Proteomic profiling of 16 cereal grains and the application of targeted proteomics to detect wheat contamination

Global proteomic analysis utilizing SDS-PAGE, Western blotting and LC-MS/MS of total protein and gluten-enriched extracts derived from 16 economically important cereals was undertaken, providing a foundation for the development of MS-based quantitative methodologies that would enable the detection of wheat contamination in foods. The number of proteins identified in each grain correlated with the number of entries in publicly available databases, highlighting the importance of continued advances in genome sequencing to facilitate accurate protein identification. Subsequently, candidate wheat-specific peptide markers were evaluated by multiple-reaction monitoring MS. The selected markers were unique to wheat, yet present in a wide range of wheat varieties that represent up to 80% of the bread wheat genome. The final analytical method was rapid (15 min) and robust (CV < 10%), showed linearity (R(2) > 0.98) spanning over 3 orders of magnitude, and was highly selective and sensitive with detection down to 15 mg/kg in intentionally contaminated soy flour. Furthermore, application of this technology revealed wheat contamination in commercially sourced flours, including rye, millet, oats, sorghum, buckwheat and three varieties of soy.