Uticaj temperature i vremena čuvanja na reološke osobine odabranih kečapa od paradajza

Abstract

This article is focused on monitoring and evaluation of rheological properties of tomato ketchups. The aim of the work was to show the importance of the knowledge about rheological properties of materials and determine qualitative changes in ketchup behaviour dependent on temperature changes and storage time. The measurements of all samples were carried out under the same conditions in approximate temperature range (5 - 30) °C. First measurements were performed at the beginning of storing, second measurements were done after two weeks of storing and last measurements were realised after four weeks of storing. There were constructed dependencies of rheologic properties on temperature and storage time and evaluated by the regression equations and the coefficients of determination. Ketchup is a non-Newtonian material, so apparent viscosity was measured. The measurements of apparent viscosity were performed on a digital rotational viscometer Anton Paar DV - 3P. Densities of measured samples were determined according to definition. We found out that apparent viscosity of samples decreased exponentially with increasing temperature, so the Arrhenius equation is valid. Ketchup's fluidity was increasing exponentially with the temperature. We also found out that apparent viscosity had decreased with storage time and on the other hand fluidity was increasing with storage time, which can be caused by structural changes in samples during storing. Temperature dependencies of ketchup densities were sufficiently characterized by decreasing linear function in measured temperature range. The calculated rheological characteristics can be used for designing of technological equipment or containers for distribution of the product to the final users. The knowledge of flow behaviour is also important for the development of new recipes and direct qualitative assessment of the products.