School of Food Science and Technology, Hunan Agricultural University, Hunan 410128, China.
Food Chem. 2018 Jun 1;250:83-88. doi: 10.1016/j.foodchem.2018.01.043. Epub 2018 Jan 5.
The dynamics of water in sodium alginate film-forming solutions during drying were investigated by low-field nuclear magnetic resonance. At the beginning of drying, three transverse relaxation times at around 1.74, 28.48 and 305.38 ms were assigned to the tightly bound, moderately bound, and free water, respectively. Moreover, the free water was evaporated, followed by the formation of water cluster in the entangled alginate chains network as the drying process continued (beyond 840 min of drying time). Towards the third stage of drying process, water clusters in alginate samples was disappeared, resulting that loosely bonded waters were constrained within the weak-gel network. The observed three relaxation times revealed the multi-exponential relaxation behavior of water in alginate, which indicated that this polymer exhibited spatial heterogeneity during drying. On the basis of diffusive exchange theory, the dimension range of alginate network decreased from 1.94-23.99 to 1.83-6.62 µm as the alginate films solidified.
采用低场核磁共振研究了海藻酸钠成膜溶液在干燥过程中水分的动态变化。在干燥初期，将三个横向弛豫时间分别分配给紧密结合、中等结合和自由水，约为 1.74、28.48 和 305.38 ms。此外，随着干燥过程的继续（超过 840 分钟的干燥时间），自由水蒸发，随后在缠结的海藻酸钠链网络中形成水簇。在干燥过程的第三阶段，海藻酸盐样品中的水簇消失，导致弱结合水被束缚在弱凝胶网络中。观察到的三个弛豫时间揭示了海藻酸钠中水分的多指数弛豫行为，表明该聚合物在干燥过程中表现出空间异质性。基于扩散交换理论，随着海藻酸钠膜的固化，海藻酸钠网络的尺寸范围从 1.94-23.99 减小到 1.83-6.62 µm。
