Obtenção e caracterização de farinha extrudada de diferentes genótipos de sorgo para o desenvolvimento de biscoitos doces

Abstract

The diversity of sorghum grains is related to their intrinsic properties, which include chemical composition, pericarp color and phenolic compounds, this later present in all sorghums and genotype dependent. This diversity can be valuable for developing new food products for human consumption and the thermoplastic extrusion is considered an interesting tool for this purpose. In the first stage of the experiment, whole flours of six Brazilian sorghum genotypes of varied pericarp color: white (CMSXS180; 9010032), red (BRS310; BRS308) and brown (BRS305; 9929034) were processed in a co-rotating twin-screw extruder at constant parameters process. Changes promoted by extrusion cooking were evaluated via specific mechanical energy (SME), die pressure (p), apparent density, expansion properties, mechanical properties, hydrothermal properties and color variation. An inverse relationship was observed between p and apparent density. Brown genotypes generated lower p and sectional expansion index (SEI) values than others. BRS305 processing presented the highest SME value and intermediate values of water absorption index (WAI) and water solubility index (WSI). BRS310 genotype achieved the highest SEI and WAI values, correlated with high WSI and intermediate p. In CMSXS180 processing was observed low WAI, high SEI and high WSI, correlated with high SME and p. These results reflect the differences in starch conversion induced by differentiated pericarps between sorghum genotypes. In the second stage of the experiment, whole flours of BRS310 and BR700 were processed at 300–700 min–1 screw speed (SS) and 14–26% feed moisture content (MC), with the other parameters fixed constant. Response surface methodology (RSM) was used to analyze the effect of SS and MC on physicochemical properties of two genotype sorghum extrudates. A two-level, two-variable, central composite rotatable design of experiments was used. Second order polynomials were used to model the extruder response and extrudate properties as a function of process variables. Responses were most affected by changes in SS and to a lesser extent by MC. Calculated SME values ranged between 596–1434 kJkg1 for BRS310 and 757–1597 kJkg1 for BR700. The high values in BR700 most likely due to high fiber and tannin content in their composition. The best extruded flours to develop cookies are characterized by minimum expansion, maximum density, low degree of gelatinization, high WSI and low cookie hardness. This set of functional properties corresponds to processes with low SME input, which were obtained at combinations of processing parameters with low SS and intermediate to high MC. It suggest the production of extruded flours at 300 min1 SS and 20% MC or 359 min1 SS and 24,2% MC.