Li S, Dickinson LC, Chinachoti P
Department of Food Science and Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003.
J Agric Food Chem. 1998 Jan 19;46(1):62-71. doi: 10.1021/jf9609441.
"Freezable" and "unfreezable" water in waxy corn starch were characterized by thermal analysis, and the mobility in those states was characterized by solid state (2)H and (1)H NMR. Water was found to be isotropically mobile for samples over a range of water contents (6.3-47% by total weight) at room temperature. Mobility increased with increasing water content and temperature. According to (1)H and (2)H NMR data, a large fraction of "unfreezable" (DSC) was relatively mobile comparable to a liquid state even down to -32 degrees C. Some anisotropically immobile D(2)O at low temperatures exhibited a solid state Pake pattern in (2)H NMR spectra, which was similar to that of frozen D(2)O (ice) with a 144 kHz splitting. The decreasing fraction of mobile water with decreasing temperature suggested that only some of the so-called "unfreezable" water could be progressively immobilized as temperature decreased. However, much of the water (>50% of water present) remained very high in mobility, regardless of the relatively rigid starch molecules in the glassy solid state.
通过热分析对糯玉米淀粉中的“可冷冻”水和“不可冷冻”水进行了表征，并通过固态氘（²H）和氢（¹H）核磁共振对这些状态下的流动性进行了表征。发现在室温下，含水量在一定范围内（占总重量的6.3 - 47%）的样品中的水具有各向同性的流动性。流动性随含水量和温度的升高而增加。根据¹H和²H核磁共振数据，即使在低至 -32℃时，很大一部分“不可冷冻”（差示扫描量热法）水的流动性与液态相当。一些低温下各向异性不可移动的重水（D₂O）在²H核磁共振谱中呈现出固态帕克双峰图样，这与具有144千赫兹分裂的冷冻重水（冰）相似。随着温度降低，可移动水的比例下降，这表明随着温度降低，只有部分所谓的“不可冷冻”水会逐渐被固定。然而，不管玻璃态固态中淀粉分子相对刚性如何，大部分水（占现有水的50%以上）的流动性仍然很高。
