The Herschel–Bulkley, Casson and Bingham rheological models were applied to describe the rheological properties of different juices. Rheological properties of juices were studied at a wide range of temperatures (5 to 100C) and shear rate range from 0.3 to 100/s using Brookfield Digital Viscometer.

Goldenberry (Physalis peruviana) juice was prepared and enzymatically treated with two dosages (300 and 600 ppm) of Pectinex Ultra SP-L, then, the juice was concentrated to 30 and 40☋rix.

Chemical, physical and sensory tests for tomato ketchups were made. The flow activation energy for viscous flow depends on the chemical composition the flow activation energy increases with the total solids contents. The effect of temperature on the viscosity can be described by means of an Arrhenius-type equation. Oscillatory test data revealed weak gel-like (dispersion structure) behaviour of the ketchup: the magnitudes of G′ were higher than those of G″, and both increased with oscillatory frequency. The η eff values decrease with an increase in temperature. Significantly higher correlation was found between η eff and temperature. The relationship between η eff and temperature of all the tomato ketchup brands under investigation was examined. The results indicated that these tomato ketchups behave as non-Newtonian fluids semi-solid and have a definite yield stress. The rheological behaviour of eight tomato ketchups measured in the shear rate range from 0.1 to 100 1/s and with oscillatory tests was studied over a wide range of temperatures (0–50 ☌) using a Physica UDS 200 rheometer.

Testing the viscosity of ketchup