Trinh Binh, Haisman Derek, Trinh Khanh Tuoc
Institute of Food, Nutrition and Human Health, Massey University, Private Bag 11 222, Palmerston North, New Zealand.
J Dairy Res. 2007 Feb;74(1):106-15. doi: 10.1017/S0022029906002366. Epub 2007 Jan 11.
Age thickening is a well known phenomenon within the dairy industry, where the apparent viscosity of concentrated dairy solutions increases with storage time under low shear. The objective of the paper is to develop new tools to analyse several aspects of age thickening, including the increases in shear thinning, the degree of thixotropy and the rate of structural build up with time, as well as irreversible structural changes and gelation. The build up of the dispersed phase structure during storage, was captured by a snap shot technique, where concentrated milk samples were stored, and aliquots were taken at periodic intervals and subjected to shear sweep tests to collect flow curves. Rheological modelling using the Herschel-Bulkley model showed an increase in yield stress and consistency, indicating a build up in structure during age thickening. The trend in apparent viscosity with storage time showed two-phases, a slow and steady increase followed by a sharp rise, which could be used to identify the onset of firm gelation. The extrapolated viscosity at infinite shear rate increased with storage time, indicating the build up in irreversible structural components during age thickening.
在乳制品行业中，老化增稠是一种广为人知的现象，即在低剪切力下，浓缩乳制品溶液的表观粘度会随着储存时间的增加而升高。本文的目的是开发新工具，以分析老化增稠的几个方面，包括剪切变稀的增加、触变性程度以及结构随时间的形成速率，以及不可逆的结构变化和凝胶化。通过快照技术捕捉储存过程中分散相结构的形成，即储存浓缩牛奶样品，定期取出等分试样并进行剪切扫描测试以收集流动曲线。使用赫谢尔-巴克利模型进行流变学建模显示屈服应力和稠度增加，表明在老化增稠过程中结构在形成。表观粘度随储存时间的变化趋势呈现两个阶段，先是缓慢而稳定的增加，随后急剧上升，这可用于确定牢固凝胶化的开始。无限剪切速率下的外推粘度随储存时间增加，表明在老化增稠过程中不可逆结构成分在形成。
