Quantitative authenticity testing of buffalo mozzarella via alpha(s1)-Casein using multiple reaction monitoring mass spectrometry

We address the detection and quantitation of bovine milk in 'buffalo' mozzarella cheese using multiple reaction monitoring (MRM) mass spectrometry (MS). Focussing on the abundant protein alpha(s1)-casein, present in both species but with 10 amino acid sequence differences, we extract a list of marker peptides specific to each species. 'Identical' peptides, exactly the same in both species, are used for relative quantitation of alpha(s1)-casein in each milk type, whereas 'similar' peptides, present in both species but differing typically by one amino acid, are used to demonstrate relative quantitation in binary cheese mixtures. In addition, we report a pilot survey of UK supermarket and restaurant products labelled as 'buffalo mozzarella', finding that 2/3 of restaurant meals and supermarket pizzas are either mislabelled or adulterated.