Maintenance of grain quality is the major consideration in postharvest handling of grains. Grain quality is influenced by variety, preharvest environment, and postharvest handling. Grain breeding programs concentrate on varietal improvement. whereas engineers improve postharvest processes to enhance grain quality. Major grain quality problems arise from lack of incentive to farmers, and are manifested in yellow rice, brokens. ageing and storage changes, variety mixing and mislabelling. and lack of screening metbods to differentiate among rices with similar starch properties and among special rices for rice food products. High aflatoxin level from fungal growth is the major problem for maize and parboiled rice. Fissuring during drying is also a quality problem in maize. Specific grain properties relevant in drying include moisture content (water activity) and both critical and equilibrium moisture contents, and hull or husk tightness. Delayed drying may result in stackbuming of wet grain due to nonenzymic browning and microbial growth and mycotoxin production in maize and parboiled rice. Improper and over-drying may reduce head rice yield and aroma. Rice varieties differ in their critical moisture content (11-16%. below which they fissure readily) and in equilibrium moisture content. Further interdisciplinary research should accelerate the solution of quality problems related to postharvest handling of grain.
