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 ofC. 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.

Key words: Rheological characteristics, consistency index, flow behavior index, Cissus populnea.