Rheological behavior of dehydrated cranberry suspensions: Analysis of the influence of temperature and solid concentration on Casson´s model parameters

Resumo

Dehydrated cranberries (Vaccinium macrocarpon) are dried fruits known for their high antioxidant potential. Changes in their mechanical and rheological properties occur when cranberries are exposed to certain conditions, such as drying or immersion in a liquid medium (rehydration). To evaluate the rheological behavior of solid suspensions made from dehydrated cranberries, the effects of different temperatures and concentrations of dissolved solids were evaluated using a factorial experimental design (2²) with three replications at the center point. Five models were used to investigate the suspensions' flow behavior: Ostwald de Waelle, Newton, Herschel-Bulkley, Casson, and Bingham. The rheometry of the suspensions showed that the fluids presented non-Newtonian behavior, with a satisfactory fit for the Casson model (R² > 0.94) in all evaluated temperature and concentration ranges. Furthermore, the effects of temperature and solid concentration of cranberry suspensions on the rheological parameters of the fitted model, Casson's initial shear stress (K_0c), and Casson's plastic viscosity (K_c) were evaluated. From the response and the contour surfaces, it was found that increasing the concentration of the suspension above 20% resulted in higher initial shear stress, which was influenced by temperature, whose increase resulted in a significant reduction in the shear stress at a concentration of 30%. The plastic viscosity (K_c) was highly influenced by the solid´s concentration, and higher temperatures caused a decrease in the value of this parameter. So, the highest value of plastic viscosity was found for concentrations above 20% and at lower temperatures. Therefore, considering the results and for practical purposes, it can be concluded that the flow of the suspensions is facilitated if rehydration is conducted at high temperatures.