Chromatography 21


The temperature program starts at 130°C with a hold time of one minute. Afterwards, heating continues with a heating rate of 5°C / minute until reaching a temperature of 240°C which then stays constant for 10 minutes. The total time is 33 minutes.


Results and Discussion


The gas chromatographic method with Flame ionisation detection has been optimised for separation of almost all fatty acid derivatised FAMEs.


From 37 fatty acids contained in the standard mix, 36 fatty acids have been identified. Two fatty acids C18:1-cis and C18:1- trans could not be separated, as they co-elute. But this has no influence on the evaluation and differentiation between saturated and unsaturated fatty acids since both co-eluting fatty acids are unsaturated.


Figure 4 shows the chromatogram of a sausage sample with the identified FAMEs which have been generated according to the ISO procedure. Obviously, fatty acids C16:0 und C18:0 are mainly present.


In comparison to the results of the ISO procedure, Figure 5 shows the chromatogram of the same sample using the microwave procedure.


A comparison of the chromatograms (Figure 4 and Figure 5) shows a significant difference in the FAMEs. The results on C18: 1-cis+cis using the microwave procedure are significantly higher in comparison to the ISO procedure.


Table 1 shows that the results of the ISO method have a significant difference in comparison to the microwave method. For a more precise comparison, the peak areas of saturated and unsaturated fatty acids are used and displayed in Diagram 1, showing the difference of the fatty acid ratios between the ISO and the microwave method on sausage samples.


Comparison of both methods show that the result of unsaturated fatty acids with the microwave technique is ten times higher than the ISO method. These elevated results on unsaturated fatty acids could be observed in the same way during determination of other food samples such as milk powder, chocolate and potato chips, as displayed in Diagram 2.


In all of the food samples determined, use of the microwave procedure has generated a higher amount of unsaturated fatty acids. This confirms the hypothesis that the new microwave procedure prevents oxidation of unsaturated fatty acids during the process, and the more gentlegentler treatment results in higher findings when using the new microwave process.


The difference in the total fat concentration of food samples which varies from 19.66% to 37% results in the difference of unsaturated fatty acids as well. The amount of unsaturated fatty acids of potato chips is at the highest level initially when the product is fresh. As soon as the oxidation process has started (after opening the plastic bag) the amount of unsaturated acids is changing.


Diagram 2. Overview of samples determined by comparing ISO procedure with microwave procedure. Abbreviations: MP = Milk powder, ISO = ISO procedure, Micro = Microwave procedure.


Table 1. Identified FAMEs of 2 procedures in direct comparison. Positive findings are marked with X.


Diagram 1. Comparison of the fatty acid ratios between the ISO and microwave method, respectively, on sausage samples.


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