Morphological, Physical, and Chemical Properties of Grain and Flour from Chalky Rice Mutants

Morphological, physical, and chemical properties of grain and flour of 20 chalky rice mutants were compared with those of a translucent parental cultivar, Koshihikari. Compound starch granules were loosely packed and single starch granules were observed in chalky parts of mutant endosperm. Chalky mutant lines were classified into milky-white and white-core lines based on the degree of endosperm chalkiness. Physical and chemical characteristics also suggest a division of chalky mutant lines into two groups, consistent with the classification made based on morphological characteristics. Milky-white mutant lines showed significantly lower grain weight, decreased starch content, and lower grain hardness than white-core mutants and Koshihikari. Rice flour prepared from milky-white mutants by dry milling showed less starch damage and finer mean particle size than white-core mutants and the parent. These results indicated that a loosely packed structure in chalky endosperm was responsible for fragile grain and that it yielded fine flour with lower damaged starch contents. Decreased starch contents of chalky mutant lines correlated to lower RVA viscosities. Milky-white mutant lines were expected to be useful to produce fine flour, which undergoes less starch damage during dry milling processing.