Gelatin Quantification by Oxygen-18 Labeling and Liquid Chromatography–High-Resolution Mass Spectrometry

Combined with high-performance liquid chromatography (HPLC) and linear-ion trap/Orbitrap high-resolution mass spectrometry, trypsin-catalyzed 16O-to-18O exchange was used to establish an accurate quantitative method for bovine or porcine gelatin. The sophisticated modifications for these two mammalian gelatins were unambiguously identified by accurate mass and tandem mass spectrometry. Eighteen marker peptides were successfully identified for the bovine and porcine gelatin, respectively. The gelatins were subjected to 18O or 16O labeling in the presence of trypsin and mixed together in various ratios for quantification. All of the 18O-labeled peptides were also confirmed by accurate mass and tandem mass spectrometry. The 10 marker peptides with the strongest signals were chosen to calculate the average ratios of 18O-labeled and 16O-labeled gelatin. The measured ratios of 18O-labeled and 16O-labeled peptides were very close to the mixing ratios of 20:1, 5:1, 1:1, and 1:5 with low standard deviation values....