2009 Volume 78 Issue 1 Pages 58-65
The distribution of seed storage proteins in rice grain of three seed-protein mutant cultivars with low ratios of digestible protein were compared with that of the normal-type cultivar “Nihonmasari”. In seed-protein mutant cultivars and “Nihonmasari”, 44—45% of the total protein and 44—48% of the digestible protein were present in the 100->80% layers. The content of the digestible protein was highest in the 100->90% layer in seed-protein mutant cultivars, but it was highest in the 90->80% layer in “Nihonmasari”. This tendency was more pronounced in low-glutelin 26-kDa-globulin-deficient cultivar than in low glutelin cultivars. In “Nihonmasari”, the contents of 37-39 kDa glutelin α and 22-23 kDa glutelin β, which are major digestible proteins, were highest in the 90->80% layer. However, in seed-protein mutant cultivars, the contents of 57 kDa excess protein and 57 kDa protein, which occupy a high percentage of digestible protein, were highest in the 100->90% layer. Therefore, it was considered that the varietal difference in the digestible protein distribution was due to the differences in the distribution of each protein fraction. Up to 10% of digestible protein is distributed in the 80->70% layer and inner layers, which indicate that the effective milling percentage to decrease digestible protein content of rice grain is about 80%.
