Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 17, 2006
Publication Date: May 10, 2006
Citation: Lin, J.T., Arcinas, A.J., Harden, L.A., Fagerquist, C.K. 2006. Identification of (12-ricinoleoyl-ricinoleoyl)-diricinoleoyl-gylcerol, an acylglycerol containing four acyl chains, in castor by lc-esi-ms. Journal of Agriculture and Food Chemistry. 54(10):3498-3504. Interpretive Summary: Acylglycerols (AG), an acyl lipid class, including the subclasses of triacylglycerols, diacylglycerols and monoacylglycerols, from various natural sources are the most abundant acyl lipid class. Ricinoleate (R), a hydroxy fatty acid (FA), has many industrial uses, such as the manufacture of aviation lubricant, plastics, paints and cosmetics. Ricinoleate occurs as AG in castor oil and about 70% of AG in castor oil is triricinolein (triricinoleoylglycerol, RRR). Glycerol contains three hydroxyl groups, therefore, up to three FA can be directly attached (esterified) to the glycerol to form AG. A fourth FA can be attached to a hydroxyl group on acyl chains. We have positively identified for the first time in a natural source a new AG containing four acyl chains, (12-ricinoleoyl-ricinoleoyl)-diricinoleoyl-glycerol (RRRR), in castor oil using ESI-MS (electrospray ionization-mass spectrometry). AG containing four acyl chains have been previously suggested or tentatively identified. However, this new acyl lipid subclass (acylacyl-diacyl-glycerol or tetraacylglycerols) was not included in the new comprehensive classification system for lipids shown in the May issue of the Journal of Lipid Research. The positive identification of an AG in a new subclass will add the new subclass into the comprehensive classification system for lipids and the new lipids will eventually become useful.
Technical Abstract: We have positively identified for the first time in a natural source a new acylglycerol (AG) containing four acyl chains, (12-ricinoleoyl-ricinoleoyl)-diricinoleoyl-glycerol (RRRR), in castor oil using ESI-MS (electrospray ionization-mass spectrometry). HPLC purified RRRR from castor oil was used for high resolution ESI-MS/MS. The precursor and fragment ions of RRRR showed the exact masses and the fragment ions of sodiated ions of both diacylglycerols and fatty acids were detected. Since in the study of ESI-MS/MS using [M + NH4]' adducts, only fragment ions of diacylglycerol can be detected, therefore, using [M + Na]' adducts is more informative than using [M + NH4]'. Incorporation of radiolabelled triricinolein (RRR) into RRRR in castor microsomal incubation showed that RRRR is biosynthesized in castor bean, and is not formed after harvest, process and/or storage. The newly identified RRRR is in the new subclass of acylacyl-diacyl-glycerol (or tetraacylglycerols) in the lipid class of acylglycerols.