|Johnson, Luann -|
Submitted to: Journal of Trace Elements in Medicine and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 15, 2010
Publication Date: October 15, 2010
Citation: Yan, L., Reeves, P.G., Johnson, L.K. 2010. Assessment of selenium bioavailablity from naturally produced high-selenium soy foods in selenium-deficient rats. Journal of Trace Elements in Medicine and Biology. 24:223-229. Interpretive Summary: The United States produces one third of world’s soybeans, and the selenium-rich Northern Plains produce a large share of the nation’s soybeans. The present study examined the bioavailability of selenium from protein isolate and tofu (bean curd) prepared from naturally produced high-protein soybeans produced in Northern Plains. We produced low-selenium status in rats by feeding them a Torula yeast-based diet, which was very low in selenium for sufficient time, and then replenished of selenium by supplementing selenium from soy protein or tofu at 20, 30 or 40 µg selenium/kg to their diets. The selenium bioavailability was determined on the ability of selenium from protein isolate and tofu to restore selenium-dependent enzyme activities and tissue selenium contents in these rats. Selenomethionine, a selenium-containing amino acid commonly from plant foods, was used as a reference. Dietary supplementation with protein isolate or tofu resulted in dose-dependent increases in selenium-containing enzyme activities in blood and liver and selenium contents of plasma, liver, muscle and kidneys. These responses indicated an overall bioavailability of approximately 101% for selenium from soy protein isolate and 94% from tofu, relative to selenomethionine. These results demonstrate that selenium from naturally produced high-selenium soybeans is highly bioavailable in this model and that high-selenium soybeans can be a good dietary source of selenium.
Technical Abstract: We assessed the bioavailability of selenium (Se) from protein isolate and tofu (bean curd) prepared from naturally produced high-Se soybeans in a Se-deficient rat model. The Se content of soybean seeds, protein isolate and tofu was 5.17 ± 0.22, 11.44 ± 0.09 and 7.37 ± 0.12 mg/kg, respectively. Male weanling Sprague-Dawley rats were depleted of Se by feeding them a 30% Torula yeast-based diet (4.05 µg Se/kg) for 56 days, and then they were replenished of Se for an additional 50 days by feeding them the same diet supplemented with 20, 30 or 40 µg Se/kg from soy protein isolate or tofu. L-selenomethionine (SeMet) was used as a reference. Selenium bioavailability was determined on the basis of the restoration of Se-dependent enzyme activities and tissue Se contents in Se-depleted rats, comparing those responses for soy protein isolate and tofu to those for SeMet using a slope-ratio method. Dietary supplementation with protein isolate or tofu resulted in linear, dose-dependent increases in glutathione peroxidase activities in blood and liver and in thioredoxin reductase activity in liver. Furthermore, they resulted in linear, dose-dependent increases in Se contents of plasma, liver, muscle and kidneys. These results indicated an overall bioavailability of approximately 101% for Se from protein isolate and 94% from tofu, relative to SeMet. We conclude that Se from naturally produced high-Se soybeans is highly bioavailable in this model and that high-Se soybeans can be a good dietary source of Se.