Application of Universal Testing Machine (Instron) for evaluation of yoghurt rheological properties

Texture is one of the most important food properties. The evaluation of texture in food products can be a useful measure to ensure food quality. Texture and curd strength of yoghurt are important quality attributes. In this study, rheological properties (force, Couchi strain, stress, Young module) of three different yoghurts (two low and high fat samples and one sheep yoghurt) were evaluated using Universal Testing Machine (Instron). Furthermore, the optimization of test conditions was carried out. The best conditions were found as follows: probe diameter 75 mm, probe penetration in container 45 mm, chart to crosshead speed ratio 2:1, crosshead speed 50 mm/min and instrument “fullscale” 5 N. The results showed that curd strength in full fat and sheep yoghurt was higher than that of low fat yoghurt, perhaps due to more fat and consequently higher dry matter of yoghurt. Stress and elasticity modules in full fat, low fat and sheep yoghurts were 2246 N and 9018.7 Pa; 1222 N and 4346.9 Pa; 2004 N and 8407 Pa, respectively. This study confirmed the possibility of application using Instron machine (model 1140) in evaluating rheological properties of yoghurt.