Structural Disorganization and Chain Aggregation of High-Amylose Starch in Different Chloride Salt Solutions

As high-amylose starch (HAS) has a higher content of linearly structured chains than other types of starch, it is more scientifically interesting to realize enhanced properties or new functions for food and materials applications. However, the full dissolution of the compact granule structure of HAS is challenging under moderate conditions, which limits its applications. Here, we have revealed that the granule structure of HAS can be easily destructed by certain concentrations of acidic ZnCl2, neutral MgCl2, and alkaline CaCl2 solutions (43, 34, and 31 wt %, respectively) at a moderate temperature (under 50 °C). The ZnCl2 and CaCl2 solutions resulted in complete dissolution of HAS granules, whereas small amounts of HAS granule remnants still existed in the MgCl2 solution. The regenerated starch from the CaCl2 solution was completely amorphous, that from the ZnCl2 solution only presented a weak peak at 17°, and that from the MgCl2 solution contained V-type crystallites. No new reflections were found on the FTIR spectra indicating that all these three chloride solutions can be considered as a nonderivatizing solvent for starch. In all the three cases, nanoparticles were formed in the regenerated starch, which could be due to the aggregation of starch chains or their complexation with the metal cation. In addition, their water absorption ratio was 1.5 to 3 times that of the control (treated in water).