Randzio Stanisław L, Flis-Kabulska Iwona, Grolier Jean-Pierre E
Polish Academy of Sciences, Institute of Physical Chemistry, ul. Kasprzaka 44/52, 01-224 Warsaw, Poland.
Biomacromolecules. 2003 Jul-Aug;4(4):937-43. doi: 10.1021/bm0340016.
High-sensitivity, temperature-controlled DSC measurements at a low heating rate and creation of differential DSC traces scaled with respect to the reference material (completely dehydrated starch or completely dehydrated fiber, or their respective blends) permitted investigation of the influence of fiber on phase transformations in the wheat-starch-water system in the course of thermal gelatinization. Thermal effects associated with water interactions over the temperature range from 283 to 384 K under atmospheric pressure were determined. These thermal effects and previous structural studies permit us to make the following observations: (1) The main endothermic transition associated with melting of the crystalline part of the starch granule followed by a helix-coil transition in amylopectin occurs over the temperature range 319-333 K independent of the water and fiber contents. Adding fiber causes that transition to disappear both in the native blends and in water suspensions at low water contents. After adding more water and heating, recrystallization is observed and the transition reappears. (2) The fiber content has practically no influence on the slow exothermic transformation, which follows melting and helix-coil transition in amylopectin, proving that the slow transformation has a specific chemical character. In this reaction, the free ends of the unwound helices of amylopectin reassociate with parts of amylopectin molecules other than their original helix duplex partner, forming physical junctions and creating more general amorphous hydrogen bonded associations. (3) The high-temperature transition and small, but reproducible, distortions on the peaks of the main endothermic transition for water contents near 70-80 wt % are associated with smectic and nematic transitions, respectively. These are significantly influenced by the fiber content; higher fiber content causes an almost complete disappearance of these transitions. (4) The slow exothermic effect appearing almost from the very beginning of the heating in the starch-water system, associated with softening and uptake of water in the amorphous growth rings of the starch granule, is significantly hindered by added fiber.
在低加热速率下进行高灵敏度、温度控制的差示扫描量热法（DSC）测量，并创建相对于参考材料（完全脱水的淀粉或完全脱水的纤维，或它们各自的混合物）进行缩放的差示DSC曲线，从而能够研究纤维对小麦淀粉 - 水体系在热糊化过程中相变的影响。测定了在大气压下温度范围为283至384 K时与水相互作用相关的热效应。这些热效应和先前的结构研究使我们能够得出以下观察结果：（1）与淀粉颗粒结晶部分熔化相关的主要吸热转变，随后是支链淀粉中的螺旋 - 线圈转变，发生在319 - 333 K的温度范围内，与水和纤维含量无关。添加纤维会导致该转变在天然混合物和低含水量的水悬浮液中消失。添加更多水并加热后，会观察到重结晶，转变重新出现。（2）纤维含量对支链淀粉熔化和螺旋 - 线圈转变之后的缓慢放热转变几乎没有影响，这证明该缓慢转变具有特定的化学性质。在这个反应中，支链淀粉解旋螺旋的自由端与支链淀粉分子中除其原始螺旋双链伙伴之外的其他部分重新结合，形成物理连接并产生更普遍的无定形氢键缔合。（3）对于含水量接近70 - 80 wt%的情况，高温转变以及主要吸热转变峰上小但可重复的畸变分别与近晶相和向列相转变相关。这些转变受纤维含量的显著影响；较高的纤维含量会导致这些转变几乎完全消失。（4）在淀粉 - 水体系中几乎从加热开始就出现的缓慢放热效应，与淀粉颗粒无定形生长环中的软化和水吸收有关，添加纤维会显著阻碍这种效应。
