Effects of the Degree of Substitution (DS) during Hydroxybutylation on the Physicochemical Characteristics of Maize Starch
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Abstract:
Hydroxybutylated maize starches with different degrees of substitution (DSs) were prepared using 1,2-epoxybutane, NaOH, and ethanol as the esterifying agent, catalyst, and dispersing agent, respectively. The microstructures of hydroxybutylated starch with different DSs were characterized by Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). A new absorption peak, ascribable to the hydroxybutyl group, was found at 1370 cm-1 in the IR spectrum of hydroxybutylated starch, confirming that hydroxybutyl groups were attached to native starch. XRD analysis revealed that hydroxybutylated starch still had an A-type X-ray diffraction pattern, confirming that the reaction mainly occurred in the amorphous region. Changes in the surface morphology of the starch granules before and after modification were observed via SEM, indicating that the reaction occurred on the surface of the starch granules. The result from the Brabender viscometer showed that the pasting temperature and set back values of the modified starches decreased significantly, whereas the peak viscosities increased. Moreover, these changes became more significant with increasing DS. When the DS reached a certain level, the hydroxybutylated starch was soluble in cold water. Thus, on increasing the DS, the transparency and freeze-thaw stability of the starch paste were substantially improved.
