Synergistic enhancement of physicochemical and immunomodulatory properties of Cyclocarya paliurus polysaccharides through co-culture solid-state fermentation with endophytic cellulase-producing fungi.

Cyclocarya paliurus (C. paliurus) polysaccharides (CP) exhibit hypoglycemic, antihypertensive, and antioxidant activities, yet their extraction efficiency and bioactivity are limited by the intact plant cell wall. Microbial fermentation, especially using endophytic fungi, offers a green strategy to degrade cell wall polysaccharides and modify their structure. In this study, two high-cellulase-producing endophytes (PZ8 and PM2) were screened from C. paliurus and used for co-culture solid-state fermentation. The fermentation significantly increased CP yield to 29.16 mg/g, reduced the molecular weight from 374.71 to 362.67 kDa, and increased neutral sugar content by 23.89%. Structural analyses (SEM, FT-IR, monosaccharide composition) revealed that fermentation induced surface lacunae, altered monosaccharide molar ratios (decrease in glucose, increase in galactose, xylose, and mannose), and introduced fucose. Notably, the fermented C. paliurus polysaccharide (FCP) exhibited markedly enhanced DPPH radical scavenging, ABTS radical scavenging, and FRAP reducing capacity compared to non-fermented CP. In RAW 264.7 macrophages, FCP promoted nitric oxide (NO), reactive oxygen species (ROS), phagocytic activity, and TNF-α/IL-6 secretion more potently than CP, indicating superior immunomodulatory effects. Collectively, co-culture solid-state fermentation with endophytic fungi is an effective approach to improve both the yield and functional properties of CP, with potential applications in functional foods and nutraceuticals.