Catcher of the Rye: Detection of Rye, a Gluten-Containing Grain, by LC-MS/MS

Rye, wheat, and barley contain gluten, proteins that trigger immune-mediated inflammation of the small intestine in people with celiac disease (CD). The only treatment for CD is a lifelong gluten-free diet. To be classified as gluten-free by the World Health Organization the gluten content must be below 20 mg/kg, but Australia has a more rigorous standard of no detectable gluten and not made from wheat, barley, rye, or oats. The purpose of this study was to devise an LC-MS/MS method to detect rye in food. An MS-based assay could overcome some of the limitations of immunoassays, wherein antibodies often show cross-reactivity and lack specificity due to the diversity of gluten proteins in commercial food and the homology between rye and wheat gluten isoforms. Comprehensive proteomic analysis of 20 rye cultivars originating from 12 countries enabled the identification of a panel of candidate rye-specific peptide markers. The peptide markers were assessed in 16 cereal and pseudocereal grains, and in 10 breakfast cereals and 7 snack foods. One of two spelt flours assessed was contaminated with rye at a level of 2%, and trace levels of rye were found in a breakfast cereal that should be gluten-free based on its labeled ingredients.