Modeling the rheological properties of currant paste as a function of plasticizers concentration, storage temperature and time and process temperature

Abstract

The steady and dynamic shear rheological properties of currant paste samples as a function of storage temperature (15, 25 and 35 °C) and time (180 days) and plasticizers content (water and/or glycerol) have been evaluated. Apparent viscosity (ηa) has been found to be significantly increased with prolonged storage, implying possible structural changes, and decreased with the increase in storage temperature and the addition of water or/and glycerol. Flow behavior index and consistency index were determined by fitting the resulting experimental data to a power law equation with high values of correlation coefficients (R2 ≥ 0.912). Furthermore, the combined effect of storage temperature, time and plasticizers concentration on the apparent viscosity was described adequately by a proposed empirical model, with low standard relative errors (SRE ≤ 0.011). Additionally, the viscoelastic properties were significantly affected by all evaluated parameters in the same way as in apparent viscosity while both moduli (G′ and G″) were modeled sufficiently (R2 ≥ 0.884) as power functions of oscillatory frequency. The heat treatment (heating from 25 to 100 °C and cooling back with a rate of 10 °C/min) applied has proved sufficient to reverse the observed storage effects. Moreover, the modified Cox-Merz rule was satisfactorily applied to describe the correlation between the apparent viscosity and the complex viscosity.