Rheology and texture analysis as a tool for process control

Rheology is a study of the material flow and deformation under applied force. Rheology of yoghurt describes physical properties that are related to texture as a significant part of sensory product quality. It describes the behavior of food and helps to better understand different processes. At the same time, texture analysis is objective instrumental technique useful in maintaining of constant quality. The aim of this study was to analyze the rheological and textural properties of yoghurt samples produced on different process lines in the dairy plant “Spasojevic”, Bajina Basta, Serbia. Rheological properties of the yoghurt samples were monitored using low amplitude strain oscillation (Rheometer, Kinexus Pro, Malvern, UK) by measuring: (i) viscosity as a function of shear rate (ii) tixotropic behavior of yoghurts. Texture of yoghurt samples was measured by back extrusion test on the Texture Analyzer (Micro Stable System, UK) using a 35 mm diameter disc. Analysis included the measurement of firmness, consistency, cohesiveness and index of viscosity. Composition including dry matter, proteins and fat content as well as pH of samples was determined. The syneresis of yoghurt was determined by measuring of whey volume expelled from samples after centrifugation. Results showed that rheological and textural properties of yoghurt are highly dependent on its composition. The significant difference in yoghurt properties produced on different production lines was found. However, it appears that the differences are induced by processing factors and present on a daily basis. Based on current results, it could be concluded that this study has provided valuable information on how to optimize the processing parameters in order to achieve a constant and high product quality.