The effects of Goami No. 2 rice, a natural fiber-rich rice, on body weight and lipid metabolism

Resistant starch formation in rice: Genetic regulation and beyond

Resistant starch (RS), a healthy dietary fiber, is a particular type of starch that has attracted much research attention in recent years. RS has important roles in reducing glycemic index, postprandial blood glucose levels, and serum cholesterol levels, thereby improving and preventing many diseases, such as diabetes, obesity, and cardiovascular disease. The formation of RS is influenced by intrinsic properties of starch (e.g., starch granule structure, starch crystal structure, and amylose-to-amylopectin ratio) and non-starch components (e.g., proteins, lipids, and sugars), as well as storage and processing conditions. Recent studies have revealed that several starch-synthesis-related genes (SSRGs) are crucial for the formation of RS during seed development. Several transcription factors and mRNA splicing factors have been shown to affect the expression or splicing of SSRGs that regulate RS content, suggesting their potential roles in RS formation. This review focuses mainly on recent research progress on the genetic regulation of RS content and discusses the emerging genetic and molecular mechanisms of RS formation in rice.

Breeding Rice lines for physio-functional food through indica ‘Zhaxima’ × japonica ‘Nanjing 46’ haploid technique

Resistant starch (RS) encompasses those forms of starch which are not accessible to human digestive enzymes and are fermented in the colons producing short chain fatty acids. The plant materials containing RS are few in the world. In this contribution, the culture ability of callus from anthers of F1 plants from, landraces, ‘Zhaxima’(Oryza sativa var. indica, high-RS rice line with 7.705 ± 0.142, g/100 g) × ‘Nanjing 46’ (Oryza sativa var. japonica, rice variety with RS content (g/100 g) of 0.200 ± 0.001 crosses were studied for obtaining high RS rice plants. The results showed that when M8 basic induction medium was added with 1.5 mg /L 2,4-D、2 mg /LNAA and 0.3 mg /L KT, the inductivity of callus was high as 32.14% for 21 d after pretreatment at 4 °C for 3 d; When MS differentiation basic medium was added with 2 mg /LKT and 3 mg /L ABA, the frequency of regeneration for callus was 50.3% with only a regeneration frequency of 4.55% grown into green seedlings. The RS content in the seeds was between those of the two parents and was partially normally distributed, the highest RS contents of the regenerated plants was as high as 7.66 ± 1.197%. This produced an efficient technology for regenerating stable rice lines with high RS and good eating quality using anthers culture.

Effect of Dietary Fiber on Serum Leptin Level: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Dietary fibers may induce satiety through affecting gastro-intestinal and peripheral appetite regulating hormones. Thus, we aimed to investigate the effect of dietary fiber consumption on serum leptin level compared to control diet, in short- and long- term trials, through a systematic review and meta-analysis.

METHODS

We searched PubMed, web of science, Scopus, ProQuest, EMBASE, and Cochrane Library to find randomized controlled clinical trials that evaluated effect of any type of dietary fiber on serum leptin level compared to control diet, until April 2019. Both short-term (1-4 days) and long-term (longer than 2 weeks) studies were selected. Mean differences (MD) of changes in serum leptin level and 95% confidence intervals were extracted from eligible studies, and random effects model was used to analyze data.

RESULTS

Thirteen studies included the systematic review and 11 entered in the meta-analysis. No significant change was seen in serum leptin level in short-term (MD=0.02, 95% CI; -0.15, 0.20, Tau²=0.0) and long-term studies (MD=-0.10, 95% CI; -0.28, 0.08, Tau²=0.0), followed by fiber consumption. However, this effect was statistically significant in obese participants (MD=-0.36, 95% CI; -0.71, -0.02, Tau²=0.0) in long-term studies. Moreover, we found no significant results in subgroups of baseline serum leptin level, intervention duration, fiber dose, and fiber type.

CONCLUSIONS

This meta-analysis found that taking dietary fiber for long term could lower serum leptin level, just in obese persons. However, further clinical trials are needed in this field to clarify this issue.

Critical roles of soluble starch synthase SSIIIa and granule-bound starch synthase Waxy in synthesizing resistant starch in rice

Changes in human lifestyle and food consumption have resulted in a large increase in the incidence of type-2 diabetes, obesity, and colon disease, especially in Asia. These conditions are a growing threat to human health, but consumption of foods high in resistant starch (RS) can potentially reduce their incidence. Strategies to increase RS in rice are limited by a lack of knowledge of its molecular basis. Through map-based cloning of a RS locus in indica rice, we have identified a defective soluble starch synthase gene (SSIIIa) responsible for RS production and further showed that RS production is dependent on the high expression of the Waxy^a (Wx^a ) allele, which is prevalent in indica varieties. The resulting RS has modified granule structure; high amylose, lipid, and amylose-lipid complex; and altered physicochemical properties. This discovery provides an opportunity to increase RS content of cooked rice, especially in the indica varieties, which predominates in southern Asia.

Glycemic Index of a Novel High-Fiber White Rice Variety Developed in India--A Randomized Control Trial Study

BACKGROUND

White rice, a common Indian staple, has a high glycemic response and is associated with high risk of type 2 diabetes. The aim of this study was to compare the Glycemic Index (GI) of a newly developed high-fiber white rice (HFWR) with that of commercial white rice (WR).

MATERIALS AND METHODS

HFWR was developed using biochemical screening approaches and classical plant breeding techniques. The GI of HFWR was determined using a validated protocol in 30 healthy participants in the year 2013 and repeated in a subsample of 15 participants in the year 2014; the results were compared with the value for WR. The incremental area under the curve was calculated geometrically by applying the trapezoid rule for both reference food (glucose) and the test foods (HFWR and WR). Proximate principles along with dietary fiber, resistant starch, and amylose content were analyzed using standardized methods.

RESULTS

The dietary fiber content of HFWR was fivefold higher (8.0 ± 0.1 vs. 1.58 ± 0.17 g%), resistant starch content was 6.5-fold higher (3.9 ± 0.2 vs. 0.6 ± 0.03 g%) (P < 0.001), and amylose content was significantly higher (32.8 ± 1.1 vs. 26.0 ± 0.2 g%) (P < 0.001), compared with WR. HFWR was found to be of medium GI (61.3 ± 2.8), whereas WR was of high GI (79.2 ± 4.8). Overall, HFWR had 23% lower GI compared with WR (P = 0.002).

CONCLUSIONS

The new HFWR variety can be considered as a potentially healthier alternative to commercial WR in rice-eating populations, on account of its lower GI and high fiber content.

Biomolecular analyses of starch and starch granule proteins in the high-amylose rice mutant Goami 2

Elevated proportions of amylose in cereals are commonly associated with either the loss of starch branching or starch synthase activity. Goami 2 is a high-amylose mutant of the temperate japonica rice variety Ilpumbyeo. Genotyping revealed that Goami 2 and Ilpumbyeo carry the same alleles for starch synthase IIa and granule-bound starch synthase I genes. Analyses of granule-bound proteins revealed that SSI and SSIIa accumulate inside the mature starch granules of Goami 2, which is similar to the amylose extender mutant IR36ae. However, unlike the amylose extender mutants, SBEIIb was still detectable inside the starch granules of Goami 2. Detection of SBEIIb after protein fractionation revealed that most of the SBEIIb in Goami 2 accumulates inside the starch granules, whereas most of it accumulates at the granule surface in Ilpumbyeo. Exhaustive mass spectrometric characterisations of granule-bound proteins failed to detect any peptide sequence mutation or major post-translational modifications in Goami 2. Moreover, the signal peptide was found to be cleaved normally from the precursor protein, and there is no apparent N-linked glycosylation. Finally, no difference was found in the SBEIIb structural gene sequence of Goami 2 compared with Ilpumbyeo. In contrast, a G-to-A mutation was detected in the SBEIIb gene of IR36ae located at the splice site between exon and intron 11, which could potentially introduce a premature stop codon and produce a truncated form of SBEIIb. It is suggested that the mutation responsible for producing high amylose in Goami 2 is not due to a defect in SBEIIb gene as was observed in IR36ae, even though it produces a phenotype analogous to the amylose extender mutation. Understanding the molecular genetic basis of this mutation will be important in identifying novel targets for increasing amylose and resistant starch contents in rice and other cereals.

Impact of down-regulation of starch branching enzyme IIb in rice by artificial microRNA- and hairpin RNA-mediated RNA silencing

The inactivation of starch branching IIb (SBEIIb) in rice is traditionally associated with elevated apparent amylose content, increased peak gelatinization temperature, and a decreased proportion of short amylopectin branches. To elucidate further the structural and functional role of this enzyme, the phenotypic effects of down-regulating SBEIIb expression in rice endosperm were characterized by artificial microRNA (amiRNA) and hairpin RNA (hp-RNA) gene silencing. The results showed that RNA silencing of SBEIIb expression in rice grains did not affect the expression of other major isoforms of starch branching enzymes or starch synthases. Structural analyses of debranched starch showed that the doubling of apparent amylose content was not due to an increase in the relative proportion of amylose chains but instead was due to significantly elevated levels of long amylopectin and intermediate chains. Rices altered by the amiRNA technique produced a more extreme starch phenotype than those modified using the hp-RNA technique, with a greater increase in the proportion of long amylopectin and intermediate chains. The more pronounced starch structural modifications produced in the amiRNA lines led to more severe alterations in starch granule morphology and crystallinity as well as digestibility of freshly cooked grains. The potential role of attenuating SBEIIb expression in generating starch with elevated levels of resistant starch and lower glycaemic index is discussed.

Health benefits of cereal fibre: a review of clinical trials

Cereal fibre and whole-grain intakes have been consistently associated in the epidemiological literature with reduced mortality and risk of chronic disease including obesity, CVD and type 2 diabetes. The present review focuses on intervention trials with three primary aims: (1) understanding the mechanisms through which fibre consumption improves health (for example, examination of intermediate endpoints reflecting improved lipid, glucose and energy metabolism); (2) close evaluation of qualitative factors which modify fibre's effectiveness including physiochemical properties (for example, solubility, fermentability and viscosity), fibre extract molecular weight, fibre particle size and botanical structure of the fibre source grain; and (3) identification of areas in which additional research is needed. The first two aims typify the goals of nutrition research, in that improved understanding of the specific factors which determine fibre's health benefits has critical implications for dietary recommendations as well as improving understanding of physiological mechanisms. The third aim acknowledges the substantial gap between recommended and actual fibre intakes in many developed countries including the USA and the UK. In recognition of this deficit in total fibre intake, food manufacturing processes increasingly utilise fibre extracts and concentrates as food additives. However, whether fibre extracts provide similar health benefits to the fibre supplied in the constituents of whole grain is largely unexplored. The relative benefits of fibre extracts compared with whole-grain fibre sources therefore represent a critical area in which additional research is needed.