of Process Sciences, Technical Univ. Berlin, Germany.
Abstract
The rheological behaviour of tomato juice, puree and
paste were measured in shear rate range 0.0 to 100 s-1 and
Oscillatory tests were studied at a wide range of temperatures
(0 - 50 °C) using a Physica UDS 200 rheometer. The results
indicated that these tomato juice, puree and paste behave as
non-Newtonian fluids (pseudoplastic) and have a definite
yield stress. The relationship between (ηeff) and temperature
of tomato products under investigation was examined. Higher
significantly correlation was found between (ηe
ff) and
temperature. The ηeff decrease with increase in temperature.
Oscillatory test data revealed weak gel-like (dispersion
structure) behaviour of the tomato products: magnitudes of G´
were higher than those of G´´, and both increased with
oscillatory frequencies. The effect of temperature on their
viscosity can be described by means of an Arrhenius-type
equation. The flow activation energy for viscous flow depends
on the chemical composition; the flow activation energy
increases with the total solids contents. Chemical and physical
tests for tomato products were made.
Key words: Tomato juice puree and paste. Rheological
parameters. Flow behaviour. Oscillatory test. Activation
energy. Chemical composition |
