Effect of decortication and protease treatment on physicochemical and functional characteristics of red sorghum (Sorghum bicolor) and yellow maize (Zea maiz) starches

Sorghum is a cereal from which starch is not commonly isolated; however, its functional characteristics are similar to other cereal starches such as maize. Red sorghum kernels were processed with and without mechanical decortication followed by steeping in a sodium bisulfite solution to 50% solids, with and without a commercial protease following by wet milling. For comparison purposes, yellow maize kernels were also protease treated and wet milled. Results indicate a significant increase on starch yield in both cereals when the decorticated sorghum or maize flours were treated with the protease from 59.11 to 63.21% and 43.59 to 58.89%, as well as purity from 96.52 to 98.45 and 95.95 to 98.75% for maize and sorghum, respectively. The combination of mechanical decortication and protease treatments increase starch gelatinization temperature from 77.5 to 81.5 degrees C, as well as a decrease on the final viscosity, indicating that the protein associated to the starch granules restricted swelling and amylose leaching during pasting. Isolated starch from decorticated sorghum kernels was lighter in color due to the removal of pericarp rich in phenolics. The mechanical decortication prior to wet milling presented the advantage of the removal of stable sorghum bran that contains an array of nutraceutical and antioxidant compounds, whereas the use of the proposed decortication followed by enzyme treatment promote higher yields of refined starch.