Effects of Delayed Drying and Storage Conditions on Milling, Color, and Viscosity Properties of Rice

Head rice yields (HRYs), kernel discoloration, and functional properties are three hallmarks of rice quality, and can be impacted after harvest by storage conditions. This study evaluated impacts on rice quality due to controlled storage at moisture contents (MCs), temperatures, and storage durations that may be incurred during Mid-South rice farming practices. Three hybrid, long-grain cultivars, harvested in Arkansas in 2014 and 2015, were stored in rough rice form at 4 MCs (12.5%, 16%, 19%, and 21%), and 5 temperatures (10°C, 15°C, 20°C, 27°C, and 40°C), for 16 weeks, with samples taken every 2 weeks. After drying and milling, HRYs, discoloration, and viscosity parameters were analyzed. All storage conditions maintained HRY for at least 12 weeks, but storage for 16 weeks at 21% MC and 27-40°C in 2014 led to large reductions in HRY; these samples also contained tremendous visible fungal growth. Discoloration, measured with an image analysis system calibrated for this study, was minimized by storage at 10-15°C and at MCs ≤19% for up to 16 weeks. Discoloration in samples stored at 20-40°C varied by cultivar and by year, with a unique pattern observed at 27°C and 21% MC in 2014. Storage at 10-15°C limited increases in peak viscosity during storage, but minimum breakdown and maximum setback were observed after 16 weeks of storage at 21% MC and 10°C. At 20-27°C, peak and final viscosities and breakdown initially increased over the storage duration, then leveled off after 8-12 weeks. At 40°C, peak viscosity and breakdown increased at first, then declined after 2-6 weeks, especially with increasing storage MCs. Final viscosities increased steadily with storage at 40°C, therefore setback increased substantially after 2-4 weeks. The results of this study support the implementation of grain cooling for HRY and color quality preservation, identify the conditions that may promote discoloration in natural-air bin dryers, and suggest maximum temperatures and storage durations for aging hybrid, long-grain rice