Kernel-based gluten contamination of gluten-free oatmeal complicates gluten assessment as it causes binary-like test outcomes

Gluten-free (GF) foods, whose claim compliance is controlled at the 'serving level', hold better chances of protecting gluten-intolerant consumers. This is particularly true for GF oatmeal, as oats are easily contaminated with gluten-rich kernels of wheat, rye and barley, which remain intact to the spoon as pill-like flakes. A single contaminant kernel in otherwise pure oats results in GF labelling noncompliance, thereby posing a risk to patients with coeliac disease. Our in-market survey of 965 GF oatmeal servings uncovered that one in fifty-seven servings exceeded the GF labelling maximum of 20 mg kg(-1) (i.e. 20 ppm). The noncompliance pattern was 'binary-like', with kernel-based contamination the suspected pass/fail driver. We have highlighted probabilities of misassessment for various sample sizes in light of oat's natural propensity for kernel-based contamination and proposed use of attribute-based sampling for compliance assessment, thereby providing a way to assess/manage/control 'rates of servings containing a contaminant kernel' within acceptable limits with high confidence.