Analysis of Molecular Species of Triacylglycerols from Vegetable Oils Containing Fatty Acids with Non-Methylene-Interrupted Double Bonds, by HPLC in the Silver-ion Mode

Abstract

The possibilities for application of silver ion HPLC to analysis of the triacylglycerols containing conjugate trienoic acids and Δ5-polymethylene-interrupted acids and proportions of triacylglycerol fractions obtained by silver-ion HPLC from the seed oil of Momordica charantia double bonds were examined, respectively. The triacylglycerols of seed oils containing conjugate trienoic acids such as α-eleostearic acid (C18 : 3 9c, 11t, 13t) and punicic acid (C18 : 3 9c, 11t, 13c) were resolved by silver-ion HPLC. Fractions were fractionated on the basis of the number and configuration of double bonds in the species, and the elution profile is quite different from that of the species comprising exclusively saturated and unsaturated fatty acids with methylene-interrupted double bonds; for instance, the species (DTc2) composed of one dienoic acid and two conjugate trienoic acids eluted much earlier than the species (D2Tc) composed of two dienoic acids and one conjugate trienoic acid, in spite of having larger number of double bonds. This means that the interaction of conjugate double bonds with silver ions is weaker than that of methylene-interrupted double bonds, presumably because of the delocalization of π-electrons in conjugate double bonds. In this instance, the strength of interaction of a conjugate trienoic double bond system with silver ions seemed to be between that of methylene-interrupted dienoic and monoenoic double bond systems. Triacylglycerols of the seeds of Ginkgo biloba have been resolved by HPLC in the silver-ion mode according to the number and position of double bonds. In this instance, the strength of interaction between the π-electrons of double bonds in the fatty acyl residues and silver ions is in the order; C18 : 3ω3>C20 : 3Δ5, 11, 14C18 : 3Δ5, 9, 12>C18 : 2ω6>C18 : 2Δ5, 9>C18 : 1ω9>C18 : 1ω7.