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Azam Eslami FARD, Somayeh Taghian DINANI; Evaluation of effects of temperature, concentration, and shear rate parameters on the time-dependent behaviour of peach syrup; Recent Advances in Food Science; 2018; 1(3): 120-133
In order to achieve a product with considerable nutritional advantages and appropriate preservability, the industrial peach syrup production has been taken into consideration. The essential point is that being aware of the exact and complete rheological properties of this product, especially its time-dependent rheological (TDR) behaviour, will play a key role in quality control and designing apparatus for industrial factories manufacturing this product. In this study, the TDR behaviour of peach syrup was investigated using a Brookfield viscometer at two concentration levels of 40 and 50 °Brix, three temperature levels of 15, 25, and 45 °C, and three shear rate (SR) levels of 20, 35, and 50 l/s. To examine the influences of the mentioned independent parameters, the graphs of shear stress (SS) versus SR and apparent viscosity (AV) versus time of applying the SR were plotted. The analysis of these graphs specified that as temperature and SR rose or the time of applying a constant SR passed, the AV of peach syrup lessened. In order to designate the TDR behaviour of peach syrup, first order stress decay model with a zero-equilibrium stress value, first order stress decay model with a non-zero equilibrium stress value, Weltman and second-order structural kinetic models were used. The results revealed that the Weltman model with an R2 equal to 0.9610 was the best model to describe the TDR behaviour of peach syrup from among the four models used. In this model, with the SR increasing, the values of parameter A (initial SS) and parameter B (describing a time-dependent behaviour and extent of structure breakdown) improved. Generally, the results displayed that peach syrup had a non-Newtonian time-dependent behaviour of the thixotropic type.