11
Flame ionisation detection has been optimised for separation of almost all fatty acid derivate 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.
Diagram 1: Comparison of the fatty acid ratios between the ISO and microwave method, respectively, on sausage samples.
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.
Diagram 2: Overview of samples determined by comparing ISO procedure with microwave procedure. Ab- breviations: MP = Milk powder, ISO = ISO procedure, Micro = Microwave procedure.
n-hexane is added, and the vial is turned twice from bottom to top.
The generation of overpressure must be avoided. The glass vial is afterwards filled with saturated sodium chloride solution up to the top. The solvent needs to be transferred with a pipette to a 10 mL GC vial, including sodium sulphate or magnesium sulphate as drying agent (approx. 0.2 g) for possible water residue. This solution is now ready for the analysis of FAMEs using GC-FID.
GC analysis:
For identification and quantification of FAMEs, a 37 Standard-Mix (Supelco) has been used and analysed on GC-2010 Plus AF with FID detector.
The following parameters have been set on the GC:
Injector: SPL (Split 1:100)
Injection volume: 1 µL Injector temperature: 250°C Column type:
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.
FAME WAX
Inner diameter: 0.25 mm Film thickness: 0.25 µm Detector Temperature: 250°C Mobile Phase:
Helium Carrier gas speed: 35 cm / second
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
Comparison of both methods shows 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 gentler 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
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56
