Influência da crioconcentração nas propriedades reológicas de sucos de uva

Abstract

Grape juice is a clear or turbid liquid extracted from grape by means of suitable technological processes. Freeze concentration is a technique that has the advantage of maintaining nutritional quality and volatile compounds from the product. Studying of the rheological behavior assay is essential to get efficiency in processes of dimensioning, reduction of expenses with formulations and preparation of the product. The objective of this study was to evaluate the influence of freeze concentration in of the rheological properties whole grape juices (green and red). It was observed that three consecutive stages of freeze concentration increased the total soluble solids content of green grape juice from 18.50 °Brix to 45.00 °Brix, which epresent 2.43 from the initial value. The red grape juice increased from 16.50 ºBrix to 44.52 °Brix, representing 2.70 from the initial value. In terms of efficiency, freeze concentration of green grape juice was more efficient than red grape juice, since the values of the effective partition constants (k) for both processes were 0.34 and 0.29, respectively. For both juices, freeze concentration was a satisfactory method for a concentrated product. The effect of temperature on the juices rheological behaviour was evaluated (from 10 to 40 ºC) through rheological analysis. The flow curves demonstrated Newtonian behavior to obtain the whole grape juices freezeconcentration, with satisfactory adjustment to Ostwald-de-Waelle equation. The effect of temperature on the apparent viscosity of the juices was verified through the Arrhenius equation and their activation energy were analysed, which higher value was obtained for freeze-concentration green grape juice.