Structure-immunostimulatory activity relationship of enzymatically degraded and partially acid-hydrolyzed Tartary buckwheat sprout pectic polysaccharides
Pectic polysaccharides from Tartary buckwheat sprout (YM) possess potent in vivo immunostimulatory activity; however, their structure-immunostimulatory activity relationship remains poorly understood. To clarify the roles of rhamnogalacturonan-I (RG-I) domains and side chains in its immunostimulatory activity, YM was subjected to pectinase-mediated enzymatic digestion (PMED) and controllable partial acid hydrolysis (CPAH), yielding two derivatives, YME and YMA, with distinct structural features. YME exhibited an elevated RG-I content enriched galactose-side chains and a moderate reduction in molecular mass, whereas YMA was completely depleted of arabinose side chains from RG-I, resulting in a marked increase in unesterified uronic acids and a drastic decrease in molecular mass. Both PMED-modified YME and CPAH-modified YMA displayed superior immunostimulatory activity relative to YM, indicating that this activity is positively associated with unesterified uronic acids and galactose-rich RG-I domains, but inversely correlated with molecular mass and arabinose-side chains. Notably, this enhanced immunostimulatory efficacy may be partially mediated by an enrichment of beneficial bacteria (e.g., Muribaculaceae, Bacteroides, Rikenellaceae_RC9_gut_group), leading to increased short-chain fatty acid production, particularly butyrate, and subsequently enhanced gut barrier function and immune responses. These findings advance the understanding of YM's structure-immunostimulatory activity relationship and highlight the potential of modified pectic polysaccharides as immune-enhancing functional food ingredients.