【作者】 付宗强；

【导师】 李栋； 汪立君；

【作者基本信息】 中国农业大学 ， 农业工程， 2014， 博士

【摘要】 天然淀粉以半结晶颗粒形式存在,其结晶性质和结晶度大小直接影响着淀粉的物理化学特性,决定着其应用方向。由于加工过程中的不完全糊化,淀粉颗粒内常残余一定数量的晶体结构。对残余一定数量晶体结构的淀粉的热特性、老化特性、与水的交互作用以及流变特性的研究,可以深入了解晶体结构对淀粉特性的影响作用,对进一步提高淀粉基食品的稳定性和加工特性有重要意义。通过预热处理和喷雾干燥两步法制备了具有不同残余晶体结构的玉米淀粉,经x射线衍射仪检测,随着预热处理温度的升高,样品的结晶度逐渐降低并最终呈现无定型状态。与天然玉米淀粉相比,样品的平均粒径减小,在较低温度(30℃)时具有较大的溶胀度,其糊化温度随着预热处理温度的升高而增大。老化研究发现,初始结晶度为20.93%的样品(天然玉米淀粉结晶度为24.77%),在30d老化期内基本没有变化；初始结晶度为16.22%的样品,总体结晶度缓慢增长,始终保持A型晶体结构；初始结晶度分别为3.13%和8.90%的样品,老化晶体增长数量约为前者的4倍,生长出B型晶体结构。老化动力学分析显示,初始结晶度高的样品颗粒内残余晶体的生长速率较快,而初始结晶度低的样品颗粒内晶核的形成和生长速率较快。淀粉与水的交互作用研究发现,在测试的含水率范围内(25-78%,w/w),随着含水率的降低,颗粒内残余晶体结构多(结晶度为20.93%)的样品的糊化曲线上依次出现了热流峰G、M1和M2,而其他残余晶体结构较少的样品的糊化曲线上始终只有热流峰M1和M2,无热流峰G。研究结果支持以下淀粉糊化机制：稳定性低的晶体先熔融,稳定性高的晶体后熔融。残余的晶体结构对淀粉颗粒内的结合水数量也有着显著的影响。在淀粉糊(悬浊液)流变测试中,当处理温度为25℃和60℃时,颗粒内残余晶体结构较少的样品即呈现出明显的流变特性。当处理温度从70℃升到80℃时,所有样品的表观粘度和储能模量均达到峰值,并随着处理温度的进一步升高而降低。在温度扫描过程中,初始残余晶体结构较多的样品呈现出较大的峰值储能模量和终值储能模量；初始残余晶体结构较少的样品的储能模量随着温度的变化较小,相对较稳定。在淀粉与面粉共混体系的流变测试中,研究了不同残余晶体结构淀粉作为替代物在不同替代比例条件下对面团流变特性的影响,结果表明：随着淀粉样品的添加,面团的表观粘度值显著增大；面团的储能模量和损失模量也明显升高,其粘弹性得到改善；面团的蠕变柔量降低,而蠕变恢复率得到提高。更多还原

【Abstract】 The starch granule is a kind of semi-crystal structure. The crystallinity of starch has an important effect on its physicochemical properties and applications. There are a certain remainder crystals in starch granules due to partial gelatinization in the production process. In this study, the research mainly focused on the thermal, retrogradation and rheological properties of starch with different remainder crystals. And interactions between starch and water during gelatinization were also investigated. This study would not only help to understand the effect of crystalline structure on the properties of starch, but also to make great importance to improve the stability of starch based food.In this study, corn starches with different remainder crystals were prepared by pre-heat treatment and spray drying process. The crystallinity of samples decreased with the pre-heat temperature increase and the granule structure changed to be amorphous at last by X-ray diffraction detection. The granule size of samples was smaller than that of native corn starch. The swelling power of samples was higher than that of native starch at30℃. There was an increase in gelatinization temperature in starch samples compared to that of native starch.The retrogradation of starches with different remainder crystals was analyzed in this study. There was no significant difference in starch sample with20.93%initial crystallinity after30days’ storage. The total crystallinity of sample with16.22%initial crystallinity increased slowly and its crystalline pattern kept A-type, while the increment of total crystallinity of samples with3.13%and8.90%initial crtsayllinity was almost four times as high as that of previous one and their crystalline pattern changed to be B-type. The retrogradation kinetics data showed that the growth of remainder crystals was faster in samples with higher initial crystallinity, while both the nucleation and growth rates of new crystals were faster in samples with lower initial crystallinity.The interactions between starch samples with different remainder crystals and water during gelatinization was investigated. All of the G, M1and M2endotherm were observed in sample with the highest remainder crystals in the moisture content range of25-78%. The G endotherm was not observed and only the Ml and M1endotherm were observed in other samples with lower remainder crystals in the entire moisture content range. The research data supported the starch gelatinization model that the less stable crystallites will melt first followed by the more stable crystallites. Remainder crystals had an important effect on the amount of unfreeze water of starch samples.The rheological properties of starch with different remainder crystals were investigated. After being treated at25℃and60℃, samples with lower remainder crystals showed strong apparent viscosity and viscoelastic properties, while samples with higher remainder crystals not. As the treatment temperature increased from70℃to80℃, the apparent viscosity and storage modulus of all the samples increased to the peak value and decreased with the treatment temperature increased higher. In the temperature sweep test, samples with higher remainder crystals presented higher peak and conclusion storage modulus; Samples with lower remainder crystals were more stable and showed lower sensitive to the change of temperature. The rheological properties of wheat flour substituted with starch with different remainder crystals were investigated. The apparent viscosity of dough increased significantly after starch samples were added into wheat flour. The presence of starch with remainder crystals improved the viscoelastic characteristics of dough. The creep compliance of dough decreased and the elastic recovery increased with the addition of starch with remainder crystals.更多还原