Modelling the Rheological Behaviour of Enzyme Clarified Lime (Citrus aurantifolia L.) Juice Concentrate

摘要

The rheological behaviour of enzyme clarified Lime (Citrus aurontifolia L.) juice was studied as a function of the total soluble solid (TSS) content (7.3-55.7°Brix), corresponding water activity (a_w) (0.985-0.831) at different temperatures (20-80°C) using co-axial controlled stress rheometer. The rheological parameter shear stress was measured up to the shear rate of 600 s~(-1). The investigation showed that the enzyme clarified lime juice and its concentrate behaved like a Newtonian fluid with the viscosity (eta) being in the range 3.964 to 50.290 mPa s depending upon the concentration and temperature used. The temperature dependency on the viscosity of lime juice was described by Arrhenius equation (gamma > 0.99) and the activation energy (E_a)of viscous flow was in the range 4.151 to 26.050 kj/mol depending upon the total soluble solids content. The effect of total soluble solid content on the flow activation energy was described by exponential type equation (gamma> 0.98) and that of water activity was described by both the power law and exponential equations (gamma > 0.99). The effect of total soluble solid content on the viscosity of lime juice followed the second order exponential equation (gamma > 0.99) at the temperature used. The effect of water activity on the viscosity was described by both the power law and exponential type relationship (gamma > 0.97). The equations relating to the combined effect of temperature and total soluble solids content/water activity on the viscosity of enzyme clarified lime juice were established.