Quality of Long-grain Rice Dried by High Temperatu Fluidization

摘要

Fluidized bed drying (FBD) shows potential to dry rice quickly and uniformly across the bed utilizing high drying air temperatures (90-200 deg C) and velocities (2-4 m/s). An air-impingement oven was used to simulate FBD of rough rice in an evaluationof high drying air temperatures on milling characteristics and physicochemical properties. The long-grain cultivar Wells at an initial moisture content (MC) of 21.9% was dried to 15% and 13% MC using drying air temperatures of 60, 90, 120, and 150 deg Cand was immediately tempered at 60 deg C or the grain temperature (GT) for 0-120 min. Head rice yield (HRY), color, degree of milling (DOM), pasting and thermal properties, degree of starch damage, and protein content were measured. HRYs could be maintained or increased using drying air temperatures of 60-150 deg C when drying to 15% MC and when drying at 150 deg C to 13% MC with tempering at GTfor at least 60 min. Significant changes in rice quality, including increased yellowing, decreased peak and final viscosity, decreased DOM, increased gelatinization temperatures, and increased starch damage, occurred when drying at 120-150 deg C and tempering at GT due to exposure of rice to high GTs (>82 deg C) for extended durations. To maintain all quality parameters, drying air temperatures generally should not exceed 90 deg C, MC after one drying pass should not be less than 15%, and rice should be tempered at GT for at least 60 min. As the rice was dried in a single layer, the reported results indicate the most severe effects of high temperature drying on subsequent rice quality.