Abstract
Consumer demand for good eating quality of cooked rice has been growing widely not only in Japan but also in other countries. Eating quality of the non-glutinous rice varieties bred in Hokkaido, northern Japan, during the past 20 years has improved drastically due to the breeding efforts focused mainly on chemical properties, such as amylose and protein concentrations. However, the effect of physical properties, such as cell morphology, on eating quality has been less studied. To clarify the relationship between physical properties and eating quality of rice, we investigated endosperm cell morphology (ECM) of grain by using a new simple method with a stereomicroscope for 18 non-glutinous varieties released over the past 100 years in Hokkaido. There were significant varietal differences in most of the ECM characteristics measured. Especially, cell density along the central line of endosperm (CLE) correlated negatively with the released year of varieties (r=–0.827, p<0.001), and decreased with the decrease in amylose and protein concentrations. The results indicated that the rice breeding in Hokkaido has changed not only the chemical but also physical properties. In addition, some varieties with similar amylose and protein concentrations showed large differences in CLE cell density. This suggests that the varietal difference in eating quality, which can not be explained by the difference in amylose and protein concentrations only, may be explained by the difference in CLE cell density. These findings will contribute to the further improvement in eating quality of non-glutinous rice.
