Physical-chemical characterization of pre-cooked mixed rice flour and barley bagasse

Abstract

The extrusion processing parameters, chemical composition and water content of the flour mixture may affect the structure of rice flour, leading to products with different rheological behavior and hygroscopicity. Therefore, this work aimed to study the rheological properties and water adsorption of mixed flours of broken rice and barley bagasse obtained by extrusion cooking. Samples were prepared from a mixture of grits/bagasse between 82/18 and 73/27 (w/w) with water content between 18.04 and 26.96%, using a single screw extruder. The rheological properties of the extruded flour were determined by a rapid viscosity analyzer to evaluate the cooking profile of the pastes by observing the pasting temperature, maximum viscosity, breakdown and retrogradation. The adsorption process was performed by weighing the samples stored at temperatures of 25, 30, 35 and 45 °C with water activity between 0.112 and 0.973. The isotherms were fitted using the following mathematical models: Halsey, Oswin, Smith, GAB and Peleg. The extruded composite flours were characterized by their lack of initial viscosity. The pasting temperature (40-67 °C), maximum viscosity (690-1146 cP), breakdown viscosity (0-175 cP) and retrogradation (613-1382 cP) were lower than for raw rice flour. The Peleg equation fitted well to the water adsorption data and can be used to represent the sigmoidal type II shape of the water adsorption isotherms for the extruded mixed flours from rice grits and barley bagasse.