Quantification method of osmotin-like proteins in sweet pepper and eggplant by liquid chromatography/tandem mass spectrometry based on the aqua technology

PR5-like protein and osmotin-like protein PR-5 are osmotin-like proteins found in sweet pepper and eggplant, respectively. These belong to the family of 5 pathogenesis-related proteins, which are considered a plentiful source of allergens. Recently, we established an assay to quantify protein NP24, an osmotin-like protein of tomato, using absolute quantification method with a stable isotope-labeled internal standard peptide (GQTWVINAPR[C-13(6),(15) N-4]) and liquid chromatography/tandem mass spectrometry. In this study, the peaks of GQTWVINAPR derived from PR5-like protein and osmotin-like protein PR-5 were detected by multiple reaction monitoring. The results indicated that the assay could be applied for the quantification of these proteins.