title: Selenium bioavailability from soy protein isolate and tofu in rats fed a torula yeast-based diet.
abstract: Selenium (Se) is an essential nutrient, and soy is a major plant source of dietary protein to humans. The United States produces one-third of the world's soybeans, and the Se-rich Northern Plains produce a large share of the nation's soybeans. The present study used a rat model to determine the bioavailability of Se from a protein isolate and tofu (bean curd) prepared from a soybean cultivar we recently developed specifically for food grade markets. The soybean seeds contained 2.91 mg Se/kg. Male Sprague-Dawley rats were depleted of Se by feeding them a 30% Torula yeast-based diet containing 5 microg Se/kg; after 56 days, they were replenished of Se for an additional 50 days by feeding them the same diet supplemented with 20, 30, or 40 microg 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 responses of Se-dependent enzyme activities and tissue Se contents, comparing those responses for each soy product to those for SeMet using a slope-ratio method. Dietary supplementation with the protein isolate or tofu resulted in dose-dependent increases in glutathione peroxidase activities in blood and liver and thioredoxin reductase activity in liver, as well as dose-dependent increases in the Se contents of plasma, liver, muscle, and kidneys. These responses indicated an overall bioavailability of approximately 97% for Se from both the protein isolate and tofu, relative to SeMet. These results demonstrate that Se from this soybean cultivar is highly bioavailable in this model and that high-Se soybeans can be good dietary sources of Se.
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center, Grand Forks, North Dakota 58202, USA. lin.yan@ars.usda.gov
authors.forename: Lin
authors.initials: L
authors.lastname: Yan
authors.forename: George L
authors.initials: GL
authors.lastname: Graef
authors.forename: Philip G
authors.initials: PG
authors.lastname: Reeves
authors.forename: LuAnn K
authors.initials: LK
authors.lastname: Johnson
mesh_terms: D000818:Animals; D001682:Biological Availability; D002175:Candida / Q000737:chemistry / Q000378:metabolism; D004032:Diet; D004044:Dietary Proteins / Q000378:metabolism; D005979:Glutathione Peroxidase / Q000097:blood / Q000378:metabolism; D008099:Liver / Q000201:enzymology; D008297:Male; D009928:Organ Specificity; D051381:Rats; D012643:Selenium / Q000032:analysis / Q000097:blood / Q000172:deficiency / Q000493:pharmacokinetics*; D045730:Soy Foods / Q000032:analysis; D030262:Soybean Proteins / Q000008:administration & dosage* / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D004044:Dietary Proteins; D030262:Soybean Proteins; D005979:Glutathione Peroxidase; D012643:Selenium