Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 2009
Publication Date: September 16, 2009
Citation: Lin, J.T. 2009. Ratios of regioisomers of triacylglycerols containing dihydroxy fatty acids in castor oil by mass spectrometry. Journal of the American Oil Chemists' Society. 86:1031-1035. Interpretive Summary: Ricinoleate, a monohydroxy fatty acid in castor oil, has many industrial uses. Dihydroxy fatty acids and triacylglycerols containing dihydroxy fatty acids have different physical and chemical properties from those of monohydroxy fatty acids and normal fatty acids, and can be used in industry for different purposes. We have previously identified twelve acylglycerols containing dihydroxy fatty acids in castor oil. The structures of the three dihydroxy fatty acids were also proposed. In this report, the contents of fatty acids at the different locations on the glycerol backbone were determined. The information could help to understand the biosynthesis of acylglycerols containing dihydroxy fatty acids as well as to develop new industrial uses.
Technical Abstract: The triacylglycerols (TAG) containing dihydroxy fatty acids have been recently identified by mass spectrometry in castor oil. These new dihydroxy fatty acids were proposed earlier as 11,12-dihydroxy-9-octadecenoic acid (diOH18:1), 11,12-dihydroxy-9,13-octadecadienoic acid (diOH18:2) and 11,12-dihydroxyoctadecanoic acid (diOH18:0). The ratios of the contents of fatty acids at the sn-2 position of the TAG were estimated by fragment ions from the loss of fatty acids at the sn-2 position as a,ß-unsaturated fatty acids by electro spray ionization-mass spectrometry of the lithium adducts (MS3). The approximate ratios of regiospecific contents of TAG (AAB, with two identical fatty acids) containing dihydroxy fatty acids in castor oil were as follows: diOH18:1-OH18:1-diOH18:1 (92%), diOH18:1-OH18:1-OH18:1 (92%), diOH18:1-diOH18:0-diOH18:1 (91%), diOH18:2-OH18:1-OH18:1 (80%) and diOH18:0-OH18:1-OH18:1 (96%). The ratios of the three different fatty acids at the sn-2 position of TAG (ABC) were estimated as about 73:17:10 (OH18:1 : diOH18:0 : diOH18:1) for diOH18:1-OH18:1-diOH18:0 and about 71:23:6 (OH18:1 : diOH18:2 : diOH18:1) for diOH18:1-OH18:1-diOH18:2. Ricinoleate (OH18:1) was predominately at the sn-2 position of TAG (AAB and ABC) containing dihydroxy fatty acids and the dihydroxy fatty acids were mainly at the sn-1,3 position in castor oil.