Impacts of Six Methods of Extraction on Physicochemical Properties, Structural Characteristics and Bioactivities of Polysaccharides from Pholiota nameko Residue

By integrating waste valorization with green extraction, in the current study, the impacts of distinct extraction methods on the extraction yield, structural characterization, in vitro antioxidant abilities and in vitro immunomodulatory activity of polysaccharides from Pholiota nameko residue (PNRP) were determined, providing assistance for the resource utilization of Pholiota nameko. Six PNRPs were obtained by hot water extraction, ultrasonic-assisted extraction, acid-assisted extraction, base-assisted extraction, acid–base extraction and hot water–alkaline-assisted extraction, named PNRP-HWE, PNRP-UAE, PNRP-AE, PNRP-BE, PNAP-ABE and PNRP-HAE, respectively. PNRPs were heteropolysaccharides with similar functional groups, abundant branched chains and a triple helix conformation, but varied monosaccharide molar ratios and molecular weights (382.6–601.7 kDa). PNRP-HAE exhibited the highest yield (3.92%) and superior antioxidant activities, including DPPH, ABTS and hydroxyl radical scavenging capacities, attributed to its low molecular weight and high xylose content. Additionally, PNRP-HAE and PNRP-UAE demonstrated potent immunomodulatory effects by enhancing macrophage phagocytosis and cytokine secretion (NO, IL-1β, IL-6, TNF-α). These findings highlight HAE as an optimal method for extracting high-quality PNRPs, offering a sustainable strategy for valorizing mushroom residue in functional foods and nutraceuticals.