Comportamento viscoso de polpas de umbu-cajá com diferentes teores de sólidos.

Abstract

This work was developed with the objective of determining the physiochemical characteristics of umbu-cajá (Spondias spp) pulp in six solid concentrations and of studying the rheological behavior of the samples in six temperatures. The umbu-cajá pulp was used in concentrations 9, 13, 15, 18, 21 e 24 °Brix in which the pH, total solid concentration, ash, insoluble solid and pectins were determined. The rheological study was developed in the temperatures of 10, 20, 30, 40, 50 and 60 °C, and the rheometrical measurements were obtained frora a RVT Brookfield viscosimeter, with rotation speed of 0.5, 1, 2.5, 5, 10, 20, 50 and 100 rpm. The data concerning experimental apparent viscosity versus temperature were adjusted according to linear equations, while the experimental data concerning sher stress versus shear rate were adjusted according to Ostwald-de- Waelle, Casson, Mizrahi & Berk e Herschel-Bulkley rheological models. The soluble solid concentration for the integral umbu-cajá pulp fruit was 13 °Brix, with a 2.6 ph, pectin concentration of 0.5% of calcium pectate, leached ashes text of 0.54 %, with total solid concentration 11.19% and 1.01% of insoluble solids. Ali samples presented non-newtonian and pseudoplastic behavior. The average apparent viscosity values varied frora 0.04 to 51.12 Pa.s, and they increased for concentrations between 9 and 18 pBrix, besides decreaseig with the raising of temperature and were predicted satisfactorily, according to a linear dependency relation with the temperature. The temperature variation had more significant influence over samples with higher solid concentration. Herschel-Bulkley model adjusted better the experimental data of shear stress and shear rate.