Factors affecting selenium-enrichment efficiency, metabolic mechanisms and physiological functions of selenium-enriched lactic acid bacteria

Selenium (Se)-enriched lactic acid bacteria (LAB) are live bacteria preparations that accumulate and bio-transform inorganic Se into organic Se forms including Se-nanoparticles (SeNPs), Se-amino acids and selenoproteins. Se-enriched LAB can play the dual role of organic Se supplement and probiotic effects, and have great applications in the food and biomedical fields. Therefore, more and more attentions have been paid on the Se-enriched LAB. This paper firstly summarized the factors affecting the Se-enrichment efficiency of Se-enriched LAB, then discussed the metabolic mechanisms and physiological functions of Se-enriched LAB, and finally reviewed their applications in food production, in order to provide a guidance for the theoretical and practical implementation of Se-enriched LAB. We concluded that 1) both biomass and the amount of Se enrichment should be used as dual indicators to screen Se-enriched LAB and comprehensively optimize the influencing factors including initial Se concentration, pH, inoculation amount, species of LAB to ensure the Se enrichment efficiency. 2) The metabolic mechanism underlining Se-enriched LAB needs to be further revealed, which will facilitate the production of higher value Se compounds by LAB. 3) The proven physiological functions of Se-enriched LAB include 5 categories: antioxidant activity, antibacterial activity, improving the physical function of animals, detoxification and disease prevention. However, the application of Se-enriched LAB in medical field currently still lacks clinical research, and convincing clinical evidence of effectiveness for Se-enriched LAB on human being must be established. 4) The application in the food field will benefit from the stable existence in the food system of Se-enriched LAB and public acceptance, which come before the various health benefits. In any case, the great potential value of Se-enriched LAB formulations deserves further comprehensive exploration and development.