Fraud in milk and dairy products occurs when cow milk is added to sheep and goat milk for economic reasons. No reliable, selective, and sensitive method exists for quantifying the milk percentage of different species. This work reports the development and validation of a proteomics-based method for the qualitative detection and quantitative determination of cow, sheep, and goat milks in the raw materials used for dairy products. β-Lactoglobulin was selected as the protein marker because it is a major protein in milk and whey powder. The tryptic peptides LSFNPTQLEEQCHI and LAFNPTQLEGQCHV were used as signature peptides for cow milk and for sheep and goat milks, respectively. The winged peptides LKALPMHIRLSFNPTQL*EEQCHI* and LKALPMHIRLAFNPTQL*EGQCHV* were designed and synthesized as internal standards. Validation of the method showed that it has good sensitivity, specificity, reproducibility, precision, and accuracy. This method is easily applicable in routine laboratory analysis without intensive proteomics background.

On page 9484 ("Sample Preparation and Tryptic Digestion") and page 9488 ("Optimization of Sample Preparation"), the incorrect reagent was mentioned. In both instances, "indoleacetic acid" should be "iodoacetamide."