Triacylglycerol composition and structure in genetically modified sunflower and soybean oils

Changes in composition were examined in oils extracted from genetically modified sunflower and soybean seeds. Improvements were made to the analytical methods to accomplish these analyses successfully. Triacylglycerols (TAG) were separated on two 300 mm × 3.9 mm 4μ Novapak C18 high-performance liquid chromatography (HPLC) columns and detected with a Varex MKIII evaporative light-scattering detector. Peaks were identified by coelution with known standards or by determining fatty acid composition of eluted TAG by capillary gas chromatography (GC). Stereospecific analysis (fatty acid position) was accomplished by partially hydrolyzing TAG with ethyl magnesium bromide and immediately derivatizing the resulting diacylglycerols (DAG) with (S)-(+)-1-(1-naphthyl)ethyl isocyanate. The derivatized sn-1,2-DAG were completely resolved from the sn-2,3-DAG on two 25 mm × 4.6 mm 3 μ silica HPLC columns. The columns were chilled to −20°C to obtain baseline resolution of collected peaks. The distribution of fatty acids on each position of the glycerol backbone was derived from the fatty acid compositions of the two DAG groups and the unhydrolyzed oil. Results for the sn-2 position were verified by hydrolyzing oils with porcine pancreatic lipase, isolating the resulting sn-2 monoacylglycerols by TLC, and determining the fatty acid compositions by GC. Results demonstrated that alterations in the total fatty acid composition of these seed oils are determined by the concentration of TAG species that contain at least one of the modified acyl groups. As expected, no differences were found in TAG with fatty acid quantities unaffected by the specific mutation. In lieu of direct metabolic or enzymatic assay evidence, the authors’ positional 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 responsible for incorporating fatty acids into TAG.