SELENIUM IN SOYBEANS: BIOAVAILABILITY AND FORM (MINERAL, ABSORPTION)

APRIL CAROL MASON, Purdue University

Abstract

Soybean protein is being used in the formulation of specialized restricted diets such as infant formula and total parenteral diets. This protein source is low in selenium and the availability of selenium from soy is not completely understood. The experiments presented here evaluate the bioavailability of different forms of selenium from intrinsically and extrinsically labeled isolated soy protein and soy flour, compare the bioavailability of selenium from soy and egg and describe some characteristics of selenium as it exists in soybeans. The metabolism of selenium was measured by whole-body and tissue radioactivity retention and selenium excretion. Selenium-75 was well absorbed from an isolated soy protein diet by rats. Selenium-75 from isolated soy protein labeled intrinsically and extrinsically with ('75)Se selenate was better absorbed than from protein labeled extrinsically with ('75)Se selenite or ('75)Se selenomethionine. Bioavailability of selenium from soy flour and egg was measured by whole-body and tissue radioactivity retention and glutathione peroxidase (GSH-Px) activity regeneration. Selenium from a soy flour diet was not as available for absorption by the rat as selenium from an egg diet. Selenium from a mixed soy flour-egg protein diet was available at an intermediate level between that of egg or soy alone. Selenium-75 from soy flour intrinsically labeled with selenite was better absorbed than ('75)Se from flour intrinsically labeled with selenate. GSH-Px levels in the liver, kidney, platelets and heart fell when rats were fed a selenium deficient diet, but were not significantly raised on 0.0825 ppm Se repletion diets. The greatest amount of ('75)Se in hydroponically grown whole soybeans was extracted in aqueous buffer and was associated with proteins of high molecular weight (greater than 100,000 molecular weight). Soybeans labeled with selenite contain more trichloroacetic acid precipitable and nondialyzable ('75)Se than do soybeans labeled with selenate. Therefore, differences in deposition of selenium in the soybean depend on the form of the mineral available to the plant during growth but not on the concentration of available selenium.

Degree

Ph.D.

Subject Area

Nutrition

COinS