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 (aw) (0.985–0.831) at different temperatures (20–80oC) 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 (η) 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 (r > 0.99) and the activation energy (Ea) 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 (r > 0.98) and that of water activity was described by both the power law and exponential equations (r > 0.99). The effect of total soluble solid content on the viscosity of lime juice followed the second order exponential equation (r > 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 (r > 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.