Targeted peptides for the quantitative evaluation of casein plasminolysis in drinking milk

In addition to proteose peptones (PP), the extent of plasminolysis in different classes of drinking milk during storage has been evaluated by the quantification of the peptides αs2-CN (f1–25) 4P and αs2-CN (f1–21) 4P by UPLC/HR-MS. The rate of increase in the levels of all the studied peptides during storage depended on the heating process. The samples of drinking milk showed different levels of plasminolysis at their expiration dates, as revealed by αs2-CN (f1–25) 4P and αs2-CN (f1–21) 4P amounts. The different treatments applied during the manufacturing of extended shelf life (ESL) milk samples resulted in different levels of plasminolysis, confirming the heterogeneity of this class of drinking milk. The peptides from αs2-CN accumulated faster than PP in all the samples with the exception of UHT milk. Therefore, these peptides can be considered as sensitive indices of early plasminolysis in pasteurised and ESL milk.