Detection of non-dairy fat in cheese by gas chromatography of triglycerides

Gas chromatography of triglycerides, as proposed by Precht for detection of foreign fat in milk fat, was used to check different types of cheese. Because lipolysis occurring in cheese ripening causes mono- and diglycerides to appear in the triglyceride peaks in gas chromatography analyses, solid-phase extraction of triglycerides prior to gas chromatography was used. In the case of slight lipolysis, i.e. when fat acidity is below 15 mmol/100 g fat, the relative percentages of the triglycerides inserted in the Precht formula allowed the cheese fat purity to be correctly evaluated. The expected results were obtained both in genuine cheese samples produced under specified industrial conditions and in commercial cheese-based products declared to contain vegetable fat. In the case of more intensive lipolysis, as in piquant Gorgonzola and in Provolone cheese, the Precht formula erroneously indicated the presence of foreign fat, probably due to the decrease in low-molecular weight triglycerides promoted by lipases. In this last case (fat acidity above 15 mmol/100 g fat) a new formula must be developed. Data reported for commercial unlipolyzed samples prove that undeclared foreign fat in processed cheese and in cheese-based products is sometimes present, often in combination with milk powder.