NMR studies of the gelation mechanism and molecular dynamics in agar solutions
NMR studies of the gelation mechanism and molecular dynamics in agar solutions
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DOI：
10.1016/j.foodhyd.2011.04.021
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发表时间：
2012-01-01
影响因子：
10.7
通讯作者：
Matsukawa, Shingo
中科院分区：
文献类型：
--
作者：
Dai, Bona;Matsukawa, Shingo
利用脉冲场梯度刺激回波（PFG-STE） H-1核磁共振（NMR）测量了不同温度下琼脂分子迁移率的变化，以阐明溶液中凝胶化的机理。在溶胶-凝胶转变温度Ts-g附近，琼脂的回波信号强度急剧下降，扩散系数D增大，随着温度的进一步冷却，扩散系数D减小。这些结果表明，琼脂中的多糖链在Ts-g附近成束聚集形成一个网络。高分子量的链在琼脂中优先聚集，可溶的，非聚集的琼脂（“溶质琼脂”）在进一步冷却后留在网络中形成松散的聚集体。这种行为的证据是从凝胶中挤出的溶质琼脂的GPC测量中获得的。这些松散的聚集体在再加热时很容易分离，而聚集的束是相当热稳定的，这与凝胶强度的热稳定性很好地对应。这些溶液中限制分子迁移率的变化是通过测量作为探针分子加入的树状大分子的D来评估的，它对伴随凝胶化的溶质琼脂的稀释很敏感。水动力屏蔽长度xi，被认为代表溶质琼脂形成的水动力网尺寸，由树突分子的D计算得到，揭示了凝胶化过程中微观环境的变化。(C) 2011 Elsevier Ltd.版权所有。
Changes in the molecular mobility of agar were measured by pulsed-field-gradient stimulated echo (PFG-STE) H-1 NMR at various temperatures in order to elucidate the mechanism of gelation in solutions. The echo signal intensity of agar decreased steeply and the diffusion coefficient D of agar increased near the sol-to-gel transition temperature Ts-g, and D decreased with further cooling. These results suggested that the polysaccharide chains in agar aggregated in bundles to form a network at around Ts-g. High molecular weight chains aggregated preferentially in agar, with the soluble, non-aggregated agar ("solute agar") left in the network forming loose aggregates upon further cooling. Evidence for this behavior was obtained from GPC measurements on the solute agar squeezed from the gel. These loose aggregates readily disassociated on reheating, whereas the aggregated bundles were quite thermally stable, which corresponded well with the thermal stability of the gel strength. The changes in the restrictions on molecular mobility in these solutions were evaluated from measurements of D of a dendrimer added as a probe molecule, which was sensitive to the dilution of the solute agar accompanying gelation. The hydrodynamic shielding length xi, which was considered to represent the hydrodynamic mesh size created by the solute agar, was calculated from D of the dendrimer, shedding light on the changes in the microscopic environment during gelation. (C) 2011 Elsevier Ltd. All rights reserved.