Novel insights into selenium-biofortified P. eryngii polysaccharides: Unveiling selenium release patterns and gut microbiota modulation through in vitro models

Selenium biofortification of P. eryngii was achieved through exogenous selenium supplementation during cultivation, significantly increasing its selenium content. In this study, a Se-enriched polysaccharide (SePEP-1) and a natural polysaccharide (PEP-1) were isolated from P. eryngii. Structural analysis revealed distinct differences between the two. The molecular weight of SePEP-1 (2.39 × 10⁶ Da) was markedly higher than that of PEP-1 (1.85 × 10⁶ Da). Although both SePEP-1 and PEP-1 were composed of glucose, galactose, and mannose, SePEP-1 exhibited a relatively lower proportion of glucose. Characterization by FT-IR, XRD, glycosidic linkage analysis, and AFM confirmed that selenium biofortification markedly altered the structural characteristics of P. eryngii polysaccharides. In vitro digestion experiments demonstrated strong resistance of both polysaccharides to gastrointestinal degradation, with minimal selenium release (<9 %) from SePEP-1. In contrast, during in vitro fermentation, SePEP-1 exhibited a strong capacity for selenium release (>85 %), accompanied by a significant increase in short-chain fatty acids (SCFAs) (p < 0.05). After 48 h of fermentation, SePEP-1 exerted remarkable prebiotic effects, significantly enriching Bacteroides and related taxa while strongly suppressing pathogenic bacteria such as Escherichia/Shigella and Salmonella. By comparison, PEP-1 selectively promoted the growth of certain Firmicutes, highlighting distinct microbial modulation patterns. Collectively, these findings demonstrate that selenium biofortification enhances the nutritional and functional properties of P. eryngii polysaccharides, providing a novel dietary strategy to improve gut health and microbial balance.