Morphological, physicochemical and structural characteristics of oxidized barley and corn starches

Barley Starch was oxidized to different levels and the morphological, physicochemical and structural of the resultant oxidized barley starch were determined and compared with oxidized corn starch at the same oxidation level. The amylose content in oxidized starches decreased with increasing oxidation level, and the extent of decrease was similar for both starch types. No evidences of alteration in morphology and X-ray diffraction pattern were noted after oxidation. The crystallinity of barley starch increased with increasing oxidation but corn starch displayed a reduced crystallinity at 5% NaOCI. The onset and peak gelatinization temperatures of oxidized starches as measured by differential scanning calorimetry showed a slight increase up to 3% NaOCI and then decreased at 5% NaOCI, whereas gelatinization enthalpy gradually decreased with increasing oxidation level. The melting temperature of retrograded oxidized starches increased with increasing oxidation. Both amylose and amylopectin were degraded during oxidation, but a higher degradation in both components as determined by high-performance size-exclusion chromatography (HPSEC) was noted for barley starch than for corn starch. Results of amylopectin chain-length distribution showed that the proportions of A and B1 chains significantly increased while that of B2+ chains significantly decreased. These results suggest that differences in the structure of barley and corn starches affected their responses to oxidation. Barley starch seemed to be more susceptible to oxidation with more significant reduction in pasting temperature, viscosity, and molecular size than corn starch.