The objective of this study was to obtain a pre-gelatinized flour from a mixed rice and bean flour, and to evaluate the influence of the formulations and processing conditions on the technological properties and protein content of the final product. A complete 2³ factorial design was adopted with central and axial points to prepare the mixed pre-gelatinized flour, varying the following parameters: percent of bean flour, moisture content and processing temperature. The responses were: protein content (Y1), water absorption index (Y2) and water solubility index (Y3). The formulations were processed in a single screw extruder. The temperature in zone 3 of the extruder varied between 46 and 114 °C, according to the experimental design. The processed products were dried in an air circulating oven at 50 °C for about 15 hours, presenting a final moisture between 4 and 6%, and were then ground in a knife mill and packed into polyethylene bags until analysed. For the protein content, only the percent bean flour was significant and with a positive effect, that is, the higher the bean flour content, the higher the protein content of the final product, independent of the processing conditions - temperature or moisture. For the water absorption index (WAI), the moisture content, temperature and moisture and temperature interaction were significant. Higher WAI values were observed at intermediate temperatures (60 to 80 °C) and high moisture contents (17 to 20%). For the water solubility index (WSI), the moisture content, temperature and moisture e temperature interaction were again significant, higher WSI values being observed at higher temperatures (100 °C) and lower moisture contents (14%). According to the experimental design, the pre-gelatinized mixed rice and bean flour showed the best technological characteristics when processed at a temperature of 70 °C with 21% moisture content and the addition of 30% bean flour to the mix.
Thermoplastic extrusion; Experimental design; Pre-gelatinized flour; Technological properties
