A targeted proteomics method for quantifying cartilage in various chicken raw materials

The presence of cartilage in poultry is considered undesirable. Four novel tryptic cartilage marker peptides derived from chicken collagen IIα1 and IXα1 were identified using LC-QToF-MS/MS in a comprehensive identification process and were not detected in tendons and skin. It was shown that the solely qualitative detection of cartilage-derived peptides is not sufficient for the identification of mechanically separated meat (MSM), as these peptides were – albeit in lower concentrations – also detected in meat intended for further processing into meat products (non-MSM). Therefore, a quantitative method (LC-QQQ-MS/MS) based on matrix-matched calibration using chicken fillets spiked with different concentrations of defatted cartilage powder (0.01, 0.05, 0.1, 0.2, or 0.5%) was developed. A satisfactory level of homogeneity of the sample material for routine analysis was achieved by extensively optimizing the sample preparation procedures, including freeze-drying, Soxhlet defatting with petroleum ether, subsequent grinding, and a substantial increase in the sample weight. The multiple reaction monitoring analysis of the cartilage-specific peptide VMQEQLSQLAASLR from collagen IXα1 exhibited the best quantification performance with low relative errors (%RE) below 15% at all cartilage concentration levels. The method developed provides a basis for evaluating the potential discrimination between MSM and non-MSM in commercial chicken raw materials.