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Impacts of Delayed Drying on Discoloration and Functionality of Rice

Haydon, Kathryn N., Siebenmorgen, Terry J.
Cereal chemistry 2017 v.94 no.4 pp. 683-692
ambient temperature, autumn, color, cultivars, discoloration, dryers, drying, grain yield, milling, rough rice, seeds, storage time, viscosity, water content, United States
In-bin, on-farm drying systems for rough rice present challenges for maintaining kernel quality when drying fronts stall and the top layer of grain maintains its harvest moisture content (MC) for extended periods. This high MC, in addition to ambient temperatures in early autumn in the Mid-South United States, creates ideal conditions for quality losses to occur. This study evaluated the effects of rough rice storage at MCs of 12.5, 16, 19, and 21% for up to 16 weeks at temperatures of 20, 27, and 40°C on milling yields, kernel color, and functionality of three long-grain cultivars. Head rice yield was negatively impacted only after other reductions in quality had occurred. Temperature-specific discoloration patterns were observed at 27 and 40°C in 2014; the uniquely discolored kernels seen in 2014 at 27°C were absent from samples in 2015 under identical conditions. Peak viscosity, breakdown, and final viscosity tended to increase over storage duration at 20 and 27°C and all storage MCs but plateaued after 8 weeks. Storage of rice at 40°C and all MCs greatly reduced peak viscosity after 6 weeks. To prevent quality losses, in-bin dryers should be monitored closely to avoid exceeding the thresholds of storage MC, temperature, and duration identified here.