Jieun Kwak

Changes in lipid substances in rice during grain development

Lipid substances, such as fatty acids, γ-oryzanol, policosanols, and tocol (tocopherol+tocotrienol), were investigated in two rice cultivars, Ilpum and Dasan, during rice development. In both cultivars, the lipid extract level decreased steadily after it reached its maximum level. Additionally, there were differences in the fatty acid composition, depending on the rice developmental stage, between the two cultivars. The γ-oryzanol level increased during rice development, and there were differences in the composition of γ-oryzanol between the two cultivars. The levels of policosanols drastically decreased during the early stage of rice development in the two cultivars. The total tocol level showed a downward trend during rice development. The predominant tocol isomer in Ilpum was α-tocopherol during rice development. In Dasan, the predominant tocol isomer was α-tocopherol at the early stage, but γ-tocotrienol at the later stage. This study provided information on the levels and composition of lipid substances, such as fatty acids, γ-oryzanol, policosanols, and tocol during rice development.

Morphological and starch characteristics of the Japonica rice mutant variety Seolgaeng for dry-milled flour

Producing good-quality, fine rice flour is more difficult than wheat flour because the rice grain is harder. The non-glutinous Japonica-type variety Seolgaeng, derived from N-methyl-N-nitrosourea (MNU) mutagenesis, and four other varieties, representing a range of amylose contents, were evaluated in this study. Dry-milled Seolgaeng rice flour exhibited an average particle size that is <70 μm, a more uniform particle-size proportion than other varieties. Moreover, we noted significant differences in the damaged starch content in flour from Seolgaeng compared to the other varieties (p<0.05). Seolgaeng flour showed a round starch structure, which would lead to better friability, finer particle size, and less damage to the endosperm during dry milling. Indeed, among all varieties evaluated in this study, dry-milled Seolgaeng flour had the finest particle size (averaging <70 μm) and exhibited less damaged starch. With its round starch granules, Seolgaeng is a suitable candidate for drymilled rice flour.

Content and characteristics of resistant starch in high amylose mutant rice varieties derived from Ilpum.

This study was conducted to analyze the starch characteristics of three rice cultivars, Goami 2, Goami 3 and Goami 4 with high amylose content and resistant starch. These rice varieties were developed by mutation breeding based on N-methylN-nitrosourea (MNU) treatment in a japonica variety, Ilpum. Resistant starch contents of three high amylose mutant rice varieties and Ilpum were 11.87~13.69% and 0.36%, respectively. The X-ray diffraction patterns of starches of three varieties, Goami 2, Goami 3 and Goami 4 displayed B-type pattern. The proportion of amylopectin short chains of 6 to 12 in DP of the high amylose mutant rice varieties was significantly lower than that of Ilpum. Resistant starch contents had positive correlation with the amylose content, total dietary fiber content, medium length chains of 13 to 24, long chains of ≥ 25 in DP of amylopectin, pasting temperature and setback viscosity.

Contrasting tocol ratios associated with seed longevity in rice variety groups

Vitamin E (tocols) is a key metabolite for efficient scavenging of lipid peroxy radicals that cause membrane breakdown during seed ageing. However, in rice, this hypothesis has been tested for very few lines only and without considering intraspecific variation in genomic structure. Here, we present a correlation study between tocols and seed longevity using a diverse rice panel. Seeds of 20 rice accessions held in the International Rice Genebank at the International Rice Research Institute, representing Aus, Basmati/Sadri, Indica, temperate Japonica and tropical Japonica variety groups, were used for tocols analysis (quantification of α-, β-, γ- and δ-tocopherol/tocotrienol by ultra-performance liquid chromatography) and storage experiments at 45°C and 10.9% seed moisture content. To examine the effects of DNA-haplotype on the phenotype, the 700 K high-density single-nucleotide polymorphism marker dataset was utilized. Both seed longevity (time for viability to fall to 50%; p 50 ) and tocols content varied across variety groups related to the heterogeneity in the genetic architecture. Among eight types of tocol homologues, α-tocopherol and γ-tocotrienol were significantly correlated with p 50 (negatively and positively, respectively). While temperate Japonica varieties were most abundant in α-tocopherol, Indica varieties recorded 1.3- to 1.7-fold higher γ-tocotrienol than those of other groups. We conclude that the specific ratio of tocol homologues rather than total tocols content plays an important role in the seed longevity mechanism.

Comparative Analysis on Quality and Bread-making Properties by Particle Size of Dry-Milled Rice Flours of Rice Varieties

This study was conducted the comparative analysis on quality and rice bread process suitability properties by four particle size classification of dry-milled flours for four rice varieties. Dry-milled rice flours were prepared by dry milling and classified according to particle size using 100, 150, 200, and 250 mesh sieves. The mean particle size by four particle size classification of 60 ~ 100 mesh, 100 ~ 150 mesh, 150 ~ 200 mesh, 200 ~ 250 mesh exhibited 118.9 μm, 87.4 μm, 65.3 μm, 46.1 μm, respectively. The particle size of dry-milled rice flours was the finer, the damaged starch content was the higher (r = − 0.570*). The particle size also had significant negative correlation with the water absorption index (r = − 0.533*, r = − 0.593*), and water solubility index (r = − 0.857**, r = − 0.584*). Dry-milled rice flours with particle size of 60 ~ 70 μm, passed through 150 and 200 mesh sieves exhibited the highest specific volume of rice bread. Whereas, the dry-milled rice flour with finer particle size above 200 mesh showed the lowest specific volume of rice bread. These results will be applied as a quality standard to aid in the selection of the most suitable dry-milled rice flour for baking.

Quality Properties of Makgeolli Brewed with Fiber-rich Rice Cultivars

Goami2, Goami3 and Goami4 were identified as fiber-rich rice cultivars which were developed by mutation breeding with Ilpum. The purpose of this study was to develop a method for producing Makgeolli with the fiber-rich rice cultivars, Goami2, Goami3, Goami4, and to investigate the characteristics of Makgeolli during the fermentation process. Makgeolli was produced herein by fermentation steamed rice (SR), raw rice flour (RF), and steamed rice flour (SF) from Goami2, Goami3, Goami4, Ilpum and Sealgaeng rice cultivars. The physicochemical characteristics including alcohol and sugar content, pH, total acidity, TDF (total dietary fiber), and color of the Makgeolli samples were analyzed. Makgeolli produced with Ilpum and Sealgaeng showed satisfactory fermention characteristics in alcohol and sugar content when SR, RF and SF were used. In the case of Goami2, Goami3, and Goami4, the use of SF resulted in 17.2~20.1% alcohol content, whereas only 10% alcohol was produced by SR. The sugar contents in the SF-makgeolli samples were also higher (9~10 °Brix) than in the SR-makgeolli (5.35~5.44 °Brix) for Goami2 and Goami4 cultivars. The dietary fiber contents of the Makgeolli samples produced using SF from the fiber-rich rice cultivars were higher (1.35~1.52 g/100 mL) than those produced with Ilpum and Sealgaeng (0.74~0.87 g/100 mL). From these results, it may be suggested that SF would be an appropriate material to brew Makgeolli using fiber-rich rice cultivars to obtain better physicochemical and functional qualities.