Abstract:

Cassava and potato starches were oxidized by sodium hypochlorite with an active chlorine content of less than 1% (mass fraction,below the same).The oxidization mechanism and the physicochemical properties of the oxidized starches were then studied,revealing that both the carbonyl content and the carboxyl content of the oxi.dized potato starch are higher than those of the oxidized cassava starch,although the carboxyl and carbonyl contents of the two oxidized starches all increase with the dosage of sodium hypochlorite. As measured by Brabender Viscog.raphy,the oxidation at low active chlorine content(≤0.3%)results in higher peak and final viscosities of the oxi.dized starch.Moreover,the absorptions at 1733 cm^-1 and 1714cm^-1 are observed in the FTIR spectra of the cassava and photo starches oxidized at an active chlorine content of 0.9%.which weaken or disappear when the oxida.tion is carried out at an active chlorine content of 0.1%.However.the absorption at 1 150cm^-1 is strengthened. It is thus concluded that a cross linking reaction takes place between the hemiacetal hydroxyl groups of the oxidized starch and the hydroxyl groups of the adjacent starch during the low-level oxidation process.

Key words: starch, oxidation, sodium hypochlorite, cross linking, mechanism