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利用粒子跟踪技术探测微观流变学研究酸纳豆胶凝胶化的动力学。

On the kinetics of acid sodium caseinate gelation using particle tracking to probe the microrheology.

机构信息

Department of Food Science and Technology, School of Agriculture, Aristotle University, GR-541 24 Thessaloniki, Greece.

出版信息

J Colloid Interface Sci. 2010 May 15;345(2):278-85. doi: 10.1016/j.jcis.2010.02.005. Epub 2010 Feb 10.

Abstract

The sol-gel transition of a model dairy system (sodium caseinate solution) which undergoes gelation by acidification has been studied by conventional bulk rheology and particle tracking microrheology, via confocal microscopy. The Brownian diffusion of fluorescent microspheres (0.21, 0.32, 0.5, and 0.89 μm in diameter) with different surface coatings (polyethylene glycol, carboxylate groups and polystyrene) was used to probe spatial mechanical properties of the gels at the scale of microns. The microrheological results are compared with the macroscopic viscoelastic properties (storage and loss shear modulus) measured in a concentric cylinder rheometer (double gap, at shear strain of 0.005 and frequency of 1 Hz). At pH values close to pI of the caseins, where formation of a protein network, i.e., gelation, became obvious from the confocal microscopy and bulk rheological measurements, all the particles had a tendency to adhere to the network. In spite of this, the microrheological values of the moduli were only slightly lower than the macroscopically determined values and the gel points calculated via both techniques tended to be in good agreement. However, the particle tracking method has higher sensitivity and can detect changes in the structuring of the system before these are registered by the bulk rheological measurement.

摘要

通过共聚焦显微镜,利用传统的体相流变学和粒子追踪微流变学研究了通过酸化进行胶凝的模型乳制品体系(酪蛋白酸钠溶液)的溶胶-凝胶转变。不同表面涂层(聚乙二醇、羧酸盐基团和聚苯乙烯)的荧光微球(直径为 0.21、0.32、0.5 和 0.89μm)的布朗扩散用于探测微米级凝胶的空间力学性质。微流变学结果与在同心圆柱流变仪(双间隙,剪切应变为 0.005,频率为 1Hz)中测量的宏观粘弹性性质(储能和损耗剪切模量)进行了比较。在接近酪蛋白等电点的 pH 值下,从共聚焦显微镜和体相流变学测量可以明显看出蛋白质网络的形成,即胶凝,所有颗粒都有倾向于附着在网络上。尽管如此,模量的微流变学值仅略低于宏观确定的值,并且通过两种技术计算的凝胶点趋于很好地一致。然而,粒子追踪法具有更高的灵敏度,可以在体相流变学测量记录到之前检测到系统结构的变化。

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