Abstract
High-amylose corn starch, which contains 50% amylose, was oxidized with sodium hypochlorite and several properties of the oxidized starches were examined. The oxidation was carried out at a pH of 11 and at 40°C. The amount of oxidant added was 1-8% as available chlorine per starch. Yield of the high-amylose starch was 90% at 8% oxidant level and that of the ordinary starch was 80% at 60% level. Viscosity was measured by the Amylography at 15% starch concentration, for viscosity was not indicated at 7% starch concentration. Transmittance of the paste was measured by the Photopastegraphy and the transmittance of high-amylose starch was very low even at 90°C. As the degree of oxidation increased, the viscosity was lowered and the transmittance was increased. Swelling power and solubility was measured at 90°C. The swelling power was decreased slowly between 1-4% oxidant level and then rapidly between 5-8%. The solubility was increased linearly in proportion to the amount of oxidant. More carbonyl and carboxyl groups were formed, as the degree of oxidation increased. Functional group contents of high-amylose starch were slightly low as compared with ordinary starch. X-ray diffraction patterns showed that even 8% oxidant level gave little effect in crystalline regions.
