Structure and functionality of cassava starch in different deep eutectic solvents/water mixtures: A comparative study

Starch, as one of the most abundant natural polysaccharides, is regarded as a sustainable material due to its renewability, biodegradability, and modifiability, and is widely used as an excellent industrial material. However, as a polyhydroxyl polymer, native starch has low solubility in most situations due to its network structure formed by intramolecular and intermolecular hydrogen bonds, which limits its industrial application. In this study, the solubility of cassava starch (CS) in a series of acidic, neutral, and alkaline deep eutectic solvents (DESs) was investigated. Relatively high solubilities of 52.8 wt%, 11.4 wt%, and 10.2 wt% were obtained in choline chloride/formic acid (CF), ethylammonium chloride/ethylene glycol (EE), and choline chloride/diethanolamine (CD), respectively. The dissolution behavior of CS in pure mixtures of these DESs and in DESs/water mixtures (2:8) was also compared. The results of gel permeation chromatography (GPC) analysis showed that the weight-average molecular weights (Mw) and number-average molecular weights (Mn) were ranked in the order CF > EE > CD. The same pattern was observed for the DESs/water mixtures (2:8), although the reduction in Mw and Mn was less distinct than in the pure DESs. The results of X-ray diffraction, small-angle X-ray scattering, and scanning electron microscope observations were consistent with the GPC data, i.e., the hydrolysis ability of CS was higher in the acidic DESs (CF) compared to the neutral (EE) and alkaline (CD) DESs. The dissolution behaviors of CS in the DESs/water mixtures were affected by the structure of the DESs and their water content. These results demonstrate that aqueous DESs serve as excellent media for starch dissolution. Moreover, this study provides a comprehensive understanding of the solubilization behavior of CS in different aqueous DESs and provides insights into the development of novel starch-based materials using DESs.