Resistant Starch Content Of Rice Research Articles

Triple gene mutations boost amylose and resistant starch content in rice: insights from sbe2b/sbe1/OE-Wxa mutants.

Previous studies have modified rice's resistant starch (RS) content by mutating single and double genes. These mutations include knocking out or reducing the expression of sbe1 or sbe2b genes, as well as overexpressing Wxa . However, the impact of triple mutant sbe2b/sbe1/OE-Wxa on RS contents remained unknown. Here, we constructed a double mutant with sbe2b/RNAi-sbe1, based on IR36ae with sbe2b, and a triple mutant with sbe2b/RNAi-sbe1/OE-Wxa , based on the double mutant. The results showed that the amylose and RS contents gradually increased with an increase in the number of mutated genes. The triple mutant exhibited the highest amylose and RS contents, with 41.92% and 4.63%, respectively, which were 2- and 5-fold higher than those of the wild type, which had 22.19% and 0.86%, respectively. All three mutants altered chain length and starch composition compared to the wild type. However, there was minimal difference observed among the mutants. The Wxa gene contributed to the improvement of 1000-grain weight and seed-setting rate, in addition to the highest amylose and RS contents. Thus, our study offers valuable insight for breeding rice cultivars with a higher RS content and yields.

Quantification of resistant starch content in rice after hydrothermal treatments using terahertz spectroscopy

Since hydrothermal treatments can enhance resistant starch (RS) content in rice and provide health benefits when consumed, a less laborious and non-destructive method to determine RS content is needed. Terahertz (THz) spectroscopy is hypothesized as a suitable method to quantify RS content in rice after hydrothermal treatment with its sensitivity for the intermolecular forces increase in the formation of RS. In this study, we first used the traditional in vitro hydrolysis method to determine the content of RS in rice. Then, the potential of starch absorbance peaks to quantify RS content after three commonly used hydrothermal methods, soaking, mild heat-moisture treatment, and parboiling, was investigated. The second derivative intensities of the peak at 9.0, 10.5, 12.1, and 13.1 THz were confirmed as being correlated with RS content and showed the high accuracy to predict RS content in samples (R2 > 0.96). Our results indicate the RS content of hydrothermally treated rice can be accurately quantified using these peaks.

Improving Agricultural Traits While Maintaining High Resistant Starch Content in Rice

BackgroundResistant starch (RS) is beneficial for human health. Loss of starch branching enzyme IIb (BEIIb) increases the proportion of amylopectin long chains, which greatly elevates the RS content. Although high RS content cereals are desired, an increase in RS content is often accompanied by a decrease in seed weight. To further increase the RS content, genes encoding active-type starch synthase (SS) IIa, which elongates amylopectin branches, and high expression-type granule-bound SSI (GBSSI), which synthesizes amylose, were introduced into the be2b mutant rice. This attempt increased the RS content, but further improvement of agricultural traits was required because of a mixture of indica and japonica rice phonotype, such as different grain sizes, flowering times, and seed shattering traits. In the present study, the high RS lines were backcrossed with an elite rice cultivar, and the starch properties of the resultant high-yielding RS lines were analyzed.ResultsThe seed weight of high RS lines was greatly improved after backcrossing, increasing up to 190% compared with the seed weight before backcrossing. Amylopectin structure, gelatinization temperature, and RS content of high RS lines showed almost no change after backcrossing. High RS lines contained longer amylopectin branch chains than the wild type, and lines with active-type SSIIa contained a higher proportion of long amylopectin chains compared with the lines with less active-SSIIa, and thus showed higher gelatinization temperature. Although the RS content of rice varied with the cooking method, those of high RS lines remained high after backcrossing. The RS contents of cooked rice of high RS lines were high (27–35%), whereas that of the elite parental rice was considerably low (< 0.7%). The RS contents of lines with active-type SSIIa and high-level GBSSI expression in be2b or be2b ss3a background were higher than those of lines with less-active SSIIa.ConclusionsThe present study revealed that backcrossing high RS rice lines with elite rice cultivars could increase the seed weight, without compromising the RS content. It is likely that backcrossing introduced loci enhancing seed length and width as well as loci promoting early flowering for ensuring an optimum temperature during RS biosynthesis.

Effects of Differences in Resistant Starch Content of Rice on Intestinal Microbial Composition.

The aim of this study was to evaluate the effects of resistant starch (RS) and fat levels on the gut microbiome in C57BL/6 mice. Three levels of RS from three varieties of rice were the major source of carbohydrates and fat levels were low (10%) and high (39%). We confirmed that RS decreased the Firmicutes to Bacteroidetes ratio, increased SCFA production by higher Bacteroidaceae and S24-7 abundance, and enriched predicted gene families of glycosidases and functional pathways associated with carbohydrate and glycan metabolism. We also found correlations between microbial taxa and tissue gene expression related to carbohydrate and lipid metabolism. Moreover, increasing RS levels resulted in a molecular ecological network with enhanced modularity and interspecific synergy, which is less sensitive to high fat intervention. Overall, RS as low as 0.44% from cooked rice can modulate gut microbiome in mice, which correlated to a protective effect against deleterious effects of an obesogenic diet.

Single Nucleotide Polymorphisms in Starch Biosynthetic Genes Associated With Increased Resistant Starch Concentration in Rice Mutant.

Resistant Starch (RS), plays a crucial role in human health and nutrition by controlling glucose metabolism. RS or dietary fibre content in rice is low because it goes through a variety of process before it is ready for cooking and consumption. Hence, this study was carried out to develop a rice mutant with increased RS. The rice mutant (γ278) with increased RS was developed by utilizing gamma (γ) rays as a mutagen. Mutant γ278 was characterized for mutations in the starch biosynthetic genes viz., GBSSI, SSI, SSIIa, SSIIIa, SBEIa, and SBEIIb to reveal the functional mutations/variations led to high RS content in rice. A total of 31 sequence variants/mutations in six genes were identified. We report the discovery of three deleterious mutation/variants each in GBSSI, SSIIa, and SSIIIa with the potential to increase RS content in rice. Further, wild × mutant crosses were made to develop an F2 population to study the effect of combination of deleterious mutations. The SNP (GBSSI:ssIIa:ssIIIa) combination responsible for high RS content in F2 population was identified and recorded highest amylose content (AC) (26.18%) and RS (8.68%) content. In conclusion, this marker combination will be highly useful to develop a rice variety with increased RS.

In Vitro Starch Digestion and Colonic Fermentation of Thai Jasmine Rice

Resistant starch (RS) enhances gastrointestinal (GI) health but RS content in rice varies depending on cooking and storage conditions. Hydrolysis rates of in vitro starch fractions in simulated GI, colonic fermentation of freshly cooked Thai jasmine rice (control) by rice cooker method (RCM) and boiling method (BM), and reheated jasmine rice stored for 3 days at 4 and −20 °C are evaluated. Storage increased RS, slowly digestible starch (SDS) content of jasmine rice cooked by RCM, and SDS content of jasmine rice cooked by BM due to the decrease in rapidly digestible starch (RDS). The effect of storage on starch fractions in jasmine rice differed with temperature. For simulated GI conditions, 50.07% of jasmine rice hydrolysate escaped hydrolysis similarly among treatments. Jasmine rice hydrolysates selectively enhanced growth of probiotic strains but not pathogenic growth with time. Maximum specific growth rates (μmax, h−1) of strains were measured as Bifidobacterium animalis 2194 &gt; Bifidobacterium bifidum TISTR 2129 &gt; Lactobacillus reuteri AC‐5 &gt; Escherichia coli E010 ≥ Salmonella serovar Enteritidis S003. With regard to quantity and quality, jasmine rice hydrolysate was not affected by cooking and storage conditions but influenced by colonic fermentation.

Resistant starch content of rice varies with rice variety but not cooking method

Rice is a staple carbohydrate in much of the world, including Hawaii. Previous work indicated that resistant starch (RS) content of rice consumed in India varied with rice variety and cooking method. This study aimed to quantify RS in 4 rice varieties commonly consumed in Hawaii (jasmine, long grain, medium grain, and short grain) cooked in three manners (baked, conventional rice cooker, and pressure cooker). Resistant starch in fresh and freeze‐dried rice was measured using AOAC method 2002.02 (n=2). ANOVA and paired t‐test were used to determine significant differences. Within each rice variety, cooking method did not affect RS content. However, within the baked method, jasmine rice had significantly more RS than medium and short grain rice. When cooked in a conventional rice cooker, jasmine rice and long grain rice had significantly more RS than short grain rice. Pressure cooked samples did not differ. Freeze‐dried samples reported significantly lower RS than fresh samples when corrected for original moisture content. In the state of Hawaii, diabetes is a major public health concern. This data will be used to evaluate glycemic response of selected rice varieties in healthy humans.