代可可脂巧克力浆的屈服应力

Yield Stress and Its Temperature Dependence of Chocolate Pastes Composed of Cocoa Butter Replacers

研究了可可粉与三种代可可脂组成的巧克力浆的流变性。在可可粉体积分数φ较低时，三种可可悬浮体均呈牛顿性，但当φ≥０．２时具有明显剪切稀化特征。悬浮体粘度服从一通用流变模型，当φ超过某一临界值而悬浮体有屈服应力时该模型自动转化为Ｃａｓｓｏｎ方程。屈服应力与颗粒体积分数的关系服从四参数方程，实验求出了全部模型参数。

The viscosity and yield stress of chocolate pastes consisting of three cocoa butter replacers (CBR) and cocoa powder were measured and studied. All tested pastes exhibit shear thinning behavior when volume fraction of particle φ ≥0.2. the shear viscosity follows a general model which reduces to Casson equation if yield stress exists when φ beyond a critical value. The relationship between yield stress and φ can be represented by a equation with 4 parameters. All model parameters were determined by experiments. The temperature dependence of yield stress of the pastes was obtained according to the collision theory of fine particles in dispersed medium.