Koshihikari, a highly palatable Japanese rice cultivar, has been the most widely distributed rice cultivar in Japan for the past 40 years. Gene loci that improve the eating quality of rice were detected on the short arm of chromosome 3 in Koshihikari. However, the physicochemical characteristics of cooked rice with the gene loci for good eating quality have not yet been elucidated. In this study, we analyzed low molecular weight compounds that may influence the characteristics of polished rice, or the taste of cooked rice and cooking water using chromosome substitution lines from Koshihikari and Nipponbare. Results showed that the profiles of low molecular weight compounds of Koshihikari and Nipponbare differed in each of the polished rice, cooked rice and cooking water. Profiles of the substitution lines of Nipponbare background with the gene loci from Koshihikari more closely resembled the profiles of Koshihikari and vice versa. Interestingly, the composition of low molecular weight compounds in addition to glutamic acid and aspartic acid, both of which are well-known contributors to good taste, differed between the lines with and without the gene loci for good eating quality. These results suggest that the gene loci alter the content of some compounds that were previously not reported as contributing factors in rice palatability.

The objectives of this study were to investigate the changes in starch hydrolysis and tissue structure of cooked rice grain during gastro-intestinal digestion in vitro under different gastric digestive conditions. Packaged cooked rice prepared by microwave oven was used as the cooked grain samples. Starch hydrolysis of the samples was evaluated using simulated gastro-intestinal digestion in vitro. Four gastric digestive conditions were employed using combinations of low/high pH level and with/without pepsin content. Mechanical properties of the samples after gastric digestion were also evaluated. Changes in tissue structure of the samples during digestion were observed using a stereo microscope and scanning electron microscopy (SEM). Starch hydrolysis was almost 0% during gastric digestion and increased from 88.1 to 100.3% at the end of small intestinal digestion, regardless of the gastric digestive condition. The sample surface before gastric digestion was smooth, whereas disintegration of the tissue structure and fibers was observed after gastric digestion. Firmness and adhesiveness of the samples were decreased after gastric digestion. Numerous cell walls were observed on the sample surface after small intestinal digestion. This study indicated that gastric digestive conditions influenced the physical properties of samples; however, they did not influence starch hydrolysis and tissue structure during small intestinal digestion.

The aim of this study was to investigate the quality of fermented seasonings from sakura shrimp, Lucensosergia lucens, prepared using various fermentation methods in order to produce unique products for the purpose of efficient utilization of valuable resources. Seven shrimp sauce mashes (moromis) were prepared from minced meat with shells of sakura shrimp using two koji molds (rice koji (RK) and sakura shrimp koji (SSK)), 15% salt, halophilic lactic acid bacterium (Tetragenococcus halophilus) and soy sauce yeast (Zygosaccharomyces rouxii). After fermentation at 30°Cfor 24 weeks, moromis were heated up to 90°C and filtrated with No. 5C. The physicochemical properties of the moromis during fermentation and the final products were investigated. The pH decrease during fermentation was faster in moromis with T. halophilus than in moromis without. Total nitrogen (TN) of all moromis increased quickly up to 4 weeks and remained almost constant up to 24 weeks. TN levels at the end of fermentation were higher in SSK moromis than in RK moromis. On free amino acid (FAA) analysis, total FAA levels of the final products were higher in SSK than in RK, while levels of Glu, Asp, Leu and Ala were high in all samples.