STEREOSPECIFIC ANALYSIS OF THE MAJOR TRIACYLGLYCEROL SPECIES CONTAINING GAMMA-LINOLENIC ACID IN EVENING-PRIMROSE OIL AND BORAGE OIL

Evening Primrose oil (EPO) and borage oil (BO) are used frequently in nutritional and clinical studies involving a disease condition with an impaired or inadequate Delta(6)-desaturase enzyme activity. This impa irment may be bypassed by supplementation with gamma-linolenic acid (G LA, 18:3n-6), an intermediate metabolite of linoleic acid (LA, 18:2n-6 ). The major individual triacylglycerol (TG) species comprising all po tential positional isomers (molecular species) from both EPO and BO we re separated, isolated by reversed-phase HPLC and subjected to HPLC st ereospecific analysis as naphthylethyl urethane derivatives. The metho d of analysis is useful since only small quantities of the individual TG species are required and prior experimentally demanding fractionati on steps are eliminated. Over 90% of the important clinical fatty acid , GLA, present in EPO and over 80% of the GLA in BO have been identifi ed and quantified in the molecular species of their respective analyze d TG fractions. Generally, within the individual GLA-containing TG spe cies from both oils, GLA is distributed asymmetrically among the three positions, preferentially at the sn-2 and sn-3 positions, although mo re so for the TG species in BO. The positional isomers of the diacid T G species were determined directly from the stereospecific analysis. F or the triacid TG species computer aided linear regression was used to determine the positional isomers. The predicted positional isomeric d istributions for the individual TG species calculated using the 1-rand om, 2-random, 3-random distribution theory from the stereospecific ana lysis of the native oils were in good agreement with the experimentall y determined values. In contrast to other seed oils the pairs of indiv idual TGs possessing chirality do not exist as racemic mixtures in eit her oil.