+-HPLC, 15 and 22 TAGs and regioisomers were obtained and identified by MS/MS, which were Ln Ln L, Ln LL, PLLn, OLL and their regioisomers and Ln Ln L, OLLn, PLLn, OLL, OOLn, PLL, OOL, SLL and their regioisomers, respectively. Compared to FAs distribution on sn-1,2,3 and TAG profiles distribution, off-line two-dimensional LC can get more TAG structural information.