A RAPID METHOD FOR DETERMINING THE OXIDATION OF N-3 FATTY-ACIDS

The stability of unsaturated fatty acids to oxidation was monitored by following gas chromatographic (GC) analyses of headspace volatiles in comparison to changes in polyunsaturated fatty acids (PUFA) and increases in malonaldehyde via the 2-thiobarbituric (TBA) assay. Pure standards of linoleic acid (Lo) and n-3 fatty acids [eicosapentaenoic (EPA) and docosahexaenoic acid (DHA)] were added to headspace vials, equilibrated in air for 10 min, followed by heating at 80-degrees-C in teflon-capped vials for different time intervals. Headspace analysis showed increases in acetaldehyde, propenal, and propanal corresponding to the oxidation of n-3 fatty acids, whereas hexanal production corresponded to losses of linoleic acid. The analysis of propanal by GC-headspace after only five minutes of heating appeared to be the most effective method of monitoring the oxidation of n-3 fatty acids, as indicated by correlations between TBA values and loss of PUFA. The oxidation of Lo, EPA and DHA appeared to be a function of the number of double bonds. Correlations between PUFA depletion, TBA values and volatile formation indicate that under the prescribed conditions of this experiment, GC-headspace analysis of propanal and pentane/hexanal is an excellent method for following the oxidation of selected n-3 fatty acids and linoleic acid.