The effect of the heat processing of soybean seed on the metabolism of its selenium in lambs

Abstract

The effect of the heat processing on the bioavailability of selenium (Se) in soybean seed containing 324 μg Se/kg dry matter (DM), was investigated by measuring the accumulation of Se in rumen bacteria, bodily tissues and whole blood of sheep fed diets containing differently heat processed soybean. Ground soybean seed was subjected to three heat processing treatments; 130 °C for 45 min (considered the ideal treatment); 150 °C for 30 min (over-processed treatment) and the untreated soybeans as the control (unprocessed). The acid detergent insoluble nitrogen (ADIN) concentrations of 32, 180 and 13 g/kg N in the respective heat treated soybeans were used as indication of relative heat damage inflicted on the protein in the soybeans. Thirty weaned Dohne Merino lambs ( ca. 5 months of age, live weight 23.9 ± 0.9 kg) were randomly allocated to three diets containing 436 g/kg of the differently treated soybean. The diets containing ca. 140 μg Se/kg DM, of which 0.95 originated from the soybeans, were fed for 85 days to the lambs after which they were slaughtered. Rumen bacteria from the unprocessed treatment contained a significantly higher concentration of Se (2918 μg/kg DM) compared to the over-processed treatment (2188 μg/kg DM). The liver, cardiac muscle, wool and whole blood from the ideal treatment contained consistently significantly higher concentrations of Se than either or both of the other two treatments, e.g. the liver contained 1535, 1327 and 1555 μg Se/kg DM in the ideal, control and over-processed treatments, respectively, the cardiac muscle 1616, 1527 and 1480 μg Se/kg DM, respectively, and in whole blood at the end of the trial 336, 278 and 265 μg Se/kg, respectively. It was concluded that the heat processing applied to the organic Se source in this trial affected the bioavailability of the Se, but the heat treatments might not have been sufficiently different to manifest distinct differences in the metabolism of Se in the body.