Characterization of time dependent behaviour of non fat and full fat stirred yoghurt
Advancing the chemical engineering fundamentals
Rheology (T2-4P)
Keywords: stirred yoghurt, time dependent viscosity, thixotropy
The effects of temperature and shear rate on time-dependent properties of two stirred yoghurt types (Non Fat and Full Fat Stirred Yoghurt) were investigated using a rotational viscometer Viscotester VT550. It is Searle type, in which the outer cylinder is fixed and the inner cylinder rotates.
Experiments were carried out at different temperatures (10, 20 and 30 ºC) and three different shearing programs (50, 200 and 445 s-1). The range of shearing time was from 0 to 8000 s at fixed shear rate.
The rheological data of both yoghurt types were presented as a function of shearing time at fixed temperature and fixed shear rate. From the obtained results, it was found that the structure of the analyzed samples reached an equilibrium condition to a time of shear of about 25 minutes more or less.
The analyzed samples exhibited a time dependent behaviour at a constant shear rate. Additionally, it was observed that the thixotropic behaviour increased with increase in the shear rate and decreased with increase in the temperature.
Finally, four different models were used to predict the time dependent behaviour of both stirred yoghurt samples for each condition of temperature and shear rate, namely: Weltmann, Hahn, First order stress decay and Second order structural kinetic models.
See the full pdf manuscript of the abstract.
Presented Thursday 20, 13:30 to 14:40, in session Rheology (T2-4P).
