Detection of recombinant bovine somatotropin in milk and effect of industrial processes on its stability

A LC–MS/MS method has been developed for the direct detection of recombinant bovine somatotropin (rbST) in milk and dairy products. The sample preparation protocol is based on a solid phase extraction step followed by precipitation with cold methanol and enzymatic digestion. The analysis is focused on the tryptic N-terminal peptide, specific of the recombinant form of the hormone and the detection is performed by LC–ESI(+)-MS/MS. This method has been validated according to the European Union criteria described in the Directive 2002/657/EC. Acceptable performances, with a decision limit (CCα) of 1.24 ng mL−1 and detection capability (CCβ) of 1.92 ng mL−1 were obtained. Calculation of repeatability and intermediate reproducibility of the signal at 100 ng mL−1 lead to relative standard deviations lower than 20%, showing the robustness of the method. Samples subjected to various industrial processes namely, heating, freezing, defatting, pasteurization and spray-drying were then analysed in order to determine the consequences of these treatments on the stability of the hormone. Results showed that temperature related processes, such as pasteurization and spray-drying induce a loss of the hormone up to 95%.