Tartary Buckwheat Bran: A Review of Its Chemical Composition, Processing Methods and Food Uses.

Tartary buckwheat (Fagopyrum tataricum Gaertn.) containing large amounts of functional compounds with antioxidant activity, such as rutin, has attracted substantial research attention due to its industrial applications. Particularly, the functional compounds in Tartary buckwheat bran, an unexploited byproduct of the buckwheat flour milling process, are more concentrated than those in Tartary buckwheat flour. Thus, Tartary buckwheat bran is deemed to be a potential material for making functional foods. However, a review that comprehensively summarizes the research on Tartary buckwheat bran is lacking. Therefore, we highlighted current studies on the chemical composition of Tartary buckwheat bran. Moreover, the processing method and food uses of Tartary buckwheat bran are also discussed.

Physicochemical Properties and In Vitro Digestibility of Starch from a Trace-Rutinosidase Variety of Tartary Buckwheat 'Manten-Kirari'.

We recently developed a novel Tartary buckwheat variety, 'Manten-Kirari', with trace-rutinosidase activity. The use of 'Manten-Kirari' enabled us to make rutin-rich food products with low bitterness. This study was intended to evaluate the physicochemical properties and in vitro digestibility of starch isolated from 'Manten-Kirari'. For comparison, the representative common buckwheat variety 'Kitawasesoba' and Tartary buckwheat variety 'Hokkai T8' in Japan were also used. The lowest content of amylose was found in 'Manten-Kirari' starch (18.1%) while the highest was in 'Kitawasesoba' starch (22.6%). 'Manten-Kirari' starch exhibited a larger median granule size (11.41 µm) and higher values of peak viscosity (286.8 RVU) and breakdown (115.2 RVU) than the others. The values of onset temperature for gelatinization were 60.5 °C for 'Kitawasesoba', 61.3 °C for 'Manten-Kirari', and 64.7 °C for 'Hokkai T8'. 'Manten-Kirari' and 'Hokkai T8' starches were digested more slowly than 'Kitawasesoba' starch. Our results will provide fundamental information concerning the expanded use of 'Manten-Kirari' in functional foods.

Development of Novel Detection Method for Rutinosidase in Tartary Buckwheat (Fagopyrum tataricum Gaertn.).

Contamination of rutinosidase is a major problem for rutin-rich food due to the hydrolysis of the functional compound rutin and generation of strong bitterness caused by the hydrolyzed moiety quercetin. This problem sometimes occurs between the trace and normal rutinosidase Tartary buckwheat varieties. Here, we developed a simple and rapid method for rutinosidase detection in 'ripening seeds using UV light' and in 'dough using alum-flavonoid complexation' from Tartary buckwheat (Fagopyrum tataricum Gaertn.). Normal rutinosidase seeds can be distinguished from trace-rutinosidase mature seeds and ripening young seeds using a rutin solution by comparing the muddiness, which corresponds to quercetin generation. In dough, we detected a threefold relative increase in rutinosidase activity corresponding to 1% contamination of normal rutinosidase flour with trace-rutinosidase flour within 65 min. These methods do not require expensive apparatuses and toxic chemicals and are therefore promising for detecting and preventing contamination by rutinosidase, e.g., in food processing factories.

Roasted Tartary Buckwheat Bran as a Material for Producing Rutin-Rich Tea Beverages.

Tartary buckwheat bran, a byproduct of buckwheat milling, is commonly treated as waste. The present study examined the rutin content during successive infusions of roasted Tartary buckwheat bran and grain to develop a functional Tartary buckwheat tea. Samples (6 g) of roasted Tartary buckwheat bran and grain were rinsed with 300 mL of hot water (>95 °C) for 0.5 min. For the first infusion test, the tea infusion sample of roasted Tartary buckwheat bran contained a distinctly higher amount of rutin (389 mg/L) than that of the roasted Tartary buckwheat grain (68 mg/L). Overall, rutin was more effectively extracted from roasted Tartary buckwheat bran, as compared to roasted Tartary buckwheat grain.

Breeding of Buckwheat to Reduce Bitterness and Rutin Hydrolysis.

Buckwheat (Fagopyrum esculentum) is recognized as an important traditional crop in some regions, and its taste is an important characteristic. Of the three cultivated buckwheat species, Tartary buckwheat (Fagopyrum tataricum) and perennial buckwheat (Fagopyrum cymosum) have strong bitterness in their seeds, which has prevented the wider use of the seeds of these varieties. In Tartary buckwheat, some studies have focused on the cause of strong bitterness generation. Tartary buckwheat seeds contain large amounts of the functional compounds rutin and rutinosidase, and rutin hydrolysis by rutinosidase has been found to be the trigger of rutin hydrolysis. Therefore, a variety with only a trace of rutinosidase and with reduced bitterness is required. The rutinosidase in Tartary buckwheat seeds consists of two major isozymes with very similar enzymatic characteristics, which can hydrolyze flour rutin within several minutes after the addition of water. Recently, the trace-rutinosidase variety Manten-Kirari in Tartary buckwheat was developed. The trace-rutinosidase characteristics were dominated by a single recessive gene. In 'Manten-Kirari' dough and foods, such as breads, confectionaries, and noodles, the rutin residual ratio was higher and bitterness was reduced compared to that of the normal-rutinosidase variety. In this review, we summarize the detailed research on the breeding of buckwheat related to reducing bitterness and rutin hydrolysis.

Important agronomic characteristics of yielding ability in common buckwheat; ecotype and ecological differentiation, preharvest sprouting resistance, shattering resistance, and lodging resistance.

Common buckwheat is recognized as a healthy food because its seed contains large amounts of protein, minerals, and rutin. However, the yielding ability of common buckwheat is lower than that of other major crops. The short growing period, moisture injury, occurrence of sterile seeds due to lack of flower-visiting insects, and yield loss due to lodging and shattering cause low and unstable grain yield. Therefore, many common buckwheat breeders have tried to increase yielding ability by improving various characteristics. Recently, new breeding objectives for improving yielding ability by increasing preharvest sprouting resistance; reducing shattering loss; introducing self-compatibility; the ecotype, and semidwarf have been reported. In this review, we introduce the research on the important agronomic characteristics, preharvest sprouting resistance, ecotype and ecological differentiation, shattering resistance, and lodging resistance in common buckwheat.

Present status and future perspectives of breeding for buckwheat quality.

Buckwheat is an important crop globally. It has been processed into cereal grain, noodles, confectionery, bread, and fermented foods for many years. Buckwheat production and processing has supported local economies and is deeply related to the culture of some regions. Buckwheat has many unique traits as a food, with a good flavor and color. In addition, buckwheat is also a healthy food because it contains bioactive compounds that have anti-oxidative, anti-hypertensive, and anti-obesity properties. Therefore, breeding of buckwheat for quality is an important issue to be addressed. Compared to other crops, there is still a lack of basic information on quality, including bioactive compounds generation and enhancement. However, some mechanisms for modifying and improving the quality of buckwheat varieties have recently been identified. Further, some varieties with improved quality have recently been developed. In this review, we summarize the issues around buckwheat quality and review the present status and future potential of buckwheat breeding for quality.

A putative AGAMOUS ortholog is a candidate for the gene determining ease of dehulling in Tartary buckwheat (Fagopyrum tataricum).

MAIN CONCLUSION: Tartary buckwheat rice-type cultivars, which allow easy dehulling, lacked periclinal cell divisions that proceed underneath the epidermis in the proximity of ovary midribs in non-rice-type cultivars. The easy dehulling in these cultivars was associated with a G→A substitution in an AGAMOUS ortholog. Ease of dehulling in Tartary buckwheat (Fagopyrum tataricum) can affect the quality of its products. Tartary buckwheat cultivars that allow easy dehulling are called rice-type cultivars. The rice and non-rice hull types are determined by a single gene, but this gene is unclear. Here, we show that cells underneath the epidermis in the proximity of ovary midribs undergo periclinal cell divisions in non-rice-type cultivars but do not in a rice-type cultivar. The cells that arose from the periclinal cell divisions later underwent lignification, which should increase mechanical strength of hulls. In RNA sequencing, a partial mRNA of an AGAMOUS ortholog in Tartary buckwheat (FtAG) was found to be absent in the rice-type cultivar. Cloning of this gene revealed that this is a 42-bp deletion due to a G→A substitution at a splice acceptor site in the FtAG genomic region. In F2 progeny derived from a cross between non-rice-type and rice-type cultivars, all the rice-type plants exhibited the homozygous A/A allele at this site, whereas all the Tartary-type plants exhibited either the homozygous G/G allele or the heterozygous A/G allele. These results suggest that FtAG is a candidate for the gene that determines ease of dehulling in Tartary buckwheat. The DNA marker that we developed to distinguish the FtAG alleles can be useful in breeding Tartary buckwheat cultivars.

Development of 'Darumadattan', a semidwarf lodging-resistant Tartary buckwheat cultivar, using gamma-ray irradiation.

We developed a new cultivar of Tartary buckwheat (Fagopyrum tataricum Gaertn.), 'Darumadattan'. This is the first semidwarf Tartary buckwheat cultivar to be developed by mutation breeding using gamma-ray irradiation. In 1999, 100 dry seeds of the leading Japanese cultivar, 'Hokkai T8' (known at that time as 'Hokkei 1'), were gamma-ray-irradiated with a total dose of 500 Gy (25 Gy/h × 20 h) at the Institute of Radiation Breeding (IRB), National Institute of Agrobiological Sciences, Hitachiomiya, Ibaraki, Japan. The seeds were sown in August 1999 in a field at IRB, and M2 seeds were collected from the eight individual plants that survived. In August 2000, 240 M2 seeds were sown in a field, and one semidwarf plant was found. The line named 'IRBFT-20' developed from the selected plant was investigated for its semidwarf characteristic and genetic stability in 2001-2005. 'IRBFT-20' was submitted for registration in 2011 and registered as the cultivar 'Darumadattan' in 2013. This name was chosen because the plants resemble "Daruma dolls" and "dattan" means "Tartary" in Japanese. 'Darumadattan' is a highly lodging-resistant and high-yielding cultivar and is expected to be used as both a commercial cultivar and a crossing parent.

Development of common buckwheat cultivars with high antioxidative activity -'Gamma no irodori', 'Cobalt no chikara' and 'Ruchiking'.

To breed new highly antioxidative common buckwheat cultivars, we selected individual plants from gamma ray-irradiated populations. Selection and propagation were repeated 4 or 5 times. This recurrent selection process resulted in many individuals with enhanced antioxidative activity. Among them, 2 individuals from the forth selection and 9 individuals from the fifth selection were developed into lines with increased antioxidative activities and diverse polyphenolic composition. From these lines, 2 new cultivars 'Gamma no irodori' and 'Cobalt no chikara' were developed. Furthermore, following the selection of individuals with high rutin contents, 'Ruchiking' was developed.

Development of a DNA marker for variety discrimination specific to 'Manten-Kirari' based on an NGS-RNA sequence in Tartary buckwheat (Fagopyrum tataricum).

To discriminate the trace-rutinosidase variety of Tartary buckwheat 'Manten-Kirari', we developed DNA markers based on RNA polymorphism. Specifically, we mapped 17.76 GB RNA sequences, obtained using HiSeq2000, to create 11,358 large contigs constructed de novo from 'Manten-Kirari' RNA derived from GS-FLX+ titanium. From these, we developed eight DNA markers corresponding to single- to four-nucleotide polymorphisms between 'Manten-Kirari' and 'Hokkai T8', which is representative of normal rutinosidase content varieties in Japan. Using these markers, 'Manten-Kirari' was discriminated from 'Hokkai T8' by eight markers, from major Tartary buckwheat varieties by three markers, and from common buckwheats by two markers. We also performed direct PCR from flour and dried noodle made with 'Manten-Kirari' and 'Hokkai T8'. Based on the results, the DNA markers developed are promising for discriminating 'Manten-Kirari'. This is the first study to develop a DNA marker to discriminate varieties in the Polygonaceae family including buckwheat species.

Isolation and characterization of genes encoding leucoanthocyanidin reductase (FeLAR) and anthocyanidin reductase (FeANR) in buckwheat (Fagopyrum esculentum).

Proanthocyanidins (PAs) are a major group of flavonoids synthesized via the phenylpropanoid biosynthesis pathway, however the pathway has not been fully characterized in buckwheat. Anthocyanidin reductase (ANR) and leucoanthocyanidin reductase (LAR) are involved in the last steps of PA biosynthesis. To isolate the genes for these enzymes from buckwheat we performed PCR using degenerate primers and obtained cDNAs of ANR and LAR, which we designated FeANR and FeLAR1. A search for homologs in a buckwheat genome database with both sequences returned two more LAR sequences, designated FeLAR2 and FeLAR3. Linkage analysis with an F2 segregating population indicated that the three LAR loci were not genetically linked. We detected high levels of PAs in roots and cotyledons of buckwheat seedlings and in buds and flowers of mature plants. FeANR and FeLAR1-3 were expressed in most organs but had different expression patterns. Our findings would be useful for breeding and further analysis of PA synthesis and its regulation in buckwheat.

Acute and Subacute Toxicity Studies on Rutin-Rich Tartary Buckwheat Dough in Experimental Animals.

In order to investigate the toxicity of rutin-rich dough from the Tartary buckwheat variety 'Manten-Kirari,' acute and subacute toxicity studies (10,000 and 5,000 mg/kg flour, respectively) were performed using rats. In the acute toxicity study, no toxic symptoms were observed and no rats died during the test. Body weight in the 'Manten-Kirari'-treated group was not significantly different when compared with that of the control group. On pathologico-anatomic observation, no unusual symptoms were observed in the 'Manten-Kirari'-treated group when compared with the control group. In the subacute toxicity study, no toxic symptoms were observed and no rats died during the test. Body weight and food intake in the 'Manten-Kirari'-treated and common buckwheat groups were not significantly different when compared with the control group. However, some investigated properties, such as urine protein and serum albumin, were significantly different in the 'Manten-Kirari' and common buckwheat groups when compared with the control group. However, these changes were not caused by toxicity, but by transient changes. On pathologico-anatomic observation, some abnormalities were observed in the liver, kidneys, heart, lung, bronchi and pituitary gland in some rats. However, the incidental rates in the 'Manten-Kirari' and common buckwheat groups did not differ when compared to controls. Therefore, these abnormalities may be caused by natural generation. Based on these results, we concluded that dough at a dose of 5,000 mg flour/kg is at a non effect level.

Discovery and genetic analysis of non-bitter Tartary buckwheat (Fagopyrum tataricum Gaertn.) with trace-rutinosidase activity.

In a screening of about 500 lines of Tartary buckwheat, we identified lines that contained no detectable rutinosidase isozymes using an in-gel detection assay. We confirmed that seeds of these individuals had only a trace level of in-vitro rutinosidase activity. To investigate the heritability of the trace-rutinosidase characteristic, we analyzed the progeny of crosses between rutinosidase trace-lines, 'f3g-162', and the 'Hokkai T8'. The F2 progeny clearly divided into two groups: those with rutinosidase activity under 1.5 nkat/g seed (trace-rutinosidase) and those with activity over 400 nkat/g seed (normal rutinosidase). The segregation pattern of this trait in F2 progeny exhibited 1 : 3 ratio (trace-rutinosidase : normal rutinosidase), suggesting that the trace-rutinosidase trait is conferred by a single recessive gene; rutinosidase-trace A (rutA). In addition, sensory panelists evaluated the bitterness of flour from trace-rutinosidase individuals and did not detect bitterness, whereas flour from normal rutinosidase individuals was found to have strong bitterness. Although at least three bitter compounds have been reported in Tartary buckwheat seeds, our present findings indicate that rutin hydrolysis is the major contributing factor to bitterness. In addition, the trace-rutinosidase line identified here, 'f3g-162', is a promising material for generating a non-bitter Tartary buckwheat variety.

Breeding of 'Manten-Kirari', a non-bitter and trace-rutinosidase variety of Tartary buckwheat (Fagopyrum tataricum Gaertn.).

Here, we developed a new Tartary buckwheat cultivar 'Manten-Kirari', whose flour contains only trace amounts of rutinosidase and lacked bitterness. The trace-rutinosidase breeding line 'f3g-162' (seed parent), which was obtained from a Nepalese genetic resource, was crossed with 'Hokkai T8' (pollen parent), the leading variety in Japan, to improve its agronomic characteristics. The obtained progeny were subjected to performance test. 'Manten-Kirari' had no detectable rutinosidase isozymes in an in-gel detection assay and only 1/266 of the rutinosidase activity of 'Hokkai T8'. Dough prepared from 'Manten-Kirari' flour contained almost no hydrolyzed rutin, even 6 h after the addition of water, whereas the rutin in 'Hokkai T8' dough was completely hydrolyzed within 10 min. In a sensory evaluation of the flour from the two varieties, nearly all panelists detected strong bitterness in 'Hokkai T8', whereas no panelists reported bitterness in 'Manten-Kirari'. This is the first report to describe the breeding of a Tartary buckwheat cultivar with reduced rutin hydrolysis and no bitterness in the prepared flour. Notably, the agronomic characteristics of 'Manten-Kirari' were similar to those of 'Hokkai T8', which is the leading variety in Japan. Based on these characteristics, 'Manten-Kirari' is a promising for preparing non-bitter, rutin-rich foods.

Traits of shattering resistant buckwheat 'W/SK86GF'.

Seed shattering is a significant problem with buckwheat, especially at harvesting time. Several reports have shown that a green-flower mutant of buckwheat, such as W/SK86GF, has a strong pedicel. Although a strong pedicel may provide some resistance to shattering in the field, no study has thoroughly examined this issue. In this paper, we demonstrate that a W/SK86GF has shattering resistance by comparing the degrees of shattering of W/SK86GF and Kitawasesoba (leading variety of Hokkaido with non-green-flower traits) through a test for four years, including a typhoon hit year in the field. In a non-typhoon year, the shattering seed ratio (shattering seed weight/(yield + shattering seed weight) × 100) of W/SK86GF at maturing time +15 days (+15D) was lower than that of Kitawasesoba. In a typhoon hit year, the shattering seed ratios of Kitawasesoba at maturing time and +15D were surprisingly high, 14.4 and 21.1%, respectively. On the other hand, those of W/SK86GF were only 3.08% and 2.57%, respectively; indicating W/SK86GF is promising as a shattering resistant line even in a typhoon hit year. From these results, shattering resistance of W/SK86GF can be evaluated after maturing time such as +15D and pedicel strength would confer W/SK86GF a shattering resistant trait.

Effects of lipase, lipoxygenase, peroxidase and free fatty acids on volatile compound found in boiled buckwheat noodles.

BACKGROUND: Relationships between buckwheat (Fagopyrum esculentum Moench) flour lipase, lipoxygenase and peroxidase activity, along with levels of individual free fatty acids (FFAs) and levels of headspace volatile compounds of boiled buckwheat noodles, were investigated for 12 different buckwheat varieties. Enzyme activities and FFA levels in flour were correlated with their respective varietal arrays of boiled noodle headspace volatile compounds, measured by gas chromatography-mass spectrometry. RESULTS: The volatiles hexanal, tentative butanal, tentative 3-methylbutanal and tentative 2-methylbutanal showed significant positive correlation with one another, indicating that they may be generated through similar mechanisms. These important volatile components of buckwheat flavor were also positively correlated with lipase and/or peroxidase activity, indicating that enzymatic reactions are important in flavor generation in boiled buckwheat noodles. On the other hand, pentanal, which showed no significant correlation with any enzyme activity, showed a significant positive correlation to the levels of C18:2 and C18:3 FFAs, suggesting the existence of a 'non-enzymatic' and/or 'uncertain enzymatic pathway' for flavor generation in boiled buckwheat noodles. CONCLUSION: Lipase and peroxidase in buckwheat flour are important for flavor generation of boiled buckwheat noodles. This information is important for increasing desirable flavor of buckwheat products as well as for selecting varieties with improved flavor.