For efficient treatment of starch using aqueous ionic liquid at room temperature

Abstract

Considering the renewability and chemical versatility of natural biopolymers, innovative solvation processes to efficiently disrupt the native supramolecular structures of (namely dissolve/gelate) natural polymers for their modification, derivation, and materials fabrication are highly demanded. This work compares the structural disorganization behavior at room temperature among waxy maize, high-amylose maize, cassava and potato starches with the 6:4 (wt/wt) 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc])/water mixture using rapid visco analysis (RVA), scanning electron microscopy (SEM), X-ray diffraction (XRD), small-angle X-ray scattering, Fourier-transform infrared (FTIR), and Raman spectroscopy. All the viscosity, morphological and structural changes show the greater susceptibility of the two A-type (cassava and waxy maize) starches to structural disruption with the aqueous IL than the two B-type (potato and high-amylose maize) ones, while cassava starch is most susceptible. The four starches, once ball-milled (for up to 5 min), display an immediate increase in viscosity with time in RVA, while a lag in viscosity increase for native waxy maize and cassava starches without ball-milling and barely any viscosity change for high-amylose maize and potato starches can be observed. This indicates that the easiness of starch gelation by the aqueous IL is not directly linked to amylose content but is controlled by the granule surface compactness (namely, how easily the aqueous IL can reach and disrupt the most vulnerable parts inside the starch granule and subsequently cause the destruction of the rest parts and the breakdown of the whole granule). The findings can provide insights into developing low-energy processes for starch processing with aqueous ILs.