The RS3 content showed a steady decrease as the level of sodium chloride in the reaction mixture increased. The maximum RS3 content was observed at the level of 0% of added sodium chloride. Results of these experiments indicated that the addition of sodium chloride impeded the hydrogen bond
formation between the starch molecules, resulting in less RS3 content. When salt was added to the starch-gum solution, the inter-molecular associations between starch molecules, starch and salt, as well as salt ions, changes the flexibility of the starch chains. In addition, the interaction between salt and water molecules restricts the molecular motion of the starch, resulting in less recombination of the amylose. There are two possible hypotheses, as follows:
On the one hand, the NaCl added to the samples ionizes after moisture treatment. Because of the presence of Na+ and Cl−, water molecules lose the ability to form a tetrahedron structure, which leads to the decrease of interactions between water and starch. This phenomenon has also been found in the
research of Viturawong [26]. On the other hand, the electrostatic force of Na+ reduces the mutual exclusion of glue molecules. The formation of gel depends on the balance of repellant and attraction. It was shown that the RS3 decrease was the result of comprehensive action of the two effects above, and the later one was stronger.