FOOD. Science. Technology. Quality

Food. SCIENCE. Technology. Quality

Food. Science. TECHNOLOGY. Quality

Food. Science. Technology. QUALITY




Rheological properties of extrudates containing wheat components


The objective of the study was to determine the effect of the following factors on the dynamic viscosity coefficient of water slurries of extrudates: wheat components added, moisture content of raw material, temperature distribution profile in a barrel, and die diameter. Rheological properties were measured using a Mettler Rheomat RM 180. A mixture of corn semolina and wheat components (wheat bran and wheat meal) was extruded using a twin screw extrusion-cooker, type 2S-9/5. For the investigated ranges of process parameters and raw material features, it was possible to obtain stable working conditions even when the content of the above indicated components was 80%. On the basis of viscosity curves representing a relationship between the viscosity and the wheat components content, it was evidenced that there existed a high potential for modifying viscosity of slurries in a range from 0.011 Pa·s to 0.018 Pa·s. The extrudates containing 80% of wheat components (meal to bran rate = 1:1) showed the highest viscosity. Furthermore, it was stated during the ensuing investigations that the viscosity of slurries highly depended on the process temperature. An increase in the temperature during the extrusion process caused a decrease in the suspension viscosity. The highest viscosity (0.016 Pa·s) was obtained when the temperature distribution in the extruder barrel, was as follows: 80/100/120/110/130°C. This fact confirmed a general rule that higher temperatures caused a more intense depolymerization of starch, and, in the consequence, a decrease in the viscosity. Additionally, slight changes were stated in the viscosity of water slurries of extrudates produced at different levels of raw material moisture. This phenomenon could be attributed to the specific construction of the counter-rotating extrusion-cooker used to perform investigations since the duration time of the material staying in it had a rigid time distribution characteristic.


extrusion, viscosity, wheat bran, wheat meal