Rheological properties of fruit purees: Effect of cooking

The rheological behaviour of different fruits (raspberry, strawberry, peach and prune), fresh or cooked, was determined using a rotational viscosimeter which allowed experiments to be conducted at different temperatures. The experiments were carried out at temperatures ran grig from 20 to 40 degrees C. The shear rate values ranged from 17.8 to 445 s(-1). The results were analysed by employing two different rheological models; Ostwald Waele and Herschel-Bulkley, and both of them fitted reasonably well the experimental data at all temperatures (R-2 > 0.998). Linear models were proposed to correlate the rheological parameters and temperature. The experimental measurements showed that the fruit purees studied have a non-newtonian behaviour and the apparent viscosity is influenced by the cooking. (c) 2006 Elsevier Ltd. All rights reserved.