Structural and Rheological Properties of Modified Water Yam Starch Through Partial Hydrolysis and Retrogradation for Enhanced Functional Applications

Water yam starch, distinguished by its high amylose content and small granule size, presents significant potential for diverse industrial applications through targeted structural modifications. This study systematically examined the combined effects of partial acid hydrolysis and retrogradation on the structural and rheological properties of water yam starch to enhance its functional utility. Acid hydrolysis resulted in a reduction of starch chain length, as indicated by increased reducing power, while subsequent retrogradation facilitated molecular re-association, leading to an increase in relative crystallinity. X-ray diffraction analysis confirmed these structural transformations, revealing diminished peak intensities in hydrolyzed starch and enhanced crystallinity in retrograded samples. Rheological assessments demonstrated substantial alterations in pasting behavior due to these modifications. Hydrolysis lowered pasting and peak temperatures while increasing peak and final viscosities, whereas retrogradation further influenced these parameters, similarly reducing pasting and peak temperatures while enhancing viscosity profiles. All modified starches exhibited Herschel-Bulkley (pseudoplastic) fluid, with retrograded samples displaying lower maximum shear stress compared to hydrolyzed counterparts. Oscillatory rheometry revealed predominantly viscous behavior across all samples (loss modulus exceeding storage modulus), though select modifications contributed to increased elasticity. These findings underscore the efficacy of controlled hydrolysis and retrogradation in precisely tuning the physicochemical properties of water yam starch, yielding materials with thixotropic behavior and adjustable viscosity. The results highlight the potential of modified water yam starch for applications in food, pharmaceuticals, and biodegradable packaging, emphasizing its versatility as a sustainable and functional biopolymer.