The influence of heat treatment of soybeans on the bio-availability of its selenium in lambs

Abstract

The aim of the present study was to investigate the bioavailability of selenium (Se) from milled soya beans, a plant protein, to lambs after various degrees of heat treatment. Thirty Dohne Merino lambs (ca. 25 kg live weight, 4 months old) were allocated randomly within sex and weight groups into three treatment groups. During the experimental period, they were fed a diet consisting of a large proportion of milled soya beans as their main source of Se and other feeds low in Se to balance the diet. Blood was drawn during this period and analysed for Se and glutathione peroxidase (GSH-Px) activity. Chemical and Se analyses were performed on the feed and soya bean samples as well as on the organs, wool and rumen fluid of the lambs. Although the ADIN concentration of the soya beans increased with increasing heat treatments, more heat damage could have been inflicted on it to differentiate the different soya bean fractions in comparison to each other. On average, the in sacco disappearance of the dry matter (DM), crude protein (CP) and Se was higher for the unprocessed soya beans compared to the two processed soya beans fractions. As a result, the lambs receiving the unprocessed soya beans (control group- C-group) had a significant higher rumen bacterial Se concentration than the lambs receiving the heat¬treated soya beans. Despite this higher concentration, the liver Se concentration of this group was statistically significantly lower compared to the two heat-treated groups. This can be interpreted that the heat processing of the soya beans enhanced its Se fraction to be taken up by the liver. However, those differences were biologically not significant. The average liver Se concentration between the lambs receiving the over- ¬processed- (a-group) and those receiving the ideal treated soya beans (I-group), did not differ, indicating that the excessive heat treatment did not influence the amount of Se reaching the lower digestive tract of the a-group. Although the Se concentration of the heart muscle of the a-group was statistically significantly lower than for the I-and C-groups, those differences biologically were not significant. Despite an increase in the erythrocyte GSH-Px activity over the duration of the trial in all three the treatment groups, no significant differences between the three treatment groups were observed at any stage. It is concluded from this study that the heat treatment of soya beans has not influenced the incorporation and the bioavailability of its Se fraction to any significant degree.