Morphology and Phase Transition of Corn Starch in a DMSO/Water Solvent System
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Abstract:
The effect of dimethyl sulfoxide (DMSO)/water mixtures at various ratios (weight ratio: 0/100, 50/50, 80/20, and 100/0) on the morphology and phase-transition (dissolution and gelatinization) of waxy corn starch was systematically studied using a polarized microscope with a hot stage, a differential scanning calorimeter (DSC), a Brabender Viscograph, a scanning electron microscope (SEM), and an X-ray diffractometer (XRD). As DMSO concentration increased, the extent of damage in morphology and crystalline structure of starch granules also increased. After treatment with pure DMSO, the granules showed an irregular shape and a disordered structure with an absence of polarization cross, and they could be dissolved in water. Moreover, gelatinization temperatures showed a downward trend after the initial increase. When the ratio of DMSO/water was 50/50, the highest gelatinization temperature was obtained (range: 76.44 ℃~91.37 ℃); then, the endothermic peak intensity and the enthalpy ?H value gradually decreased. In pure DMSO, no apparent phase transition peak occurred. The peak viscosity of starch pastes in DMSO was higher than that in water, and the maximum viscosity was reached when the ratio of DMSO/water was 80:20.
