Highly efficient esterification of waxy maize starch in choline chloride/acetic acid acidic deep eutectic solvent system

In this study, to address the issue of solvent selection in the chemical modification of starch, a method was developed for the efficient esterification of waxy maize starch (WMS) using an acidic deep eutectic solvent composed of choline chloride and acetic acid (CCHAc-ADES). The impact of different mass fractions of CCHAc-ADES on the degree of substitution and reaction efficiency of lauric acid starch esters was explored. It was found that under the conditions of 70 wt% CCHAc-ADES, starch esters with the highest degree of substitution of 0.161 were successfully prepared, achieving an esterification efficiency of 79.63 %. ¹³C and ¹H nuclear magnetic resonance spectroscopy, X-ray diffraction and gel permeation chromatography revealed that CCHAc-ADES acted within the surface voids of WMS particles without seriously damaging the WMS structure, making it a favorable solvent for chemical modification of WMS. By monitoring changes in the morphology, relative crystallinity, particle size, and hydrophobicity of esterified WMS in CCHAc-ADES, the formation mechanism of lauric acid starch esters was inferred, primarily related to the competitive hydrogen bonding of CCHAc-ADES with WMS. The method proposed in this study allows for the preparation of long-chain fatty acid starch esters without the use of any additional chemicals or enzymes, offering significant guidance for the application of deep eutectic solvents in green synthesis.