羟丁基化水平对玉米淀粉理化性质的影响

Effects of the Degree of Substitution(DS) during Hydroxybutylation on the Physicochemical Characteristics of Maize Starch

以玉米淀粉为原料,1,2-环氧丁烷为醚化剂,氢氧化钠为催化剂,乙醇为分散剂,制备出不同取代度的羟丁基淀粉。采用傅里叶变换红外仪、X射线衍衍射仪和扫描电镜等对不同取代度的羟丁基淀粉的微观结构进行表征。红外分析表明羟丁基淀粉在1371cm-1出现羟丁基的吸收峰,证明已经接上了羟丁基基团。X射线衍射分析羟丁基淀粉仍属于A型衍射图,证实了该反应主要发生在无定形区。通过扫描电子显微镜分析变性前后的表面形貌变化,表明该反应发生在淀粉颗粒表面。布拉班德粘度仪测试结果表明,淀粉糊化温度降低,回复值降低,糊峰值黏度升高,且随着取代度的提高,变化越明显,当取代度达到一定程度时,羟丁基淀粉冷水可溶。随着羟丁基取代度的增大,淀粉糊的透明度及冻融稳定性都有显著的提高。

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.