What is "selenium yeast"

n. A material, produced by fermentation of ''Saccharomyces cerevisiae'' in the presence of selenium, that has selenium atoms incorporated into the amino acid methionine

Selenium yeast, produced by fermenting Saccharomyces cerevisiae in a selenium-rich media, is a recognized source of organic food-form selenium. In this process, virtually all of the selenium structurally substitutes for sulfur in the amino acid methionine thus forming selenomethionine via the same pathways and enzymes that are used to form sulfur-containing methionine. Owing to its similarity to S-containing methionine, selenomethionine is taken up nonspecifically and becomes part of yeast protein. It is this metabolic route that makes selenium yeast valuable in animal and human nutrition, since it offers the same organic form of selenium produced by food-chain autotrophs (i.e., most plants and certain blue-green algae).