Structural characterization, antioxidant activity, and fermentation characteristics of Flammulina velutipes residue polysaccharide degraded by ultrasonic assisted HO-Vc technique.

Adhere to the concept of low-carbon environmental protection and turning waste into treasure, polysaccharides from Flammulina velutipes residue polysaccharide (FVRP) has been developed and possesses diverse bioactivities, comprising antioxidant, hypoglycemic, and relieving heavy metal damage, which still has the disadvantages of high molecular weight and low bioavailability. The current work is the first to prepare a degraded polysaccharide (FVRPV) from FVRP by ultrasonic assisted HO-Vc technique in order to reduce its molecular weight, thereby improving its activity and bioavailability. Our results found that the molecular weight and average particle size were declined, but the monosaccharide composition and characteristic functional group types of FVRPV had no impact. The structural changes of polysaccharides analyzed by XRD, Congo Red test, I-KI, SEM, and methylation analysis indicated that the surface morphology and glycosidic bond composition of FVRPV possessed longer side chains and a greater number of branches with an amorphous crystal structure devoid of a triple helix configuration, and had experienced notable alterations after ultrasonic assisted HO-Vc treatment. Meanwhile, the in vitro antioxidant capacity of FVRPV had significantly increased compared to FVRP, implying ultrasonic assisted HO-Vc technique maybe a effective method to enhance the bioactivity of polysaccharides. In addition, the content of polysaccharide, reducing sugar, and uronic acid in FVRPV was significantly decreased, but antioxidant capacity of fermentation broth was stronger by in vitro human fecal fermentation. The 16S rDNA sequencing data displayed that FVRPV can enrich probiotics and reduce the abundance of pathogenic bacteria through different metabolic pathways mediated by gut microbiota, thereby exerting its potential probiotic effects. The interesting work provides a novel degraded polysaccharide by ultrasonic assisted HO-Vc technique, laying a foundation for developing FVRPV as a new antioxidant and prebiotic.