Fate of glyphosate in wheat during milling and bread production

Abstract

Background and objectives: Glyphosate is an active ingredient in widely used herbicides; its residues have been observed in grain and grain-based foods. This work investigated the fate of glyphosate and its degradation product aminomethylphosphonic acid (AMPA) in milling fractions of wheat and during the bread making process. Samples of wheat were pearled to obtain successive fractions representing outer kernel layers. Straight grade flour and bread were prepared from the two samples with the highest glyphosate concentration (2.1 and 2.8 mg/kg). Findings: All pearling and milling product fractions, dough, fermented dough, bread crust, and bread crumb were analyzed for glyphosate and AMPA using solvent extraction with derivatization and liquid chromatography–tandem mass spectrometry. Glyphosate was the only residue detected in samples. On average, the pearling experiment demonstrated that 50% of the total glyphosate mass resided in the outer 17% of the kernels. Similarly, 81% of the total glyphosate mass in the wheat was associated with the bran, shorts, and feeds milling fractions. No changes in glyphosate concentration were observed during the preparation of dough, fermented dough, and bread. Conclusions: Milling provides the best opportunity for reducing exposure to glyphosate, as the baking process did not affect glyphosate residues. Concentrations in bread made from straight grade flour will be approximately 4× lower than that made from whole grain flour. Significance and novelty: The use of Canada Western Red Spring from commercial wheat shipments provide realistic glyphosate residue concentrations and also reflect the predominance of this type of wheat used in Canada and elsewhere for bread. Therefore, the outcomes from this study are particularly relevant for estimating consumers’ dietary exposure.