Rheological properties of blueberry puree for processing applications

Rheological properties of purées made from small fruits like blueberries are important for application in handling and thermal processing where their physical and/or chemical attributes can be altered. Flow of purées made from highbush blueberry (Vaccinium corymbosum L.) was investigated in the 10–1000 s−1 shear rate range with the objective of determining the influence of temperature and solids content on the rheological properties. The rheological behavior was well described by the three-parameter Sisko model. The activation energy of flow (EaEa) calculated with respect to apparent viscosity at 100 s−1 increased from 11.4 to 17.1 kJ/mol for purée with 10% and 25% total soluble solids, respectively. When evaluated in terms of consistency coefficient, the activation energy varied between 10.7 and 21.7 kJ/mol within the same range of solid contents. For the conditions investigated, a mathematical model that is suitable for describing the influence of temperature and dissolved solids on the apparent viscosity of blueberry purée was obtained. The rheological behavior of 10–20 Brix blueberry purée was well predicted (R2=0.99R2=0.99). Further investigation is needed to improve the model to cover a wider Brix range.