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

摘要

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 of the oxidized starches decreased with increasing oxidation level, and the extent of this decrease was similar for both starch types. No evidence of alterations in morphology or X-ray diffraction patterns were observed after oxidation. The crystallinity of barley starch increased with increasing oxidation but corn starch displayed reduced crystallinity at 5% NaOCl. The onset and peak gelatinization temp. of oxidized starches as measured by DSC showed a slight increase up to 3% NaOCl and then decreased at 5% NaOCl, whereas gelatinization enthalpy gradually decreased with increasing oxidation level. The melting temp. of retrograded oxidized starches increased with increasing oxidation. Both amylose and amylopectin were degraded during oxidation, but higher degradation in both components as determined by high-performance size-exclusion chromatography, occurred in barley starch than in corn starch. Results of amylopectin chain-length distribution showed that 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 temp., viscosity, and molecular size than corn starch.