One-pot acid ethanol hydrothermal synergistic modification of starch: Sequential mechanism and structural tailoring...

This study developed a mild and efficient one-pot acid-ethanol hydrothermal synergistic modification strategy for preparing highly adsorptive V-type starch. Suitable processing temperatures under relatively low ethanol concentrations (35% and 40%) were identified by DSC, and key process parameters including HCl concentration, reaction time, and agitation speed were systematically optimized. Under optimal conditions (35% ethanol, 80 °C, 1.2% HCl, 15 min, 400 rpm), the resulting modified starch exhibited an oil adsorption capacity of 376.80%, which was significantly improved from 107.45% for native normal maize starch, representing a 3.5-fold enhancement. Significantly outperforming samples treated with individual modification methods. To elucidate the formation mechanism, the crystalline structural evolution and adsorption performance of starch under four treatment conditions (hydrothermal, ethanol-hydrothermal, acid-hydrothermal, and ethanol-acid-hydrothermal treatments) were systematically investigated using XRD, FTIR, SEM, and adsorption tests. The results revealed a sequential synergistic interaction between ethanol and HCl during the one-pot process: heating unwound the starch double helices, while ethanol simultaneously promoted the formation of V-type complex with leached amylose and restrained excessive double helix unwinding; subsequently, HCl preferentially hydrolyzed amorphous regions, further enhancing V-type crystallinity and generating microporosity. This cooperative process yielded a unique "microporous + deep-cracked" morphology, improved crystalline order and hydrogen-bond networks, and maintained high product yield owing to the protective role of ethanol. This study clarifies the synergistic roles of ethanol and acid in modulating the molecular structure of starch, while also providing a theoretical foundation and a scalable efficient processing route for preparing functional starch-based adsorbents with potential applications in areas such as powdered oil formulations and bioactive compound encapsulation.