Influence of pulsed electrical discharge, hydrostatic pressure and temperature on rheological properties of sunflower cake during oil pressing.

For the successful implementation of emerging electrical technologies in the oil pressing process, optimization of process parameters in combination with parameters from electrical process are crucial. The rheological property could be a simple and reliable efficiency indicatort of oil pressing. Knowledge of rheological properties is necessary for the design and development of appropriate equipment and process calculations. The objective of this work was to evaluate the effect of the following pre-treatments: pulsed electrical discharge (PED), temperature (28, 38 and 45 °C), overpressure (980, 1805 and 2800 Pa) and effect of initial oil content (40, 48.5 and 56%) on rheological properties of sunflower seed cake. The rheological behavior of sunflower seed cake was determined by using a rotational viscometer with a hydraulic system and thermostatic bath attached to the equipment. Using the mathematical apparatus and experimental data it was observed that the plastic viscosity of sunflower seed cake corresponds to the viscosity of the vegetable oil, which confirmed Bingham rheology assumption put forward in this work. Samples treated by PED had a modified material structure with an oil droplets and oil film on the surface. Single PED pre-treatment decreased initial shear stress from 24.36 to 22.89 Pa in samples where number of PED was 1800 per 60 s. Decrease in initial shear stress from 30.3 to 25.1 Pa was also observed when combination of temperature, pressure and PED was applied on seed cake. Reduction of the shear stress value, due to PED pre-treatment, enables to spend less energy during the oil pressing process. A positive linear relationship for overpressure and negative linear relationship for oil content and number of discharges on shear stress were obtained. The effect of temperature characterized by a decreasing of the plastic viscosity of the test material from 0.0985 to 0.0917 Pa s. The obtained parameters of the engineering rheological model allow prediction of rheological behavior of sunflower seed cake viscoplasticity flow over a wide range of shear rates in the pressing channel of the oil press.