Hierarchical structural transformation of corn starch in NaOH solution at room temperature

Abstract

Starch gelatinization at room temperature is an important concern for industrial communities. Alkali solution can be used for starch gelatinization at room temperature. However, starch multi-scale structural transformation in alkali solution as a function of concentration and its application in starch gelatinization at room temperature were not revealed yet. This study investigated the changes of starch multi-scale structures as a function NaOH concentration (0.10–0.30 M) and presented the underlying mechanism of starch gelatinization. The NaOH solution resulted in degradation of α-1,4 and α-1,6 linkage, and in turn, contributed to a reduction of starch molar mass as a function of NaOH concentration. At low concentration (0.10 M), α-1,6 linkages degraded and ordered structures (e.g., short-range ordered structure, helical structure, crystalline structure, and lamellar structure) slightly disassociated. In the solution with an intermediate NaOH concentration (0.10–0.20 M), both α-1,4 and α-1,6 linkages breakdown and the content of ordered structures significantly decreased along with swelling of semi-crystalline structures. As the NaOH concentration was higher than 0.20 M, both α-1,4 and α-1,6 linkages degraded and the ordered structures seriously disrupted along with compete disappear of helical structure, crystalline structure, and lamellar structure. Comparing with the gelatinization behaviors in ionic liquids with heating, starch did not show a more serious degradation in the NaOH solution. Accordingly, the NaOH solution with a concentration higher than 0.20 M can be used for starch gelatinization at room temperature.