Effect of Moisture, Pressure, and Temperature on Enzymatic Starch Degradation of Barley and Sorghum Grain

Abstract

Barley and sorghum grain were processed with various combinations of moisture, heat, and pressure. Percent starch digestion was determined by incubating ground samples of the processed grain with a buffered homogenate of bovine pancreas for 30min at 40C. Addition of water to the grain by soaking or by steaming at atmospheric pressure did not greatly improve enzymatic starch degradation of barley or sorghum grain. Application of pressure to the grains (with hydraulic press or roller mill) increased in vitro starch digestibility over untreated grains. The pressure response was greater with moist grains than with dry grains. Enzymatic starch degradation was greatest for processing treatments involving application of moisture, heat, and pressure. Starch digestibility of pressure cooked grains was increased at each increment of steam pressure from 1.4 to 7.0 kg/cm2. Flaking the grains after steam processing or pressure cooking markedly improved enzymatic starch degradation. The optimum cooking pressure for both grains (with flat flaking) appeared to be 4.2 kg/cm2. The critical pressure (with a hydraulic press) for improving enzymatic starch degradation of dry, steamed, and soaked sorghum grain occurred at 140 kg/cm2 with the pressure plates at room temperature. Increased pressures to 1,400 kg/cm2 did not improve digestion. When the pressure plates were preheated to 98C, the critical pressure remained at 140 kg/cm2 for dry sorghum grain, but starch degradation was improved in the steamed and soaked grains at both 35 and 140 kg/cm2.