Rapid determination of selenium in grain

Abstract

The development of selenium (Se)-enriched foods to reduce cancer risk would require servings to provide amounts of Se that, when added to daily Se intakes from other foods, would raise consumers' plasma Se levels to those associated with reduced cancer risk, e.g., >120 ng/ml (Duffield et al, JNCI 95:1477, 2003). For Americans consuming 85–175 ug Se/d, 50–100 ug added Se/d would meet that target safely. To provide such amounts, foods consumed in servings of 50 g/d (e.g., 2 slices bread) would need to contain 1.8 ug/g. Grains produced on high-Se soils of the Northern Plains offer opportunities, as they can contain 2–10 ug Se/g; however, this advantage is lost by the mixing, in elevators/mills, with grain of lower Se content, as it is currently not practical to sort grains by Se content. We addressed this problem by developing a rapid method to identify Se-rich grains. It involves 4 steps: 1) pulverization in a Teflon ball mill; 2) aqueous slurrification; 3) drying on a polyacrylic disc; 4) measurement of fluorescence in response to low-angle X-irradiation (Bruker Picofox X-ray spectrometer, Madison, WI). With wheat grain, this method can detect Se concentrations ≥0.4 ug/g with 95% confidence and takes <30 min, compared to 1–2 days by other methods. This XRF-based method offers a means of identifying high-Se grains that is sufficiently accurate, robust and efficient for use in handling grains in food processing. Supported by USDA.