12 May / June 2016 Table 1: Identified FAMEs of 2 procedures in direct comparison. Positive findings are marked with X.
The focus of this comparison is on the ratio between saturated and unsaturated fatty acids (milk powder, chocolate, sausage, chips). The results show that the ratio of fatty acids differs between ISO and microwave procedure. The proportion of unsaturated fatty acids is always higher when the microwave procedure is applied.
The higher rate of findings of unsaturated fatty acids confirms the sensitivity of the unsaturated fatty acids related to the oxidation by air and heat influence.
The DIN procedure is an open system and requires heat over a long period of time which has an influence on the unsaturated fatty acids (oxidation). The microwave system is a closed system with a significant shorter heat application and reduced oxidation of unsaturated fatty acids. The microwave procedure is therefore a gentler and preferable method as far as unsaturated fatty acids are concerned.
References
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.
Conclusion
The declaration of food samples is increasingly more complex. For consumers, the declaration is very important and therefore needs a certain transparency. The EU regulation 1169/ 2011 demands a detailed declaration of food samples. Most important is the differentiation of total fat in saturated and unsaturated fatty acids, which is the top criteria for the consumer to differentiate between healthy and unhealthy food, as has been the subject of two studies. The determination of total fat content as well as unsaturated and saturated fatty acids is regulated in ISO norms.
In this work, two methods have been developed. The first method represents a procedure for digestion and extraction of the total fat content in a closed microwave system, based on a method of Weibull-
Stoldt. Food samples from different areas (dairy products, luxury foods, meat and pastries) have been selected, and the application of the total fat determination using the microwave method in a closed system has been evaluated. It has been found to be a universal method for the determination of the total fat content in different food areas.
The second method corresponds to a microwave method, also in a closed system for derivatisation of fatty acid in FAMEs which are then analysed in a GC-FID system. The use of the developed microwave extraction method shows that the method is best suited for determination of the total fat content of food samples.
In the second method, food samples have been analysed for 37 different fatty acid methyl esters. This enables a comparison between the DIN method for digestion and extraction of the total fat content of a food sample with an ISO method for derivatisation of extracted fatty acids in FAMEs, with the developed microwave procedure consisting of microwave extraction method (MEM) and microwave derivatisation method (MDM).
1. Verordnung (EU) Nr. 1169/2011 des Europäischen Parlaments und des Rates vom 25. Oktober 2011 betreffend die Information der Verbraucher über Lebensmittel und zur Änderung der Verordnungen (EG) Nr. 1924/2006 und (EG) Nr. 1925/2006 des Europäischen Parlaments. at <http://
eur-lex.europa.eu/LexUriServ/LexUriServ. do?uri=OJ:L:2011:304:0018:0063:de:PDF>
2. LFGB. Bestimmung des Gesamtfettgehalts in Fleisch und Fleischerzeugnissen-Gravimetrisches Verfahren nach Weibull-Stoldt. 3 (2014).
3. Matissek, R., Steiner, G. & Fischer, M. Lebensmittelanalytik. (2010). doi:10.1007/978-3-540-92205-6
4. Norm, D. Gaschromatographie von Fettsäuremethylestern Teil2: Herstellung von Fettsäuremethylestern. 25 (Perinorm, 2011).
5. Reaktionsmechanismus_Veresterung. gif (GIF-Grafik, 600 x 184 Pixel). at http://
www.mn-net.com/Portals/4/images/ Redakteure_Chroma/GC/Biodiesel-
Reaktion-DE600.gif
6.
Veresterung_FAMES.jpg (JPEG- Grafik, 801 × 647 Pixel). at http://www.
mobilohnefossil.de/images/user/ Biodiesel-Veresterung.jpg
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