Physicochemical properties of common and waxy corn starches oxidized by different levels of sodium hypochlorite

Structure and physicochemical properties of oxidized common and waxy corn starches by different levels of sodium hypochlorite (0.25–3.0% active chlorine based on dry starch weight) were studied. The oxidized common corn starch generally had a higher carboxyl content but a similar carbonyl content compared with the oxidized waxy corn starch. The introduction of carboxyl and carbonyl groups promoted starch hydration and swelling. The gelatinization temperature of the oxidized starches increased but the enthalpy remained unchanged. Oxidation at low concentrations of chlorine (≤1.0%) produced starch with significantly higher peak and final viscosities and less breakdown as measured by Micro Viscoamylography. The carboxyl groups formed hemiacetal crosslinks that strengthened the starch integrity. However, as more amylose and amylopectin were degraded at higher oxidation levels, the depolymerization of starch molecules overrode the effects of crosslinking. Both amylose and amylopectin were oxidized and degraded during oxidation but amylose was more susceptible to oxidation.