Rheological study of ternary mixtures and pectic gels of red fruit pulps

In this work, the rheological behaviour of ternary mixtures of strawberry, blackberry and raspberry pulps in steady shear was studied using the response surface methodology. In addition, the rheology of pectic gels extracted from these pulps was investigated by means of oscillatory shear tests. The flow curves were adequately described by the rheological model of Herschel-Bulkley. All the formulations analysed exhibited shear-thinning behaviour. The rheological responses were influenced by the difference in pulp proportions and also by the temperatures (20 and 60 degrees C). The quadratic and cubic models used to fit the response were considered suitable owing to the higher values of determination coefficient (R-2). The pectic gels from strawberry, blackberry and raspberry showed a strong gel character, with strawberry presenting the stronger gel, which was confirmed by the Cox-Merz experiment, degree of esterification and average molecular weight data.