Effects of drying conditions of classified grain on flour quality were examined to develop a drying classification according to the moisture content using the grain thickness classification. The grain classification was made with a 3.2mm sieve. Then the respectively classified grain groups were dried. The drying conditions were thin-layer drying at 50°C and 60°C, and no-air-flow condition at 40°C, 50°C and 60°C. The flour color was measured with a spectral diffraction colorimeter (CM3500; Konica Minolta Holdings Inc.) and starch properties were assessed using a Rapid Visco Analyzer (RVA-3D; Newport Scientific Pty. Ltd.).
Flour color was improved as the following order of groups: thinner, not-classified, and thicker. The starch quality of the thinner group, which has low moisture content, was hard to degrade, but that of the thicker grain, which has high moisture content, was easily degraded.
In thin-layer drying, the drying temperature did not affect flour quality. In no-air-flow condition, 40°C caused starch degradation, 60°C caused flour color degradation, and 50°C caused no major degradation.
Previously, 40°C drying had been inferred as sufficiently safe for high moisture grain. However, these results show that 40°C drying without airflow degrades the grain and that 60°C drying with sufficient airflow does not cause degradation.
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