Effects of Different Degrees of Gelatinization on Structural, Physicochemical and Digestive Properties of Kudzu Starch

Kudzu (Pueraria spp.) starch, valued for its transparency, viscosity, and stability, has broad potential in functional and instant food applications. However, its limited cold-water solubility and inconsistent functional performance across cultivars hinder wider utilization. To improve its processability and nutritional functionality, this study aimed to elucidate how the degree of gelatinization (DG)—a structural indicator of starch transformation—can be precisely controlled and used to modulate starch properties. Starches from two typical kudzu cultivars, K10 (Pueraria thomsonii) and K27 (Pueraria lobata), were subjected to hydrothermal treatment (45–95 °C) to obtain samples with defined DG levels. DG was quantitatively determined by enzymatic assay, differential scanning calorimetry (DSC), and iodine-binding analysis, enabling method cross-validation. Increasing DG enhanced iodine complexation capacity, elevated gelatinization temperatures, and reduced enthalpy change and crystallinity. K27 exhibited more pronounced physicochemical transitions at lower DG than K10, indicating cultivar-specific sensitivity. In vitro digestion revealed that hydrolysis kinetics gradually approached and eventually conformed to a first-order model as DG increased, confirming a DG-dependent shift in digestibility. These results establish DG—rather than processing temperature—as the primary factor governing kudzu starch functionality and provide a methodological basis for designing starch-based foods with tailored glycemic and textural properties.