基于改良挤压法处理高直链早籼米的淀粉老化行为与结构变化的关系

The products from rice starch inevitably happen to retrograde after cooking and storage, which results in the deterioration of desirable qualities. Starch retrogradation is of great interest since it profoundly affects the quality, acceptability and shelf-life of starch-containing foods. In our previous work, it was found that correlation existed between retrogradation behavior and physico-chemical properties of high-amylose long rice starch by Improved Extrusion Cooking Technology (IECT). However, the relationship between retrogradation behavior and molecule or fine structure of rice starch need to be further researched. Therefore, the rice starch with high amylose is chosen as material, IECT is used as a treatment method, the IECT effect on retrogradation behavior and molecule or fine structure of rice starch will be investigated, including detecting and comparing the differentiation of retrogradation behavior (microstructure, thermal properties, rate of retrogradation, syneresis); expressing and analyzing changes of molecule structure (long range molecule order, short-range molecular order, double helix structure) and fine structure (weight average molecular mass, number average molecular mass, distribution of fractions, degree of polymerization). The model of the relationship among the changes induced by the different factors will be established between retrogradation behavior and molecule or fine structure of rice starch, which can be used to interpret the relationship between retrogradation behavior and molecule or fine structure of rice starch. Those studies can provide the theoretical principle for the mechanism of retrogradation and complicated structure for rice starch during the production.

大米淀粉制品经蒸煮后贮藏过程中发生老化行为导致其品质降低和影响货架期是学界关注的热点问题。本项目前期报道采用改良挤压技术(IECT)处理高直链早籼米淀粉的老化行为改变与理化性质变化密切相关，然而淀粉老化行为与分子结构和精细结构变化的关系还有待深入研究，由此，本项目以高直链淀粉含量早籼米淀粉为对象，以IECT为手段研究其老化行为与分子结构和精细结构变化的影响，测定和比较处理前后老化行为(微观形貌、热力学性质、老化速率、脱水收缩作用)变化的差异性；表征和分析处理前后的大米淀粉分子结构(长程晶体结构、短程序列晶体结构、淀粉双螺旋结构)和精细结构(数均分子量和重均分子量、链长分布、聚合度)的变化影响；建立早籼米淀粉老化行为与分子结构和精细结构因素变化关系的数学模型进行预测与模拟，揭示早籼米淀粉的老化行为与分子结构和精细结构变化之间的关系。为阐析淀粉老化机理和解析籼米淀粉大分子复杂结构提供理论参考。

大米淀粉制品经蒸煮后贮藏过长中发生老化行为导致其品质降低和影响货架期是科学领域关注的热点问题。关于改良挤压处理(IECT)对淀粉老化性质和结构变化关系有待深入探讨。本项目通过研究原料籼米淀粉(NRS，直链淀粉含量28.9%) 经过IECT处理后老化性质实验，得到糊化冻干的淀粉(GRS)，在4℃条件下储存老化冻干后得到籼米淀粉(RRS)。结果表明RRS的老化程度和老化速率变低。NRS的糊化焓为9.75 J/g，GRS和RRS的糊化焓从0.49J/g增加到3.68 J/g，同时老化程度从10.36%增加到37.74%。此外，老化常数速率为0.21 d-1，与其他文献相比较低，而阿弗拉米指数为0.89，与其他文献相比较高。RRS从X衍射分析的相对结晶度为12.7%，红外图谱得到的吸光度比为0.63，这些结果都表明经过IECT处理的大米淀粉老化程度较低, 大米淀粉从A型结晶变成无定型结构和B型结晶。在研究IECT处理后淀粉和原淀粉的冻融稳定性过程中发现，析水率结果和微观形貌表明IECT处理淀粉比原淀粉冻融稳定性要好，IECT处理后淀粉在冻融循环过程中流变学性质变化不明显，X衍射图谱和碘结合力图谱表明IECT处理可以有效抑制大米淀粉中直链淀粉的团聚，即抑制淀粉老化。此外，在IECT处理后的淀粉在20°时的衍射峰时IECT过程中直链淀粉-脂质复合物的特征峰，也是IECT处理抑制老化的原因之一。在研究IECT制备的预糊化淀粉时发现IECT有助于提高淀粉低温时水吸收度和水溶解度，淀粉的热糊稳定性，抑制淀粉的短期老化。这些性质的变化主要是由于淀粉分子在挤压过程中分子尺寸的降解，而链长分布没有明显变化，淀粉的降解主要是发生在支链淀粉的1,6糖苷键和分支点附近的1,4糖苷键。这些结果表明淀粉经过IECT在特定条件下处理可有效抑制老化。本项目为解释挤压过程淀粉老化性质变化提供理论依据，为淀粉大分子精细结构的解析和淀粉在食品工业中的应用提供理论参考。