Bioavailability of selenium in the defatted dark muscle of tuna

The content and bioavailability of selenium (Se) in the dark muscle of tuna (DMT) were studied. Fluorometric analysis showed that DMT contained 2.0-4.7 µg g^-1 Se. A large part of Se of the DMT was recovered in the dry powder of the defatted fraction prepared by successive treatment with acetone and n-hexane/ethanol. On trypsin digestion of the defatted DMT, release of Se paralleled that of nitrogen and about 70% of Se was released within 4 h. Male weanling ddY mice were fed a Torula yeast-based Se-deficient diet (basal diet) for 3 weeks, and then fed the basal diet or a diet supplemented with a 0.05-0.25 µg g^-1 Se as either sodium selenite or the defatted DMT for a further 1 week. Se contents and GSHPx activities in the liver increased gradually with increases in the amount of supplemented Se. No differences were observed between selenite and defatted DMT in the effect on Se content. At low Se levels, the effect of Se in the defatted DMT on the liver GSHPx activities was inferior to that of selenite, but at a high Se level, Se in the defatted DMT showed a greater effect. The bioavailability of Se in the defatted DMT, as assessed by slope ratio analysis using selenite as the reference Se, was 87% for the liver Se content and 168% for the GSHPx activity. The results indicate that the defatted DMT contains high levels of Se in a nutritionally available form.