Effect of temperature, moisture and lipid content on the rheological properties of rice flour

The rheological properties of rice flour (RF) with 21%, 25% and 29% moisture (wet basis) and 3%, 5% and 7% lipid contents were studied using a capillary rheometer in a wide temperature and apparent shear rates ranges. The material exhibited a pseudoplastic flow behaviour, described by the power law model and its viscosity decreased with the increase of temperature, moisture and lipid content (up to 5%). Samples with 7% lipid content show wall-slip effects for all temperature and moisture content conditions. The consistency coefficient decreased with the increase of temperature, but not with the moisture or lipid content. The flow behaviour index did not exhibit a defined trend with the increase of any variable, i.e., temperature, moisture or lipid content. Two rheological models for the prediction of viscous behaviour of rice flour, both with a 96% accuracy, were determined with a multivariable linear regression method. The first model takes into account temperature, moisture content and shear rate while the second includes the lipid content. Finally, the degree of transformation induced by the processing of rice flour in the capillary rheometer, at different temperatures and moisture contents, was studied using a differential scanning calorimeter (DSC).