RHEOLOGICAL ANALYSIS OF INCORPORATED PSYLLIUM YOGURT

The study of rheology is indispensable in food processing operations where the rheological properties of the product affect the quality of the finished product. The objective of this work was to evaluate the rheological behavior of yogurts with the addition of ground whole psyllium and its mucilage and compare it with a standard formulation. Formulations incorporated with 1% (F1) and 2% (F2) of psyllium and formulations incorporated with 1% (F3) and 2% (F4) of psyllium mucilage were prepared, in addition to a standard formulation (C). The rheometric analysis was performed in a viscometer (Brookfield DV-III Ultra) with concentric cylinders. The samples were analyzed at a temperature of 10 °C, varying the spindle rotation speed from 10 to 110 rpm, with readings being taken at ascending and descending speeds (nine in each). For each speed, the shear stress, the shear rate and the apparent viscosity were recorded. The data obtained were used to predict the rheological behavior of each sample, based on the models predicted in the literature. All formulations showed a decrease in viscosity with increasing shear rate. For ascending velocities, formulations C, F1 and F2 were fitted by the Bingham model, while formulations F3 and F4 were fitted by the Ostwald de Waelle model. For descending speeds, formulations C, F3 and F4 were fitted by the Herschel-Bulkley model, while formulations F1 and F2 were fitted by the Bingham model. The rheometry showed that the addition of psyllium and its mucilage alter the rheological characteristics of the yogurt (compared to the standard), both from the point of view of the increase in viscosity and the behavior of the fluid, since the samples added with psyllium do not presented the phenomenon of thixotropy, related to the formation of gel-sol, generally observed in yogurt samples.