Rice grain quality: related properties and effective factors

Rice provides food for more than half of the world's population. Unlike other cereals used in the form of processed, rice is mostly consumed directly with removal of paddy and brown husks. Therefore, considering rice grain quality is one of the main factors in product marketability and consumption. Rice grain quality can be considerd and evaluated by assessment of four properties: physical, chemical, sensory and nutritional value. Physical properties such as grain shape, chalky grains, transparency and uniformity of grains. Grain size, chalkiness and color are important features that affect consumer choice. Grain cooking properties (chemical factors) mainly include apparent amylose content, gelatinization temperature, and gel consistency. Also, the viscosity properties of starch grains are considered as an important secondary difference in cultivars with similar amylose content. Sensory characteristics include aroma, grain hardness after cooking, color and taste which are important and favorite characteristics for rice consumers in the world. Major nutrients in rice include; starch, protein, fats, and non-starch polysaccharides. The key period for the formation of grain quality characteristics of rice is early and mid-grain filling stages. In addition to genetic factors, the cooking quality of rice is strongly influenced by environmental conditions, as the rice garin quality may vary from year to year or even from field to field. Rice grain quality prediction requires the association of genetic information with grain quality phenotypes in different environments. Despite the negative relationship between quality properties and grain yield in rice, targeted cross-breeding to transfer the quality related traits of local rice cultivars to improved commercial cultivars with reasonable levels of tolerance to environmental stresses as well as optimum crop management practices, are among the promising strategies for improving the rice grain quality.