Reidratação de blueberry desidratada e comportamento reológico de suspensões

Abstract

Blueberry is a fruit with high moisture content, and it has limited availability to the consumer at certain times of the year. So, drying of the fruit is commercially interesting. Studies of drying / rehydration kinetics allow obtaining the necessary data to improve operations and equipment construction. The study of the rheological behavior generates results of interest for the transport of fluids in pipes. This work aimed to evaluate the rehydration kinetics of dehydrated blueberries and the rheological behavior of dried fruit suspensions. The blueberries were rehydrated in water and milk for 330 minutes at temperatures of 3, 29 and 45 ºC and the mass gain was accompanied by periodic successive weighing. Experimental data on rehydration kinetics in both media were adjusted to Fick's Law and to the seven empirical / semi-empirical models commonly used to describe food drying. The rheological behavior was studied by testing the hardness of fruits before and after rehydration (water / 29 ° C / 45 min); and the shear stress variation versus the deformation rate of rehydrated blueberry solids suspensions. The experimental data were adjusted to six mathematical models commonly used to describe the rheological behavior of foods. A factorial design 22 with three central points was used to evaluate the influence of the temperature of analysis and concentration of suspended solids on the rheological behavior of dehydrated berries. Fick's Law was reasonably adjusted to rehydration data, and it was possible to verify that the milk diffusion coefficients for fruits were higher than those for water, a fact related to mass transport. Diffusion coefficients were higher with increasing rehydration temperature. The best fit of the experimental data during the rehydration of the berries in water to the Logarithmic models at 3 ° C, Verma and Diffusion approximation at 29 ° C and Verma, Logarithmic and Diffusion approximation at 45 ° C was verified. For rehydration in milk, the models that presented the best fit to the experimental data were those of Page and Henderson and Pabis at 3 ° C and Verma, Logarithmic and Diffusion approximation at 29 ° C. It was found that the hardness of rehydrated blueberries was lower than that of dehydrated ones and that the hardness of rehydrated berries in milk was significantly higher than that of rehydrated in water. All experimental rheometry data of the rehydrated blueberry suspensions were suitably adjusted to the Bingham model, whose parameters were used as experimental planning responses. The effects of the independent variables and their interactions were not significant on Bingham's yield stress and plastic viscosity responses within the studied ranges of temperature and concentration. The tendencies of increase of the limit tension with the increase of the variables and reduction of the plastic viscosity with the increase of the temperature were verified.