BRS CARMEM GRAPE JUICE CONCENTRATES: RHEOLOGICAL BEHAVIOR AND KINETICS STUDY OF ITS ANTHOCYANIN THERMAL DEGRADATION

Grape juices concentrated have a wide use, as they can be used in the wine industry as a chaptalization agent, in the production of fruit-based products such as jams, marmalades, jellies and various other food products. BRS Carmen is a late-ripening hybrid grape, resistant to fungal diseases. It was developed from the cross between Muscat Belly A and BRS Rúbea for the purpose of producing table wines and juices. During the process of concentrating of the grape juice and producing of derivatives, changes in temperature and concentration can affect some rheological parameters and some polyphenols such as anthocyanins. Thus, the study of the rheological behavior and kinetics of thermal degradation of anthocyanin is necessary, as a strategic tool to obtain processing conditions and preservation of processing characteristics. For the rheological behavior, the shear stress and strain rate data were adjusted using the OriginPro 8.0 software (OriginLab Corporation, Northampton, MA, USA) to the Newton, Ostwald-de-Waele, Bingham and Herschel-Bulkley models with in order to predict the consistency coefficient (k) and the flow behavior index (n) at different temperatures (274.15 - 343.15 K) and solids concentrations (13 - 45 ºBrix). Thermal degradation kinetics of anthocyanins was studied at temperatures between 274.15 and 363.15 K and at the same solid concentrations as in the rheological study. These conditions, the kinetic parameters of degradation were defined, namely: rate constant (k) and half-life (t1/2). The influence of temperature was given by the Arrhenius model. Statistical analyzes were obtained using the Minitab 19 software (Lead Technologies, State College, PA, USA) and submitted to ANOVA and Tukey’s multiple comparisons test (5% confidence level). The Ostwald-de Waele model fitted the concentrates rheological behavior with high accuracy. (R²>0.9999). The consistency coefficient varied significantly with increasing temperature and ºBrix and, therefore, it is possible to affirm that the consistency coefficient increased with solids concentrations and decreased with temperature. The flow behavior index also varied significantly with ºBrix and with temperature, but it was not possible to observe variations between all temperatures. The thermal degradation followed a first-order kinetic model. The kinetic rate constant of thermal degradation increased with increasing temperature and solids concentrations. The half-life (t1⁄2) decreased with increasing temperature and solids content. In addition, a decrease in activation energy was observed with increasing concentration. Thus, it is possible to conclude that the variation of concentration and temperature interfere in the rheological parameters and degradation kinetics and, with this, it is possible to predict an optimal condition for each situation.