Selenium

The compound determines the grade. Sodium selenite and sodium selenate are sold in food and pharmaceutical grade at assays around 98 to 100 percent, in anhydrous and pentahydrate forms, and separately in feed grade of lower purity. L-selenomethionine is sold at 98 percent and above with the selenium content declared at roughly 40 percent of the molecule, and the enantiomeric purity is a specification in its own right because the racemic material is a different ingredient. Selenium enriched yeast is graded by total selenium, typically 1000 to 2000 mg/kg, and by the proportion of that selenium present as selenomethionine, with a limit on residual inorganic selenium.

Across all forms the commercially important variants are dilutions. Because the nutritional dose is measured in micrograms, the pure salts are rarely used directly; triturations and premixes carried on maltodextrin, dicalcium phosphate or lactose at declared selenium contents of 0.1 to 2 percent are the normal trading form for food and supplement manufacture, along with coated and microencapsulated selenite for feed, where dust control and reduced reactivity matter. Particle size is specified for blend uniformity rather than for solubility.

In the United States sodium selenite, sodium selenate and selenium enriched yeast serve as permitted nutrient sources, and the Food and Drug Administration lists selenium compounds among the nutrient substances that may be added to foods; selenium is a required nutrient in infant formula under the infant formula regulations, and the regulations specify the permitted sources. Selenium yeast and selenomethionine have been the subject of GRAS notifications for defined uses. Use in animal feed is governed by a separate food additive regulation that limits the selenium level in complete feed by species. Supplement grades are made under 21 CFR Part 111.

In the European Union the selenium sources that may be added to foods and to food supplements are set out in the annexes to the fortification regulation and to the food supplements directive, and they include sodium selenate, sodium hydrogen selenite, sodium selenite and selenium enriched yeast; a source not on those lists cannot be used. Selenium compounds are nutrients rather than additives, so they carry no E number. Use in infant formula follows the compositional rules for infant and follow on formula, and use in feed is authorised through the feed additive framework with maximum contents set per species. Codex addresses selenium through the advisory list of nutrient compounds for use in foods for special dietary uses and through the infant formula standard. Because the margin between an adequate and an excessive intake is narrow for this element, both jurisdictions control it through maximum permitted levels in the finished food and feed rather than through the ingredient specification alone.