Determination of omega-3-fatty acids in supplemented food samples

Different methods for the determination of n3-polyunsaturated fatty acids ( n3-PUFA) in supplemented food samples are presented and compared concerning their applicability to samples containing starch or high amounts of fat. In the presence of starch, a hydrolysis step is necessary because of lipid- starch-complexes, which prevent a complete extraction by classical extracti on methods. The method applying ethanol and sulfuric acid is advantageous c ompared to the method of Weibull-Stoldt concerning ruggedness and repeatabi lity. The analysis of the ethanol-sulfuric acid extracts containing fatty a cid ethyl esters can be performed by gas chromatography (GC) or supercritic al fluid chromatography (SFC) without further derivatization. The recovery of n3-PUFA in supplemented bread by this determination method was about 65% . 30% of the losses originate from adsorption of n3-PUFA on the hydrolyzed bread matrix, from degradation during the sample preparation and from the f act that the unsaturated fatty acid ethyl esters are not completely extract ed from the bread matrix. Minor losses caused by volatility of the ethyl es ters in water vapour and degradation during baking have been observed. They can be estimated to be smaller than 5%. The determination of polyunsaturated fatty acids in food samples with high amounts of fat has to be divided in two cases. If the sample itself contain s polyunsaturated fatty acids bound to e.g. triglycerides and the content o f supplemented fatty acid ethyl esters should be determined, one should use the soxhlet extraction. These extracts contain triglycerides and have to b e determined by SFC. If the whole content of n3-PUFA has to be determined, the method using ethanol and sulfuric acid should be used. Then, the quanti tation can be carried out by GC or SFC. The recovery for the soxhlet-extrac tion is about 100%, for the method applying ethanol and sulfuric acid about 95%.