Indexed on: 05 Jul '11Published on: 05 Jul '11Published in: Journal of the American Oil Chemists' Society
Rheological behavior of six crude rapeseed oils with different extraction methods including hot-pressing, solvent-extraction and cold-pressing were studied. Viscosities of the oils were measured with shear rates ranging from 0.1 to 200 s−1 at three different temperatures. The Casson model was used to fit the experimental data and the Arrhenius equation was applied to estimate the energy of activation for viscosity (Ea). The extraction methods affected the total tocopherol, total phytosterols, total phenols, phosphorus and fatty acid composition. The hot-pressed medium-erucic rapeseed oil (HMRO) had the greatest viscosity, and the cold-pressed low-erucic rapeseed oil (CLRO) had the lowest viscosity among all the oils with shear rates >5 s−1 at 10 °C. The crude rapeseed oils exhibited Newtonian behavior at higher shear rates. The significant difference of viscosity of the six oils was reduced with increasing temperature, and there was no significant change (P > 0.01) among the oils with a shear rate of 100 s−1 at 50 °C. According to the values of Ea, the following order of a change in viscosity was obtained as follows: CMRO > SMRO > HMRO > CLRO > SLRO > HLRO(C, cold pressed; S, solvent extracted; H, hot pressed; M, medium erucic; L, low erucic; RO, rapeseed oil). Minor components may be the contributing factors for the values of Ea of rapeseed oils. The higher shear limiting viscosity (ηc) values calculated by the Casson model decreased as the temperature increased, but no significant change (P > 0.01) was observed for ηc by using different extraction methods at 50 °C.