Rheological behaviour of blueberry cloudy juice (Vaccinium corymbosum L.)

The rheological behaviour of blueberry cloudy juice (Vaccinium corymbosum L.), prepared from fresh berries, was studied as a function of solids concentration, in the range 25-61 °Brix, at different temperatures (5-50 °C), with a control rate (CR) rheometer. Cloudy juice was concentrated by vacuum evaporation, and solutions at other concentrations were prepared from the concentrate by adding the liquid collected as distillate. The juices were slightly thixotropic between 45 and 61°Brix. For lower concentrations, the thixotropy was low and could be easily eliminated by shearing. The power law model was applied to fit the pseudoplastic behaviour. The activation energy for flow, evaluated with the Arrhenius-Guzman equation, increased with solids concentration and ranged from 4.6 to 24 kJ gmol^-1. A non-linear correlation, accounting for temperature and concentration effects on the consistency coefficient, was identified.