Effect of temperature, concentration, and pressure on the viscosity of pomegranate and pear juice concentrates Original Research Article

Viscosities of two fruit (pomegranate, Punica granatum L., and pear, Pyrus communis) juices have been measured with a capillary flow technique. The range of measurements was for pomegranate juice: from 293.15 to 363.15 K at atmospheric pressure 0.101325 MPa and for concentrations 23, 30, 35, and 40 °Brix; for pear juice: from 298.15 to 363.15 K at atmospheric pressure and for concentrations 20, 25, and 30 °Brix. For two selected concentrations (11.0 °Brix for pomegranate and 15.2 °Brix for pear juice) the measurements were performed at three pressures (0.101325, 5, and 10 MPa) in the temperature ranges between 292.95 and 402.95 K for pomegranate juice and from 294.10 to 402.71 K for pear juice. The total uncertainty of viscosity, pressure, and temperature measurements were estimated to be less than 1.7%, 0.006%, and 0.025 K, respectively. The effect of temperature, pressure, and concentration on viscosity of pomegranate and pear juices were studied. Arrhenius type correlation equation for viscosity was used to represent the temperature dependence of viscosity. The values of the Arrhenius equation parameters (flow activation energy) were calculated for the measured viscosities of pomegranate and pear juices as a function of concentration and pressure. The AAD between measured and calculated values from this correlation equation for the viscosity was 2.0% for both pomegranate and pear juices. Different theoretical models for the viscosity of fruit juices were stringently tested with new accurate measurements on pomegranate and pear juices. The predictive capability of the various models was studied. The behavior of the concentration, temperature, and pressure dependences of the viscosity of pomegranate and pear juices are discussed in light of the various theoretical models for viscosity of fruit juices.