The objective this study was determinate the rheological behavior of pineapple juice natural and treated with pectinolytic enzymes. Tests for optimization of enzyme activity used in treatment were realized using a complete factorial planning 2k, with three repetitions of center point and two independent variables (temperature and time of treatment). In evaluation of rheological behavior of pineapple juice, were utilized two samples submitted to sieving (N and D), analyzed in four different temperatures (10, 25, 50 e 65 °C). The rheological analyses were realized using a Brookfield concentric cylinders viscometer and the relationship in the temperature and apparent viscosity was described by an equation type Arrhenius. The experimental data were adjusted by the Mizrahi-Berk model. The optimization tests indicated by ANOVA and response surface methodology that the variables temperature and time of treatment have statistically significant effect (p<0,05) on concentration of pectin present in the samples. The enzymatic treatment was carried with an enzyme concentration of 150 mg.L-1, temperature at 50 °C and treatment time of 80 minutes. The model used was adequate to describe the rheological behavior of the juices according to the parameters R², χ² e Bf. The reduced values of the behavior index (0.61-0.83 for natural juice and 0.57-0.72 for despectinized juice) indicated the pseudoplastic behavior (n<1). The temperature influenced the yield stress and apparent viscosity of the juices analyzed, where the minors values were observed in samples treated at 65 °C, 2.4 mPa.s and 1.4 mPa.s, respectively, for the natural and despectinized samples. The equation of Arrhenius described satisfactorily the effect of temperature in the apparent viscosity. The activation energy values (Eat) was of 4.54 Kcal.g.mol-1 and 4.89 Kcal.g.mol-1, respectively, for the natural and despectinized samples of pineapple juice, increasing with enzymatic treatment. The enzymatic treatment decreased the values of rheological behavior parameters for samples of pineapple juice, and the apparent viscosity for all temperatures used, where the largest percentage reduction was observed at 65 °C (41.66%).
Fruit juice; apparent viscosity; Arrhenius equation; despectinization
