Submitted to: International Symposium on Biocatalysis and Biotechnology: Functional Food and Industrial Products
Publication Type: Proceedings
Publication Acceptance Date: August 15, 2006
Publication Date: November 26, 2006
Citation: Lin, J.T., Arcinas, A.J., Fagerquist, C.K. 2006. Identification of the molecular species of triacylglycerols by hplc and an acylacyl-diacylglycerol (tetraacylglycerol) by using resolution electrospray ionization tadem mass spectrometry in castor oil. International Symposium on Biocatalysis and Biotechnology: Functional Food and Industrial Products. Interpretive Summary: Ricinoleate (R, a hydroxyl fatty acid) has many industrial uses such as the manufacture of aviation lubricant, plastics, paints and cosmetics. Ricinoleate and other fatty acids (FA) occur as acylglycerols(AG) in castor oil and castor oil is the only commercial source of ricinoleate. It is important to know the contents of castor oil for industrial applications and for the development of a transgenic plant that produce ricinoleate. Among the seventeen molecular species of acylglycerols identified in castor oil, we have identified a new subclass of acyl lipid, tetraacylglycerol. Monoacylglycerols, diacylglycerols and triacylglycerols are the three other subclasses of acylglycerols established earlier and acy groups are attached to glycerol backbone directly. The fourth acyl group of tetraacylglycerol is attached to the hydroxyl group on acyl chain.
Technical Abstract: Seventeen molecular species of acylglycerols (AG) in castor oil have been identified and quantified. The quantification of molecular species of AG was based on the percentage peak area in the HPLC chromatogram using ELSD. Triricinolein (triricinoleoylglycerol, RRR) constituted about 71 % of castor oil. The contents of the molecular species of diricinoleoyltriacylglycerol (RR-TAG) were in total about 18% and were in the order of RRO (8.8 %), RRL (6.6 %), RRS (1.1 %), RR-lesqueroleate (0.67 %), RRP (0.47 %) and RRLn (0.15 %). The level of R-TAG was about 0.3%. The level of TAG containing no ricinoleate was less than 0.1%. Diricinoleoylglycerol, a diacylglycerol, was also identified and quantified (0.14%) in castor oil. 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/MS (electrospray ionization-tandem mass spectrometry). HPLC purified RRRR from castor oil was used for ion trap and high resolution ESI-MS/MS. The precursor and fragment ions of [RRRR + Na]+ showed the exact masses, and the sodiated fragment ions of both diacylglycerols and fatty acids were detected. Since in the study of ESI-MS/MS using [AG + NH4]' adducts, fragment ions of fatty acid cannot be detected, using [AG + Na]' adducts are more informative than using [AG + NH4]'. Incorporation of radiolabeled triricinolein (RRR) into RRRR in castor microsomal incubation showed that RRRR is biosynthesized in castor bean. This newly identified and biosynthesized RRRR is in the new subclass of acylacyl-diacyl-glycerol (or tetraacylglycerols) in the lipid class of AG.