The invention relates to a selenium-enriched biomass containing live microorganisms selected from the group consisting of Lactobacillus reuteri, Lactobacillus ferintoshensis, Lactobacillus buchneri/parabuchneri and combinations thereof, a method of preparation of the said selenium-enriched biomass, as well as food preparations, nutraceutical products and food supplements containing the said biomass. Moreover, new strains of lactobacilli are described that are able to concentrate selenium in very high amounts, and are therefore particularly useful for use in the method of the invention.