Rheological characteristics of food gum (Cissus populnea)

Abstract

The rheological characteristics (consistency and flow behavior indices) of food gum (Cissus populnea)
exudates obtained from the fresh leaves and stem as well as dried leaves and stem were determined at
20, 30, 40, 50 and 60°C using a rotational viscometer at shear rates of 0.1, 0.2, 0.5, 1.0 and 1.5 rpm for
effective design and simulation of its momentum transfer process and system. The experimental design
used for the study of consistency and flow behavior indices of C. populnea at 20 - 60°C was
Randomized Complete Block Design (RCBD). The study revealed that consistency index (K) of C.
populnea exudates generally increased with increase in temperature. The K values for the fresh were
generally higher than the dried materials. The K values of the fresh stem exudates, which is more
viscous, were significantly (P 0.05) different from the less viscous fresh leaves exudates, but did not
show significant (P 0.05) difference with the dried leaves which became concentrated due to drying.
The flow behavior index did not show any defined trend with changes in temperature, and was not
significantly (P 0.05) different. The exudates generally exhibited pseudoplastic behavior at all the
temperatures studied. A study of the apparent viscosity of the exudates between temperatures of 20 -
150°C shows that apparent viscosity increased with increase in temperature below the boiling point of
70°C. However, above the boiling point, the apparent viscosity decreased with increase in temperature.
The viscosity-temperature data were fitted in Arrhenius-type equation and yielded activation energies
between 0.997 to 2.431 KJ/mol°C, corresponding to temperature range between 20 - 70°C and 1.632 to
2.580 KJ/mol with K corresponding to temperature range between 70 - 150°C.