Physicochemical, Thermal and Rheological Properties of Native and Oxidized Starch from Corn Landraces and Hybrids

Native starch was isolated from three corn landraces and a hybrid variety. The starches were oxidized with several concentrations of NaOCl (0.8, 2 and 5% w /w active chlorine). The physicochemical and functional properties of oxidized starches were compared with those of native starches of the same source. The oxidation treatment increased the content of carboxyl and carbonyl content in the starches confirming that NaOCl effectively oxidized the polysaccharides. The oxidation treatment decreased the content of non-starch components and increased the whiteness ( L * values of tristimulus color) of starches. The oxidation also increased the water retention capacity of starches. The values of the thermal and rheological properties of starches decreased as the oxidation intensity increased. The high number of carbonyl and carboxyl groups in oxidized starches favored starch depolymerization and increased the affinity of starch for water. The crystallinity of starches was not affected by oxidation, where the most intense diffraction peaks in both native and oxidized corn starches were observed at 2θ = 15, 17, 18 and 23°. The hardness of starch gels decreased with oxidation.