SEPARATION AND QUANTIFICATION OF THE TRIACYLGLYCEROLS IN EVENING PRIMROSE AND BORAGE OILS BY REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Evening primrose and borage oil are used frequently in nutritional and clinical studies where an impaired Delta(6)-desaturase enzyme activit y may be bypassed by supplementation with gamma-linolenic acid (GLA, 1 8:3n - 6). The separation and quantification of the triglycerides of b orage oil and evening primrose oil has been carried out using reversed -phase HPLC with UV detection. Borage oil was found to have 34 UV-dete ctable fractions and evening primrose 22. The TG fractions were collec ted manually, their fatty acid composition determined and quantified w ith an internal standard. The probable identity of the individual TG f ractions was deduced using the fatty acid composition of the TG fracti ons, calculated theoretical carbon numbers (TCN) for the various TG sp ecies and the predicted probability of occurrence. Correction factors, U-i, for GLA (18:3n - 6), gadoleic acid (20:1n - 9), erucic acid (22: 1n - 9) and nervonic acid (24:1n - 9) were estimated to be 0.3-0.4, 0. 6, 0.4 and 0.3, respectively, and are used along with other known U-i correction factors for unsaturated fatty acids to calculate TCN values for all the TG species. These U-i values represent the loss in affini ty of the unsaturated fatty acid for the reversed-phase C-18 stationar y phase. The reversed-phase HPLC trace of borage oil is much more comp lex compared to evening primrose oil. Apart from differences in the to tal fatty acid composition there are substantial differences in the qu antity of individual TG species present in the two oils. The clinicall y important fatty acid, gamma-linolenic acid, is distributed much more widely throughout the TG species of borage oil compared to evening pr imrose oil. Over 90% of the GLA present in evening primrose occurs in the first 9 eluting TG species whereas only about 65% is found in thes e TG species of borage oil.