酸奶的稳态剪切速率扫描特性的研究

Studies on the properties of shear rate sweep of yoghurt under the steady state

以酸奶为研究对象,本文建立了通过稳态剪切速率扫描评价酸奶特性的测试方法。对9类市面上流行的酸奶(包括7类类固体酸奶与2类饮用型酸奶)进行稳态剪切速率扫描,结果表明:酸奶具有明显的剪切稀化现象,剪切速率越低时酸奶的黏度衰减越快,当剪切速率增加后黏度衰减逐步减慢。另外,通过黏度曲线上不同剪切速率下的黏度可以用来评价酸奶的持水性、口感及管道流动与灌装情况,通过不同剪切速率下的剪切应力曲线上的平台区可以反映酸奶的屈服应力,其大小可以表征酸奶的持水性与结构稳定性,对于饮用型酸奶则无屈服应力的存在。本文还对方法的实验参数进行了优化,研究了上样后不同平衡时间对黏度测定的影响,以及研究了实验测试时达到稳态条件所需的最长时间。

A method for determination of evaluation of yoghurt properties by shear rate sweep under the steady state creep was established.The experiments of shear rate sweep on the 9 kinds of popular yogurts on the market including 7 solid-like yoghurts and 2 drinking-type yoghurts were tested.The results show that yoghurt has obvious phenomenon of shear thinning,the lower the shear rate is,the faster the viscosity of the yoghurt decreases,while the shear rate increases the viscosity attenuation gradually slows down.In addition,the viscosities on the viscosity curve at the different shear rate can be used to evaluate the water-holding property,mouth feel,pipe flow and filling,the platform on the shear stress curve as a function of shear rate can also be used to illustrate the yield stress which characterizes the water-holding property and structure stability while for drinking-type yoghurt there exists no yield stress.Meanwhile the experimental parameters of the method were optimized.The effect of different equilibrium time after loading the sample before test on the viscosity as well as the maximum time needed for steady state were studied.