The Effect of Selenium Supplementation on Amino Acid Accumulation by the Yeast Saccharomyces cerevisiae and Rhodotorula glutinis

Selenium-enriched yeast is considered the most bioavailable dietary form of this trace element. It is already authorised for use in food and feed, making it a key vehicle for closing nutritional Se gaps worldwide. Understanding how selenium accumulation reshapes the amino-acid balance of yeast biomass is crucial for diet-related health benefits and optimising biotechnological processes that rely on high-quality microbial protein. The effect of selenium on yeast amino-acid metabolism is an important area of research due to its potential applications in biotechnology and functional food production. In the presented work, changes in the amino acid profile and protein quality in <i>Saccharomyces cerevisiae</i> ATCC 7090 and <i>Rhodotorula glutinis</i> CCY 20-2-26 cells grown in the presence of different selenium concentrations (0-40 mg Se⁴⁺/L) for 24 and 48 h were analyzed. The amino acid content was assessed, and the Chemical Score (CS) and adjusted Essential Amino Acid Index (EAAI) were determined. The results showed that moderate selenium concentrations (2-10 mg Se⁴⁺/L after 24 h) promoted the accumulation of essential amino acids, such as lysine (53.3 mg/g) and valine (38.0 mg/g) in <i>S. cerevisiae</i> and lysine (42.8 mg/g) and valine (41.6 mg/g) in <i>R. glutinis</i>. High values of protein quality indices were also obtained under the same conditions-CS exceeding 200% and adjusted EAAI reaching 1.71 for <i>S. cerevisiae</i> and 2.05 for <i>R. glutinis</i>. It is worth noting, however, that EAAI was presented without methionine and tryptophan. In turn, higher selenium concentrations and longer cultivation time decreased these parameters, especially in the case of <i>S. cerevisiae</i>. The obtained data confirm that <i>R. glutinis</i> may be a promising source of high-quality protein in selenium-enriched products.