Rheological Behavior and TERMAL Degradation Kinetics of Anthocyanins of BRS CARMEM Grape Concentrated Juice

The use of BRS Carmem grape becomes favorable due to the extension of the harvesting and processing period. During the grape juice concentration process, changes in temperature and concentration might affect some rheological parameters and polyphenols such as anthocyanins. Therefore, studying the rheological behavior and thermal degradation kinetics of anthocyanins is mandatory, as it may be a strategic tool for obtaining optimal conditions for processing and preserving the juice features. Rheological models were fitted to predict the consistency coefficient (K) and fluid behavior index (n) at different temperatures (1°C–70C) and solid concentrations (13°Brix–45°Brix). The thermal degradation kinetics of anthocyanins was studied to define the rate constant (k) and half-life (t_1/2) at temperatures between 1°C and 90°C at the same solids concentrations as in the rheological study. The model that best-fitted rheological data was the Ostwald-de-Waele model (R² > 0.999). The consistency coefficient (K) tends to increase with°Brix and decrease with temperature (p < 0.05). The fluid behavior index (n) also varied significantly with°Brix and temperature, but it was not possible to observe variations among all temperatures. Anthocyanins degradation followed a first-order reaction model. Anthocyanins degradation rate tends to increase with higher temperature and solids content, and half-life (t_1/2) tends to decrease with increasing temperature and°Brix. Furthermore, using the Arrhenius model, a decrease in activation energy was observed with increasing concentration. Thus, it was possible to conclude that the variation in concentration and temperature interferes with the rheological parameters and degradation kinetics.