Fransson Sophia, Lorén Niklas, Altskär Annika, Hermansson Anne-Marie
SIK, The Swedish Institute for Food and Biotechnology, Gothenburg, Sweden.
Biomacromolecules. 2009 Jun 8;10(6):1446-53. doi: 10.1021/bm900049a.
The effect of confinement on the structure evolution and final morphology during phase separation and gelation of gelatin and maltodextrin was investigated and compared to the structures seen in bulk phase. Emulsion droplets with diameters from 4 to 300 mum were analyzed using confocal laser scanning microscopy and image analysis. With the confocal laser scanning microscope it was possible to follow the entire phase separating process inside the droplets in real-time. The samples were either quenched directly from 70 degrees C down to 20 degrees C or exposed to holding times at 40 degrees C. Different cooling procedures were studied to examine the structure evolution both before and after gelation in the restricted geometries. The concentration of the biopolymer mixture was kept constant at 4 w/w% gelatin and 6 w/w% maltodextrin. The results revealed that the size of the confinement had a great effect on both the initiation of phase separation and the final morphology of the microstructure inside the emulsion droplets. The phase separation in small droplets was observed to occur at a temperature above the phase separating temperature for bulk. Small droplets had either a microstructure with a shell of maltodextrin and core of gelatin or a microstructure where the two biopolymers had formed two separate bicontinuous halves. The initiation of phase separation in large droplets was similar to what was seen in bulk. The microstructure in large droplets was discontinuous, resembling the morphology in bulk phase. The kinetics had an effect on the character of the maltodextrin inclusions, as the cooling procedure of a direct quench gave spherical inclusions with an even size distribution, while a holding time at 40 degrees C resulted in asymmetrical and elongated inclusions.
研究了受限条件对明胶和麦芽糊精相分离及凝胶化过程中结构演变和最终形态的影响，并与本体相中观察到的结构进行了比较。使用共聚焦激光扫描显微镜和图像分析对直径为4至300μm的乳液滴进行了分析。利用共聚焦激光扫描显微镜可以实时跟踪液滴内部的整个相分离过程。样品要么直接从70℃骤冷至20℃，要么在40℃下保持一段时间。研究了不同的冷却程序，以考察在受限几何结构中凝胶化前后的结构演变。生物聚合物混合物的浓度保持恒定，为4 w/w%的明胶和6 w/w%的麦芽糊精。结果表明，受限尺寸对乳液滴内相分离的起始和微观结构的最终形态都有很大影响。观察到小液滴中的相分离发生在高于本体相分离温度的温度下。小液滴要么具有麦芽糊精壳和明胶核的微观结构，要么具有两种生物聚合物形成两个独立双连续半部的微观结构。大液滴中相分离的起始与本体中观察到的相似。大液滴中的微观结构是不连续的，类似于本体相中的形态。动力学对麦芽糊精内含物的特征有影响，因为直接骤冷的冷却程序产生尺寸分布均匀的球形内含物，而在40℃下保持一段时间则导致不对称且拉长的内含物。
