Identification of (12-Ricinoleoylricinoleoyl)diricinoleoylglycerol, an Acylglycerol Containing Four Acyl Chains, in Castor (Ricinus communis L.) Oil by LC-ESI-MS

An acylglycerol (AG) containing four acyl chains, (12-ricinoleoylricinoleoyl)diricinoleoylglycerol (RRRR), was positively identified for the first time in a natural source in castor oil using electrospray ionization tandem mass spectrometry (ESI-MS/MS). HPLC-purified RRRR from castor oil was subjected to ion trap and high-resolution ESI-MS/MS. The precursor and fragment ions of [RRRR + Na]+ showed the expected masses, and the sodiated fragment ions of both diacylglycerols and fatty acids were detected. Because fragment ions of fatty acids from [AG + NH4]+ adducts cannot be detected by ESI-MS/MS, [AG + Na]+ adducts are more informative. Radiolabeled triricinolein (RRR) was incorporated into RRRR in castor microsomes, indicating that RRRR is biosynthesized in castor bean. This newly identified and biosynthesized RRRR represents a new AG subclass of tetra-acylglycerols (or acylacyldiacylglycerol). Keywords: Castor oil; ricinoleate; acylglycerol; tetra-acylglycerol; acylacyldiacylglycerol; biosynthesis; HPLC; Ricinus communis L.