Abstract
Casein can legally be substituted with cheaper leguminous proteins in processed foods, such as imitation cheese, as long as the ingredients are declared. The detection of illegal admixtures of leguminous protein requires analytical procedures to identify an undisclosed adulteration of milk products. To investigate the suitability of stable isotope analyses as an alternative to more sophisticated methods, variations in d15N of soya (n = 27) and peanut (n = 10) protein, as well as casein (n = 14) were determined. Significant differences were established between d15N of casein (4.45 – 6.94‰) and soya (0.25 – 2.37‰) as well as peanut (0.70 – 2.13‰) protein. An average limit of detection for leguminous protein in casein was determined to be 2.1%, provided both components were available for additional analyses. Under practical conditions of food control, i.e., without having access to the actual ingredients, the variability of d15N resulted in an average limit of detection of 26.4%. Because protein d15N can be determined rapidly in crude food samples without elaborate sample preparation, stable isotope analysis can be used as a rapid screening method to determine the presence of higher amounts of leguminous protein in cheese and, in particular, to easily distinguish imitation cheese from cheese.
Highlights
Wide areas of food production are dominated by economic forces towards the aim of optimizing profits
This study investigated the suitability and sensitivity of isotope ratio mass spectrometry (IRMS) for determining the authenticity of cheese by focussing on nitrogen isotopes and its variation in proteins of different origin
A validated procedure for stable isotope analysis in cheese is based on the preliminary isolation of the protein fraction, i.e. of casein (Camin et al, 2015)
Summary
Wide areas of food production are dominated by economic forces towards the aim of optimizing profits. The substitution of ingredients with cheaper components or the use of surrogates can be a logical consequence. Processed food items such as baked goods, pizza or other instant meals have frequently been shown to contain imitation cheese. The milk fat and/or casein in imitation cheese are replaced by vegetable fats or proteins. A common substitute for milk fat is palm oil, whereas casein can be replaced by soya or peanut protein. According to EU regulation 1234/2007 (EU, 2007), cheese is a product that is made exclusively from milk, with the exception of agents required for production, and a product in which the dairy ingredients have been neither fully nor partially replaced. Imitation cheese products marketed under the term “cheese” must be rejected, which requires suitable detection methods in food control
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