Comparative assessment of potato starch dissolution and functionalization in conventional and water-modified deep eutectic solvents.

Native starch is insoluble in most conventional organic solvents because of its semi-crystalline structure stabilized by extensive hydrogen bonding, which limits homogeneous chemical modification. In this study, two deep eutectic solvents (DESs) based on benzyltriethylammonium bromide (BTEAB)/urea and BTEAB/urea containing 10 wt% water (DES-H2O) were developed as environmentally friendly media for starch dissolution and subsequent esterification with maleic anhydride. The DESs acted simultaneously as solvent, reaction medium, and catalyst, eliminating the need for additional catalysts or volatile organic solvents. The water-containing DES exhibited superior starch dissolution efficiency, dissolving up to 16 wt% starch at 70 °C. Structural characterization by XRD confirmed the disruption of the native crystalline structure and the formation of an amorphous material after DES treatment. Successful esterification was verified by FTIR-ATR and NMR analyses through the appearance of characteristic maleate ester signals. SEM observations revealed significant morphological changes following dissolution and modification, while thermal analysis showed reduced thermal stability associated with starch functionalization. These results demonstrate that water-modified BTEAB/urea DESs provide an efficient and sustainable platform for the homogeneous dissolution and esterification of starch under mild conditions.