Influence of Different Selenium Biofortification Methods on Structural Features and Antioxidant Bioactivities of Pleurotus geesteranus Polysaccharides

Selenium (Se) biofortification is considered an effective approach to enhance the nutritional and functional properties of fungal polysaccharides. In this study, Pleurotus geesteranus was biofortified with different Se sources including sodium selenite [Se(IV)], sodium selenate [Se(VI)], potassium 2-selenocyanatoacetate (PSeCA), and selenium ore powder (SeOP) to obtain Se-enriched polysaccharides by ultrasound-assisted extraction (UAE). UAE parameters were optimized via a Box–Behnken design; the optimized UAE model exhibited high predictability (R2 = 0.9886, CV = 1.71%), enabling reliable scale-up for industrial extraction, with the PSeCA group achieving the highest polysaccharide content (75.12 mg/g) and Se level (13.85 mg/kg) compared to the control and other Se-fortified groups. The monosaccharide composition analysis on polysaccharides revealed that Se(IV) and Se(VI) primarily increased mannose and fructose contents, whereas PSeCA and SeOP exhibited characteristic glucose-dominant profiles. Furthermore, the molecular weight (Mw) distribution of fungal polysaccharides could be altered under biofortification conditions. In addition, polysaccharides of each group revealed different antioxidant bioactivities among tested free radicals. The result indicated that PSeCA as an organic Se source, rarely studied, has promising potential in P. geesteranus biofortification for obtaining antioxidant Se-polysaccharides.