TRIACYLGLYCEROL COMPOSITION AND STRUCTURE IN GENETICALLY-MODIFIED SUNFLOWER AND SOYBEAN OILS

Changes in composition were examined in oils extracted from geneticall y modified sunflower and soybean seeds. Improvements were made to the analytical methods to accomplish these analyses successfully. Triacylg lycerols (TAG) were separated on two 300 mm x 3.9 mm 4 mu Novapak C18 high-performance liquid chromatography (HPLC) columns and detected wit h a Varex MKIII evaporative light-scattering detector. Peaks were iden tified by coelution with known standards or by determining fatty acid composition of eluted TAG by capillary gas chromatography (CC). Stereo specific analysis (fatty acid position) was accomplished by partially hydrolyzing TAG with ethyl magnesium bromide and immediately derivatiz ing the resulting diacylglycerols (DAG) with (S)-(+)-1-(1-naphthyl)eth yl isocyanate. The derivatized sn-1,2-DAG were completely resolved fro m the sn-2,3-DAG on two 25 mm x 4.6 mm 3 mu silica HPLC columns. The c olumns were chilled to -20 degrees C to obtain baseline resolution of collected peaks. The distribution of fatty acids on each position of t he glycerol backbone was derived from the fatty acid compositions of t he two DAG groups and the unhydrolyzed oil. Results for the sn-2 posit ion were verified by hydrolyzing oils with porcine pancreatic lipase, isolating the resulting sn-2 monoacylglycerols by TLC, and determining the fatty acid compositions by CC. Results demonstrated that alterati ons in the total fatty acid composition of these seed oils are determi ned by the concentration of TAC species that contain at least one of t he modified acyl groups. As expected, no differences were found in TAG with fatty acid quantities unaffected by the specific mutation. In li eu of direct metabolic or enzymatic assay evidence, the authors' posit ional data are nevertheless consistent with TAG biosynthesis in these lines being driven by the mass action of available acyl groups and not by altered specificity of the acyltransferases, the compounds respons ible for incorporating fatty acids into TAG.