稻壳内湿热处理条件下缓慢消化淀粉的形成及其分子特征

Consumption of food containing slowly digestible starch (SDS) may provide sustained glucose release with a low initial glycemia and subsequently a slow and prolonged release of glucose. Foods containing SDS may also improve overall blood glucose control in patients suffering from diabetes mellitus, reduce blood lipid levels and improve physical performance and glucose tolerance. Most scientists worked on the Heat Moisture Treatment (HMT) on the commercial starch and laboratory isolated starch. But during traditional HMT process, cooling water will result in partial starch granule surface gelatinization. In this study, HMT rice kernels prepared by heating the kernels and then subjected to various temperature cycling (TC) and isothermal holding (IH) conditions to accelerate recrystallization of starch polymers within the endosperm cells of the kernels. It was hypothesized that treatment of rice starch within cells would result in greater retrogradation than treatment of isolated starch because of restricted polymer movement during gelatinization and that HMT followed by TC or IH would allow the starch polymers to rearrange within amorphous or crystalline regions more effectively if the granules were confined within the cells so that swelling and any displacement of molecular within the granules would be constrained (limited). Kernels of normal maize were subjected to a HMT followed by a temperature cycling (TC) regime that was previously shown the produce SDS. Eight different genetic rice kernels, including two mutants of rice samples, will be conducted with HMT treatment followed by TC or IH. The starch digestibility and physicochemical properties will be measured. Amylopectin chain length distribution, amylose leaching, morphological change and degree of crystallinity during the treatment will be developed. The internal structure change within the amorphous and crystalline regions will be assessed. The relationship between the digestion and physicochemical property of in-kernel HMT rice starch and its molecular structure will be investigated. This research has broad implications for understanding the mechanism of the slowly-digesting modified food starch.

含有缓慢消化淀粉的食品可缓慢并持续的提供能量，有助于控制和预防糖尿病的发生。传统湿热处理仅限于商业淀粉,存在着冷凝水蒸汽回流所导致部分淀粉糊化的缺点。本项目拟采用直接对稻谷进行湿热处理的方式，运用稻壳作为天然屏障，将淀粉分子的运动限制在稻壳内，使淀粉分子在无定型区和结晶区重新排序堆积，最大限度地提高缓慢消化淀粉的含量。选择8种不同基因型（包括突变体）的水稻作为原料，利用酶学消化法分离制备缓慢消化淀粉和抗性淀粉，研究稻壳内湿热处理条件下缓慢消化淀粉的形成机理。利用现代仪器分析技术研究稻壳内湿热处理条件下缓慢消化淀粉的直链淀粉渗出量、支链淀粉链长分布、结晶结构、短程结构、淀粉颗粒的形貌变化规律，建立或完善淀粉分子结构与理化特性、功能特性之间的关系，阐明缓慢消化淀粉形成的分子机理，为富含缓慢消化淀粉稻米的生产及提高或完善大米的深加工技术提供理论基础。

采用简单的物理修饰法，利用纯天然的资源水和热等，以稻壳当作天然的保护屏障，对大米淀粉进行湿热处理，研究其缓慢消化淀粉的形成机理。将湿热处理应用于仍包埋于稻壳内大米淀粉，在冷凝的过程中，即使水分回流到稻壳表面，对稻壳内的淀粉也无影响，并且稻壳内的淀粉分子的运动被限制在稻壳内部，因此可能会产生更高的重结晶率，降低淀粉消化率。本项目选择蜡质、低直链和高直链淀粉大米淀粉作为研究对象，在100℃、25％湿度、16小时反应条件下，观察稻壳内湿热处理大米淀粉的缓慢消化淀粉的形成机制。研究结果表明，直链淀粉含量是决定稻壳内湿热处理大米淀粉理化性质的重要因素。稻壳内湿热处理大米淀粉的直链淀粉浸出率、膨胀力和溶解度在处理过程中均有降低。两种湿热处理技术的热力学温度由于处理方式的不同而受到不同程度的影响。稻壳内湿热处理蜡质和低直链大米淀粉中的相对结晶度增加，但稻壳内湿热处理高直链大米淀粉的相对结晶度降低。淀粉消化率结果表明，稻壳内湿热处理技术可以更有效地用于提高缓慢消化淀粉和抗性淀粉的含量。本研究为富含缓慢消化淀粉稻米的生产及完善大米的深加工技术提供了理论基础。