Structural and rheological properties of polysaccharide from Sida cordata leaves for bio-functional food applications

This study reports the structural, rheological, and bio-functional properties of Sida polysaccharide (SPS) extracted from Sida cordata leaves. SPS was obtained via aqueous extraction and identified as a branched rhamnogalacturonan-I (RG-I) type heteropolysaccharide enriched in rhamnose, galactose, and uronic acids, with a high soluble dietary fibre content (~60 %). Linkage analysis revealed dominant 4-linked galactose (59.6 mol%) and 3,4-linked glucuronic acid (23.9 mol%), consistent with a branched RG-I backbone carrying uronic acid-rich domains. FTIR and NMR confirmed typical polysaccharide functional groups, while HPSEC estimated a molecular weight of ~970 kDa. The mineral composition (notably Ca²⁺ and Mg²⁺) and broad particle size distribution (10-1000 μm) were found to modulate hydration and rheological responses. Functionally, SPS exhibited strong antioxidant activity, maintained cell viability, and inhibited 3 T3-L1 adipocyte differentiation, effects attributed to its uronic acid content, galactan branching, and high molecular weight. Rheological studies demonstrated shear-thinning and pH-responsive weak-gel behaviour, further supported by mineral-mediated cross-linking. When incorporated into vegetable soup, SPS effectively replaced corn starch, enhancing viscosity, mineral content, and storage stability without compromising sensory quality. These findings highlight SPS as a structurally unique, multifunctional hydrocolloid with potential applications in bio-functional food formulations.