Processing and characterization of extruded pearl millet flours from decorticated and whole grains

Different processing methods can be applied to pearl millet (Pennisetum glaucum (L.) R. Br.) grains, like milling, decortication, and extrusion. Significant nutrient losses happen in the production of refined flours by removing the germ and bran, therefore, the use of whole grains in the bakery industry has increased in Brazil. Thus, the objective was to produce refined and whole-grain pearl millet flours, cooked by the thermoplastic extrusion process or not, and to characterize them in terms of granulometry, color, and water absorption index (WAI). The whole grains of pearl millet (ADRG 9070 – Atto Sementes®) were cleaned and the decortication, when applied, was made by mechanical abrasion. To obtain the extruded flours, the raw flours (decorticated or not) were fed at 10 kg.h-1 into a twin-screw extruder with speed of 250 rpm and temperature profile of 25, 25, 60, 90, 120, 120, 120, 90, 60 and 60 ºC, the extrudates were dried in an air circulation oven and milled. The raw whole-grain flour presented a lower value of L* (71.74), due to the reduced content of pigments responsible for a grayish color, and the extrusion did not change the luminosity (p>0.05) of the flours. The raw whole-grain flour showed the highest level (19.3%) of coarse particles, while the raw refined flour showed a higher amount (54.37%) of fine particles. Regarding the extruded flours, similar percentages of fine, intermediate, and coarse particles were obtained (p>0.05). The refined samples showed a lower WAI than the whole-grain flours, because of the reduction in dietary fibers. The extrusion increased (p<0.05) the WAI of the whole-grain flour. It is concluded that the decortication and the extrusion affected the characteristics of the flours and both extruded flours present the potential to be used in the production of different foods, such as in the bakery industry.