Document Type : Original Article
Authors
1
Global Innovation Center, Kyushu University, Minami-ku, Fukuoka 8128540, Japan.
2
2-162-1 Kanbayashi, Nonoichi, Ishikawa 921-8589, Japan.
3
Nurudomachi, Ryugasaki, Ibaragi 301-0803, Japan.
4
339-3 Satsumacyou, Hikone, Shiga 521-1141, Japan.
5
83 Kurokawa, Aso, Kumamoto 869-2225, Japan.
Abstract
To clarify the index traits for evaluating the eating quality of rice produced under high-temperatures, during the ripening period in Japan, the relationship between palatability and appearance quality, grain size, grain weight, and physicochemical properties of rice produced over a wide range of areas were analyzed and its factors were investigated. Palatability was positively correlated with the percentage of perfect rice grain (as an indicator of appearance quality) and grain thickness of brown rice; palatability deteriorated when the percentage of perfect rice grain was < 60%. On the other hand, there was no significant relationship between palatability and grain length, width, protein content of brown rice, and amylose content of milled rice. Palatability was negatively correlated with the hardness/adhesion (H/-H) ratio in texture characteristics of cooked rice (an effective indicator of palatability). A quadratic curve relationship between palatability and moisture content of brown rice (MR) was observed. It was concluded that MR was neither too high nor too low for palatability and that the suitable moisture content from the viewpoint of palatability is 14.0-15.0%. The differences in palatability due to differences in MR were larger than those due to differences in the production area, suggesting that moisture content was a primary factor in the differences in palatability among districts. These results indicate that, as indicator traits for evaluating the eating quality of rice produced under high-temperatures during the ripening period, the percentage of perfect grain and thickness of brown rice grain is effective for grain traits, and the H/-H ratio of cooked rice and MR are effective for physicochemical properties. The findings of this study can be used to select highly palatable rice cultivars with heat temperature tolerance and for index traits for highly palatable rice production.
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