预糊化处理对荞麦淀粉理化特性的影响

Effect of pre-gelatinization on physical and chemical properties of buckwheat starch

【目的】研究热烫和微波预糊化处理对荞麦淀粉理化性质的影响,为荞麦面制品的开发及在主食中的应用提供理论依据。【方法】通过水洗法提取荞麦淀粉,利用热烫和微波对其进行预糊化处理,通过扫描电子显微镜观察荞麦淀粉颗粒形貌,利用差示扫描量热仪测定荞麦淀粉焓变(ΔH),利用傅立叶红外光谱仪扫描荞麦淀粉红外光谱图,通过流变仪测定剪切速率对荞麦淀粉剪切黏度和剪切应力的影响,并采用Herschel-Bulkley方程进行拟合分析,得到稠度系数K、流动特征指数n、屈服应力τ0。利用十八角度激光散射联用系统测定荞麦淀粉分子质量分布情况,得到重均分子量Mw、数均分子量Mn、分子质量分布系数Mw/Mn及均方根旋转半径Rz。【结果】经过热烫和微波处理后,荞麦淀粉颗粒表面变得粗糙且出现凹坑,ΔH从10.870J/g降至9.388和8.896J/g,红外光谱中波数995与1 022cm-1峰强的比值从0.78上升至0.81和0.85。随剪切速率的增加,3种荞麦淀粉剪切黏度均下降,剪切应力均增加,但预糊化处理荞麦淀粉的以上2个指标均低于未经处理的荞麦淀粉。热烫和微波预糊化处理后,荞麦淀粉的τ0从0.744 4Pa分别升高至1.667 4和1.913 2Pa,K从28.058 7Pa·sn分别降至12.808 7和8.862 1Pa·sn,n从0.409 1分别降至0.388 9和0.376 2,Mw/Mn从1.279分别升至1.317和1.365,Rz从392.5nm分别降至365.8和335.4nm。预糊化处理使淀粉颗粒拥有更紧密的晶区结构,淀粉分子链断裂,分子间作用力变大,分散程度增强。【结论】2种预糊化处理均可以改变荞麦淀粉的理化特性,但以微波处理的影响更显著。

【Objective】This study investigated the effects of blanching and microwave pre-gelatinization on the physical and chemical properties of buckwheat starch to provide basis for the development of buckwheat flour and its application in staple food.【Method】Buckwheat starch was extracted by washing with water and pre-gelatinized by blanching and microwaving.The morphology of particles was observed by scanning electron microscopy.The enthalpy change(ΔH)was measured by differential scanning calorimetry(DSC),the infrared spectrum was obtained by Fourier infrared spectroscopy(FTIR),and the effect of shear rate on shear viscosity and shear stress was measured by rheometer.The consistency coefficient K,flow characteristic index n and yield stressτ0 were obtained by using Herschel-Bulkley equation.The molecular mass distribution was determined by 18 angle laser scattering system.The molecular weight distribution coefficient(Mw/Mn)and root-mean-square rotation radius(Rz)were also calculated.【Result】After blanching and microwave treatments,the surface of buckwheat starch granules became rough and pits appeared.ΔH decreased from 10.870 J/g to 9.388 and 8.896 J/g,and the ratio of IR spectrum 995/1 022 cm^-1band increased from 0.78 to 0.81 and 0.85,respectively.With the increase of shear rate,the shear viscosity descreased and shear stress increase,but the pregelatinized buckwheat starch were lower than the untreated buckwheat starch.After blanching and microwave treatment,τ0 increased from 0.744 4 Pa to 1.667 4 and 1.913 2 Pa after blanching and microwave treatments,K decreased from 28.058 7 Pa·s^n to 12.808 7 and 8.862 1 Pa·s^n,n from 0.409 1 to 0.388 9 and 0.376 2,and Mw/Mn increased from 1.279 to 1.317 and 1.365,Rz decreased from 392.5 nm to 365.8 and 335.4 nm.Pre-gelatinization resulted in closer crystal structure of starch particles,breaking of starch molecular chain,and increase of intermolecular force and degree of dispersion.【Conclusion】The physicochemical properties of buckwheat starch could be changed by both pre gelatinization treatments,and the effect of microwave treatment was larger.