Effects of Extraction Methods on the Structural Characteristics and Bioactivities of <i>Houttuynia cordata</i> Polysaccharides

During the extraction process of Houttuynia cordata polysaccharides (HCPs), different extraction methods significantly influence their structural characteristics, thereby influencing their biological activities. This study compared the structural differences of HCPs prepared by five extraction methods (hot water, ultrasound-assisted, enzymatic, acid, and alkaline extraction) and evaluated in vitro antioxidant and α-glucosidase inhibitory activities of HCPs. An orthogonal partial least squares-discriminant analysis (OPLS-DA) model was applied to analyze the relationship between extraction techniques and structural characteristics of HCPs. The results revealed that distinct extraction methods primarily influenced molecular weight, degree of methylation (DM), and galacturonic acid (GalA) content of HCPs. Ultrasound, enzyme, and alkali treatments all disrupted the GalA structure, increased the molar ratio of neutral sugars, and reduced both molecular weight and DM. Notably, alkali-extracted HCPs exhibited the lowest molar ratio of GalA, the most significant reductions in DM (6.43%) and molecular weight (119 kDa). In contrast, acid extraction preserved relatively high DM (45.08%) and molecular weight (236 kDa). Surface morphology analysis further confirmed that alkali- and ultrasound-treated HCPs exhibited more fragmented structures. Functionally, alkali-extracted HCPs exhibited the highest antioxidant capacity (IC₅₀ = 0.26 mg/mL for DPPH and 0.17 mg/mL for ABTS, FRAP: 0.92 mmol TE/g DW) and α-glucosidase inhibitory activity (IC₅₀ = 0.097 mg/mL). Therefore, alkaline extraction is an efficient strategy for enhancing the functional properties of HCPs. This study elucidates the relationships among extraction methods, polysaccharide structure, and bioactivity, providing valuable guidance for the preparation of HCPs with specific structural and functional characteristics. PRACTICAL APPLICATIONS: This study employed five extraction methods (hot water, ultrasound-assisted, enzymatic, acid, and alkaline extraction) to prepare HCPs, and systematically compared their structural characteristics, in vitro antioxidant activity and α-glucosidase inhibitory activity. The relationship between extraction methods and structure of HCPs was elucidated, providing guidance for the targeted preparation of HCPs with specific structural features and enhanced bioactivity.