Ratios of Regioisomers of Minor Acylglycerols Less Polar than Triricinolein in Castor Oil Estimated by Mass Spectrometry

We have recently reported the identification of forty new minor molecular species of acylglycerols containing hydroxy fatty acids less polar than triricinolein by electrospray ionization mass spectrometry of the lithium adducts. The ratios of regioisomers of triacylglycerols (ABC and AAB types) and tetraacylglycerols (AAAB type) identified were estimated by the relative abundances of the fragment ions from the neutral losses of fatty acids as α,β‐unsaturated fatty acids at the sn ‐2 position. The order of the contents of regioisomers of triacylglycerols with the fatty acids at the sn ‐2 position are: nonhydroxy fatty acids > monohydroxy fatty acids > dihydroxy fatty acids > trihydroxy fatty acids. For tetraacylglycerols (AAAB type) such as ricinoleoylricinoleoyl–ricinoleoyl–oleoyl–glycerol (RRRO), ricinoleoylricinoleoyl chain was predominately at the sn ‐2 position, while ricinoleate was not detected at the sn ‐2 position.