Structural, Physicochemical and Thermal Properties of OSA-modified Waxy Maize Starch

Abstract

The aim of current work was to carry out a fine characterisation of the structural, physicochemical, and thermal properties of octenyl succinic anhydride (OSA)-modified waxy maize starch known under the marketed name Gel ‘N’ MeltTM. Both Fourier transform infrared spectroscopy and proton nuclear magnetic resonance analyses revealed the presence of new absorption bands and confirmed the structure of OSA-modified starch in comparison with those of native starch. The results of proton nuclear magnetic resonance analysis were consistent with those obtained using the titration method. The molecular weight obtained was regarded as higher than those found for other starch modified sources; an inverse correlation between the degree of substitution and the molecular weight was deduced: a decrease in the degree of substitution was followed by an increase in the molecular weight. In addition, X-ray diffraction and scanning electron microscopy revealed the loss of the ordered A-type crystalline structure, which is characteristic of polymers with low degree of substitution. Also, a coexistence of individual and aggregate particles was observed, supported by the extent of the fusion of grains. These results were corroborated by thermal analysis experiments, which showed a total loss of the crystallinity of the heated grains.