Determination and Modeling of Rheological Properties of Pumpkin Concentrate (Cucurbita maxima)

A rotational viscometer used to evaluate rheological parameters of pumpkin concentate with concentrations of 35, 50, and 65oBrix at respectively 35, 45, and 65oC. Then various mathematical models including Ostwald-de-Waele (power-law fluid), Bingham, Casson plastic, Herschel-Bulkley, Modified Casson and Sisko, which applied to define the flow characteristics of pumpkin concentrate. The results showed that the pumpkin concentrate behaves as non-Newtonian, shear thining fluid (n<1) in concentration and temperature ranges of 35-65oBrix and 35-65oC, respectively. The relationship between shear stress and shear rate of pumpkin concentrate showed that only Modified Casson models could describe the rheological parameters of pumpkin concentrate. Mathematical calculations showed that the consistency coefficient and fluid behavior index parameters of pumpkin concentrate were temperature dependence and time-independent, respectively. The Arrhenius equation showed that the activation energy (Ea) of pumpkin concentrate depends on two important parameters of brix concentration and apparent viscosity and changed from 0.076 to 20.34 (kJ/mol). The power-type and exponential-type equations adequately described the effect of concentration on the apparent viscosity of pumpkin concentrate. However, the exponential-type equation had a better fit for describing of noted behavour.