搅拌型酸奶应力松驰行为的研究

Stress relaxation behavior of stirred yoghurt

目的以搅拌型酸奶为研究对象,建立一种应力松驰行为评价的测试方法。方法对酸奶施加应变,研究其松驰模量随时间的变化规律,并对方法的实验参数进行优化,并对市面上流行的7类搅拌型酸奶进行应力松驰行为的测试。结果通过应变扫描确定了酸奶的线性粘弹性区域,结合不同应变大小时的应力松驰实验结果,最终选择1%作为酸奶应力松驰实验特性研究时的应变值;进一步研究了不同松驰时间对松驰模量的影响,最终选择60 min作为松驰时间。酸奶在松驰初始阶段及松驰结束时的松驰模量差异明显,可以评判酸奶的弹性大小与松驰时间内松驰模量的损耗情况。酸奶的应力松驰行为可以通过6个Maxwell模型进行表征,不同松驰时间下起主要作用的应力松驰特征模量与特征时间的Maxwell模型数存在明显差异。结论通过应力松驰行为的测试可以评价搅拌型酸奶的粘弹性特性。

Objective To establish a method for determination of stress relaxation behavior of stirred yoghurt. Methods A certain strain was applied on the yoghurt and the curve of stress relaxation modulus was obtained as a function of time, and the experimental parameters were optimized and the stress relaxation behaviors of 7 kinds of popular stirred yogurt on the market were tested. Results The strain applied in the test was finally ascertained to be 1% through confirmation of linear visco-elastic region by strain sweep in combination with the results of stress relaxation properties tests under the conditions of different strains. Meanwhile, the effect of different relaxation time on the relaxation modulus was further investigated and 60 min was selected eventually as the relaxation time in the test. There were obvious differences between relaxation modulus at the initial and end time which could be used to evaluate the elasticity of yoghurt and loss of relaxation modulus in the relaxation time. In addition, the stress relaxation behavior of yoghurt could be characterized with 6 Maxwell models, and there were evident differences in the number of Maxwell models with stress relaxation characteristic time and modulus playing an important role at different relaxation time. Conclusion The viscoelasticity property of stirred yoghurt can be evaluated by the method of analysis of stress relaxation behavior.