Production of bioactive selenium enriched crude exopolysaccharides via selenourea and sodium selenite bioconversion using Trametes versicolor

Abstract

During a bioconversion to crude exopolysaccharides enriched with selenium from selenourea (SU-cEPS) and sodium selenite (SE-cEPS) in Trametes versicolor submerged culture, high selenium accumulation was achieved. The FTIR analysis detected two major fractions of selenium-cEPS samples: polysaccharides and proteins, indicating their proteoglycan character. Higher carbohydrate (595.98 ± 35.35 mg/g) and β-glucan (31.12 ± 1.76 mg/g) content of SE-cEPS compared to the SU-cEPS was established. Due to the partial dissolution of selenium-cEPS, the antibacterial and antioxidative potential of their soluble fractions (selenium-cEPSsol) were studied. Results indicated that selenium incorporation from different sources into mushroom's exopolysaccharides affected their biological activities. Analysis revealed that all tested Gram-positive and Gram-negative bacterial strains were susceptible to selenium-cEPSsol, with more pronounced microbicidal activity of SE-cEPSsol against Gram-positive bacteria. Although no differences between samples were observed regarding activity on Gram-negative bacteria, selenium incorporation into exopolysaccharides influenced their antibacterial activity against two Escherichia coli species. The HPLC amino acid analysis showed cationic character of selenium-cEPS protein fraction, indicating its potential participation in antimicrobial activities. Selenium-cEPSsol showed significant capacity to reduce the DPPH free radicals and a high ability to chelate Fe2+ ions as a consequence of its ligand characteristic and capability to coordinate with metal ions. Presence of D-rhamnose was confirmed in SE-cEPS, and it has contributed to its higher chelating ability compared to the SU-cEPSsol. The partial dissolution feature of selenium-cEPS samples, as well as established biological activities of the selenium-cEPSsol can be further investigated and applied in the food industry for elimination causatives of the oxidative stress and food-related pathogens.