In processed foods it is permitted to partially or completely replace milk fat with cheaper animal or plant fats – provided that these additives are declared. But because this is not allowed in pure milk products, the purity of milk fat in these products is controlled using methods like triglyceride analysis.
The method for determining milk fat purity by gas chromatographic (GC) analysis of triglycerides was developed at the Max Rubner-Institut and initially established as a DIN norm in Germany and an EU reference method at European level. The principle is based on low-resolution GC analysis of the fat extracted from a sample; the results are then fed into triglyceride equations. If the milk fat is pure, the results will only vary within a certain defined range. If they fall outside this range, it is clear that foreign fat has been added.
This procedure for establishing the purity of milk fat is used for various products, including some processed foodstuffs, in the context of controls in the market regulation and customs sectors, but also for production quality control and foodstuff monitoring for consumer protection. Against the backdrop of trade globalisation, this method has since been adopted worldwide as an international standard ISO 17678:2010 / IDF 202:2010.
In order to adjust to modern instrument-based techniques as well as to clarify the areas of application the method is continually updated on the basis of the ISO/IDF standard. It is, however, currently impossible to apply the method to cheese due to potential lipolytic changes in the lipid composition (triglyceride degradation) during ripening. A future addition to the standard is therefore planned which will allow it to be employed for cheese with minimal ripening-related changes by introducing a threshold for free fatty acid content. It will also include an appropriate method for fat extraction and will incorporate information on applying the method to milk fat from certain Asian regions and mountain pastures where different feeding factors can affect the composition in particular ways.