Rheological properties of rice bran (Oryza sativa L.) oils processing and soapstock distillation residue

The oil extraction process involves different temperatures and the knowledge of viscosity is necessary for the design and development of appropriate equipment and processes calculations. The aim of this study was to evaluate the effect of temperatures (30, 45, 60, 75, 90 °C) in the initial stage of rice bran (Oryza sativa L.) oil processing (crude oil, degummed oil) and evaluate the effects of temperature on viscosity in the rice bran oil soapstock distillation residue (RDS), with great potential for use in food and pharmaceutical industry. The rheological behavior of the oils was determined by using a concentric cylinder rotational viscometer, with a thermostatic bath attached to the equipment. The viscosity values found at constant shear rate (40 s−1) and 30 °C was 0.1240, 0.0699, 0.1720 Pa s for crude oil, degummed oil, and RDS, respectively. The viscosity curves vs. shear rate were applied to Bingham and Casson models, except for the crude oil where only the Bingham model has obtained a good adjustment. The shear stress curves vs. shear rate were applied to Newton and Ostwald-de-Waele models. Excepting the crude oil, all the other adjustments had a coefficient of determination (R2) greater than 0.97, indicating a good adjustment of the experimental curves. Based on the degree of viscosity reduction (DVR) and it was found that the viscosity of all the three oils reduced approximately 90% from 30 to 90 °C and the Andrade model was obtained a good adjustment to the data of viscosity curves vs. temperature. Finally, it was found that the viscosity of the three oils studied decreases sharply with increasing temperature, and the RDS has the highest viscosity among the tested oil, followed by crude oil and crude degummed oil. A correlation between the unsaturation degree of fatty acids and oils viscosity has not been found.

► We evaluate the effects of temperature on oils viscosity of rice bran oil processing.
► The rheological models were obtained a good adjustment to the oils data.
► The Andrade model was obtained a good adjustment to the oils data.
► The rice bran crude oil has shown to be rheologically unstable at high temperatures.