Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/15/2007
Publication Date: 2/21/2007
Citation: Lin, J.T., Arcinas, A.J. 2007. Regiospecific analysis of diricinoleoylacylglycerols in castor (Ricinus communis L.) oil by electrospray ionization-mass spectrometry. Journal of Agricultural and Food Chemistry. 55: 2209-2216. Interpretive Summary: Ricinoleate, an industrially useful hydroxyl fatty acid occurs abundantly in castor bean, in addition to the toxin, ricin. We have used mass spectrometry to show the location of the non-ricinoleoyl chain on molecules of triglycerides in castor oil. The determination of the location of the non-ricinoleoyl fatty acid on molecules of triglycerides identifies the enzymatic step driving non-ricinoleoyl fatty acid into triglycerides in the biosynthetic pathway of castor oil. The enzymatic step, phospholipase C hydrolysis of phosphatidylcholine, can be the target for blocking the incorporation of non-hydroxyl fatty acids into triacylglycerides to increase the content of ricinoleate in transgenic seed oils.
Technical Abstract: HPLC fractions of diricinoleoyl-acyl-glycerols containing one non-ricinoleoyl chain from castor oil were used to identify the regiospecific location of this non-ricinoleoyl chain on glycerol backbone using electrospray ionization-MS3 of lithium adducts. The regiospecific ions used were from the loss of unsaturated fatty acid specific at sn-2 position. The content of 1,3-diricinoleoyl-2-oleoyl-sn-glycerols (ROR) in the three stereospecific isomers, RRO, ROR and ORR, combined is about 88%. The contents of other 1,3-diricinoleoyl-2-acyl-glycerols in the three stereospecific isomers combined are as follows: 1,3-diricinoleoyl-2-linoleoyl-sn-glycerol, 95%; 1,3-diricinoleoyl-2-linolenoyl-sn-glycerol, 96%; 1,3-diricinoleoyl-2-stearoyl-sn-glycerol, 100%; 1,3-diricinoleoyl-2-palmitoyl-sn-glycerol, 78%; and 1,3-diricinoleoyl-2-lesqueroloyl-sn-glycerol, 31%. These non-hydroxyl fatty acids are mostly at sn-2 position of triacylglycerols in castor oil. On the biosynthetic pathway of castor oil, the phospholipase A2 hydrolysis of phosphatidylcholine (PC) containing non-hydroxyl fatty acid at sn-2 position is either blocked or partially blocked in vivo. 1,3-Diricinoleoyl-2-lesqueroloyl-glycerol is about one third of the three isomers combined. 2-Lesqueroloyl-PC can be hydrolyzed by castor phospholipase A2 as well as 2-ricinoleoyl-PC. Phospholipase C hydrolysis of PC can be the target to block the incorporation of non-hydroxyl fatty acids into triacylglycerols to increase the content of ricinoleate in transgenic seed oils.