The influence of ultrasound on the degree of oxidation of hypochlorite-oxidized corn starch

Oxidized corn starch was prepared with and without sonication at different levels of sodium hypochlorite (0-2 g active chlorine/50 g starch) and treatment time (15 and 30 min). Gel permeation chromatography revealed that weight average molecular weight decreased while polydispersity index increased with increase in active chlorine concentration and treatment time. It was found that carbonyl and carboxyl contents, and swelling power of oxidized corn starch generally increased with progressive increase in active chlorine level, treatment time and in the presence of sonication. A reversed trend was observed for the solubility. Peak viscosity was found to decrease with increase in active chlorine concentration to a threshold level of 1 g active chlorine/50 g starch, after which peak viscosity increased as the active chlorine level was increased. Breakdown values and final viscosities were increased and decreased respectively with progressive increase in active chlorine concentration. These phenomena became significant as the starch was subjected to sonication and longer treatment time.

► Oxidized starch prepared with and without sonication was characterized. ► Higher degree of oxidation was achieved with sonication. ► Starch subjected to sonication only showed higher weight average molecular weight.