Preparation and characterization of achira starch oxidized by different concentration of sodium hypochlorite

In this study, achira (Canna edulis) starch was oxidized by sodium hypochlorite and the effects of different concentration of oxidation agent (1, 2, 3 and 5%) on the physicochemical properties, morphological properties and crystallinity of achira starch (AS) was investigated. The carbonyl and carboxyl content, starch colour parameters, swelling capacity, solubility, IR spectra, SEM and XRD of native and oxidized achira starch (OAS) were evaluated. IR spectra of oxidized starch samples showed a new absorption peak which was assigned to the characteristic peak of carbonyl C=O, proved that starch had been oxidized. At lower concentration of sodium hypochlorite, there was no clearly change on the morphology of OAS granules, however, at higher concentration of oxidant (5%), there were some indentations and cracks on the surface of OAS-5 starch granules. Oxidation with sodium hypochlorite has no significant effect on the crystallinity of the starch. Both AS and OAS granules showed the typical B-type X-ray diffractogram, indicating that the oxidation occurred in the amorphous region. After treating with oxidized agent, content of carboxyl groups increased significantly, whereas content of carbonyl groups slightly increased. The total oxidation degree of OAS samples increased with the increase of the concentration of hypochlorite treatment. Oxidation with sodium hypochlorite clearly increased both the swelling capacity and solubility of achira starch. Whiteness of starch was also improved.