A New Model to Describe Flow Behaviour of Concentrated Orange Juice

Abstract

The knowledge of rheological behaviour of juices and fruit derivatives is very useful both in the prediction of their stability and in process design, and it depends on the type of juice and on the raw material with which they are produced. Most of the equations that have been used to quantify flow behaviour describe the evolution of shear stress with the change of shear rate. Nevertheless, the essential variable in equipment design is viscosity. In this way, a mathematical model to easily describe the evolution of apparent viscosity of these non-Newtonian fluids with the shear rate would be very useful. In this work, a mathematical expression has been developed, fitted to experimental data and compared with the HerschelBulkley one. The obtained parameters with concentrated orange juice followed these trends: equilibrium apparent viscosity (η ∞ ) scarcely changed with temperature. Static apparent viscosity (η 0 ) decreased with increasing temperature, contrary to what happened with the flow behaviour constant k.

Rheological evaluation of Prunus mume pulp

“…All the samples (6, 7, 8 and 9 °Brix) evaluated at temperatures from 15 to 75 °C, showed a non-linear relation between shear stress and shear rate, indicating non-Newtonian behaviour, similar to that reported by several authors (CHIN et al, 2009;FALGUERA and IBARZ, 2010;IGUAL et al, 2010;TIZIANI and VODOVOTZ, 2005) for fruit juices. Preliminary experiments showed no significant dependence or slight thixotropy for mume pulp (BELIBAGLI and DALGIC, 2007).…”

“…In the same temperature range, carrot juice at 8.04 °Brix showed a consistency index of 0.03067 Pas n (VANDRESEN et al, 2009).This indicates that mume pulp, in addition to its soluble solids, has other factors which increase its consistency, such as pectin and low pH values, and that an increase in pectin results in an increase in the consistency index. The values for the consistency index of mume pulp were similar to those obtained for concentrated orange juice (FALGUERA and IBARZ, 2010). Tables 3 and 4 show that the values for the fluid behaviour index (n) were higher than those determined by the power law (Table 2).…”

“…Table 1 showed that the yield stress (τ 0 ) did not show consistent behaviour with regards to the variation in temperature between 15 and 75 °C for mume pulp from 6 to 9 °Brix. This situation was reported by Falguera and Ibarz (2010) for concentrated orange juice (65.3 °C with 6% pulp) at temperatures from -12 to 30 °C. However, it can be seen that the values for yield stress increased with an increase in concentration from 6 to 9 °Brix.…”

“…The Arrhenius equation is commonly used for rheological studies reported in the literature, and the effect of temperature on the viscosity can be determined in juices and pulps (ARSLAN et al, 2005;BELIBAGLI and DALGIC, 2007;FALGUERA and IBARZ, 2010;VANDRESEN et al, 2009):…”

“…The effect of temperature and concentration on the flow properties must be known to calculate and choose the right kind and size of equipment to ensure adequate heat and mass transfer operations (ALTAN and MASKAN, 2005;CHIN et al, 2009;FALGUERA and IBARZ, 2010;NINDO et al, 2005). The aim of this work was to evaluate the rheological behaviour of mume pulp at different concentrations and temperatures and fit the data obtained to well-known rheological models.…”