AOAC GFA Stakeholder Program Meeting Book (March 15, 2023)

ANNEX B Until such time as a reference materials are available, the gluten source for all prepared samples should be commercial, unbleached whole wheat, whole rye, whole barley or whole oat flour. The chosen flour should be analyzed for Dumas or Kjeldahl nitrogen. Convert to percent crude protein by multiplying the nitrogen value by 5.83. Then convert to percent gluten by multiplying the crude protein value by the following factors, depending on the grain: Wheat 0.74 Rye 0.52 Barley 0.78 Oats 0.15 These conversion factors are suggestions, and may vary across different grain samples. The factors come from two publications (1,2); the conversion factors for wheat rye and barley are based on the wet chemistry method described in Wehling and Scherf (2). Method developers may also use the wet chemical method in Wehling and Scherf (2) to arrive at the gluten content for their own wheat, rye and barley flours. Schalk K, Lexhaller B, Koehler P, Scherf KA (2017) Isolation and characterization of gluten protein types from wheat, rye, barley and oats for use as reference materials. PLoS ONE 12(2): e0172819. doi:10.1371/journal.pone.0172819 Wehling, P and Scherf, KA (2020) Preparation of Validation Materials for Estimating Gluten Recovery by ELISA According to SMPR 2017.21. Journal of AOAC International 103(1): 210-215. The data in the reference 1 paper by Schalk et al, may not pertain to this standard as flours in that paper were processed as sieved to 200 um to produce white flours, not whole grain flours as will be used here. The Wehling/Scherf paper (ref #2 here) used unseived whole-grain flours, so the gluten fractions in that paper will be more suitable for this standard.

Note: This change was made in the last round of WG comments – the numbers in this current draft are from the Wehling/Scherf paper.

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