Summary

The flow properties of ketchup were assessed upon addition of commonly used food thickeners: guar, xanthan and CMC gum at three different concentrations (0.5%, 0.75% and 1%) and four temperatures (25, 35, 45 and 55 C). The ketchup without supplementation served as a control. All ketchup formulations exhibited non-Newtonian, pseudoplastic behaviour at all temperatures and hydrocolloid levels. The Powerlaw and Herschel-Buckley model were successfully applied to fit the shear stress versus shear rate data. The flow behaviour indices, n and n¢, varied in the range of 0.189–0.228 and 0.216–0.263, respectively. The consistency coefficients, k and k¢, were in the range of 8.42–27.22 and 6.56–20.10 Pa sn , respectively. The addition of hydrocolloids increased the yield point (s0) and apparent viscosity of the ketchup in comparison to that of the control. The Arrhenius equation was successfully used to describe the effects of temperature on the apparent viscosity of the prepared formulations. The Ea value appeared in the range between 5492.6 and 21475.8 J mol)1 .