Oxidation of cornstarch using oxygen as oxidant without catalyst

In the present work, oxygen was used as an environmentally friendly oxidant without catalyst, resulting in a waste free and simple method for starch oxidation. The oxidation was performed under the conditions of oxygen in sodium hydroxide at about 100 °C. It was found that the oxidation of the native cornstarch in this system depends upon the amount of sodium hydroxide, the temperature and the duration of the oxidation treatment. Twenty one gram NaOH, 100 °C and 3.0 h are the optimum conditions for getting the desirable water-soluble oxidized starch with carboxyl content of 3.6 g/100 g. The microstructure of oxidized cornstarch was characterized by scanning electron microscopy (SEM), Fourier transform-infrared (FT-IR), Carbon-13 nuclear magnetic resonance spectroscopy (13C NMR) and chemical analysis methods. The results showed that the oxidation reaction introducing carboxyl and carbonyl groups took place at OH groups of C2, C3 and C6 in the glucose units and did not cause the breakage of C–O–C linkages.