plants
Review
Tartary Buckwheat in Human Nutrition
Zlata Luthar 1 , Aleksandra Golob 1 , Mateja Germ 1 , Blanka Vombergar 2 and Ivan Kreft 3, *
1
2
3
*
Biotechnical Faculty, University of Ljubljana, SI-1000 Ljubljana, Slovenia; zlata.luthar@bf.uni-lj.si (Z.L.);
aleksandra.golob@bf.uni-lj.si (A.G.); mateja.germ@bf.uni-lj.si (M.G.)
The Education Centre Piramida Maribor, SI-2000 Maribor, Slovenia; blanka.vombergar@guest.arnes.si
Nutrition Institute, Tržaška 40, SI-1000 Ljubljana, Slovenia
Correspondence: ivan.kreft@guest.arnes.si; Tel.: +386-1-3007981
Abstract: Tartary buckwheat (Fagopyrum tataricum Gaertn.) originates in mountain areas of western
China, and it is mainly cultivated in China, Bhutan, northern India, Nepal, and central Europe.
Tartary buckwheat shows greater cold resistance than common buckwheat, and has traits for drought
tolerance. Buckwheat can provide health benefits due to its contents of resistant starch, mineral
elements, proteins, and in particular, phenolic substances, which prevent the effects of several chronic
human diseases, including hypertension, obesity, cardiovascular diseases, and gallstone formation.
The contents of the flavonoids rutin and quercetin are very variable among Tartary buckwheat
samples from different origins and parts of the plants. Quercetin is formed after the degradation of
rutin by the Tartary buckwheat enzyme rutinosidase, which mainly occurs after grain milling during
mixing of the flour with water. High temperature treatments of wet Tartary buckwheat material
prevent the conversion of rutin to quercetin.
Keywords: Tartary buckwheat; retrograde starch; proteins; phenolic substances; flavonoids; anti-virus
Citation: Luthar, Z.; Golob, A.; Germ,
M.; Vombergar, B.; Kreft, I. Tartary
Buckwheat in Human Nutrition.
Plants 2021, 10, 700. https://doi.org/
10.3390/plants10040700
Academic Editor:
Manuel Viuda-Martos
Received: 6 March 2021
Accepted: 2 April 2021
Published: 5 April 2021
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4.0/).
1. Introduction
Tartary buckwheat (Fagopyrum tataricum Gaertn.) originated in western China [1],
and it is grown in mountain areas of China, Bhutan, northern India, and Nepal [2,3].
In the same countries in regions with less harsh climatic conditions, Tartary buckwheat
is grown along with common buckwheat (Figure 1). In Europe, Tartary buckwheat is
traditionally cultivated and widely used in Luxemburg, and in adjacent areas of Belgium
and Germany, and it is also known in Slovenia and Italy [3–5]. Tartary buckwheat is also
grown traditionally in Bosnia and Herzegovina as well as in a mixed crop with common
buckwheat. Recently, it was reported that more than 100 hectares of Tartary buckwheat are
grown annually in Värmland, Sweden [6].
Collection of Tartary buckwheat samples from Slovenian fields started in the late 1970s.
At that time, it was cultivated by only a few farmers, and instead, in many buckwheat
fields, it coexisted with common buckwheat, but as a weed. A pluriannual research project
for the Luxembourgish Ministry of Agriculture has boosted research into, and cultivation
and development of, Tartary buckwheat in Europe [3,4].
Common and Tartary buckwheat have different growth characteristics [7]. Tartary
buckwheat is known to be resistant to the effects of cold weather, due to its epigenetic regulation by DNA methylation [8]. It is also more drought resistant than common buckwheat.
Indeed, Tartary buckwheat has traits of drought tolerance, while common buckwheat has
properties of drought avoidance [9].
The genus Fagopyrum includes 21 species [1,10]. Two of these, Fagopyrum esculentum
and F. tataricum, are used in human nutrition, and the wild species Fagopyrum cymosum is
used in traditional Chinese human and veterinary medicines. Wild relatives of cultivated
buckwheat have spread through the mountain areas of south-western China [11], where
recently a new self-compatible species was found and described as Fagopyrum longistylum
Plants 2021, 10, 700. https://doi.org/10.3390/plants10040700
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by M. Zhou and Y. Tang [12]. F. longistylum and other wild buckwheat species can serve as
donors of genes in the breeding of cultivated buckwheat species [13].
Figure 1. Tartary buckwheat (right, green flowering) and common buckwheat (to the left, white
flowering) plants, and seeds.
Tartary buckwheat includes a genotype called “rice-Tartary buckwheat”. Removal
of the husk (husking) of this variant is easier in comparison to other Tartary buckwheat
variants, as the husk is thinner and more brittle [14]. Comparative analysis of the transcriptomes of these two Tartary buckwheat genotypes has shown that 9250 genes are
differentially expressed between them. These include differences in regulatory and structural genes that affect the chemical components of the cell wall. As Tartary buckwheat
normally has a thicker and more robust husk than common buckwheat, this rice-Tartary
buckwheat variant is important for easy husking to obtain groats.
Tartary buckwheat accessions reveal multiple domestication sites, as has been shown
by sequencing of large numbers of Tartary buckwheat samples [12]. Intraspecific crosses
that included Tartary buckwheat have led to several new hybrid species, among which
the best known is probably Fagopyrum giganteum Krotov, which was originally defined
by Krotov and Dranenko at the Ustymivska Experimental Station in Ukraine [15,16]. The
wild species Fagopyrum homotropicum has been an important source for the development of
self-pollination in cultured buckwheat species [17].
Buckwheat intake has protective effects against several chronic diseases, including
hypertension, obesity, cardiovascular diseases, and gallstone formation [18]. These effects are mainly attributed to the resistant starch, protein, and phenolic substances in
the buckwheat grain.
2. Resistant Starch
The amylose content of starch is the basis for the appearance of retrograde starch [19].
Amylose is the starting material to obtain resistant starch using various hydrothermal
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treatments [20]. Resistant starch is the part of starch that is not digested by human enzymes
before entering the colon. The amount of resistant starch is affected by the composition of
the starch, in terms of its high amylose content, and depending on ecological and genetic
factors [21–23]. In Tartary buckwheat variety Xinong9920, starch peak viscosity was 2121 cP,
and in the same conditions the peak viscosity of variety Xinong9940 was significantly less,
namely 1928 cP [22]. In the experiment with phosphorus fertilization it was in Tartary
buckwheat at 75 kg/ha P dose in starch 24.7% apparent amylose in total starch (27.0% in
non-fertilized), and in another experiment 27.4% (28.6% in non-fertilized) in total amount
of starch [23].
Fertilization of Tartary buckwheat with phosphate affects its growth, development and
quality. Zhang et al. [23] showed that fertilization with different phosphorus (P) levels (from
15–135 kg/ha) affects the characteristics of starch from Tartary buckwheat. The increasing
P content initially decreased and after that increased the apparent amylose content and
mean diameter of the starch granules. These effects had impact on starch retrogradation,
the process whereby following mixing of starch with hot water, the disaggregated amylose
and amylopectin chains then undergo recombination upon cooling, to form a more ordered
structure. The retrogradation rate of Tartary buckwheat starch pastes increased during the
first 8 h after the start of cooling and then gradually stabilized. Increased amylose content
promotes rapid retrogradation, and slow starch retrogradation is an effect of amylopectin
molecules. Accordingly, starch from Tartary buckwheat exposed to high-P treatments has a
high number of branched long-chains of amylopectin, because a high in situ concentration
of long chains occurs during the process of reformation of the starch helices. Hydrothermal
treatment of Tartary buckwheat grain starch enhances the levels of slowly digestible starch
due to the retrograde starch [24].
Buckwheat grains have relatively small starch granules, with an amylose content of
the grain starch higher than that of cereals [25]. As Tartary buckwheat has a high flavonoid
content, which can interact with starch molecules, Tartary buckwheat can be used for the
production of foods with a low glycemic index [22]. Increased resistant starch is obtained
by cooking the buckwheat groats [25], and also by cold plasma treatment and quercetin
complexation [26]. This digestion of resistant starch is part of our dietary fiber, and it acts
as a prebiotic.
Different Tartary buckwheat varieties have different starch characteristics, and thus
it is necessary to take this into account during the processing of buckwheat [22]. The
buckwheat growing conditions, the availability of organic matter during buckwheat grain
filling and ripening, and also the hereditary characteristics of the buckwheat, all have
an important effect on the size of the starch granules and the starch amylose content.
Hydrothermally processed buckwheat samples contained up to 4% retrograde starch,
in comparison to untreated and dry-heated buckwheat, which contains only about 1%
resistant starch, as dry matter [19,27,28].
Progress in research into common and Tartary starch grain size and shape was reviewed by [22]. The lower starch glycemic index and insulin index after heating has been
attributed to the formation of amylase-resistant starch [29].
Lactic acid bacterial cultures and bifidobacteria can be used to prepare beverages from
common buckwheat starch-rich products. Tartary buckwheat bread products are also made
from fermented dough in Slovenia [30,31].
3. Protein
Buckwheat grain is considered a pseudocereal with high nutritional value because of
its protein composition. Although buckwheat grain has a low protein content (common
buckwheat, 10.6 g/100 g dry weight; Tartary buckwheat, 10.3 g/100 g dry weight), it has a
balanced amino-acid composition, with high levels of essential amino acids, such as leucine
and lysine (common buckwheat: 6.92, 5.84 g/100 g protein; Tartary buckwheat: 7.11,
6.18 g/100 g protein; respectively) [2]. The high content of protein, flavonoids and trace
elements in certain buckwheat grain milling fractions suggests their use in special dietary
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products [32]. Buckwheat grain protein can also contain Se [33], which is an essential trace
element in human nutrition.
Different hydrothermal treatments of buckwheat grain have been studied to determine
the impact of polyphenol levels on protein digestibility [29]. In a rat model system, considerable interactions were seen between polyphenols and protein during the hydrothermal
treatments. These interactions reduced the digestion of the buckwheat grain protein in
the small and large intestines. However, microbial processes in the colon enhanced the
digestibility of the protein in the hydrothermally processed buckwheat that was otherwise
blocked by polyphenols [29]. The authors established that polyphenols that are naturally
present in buckwheat husks lower the true digestibility of buckwheat grain protein, but do
not adversely affect the biological value. As reported by Ikeda et al. [34], tannic acid and
catechin have significant inhibitory effects on in vitro peptic and pancreatic digestion of
buckwheat globulin. Ikeda et al. [34] and Ikeda and Kishida [35] studied the in vitro digestibility of buckwheat grain protein and the impact of secondary buckwheat metabolites.
Evidence in the literature indicates that buckwheat grain protein can reduce cholesterol
levels in serum by increasing fecal excretion of steroids, which is induced by binding
of steroids to undigested protein. According to Ma and Xiong [36], digestion-resistant
peptides are largely responsible for bile acid elimination. These effects are most probably
connected with the limited digestibility of buckwheat grain protein.
As buckwheat grain does not contain gluten proteins, it is used for the preparation
of foods for patients with celiac disease [37,38]. Although buckwheat allergy is not very
common, allergic disorders associated with eating buckwheat-based foods have been
reported [39–41]. The low molecular weight buckwheat grain proteins that are associated
with such allergies are located in the grain embryo, and not the endosperm [42].
During the traditional hydrothermal preparation of buckwheat groats, there is migration of the substances from the grain pericarp into the groats [43,44]. In the processing of
buckwheat grain for different food products, there are various interactions possible among
the constituents, and especially during hydrothermal treatments.
Jin et al. [45] suggested that buckwheat grain can be treated to improve the protein
digestibility and the bioactivity of common and Tartary buckwheat protein. In this way,
buckwheat grain can be used as a plant-based protein source for improvement of the global
protein supply.
4. Mineral Elements
Tartary buckwheat grain and grain products have high levels of mineral elements [3].
These levels depend on the milling process, with the highest levels of mineral elements
in the bran; less is in the dark flour, and the least in the fine, light flour. Rb and Ag levels
are higher in common buckwheat than in Tartary buckwheat, although the levels of other
mineral elements (e.g., Se, Zn, Fe, Co, Ni, Sb, Cr, Sn) are higher in Tartary buckwheat.
However, the levels of all of the elements studied are a lot higher in Tartary buckwheat leaf
flour than in the grain or the milled products of the grain.
Tartary buckwheat leaf infusions contain decreasing levels (in order) of Zn, Cu, Cr,
Ni, Pb, and Cd [46]. The Cr concentrations in infusions from the whole plant and from
the grain bran and embryo were reported in this study to be in the range of 2.5 mg/kg to
3.2 mg/kg. In samples collected from commercial markets in China, the part of the plant
used and the processing methods were seen to impact upon these metal concentrations in
the products. For the content of Cr, the Tartary buckwheat for these infusions needs to be
grown in a clean environment.
Using the Tartary buckwheat green parts or bran in infusions has indicated that in
comparison to beverages from groats, these infusions contain higher concentration of
Cd (0.5–1.2 mg/kg), Pb (0.3–0.4 mg/kg), Cu (5–8 mg/kg), and Zn (30–50 mg/kg) [46].
Should the plant leaves and grain husks be contaminated with soil particles, it is possible
that polluted soil represents the direct source of the contamination of Tartary buckwheat
with metals. On the other hand, metal ions can bind to flavonoids, which might facilitate
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the absorption of metals into Tartary buckwheat plants, and their allocation thus to the
parts that are rich in flavonoids. According to Li et al. [46], the Pb levels in leaves are not
related to the flavonoids content, or to the total phenolics content. Tartary buckwheat grain
flour from Luxemburg, in Europe, had only 0.32 mg/kg Cr in the dark flour, and only
0.10 mg/kg Cr in the fine flour [3].
Common buckwheat can accumulate Al in its leaves, although this Al storage is not
expressed in the grain. This appears to be because there is no Al transportation via the
phloem, and Al is not mobile after its accumulation in leaves. The accumulated Al in older
leaves appears to originate from the roots, and therefore, green parts of buckwheat plants
can be used to remove Al from the soil [47–49].
Buckwheat is known to be suitable for biofortification with Se while it can accumulate
substantial amount of Se. As such, it can be a source of Se for the human diet [33,50].
Salicylic acid can increase the Se levels in plant tissues [51]. Of note, patients with severe
COVID-19 infection have vitamin D and Se deficiencies. Indeed, as Se appears to enhance
the cytotoxic effector cells, Se deficiency is a possible risk factor for COVID-19 mortality [52].
5. Phenolic Substances
Yu et al. [53] compared the rutin and quercetin contents across 44 Tartary buckwheat
grain and sprout samples from China, Nepal, Bhutan, India, Japan, Pakistan, and Slovenia.
These were very variable for these different origins (Table 1). The samples from Nepal had
the highest concentrations of rutin in the grain (13.3 g/kg) and sprouts (54.4 g/kg). For
quercetin, the sprouts contained 10–90-fold that seen in the grain [53]. Therefore, Tartary
buckwheat sprouts have great potential for production of flavonoids and for functional
foods that are rich in flavonoids.
Table 1. Results on concentration of rutin in Tartary buckwheat samples (in dry matter, HPLC 1200
series Agilent, column YMC-pack OSD-AC18, 4.6 mm ID × 250 mm, S-5 µm, YMC Co., LTD., Japan),
adapted from Yu et al. [53].
Location
Range of Rutin Concentration
in Grain (mg/100 g)
Range of Rutin Concentration
in Sprouts (mg/100 g)
Bhutan
(n = 3)
753.8–911.5
3039.3–3160.2
China
(n = 28)
364.2–1247.5
328.8–5214
India
(n = 2)
304.5–487.5
1542–1822.7
Japan
(n = 2)
769.1–902.4
3177.2–3825.7
Nepal
(n = 5)
583–1326.5
3313–5440.4
Pakistan
(n = 2)
675.2–901.3
2716.1–4088.6
Slovenia
(n = 2)
625.4–798.6
3382.6–3603.8
According to Klykov et al. [54], in samples from the far east of Russia, common
buckwheat grain contained 0.1% rutin by weight, Tartary buckwheat 2.4%, and cymosum
buckwheat 1.1%. At full flowering, the aboveground parts of common buckwheat had 3.1%
to 3.8% rutin, which produced 92 kg to 121 kg rutin/ha; the same for Tartary buckwheat
indicated 4.1% to 4.4% rutin, for 107 kg to 129 kg rutin/ha, and for cymosum buckwheat,
~4.1% rutin for ~83 kg rutin/ha [54]. Of note, Tartary buckwheat with a dark grain cover
contains more rutin than Tartary buckwheat varieties with other grain colors [55]. Addi-
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tionally, ozone levels in the atmosphere can affect the biosynthesis of phenolic substances
in Tartary buckwheat [56–58].
Milling of the grain of Tartary buckwheat and mixing the flour with water results in the
formation of quercetin, as a degradation product of rutin by rutinosidase (Figure 2) [59–63].
However, superheated steam or saturated steam can be used to inactivate the rutindegrading enzymes in buckwheat flour in less than 90 s. In contrast, under far infrared
drying, these rutin-degrading enzymes persist at 150 °C for 40 min [64].
Figure 2. Rutin transformation to quercetin and rutinose.
Ingested quercetin can cross the blood–brain barrier and accumulate in the brain
tissue [65]. Indeed, important bioactivities have been established for quercetin and its
derivatives not just in blood vessels, muscle, and the gastrointestinal system, but also in
the brain. Quercetin and other phenolics have been isolated from stool samples of people
who had eaten food rich in phenolic substances [65]. The presence of phenolic substances
in the colon can reduce the virus loads in the stools.
In Tartary buckwheat, quercetin complexation with starch molecules has an impact
on the in vitro digestibility of the starch and the appearance of resistant starch, thus
altering the physicochemical properties of the Tartary buckwheat starch [66]. The effects
of this quercetin–polyphenol complexation indicate that food products based on Tartary
buckwheat will show lower digestibility. Indeed, the quercetin in Tartary buckwheat can
reduce body weight, serum triacylglycerols, and low-density lipoprotein. In rats, a diet
with 0.1% quercetin was shown to have significant effects towards lowering low-density
lipoprotein concentrations in serum, with no such effects on high-density lipoprotein.
Tartary buckwheat has also been shown to prevent increases in body weight and fat
deposition during high-fat intake in rats, although on the other hand, this was reported
to protect against hepatic stenosis [67]. A buckwheat diet can also reduce insulin and
ameliorate glucose intolerance in humans [19].
Rat experiments with common buckwheat have further suggested the complexity of
the impact of the gut microbiota. Indeed, Peng et al. [67] suggested that the link between
weight gain and the gut microbiota is very complex, with the need for further studies here.
Interestingly, it has been shown that rutin-enriched Tartary buckwheat flour extracts
provide better flavonoid oral absorption, with the phenolic substances in the blood detectable for longer than with standard rutin, and even longer than for a native Tartary
buckwheat grain flour extract [45]. Rutin is in the most part bound to other grain substances
and structures. Indeed, extraction of rutin from untreated Tartary buckwheat grain flour
showed 0.57 g rutin/100 g flour, while autoclaving resulted in 3.03 g/100 g flour, boiling
resulted in 2.97 g rutin/100 g flour, and steaming resulted in 2.50 g/100 g flour [45,68].
Dzah et al. [68] also studied solid–liquid extraction conditions for Tartary buckwheat,
where they indicated that the extraction of phenolic compounds from Tartary buckwheat
flour can be performed at < 65 °C.
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The rutin and quercetin in Tartary buckwheat grain have an impact upon the physicochemical properties of the starch after cooking. The aging enthalpy of retrograde starch
is lowered, and the viscosity of Tartary buckwheat starch and paste is increased. Starch–
phenolics binding is stronger than that of the complex of starch and iodine. Starch is
gelatinized and retrograde, and the morphology is affected by quercetin and rutin [69].
Among the phenolics, some resveratrol has been reported for flours of common
buckwheat grain [70]. Nemcova et al. [71] reported from 1.0 mg/kg to 1.7 mg/kg transresveratrol for common buckwheat grain, while for Tartary buckwheat grain, there was
~3.5 mg/kg trans-resveratrol. Li et al. [72] reported that the resveratrol in Tartary buckwheat
bran does not show any detectable resveratrol in a bound form.
Chen et al. [73] suggested a new three-solvent mix for efficient and comprehensive
extraction of phenolics from Tartary buckwheat: acetone, ethyl acetate, and ethanol. This
method is valuable for evaluation of the Tartary buckwheat functional properties. Extraction of rutin from buckwheat samples is more effective with around 70% ethanol, instead
of more concentrated extractions [74]. As rutin and other phenolic substances can be
bound to different compounds and grain structures, effective extraction can take several
hours [30,31,59].
Buckwheat phenolic compounds can inhibit fungal development due to the phenolic hydrophobic interactions with cell membranes [75]. This effect is important for the
antifungal properties of sourdoughs. Lactic acid bacteria can split flavonoid glycosides
to flavonoid aglycones and a sugar, and can further metabolize aglycones. The resulting
metabolites, which include lactic acid and other organic acids, also serve to increase the
antifungal activity of buckwheat sourdough. This might explain the prolonged shelf life of
Tartary buckwheat sourdough bakery products [75].
The slow digestion properties of starch were studied by Luo et al. [76], following
ethanol extract of Tartary buckwheat. The slow digestibility of this starch appeared to be
due to the impact of phenolic substances on the starch. In their in vivo experiments, mice
showed reduced postprandial glycemic responses. These data of Luo et al. [76] for Tartary
buckwheat grain and glycemic responses were similar to those obtained earlier in common
buckwheat [19].
Phenolic compounds are often transformed in the gut before their absorption. The
gut microbiota is important in this process [77]. Large-sized dietary phenolics are poorly
absorbable, while small-sized products of microbial conversion are more easily absorbed
in the colon.
Wieslander et al. [78,79] performed a comprehensive double-blind crossover study
with 62 adult female participants, who additional to their normal diet, consumed either
359.7 mg rutin per day (high rutin diet; as Tartary buckwheat cookies), or 16.5 mg rutin per
day (low rutin diet; as common buckwheat cookies). After two weeks, the groups changed
their type of cookies (and hence rutin intake levels) for the following two weeks. Serum
levels of myeloperoxidase (as an inflammation marker) were reduced significantly in the
women who changed from low to high rutin in the diet (week 2 vs. week 4: reduction
of 55.4 µg/mL; p < 0.02) [78]. The higher rutin in the Tartary buckwheat cookies was
also related with strongly improved fatigue symptoms in comparison to the baseline,
according to the reduction in a visual analogue rating scale (32 vs. 22; p < 0.01). For
total serum cholesterol levels, these were significantly reduced from baseline to four
weeks for the combination of the data for low and high rutin regardless of the order of
intake (5.31 vs. 4.59 mmol/L; p < 0.001). The authors reported that this indicated that the
cholesterol lowering effect was not related to the content of rutin in the cookies, but to
other constituents of the buckwheats as well. Vogrinčič et al. [80] reported that flavonoids
are important in the antigenotoxic effects of Tartary buckwheat, although other buckwheat
metabolites have also important effects.
Cyclitols (also known as D-chiro-inositols) have also been reported for Tartary buckwheat grain (0.18–0.20%) [81]. The synthesis of cyclitols is triggered by environmental
parameters like salt stress and drought, and they can function as cryoprotectants. Ac-
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cumulation of cyclitol metabolites is directly connected with abiotic stress factors. The
environmental conditions of plants thus have an impact on the regulation of metabolic
pathways for synthesis and accumulation of cyclitols [82]. These compounds are known to
have anti-diabetic, anti-inflammatory, and other bioactivities in humans, as reviewed by
Ratiu et al. [82].
Non-invasive methods for distinguishing between Tartary and common buckwheat
samples based on flavonol accumulation in the green parts of the plants have been suggested [83]. Here, p-anisic acid in buckwheat leaves indicates Tartary buckwheat, rather
than common buckwheat.
Consumption of Tartary buckwheat infusions is a tradition that is popular in China,
and recently its consumption has spread also to Japan and Europe [84]. It was reported for
a mouse model that herb extracts in combination with Tartary buckwheat grain infusion
can reduce blood glucose levels, and lower serum triglycerides, total cholesterol, and
high-density lipoprotein-cholesterol levels.
Tartary buckwheat grain malt is also used in the preparation of drinks and cookies.
The malt is rich in orientin, vitexin, rutin, and quercetin, although the flavonoid levels
in cookies made with Tartary buckwheat grain are lower than expected in terms of the
amounts of raw Tartary buckwheat grain, soaked or germinated grain, or malt. Interestingly,
the levels of these flavonoids in Tartary buckwheat malt were higher than in the intact,
soaked, or germinated Tartary buckwheat products [37,85]. In the raw Tartary buckwheat
it was 2.2 mg/g d.w. of rutin, and in whole Tartary buckwheat malt 3.7 mg/g d.w. of
rutin [37].
Li et al. [72] reported antiproliferative effects of phenolic Tartary buckwheat extracts
on human breast cancer cells in an in vitro cell model. These data remain to be confirmed
by in vivo experiments.
In hydrothermally treated buckwheat, during the soaking of the grain, rutin moves
from the bran fraction into the endosperm, which results in higher amounts of rutin in the
flour [86]. Similar migration of smaller molecules from husk to groats during hydrothermal
treatment was shown earlier for common buckwheat [43].
The anthraquinone content in Tartary buckwheat has been studied in relation to
the color of the grain husk [87]. The fagopyrin (Figure 3) levels are at their highest
during seed germination, and light is important for the transformation of protofagopyrins
into fagopyrins, as increased fagopyrin levels have been shown to accompany increased
light conditions [88,89]. The consumption of green parts of buckwheat plants can cause
fagopyrism, which involves photosensitization with serous exudate, skin irritation, and
edema [88,89]. In fungi, fagopyrin is involved in the regulation of mycelial growth and
morphology, and in pathogenicity [90].
Figure 3. Fagopyrin.
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Emodin (Figure 4) has been reported for the bran and leaves of Tartary buckwheat [91].
It appears to be a precursor in the synthesis of hypericin, and of Tartary buckwheat
fagopyrin [92]. Of importance here, emodin isolated from Tartary buckwheat grain has been
shown to dock into all three active sites of the RNA-binding domain of the nucleocapsid
phosphoprotein of SARS-CoV-2 [91–94].
Figure 4. Emodin.
Quercetin has potential therapeutic effects against acute kidney injury, and for treatment of impaired renal function. Tartary buckwheat grain extracts are rich in such
flavonoids, and these can alleviate ethanol-induced liver injury in rats [87]. Rutin also
protects type 2 diabetic mice against liver injury [95]. The same function is seen for Tartary
buckwheat grain extracts, through inhibition of mitochondrial cell death [96,97]. In vivo
pharmacokinetics have also provided support for the administration of Tartary buckwheat
extracts to prevent alcoholic liver disease in humans [98].
Rutin is reported to also be effective in wound healing and in hyperglycemic rats, as it
can reduce oxidative stress and inflammatory responses, to thus reduce the risk of ulcer
formation [99]. Rutin induces activities of glutathione peroxidase, which protect the testis
of adult rats against the effects of ethanol [100]. Tartary buckwheat flavonoids improve
vascular sensitivity and show antihypertensive effects in spontaneously hypertensive
rats [101].
Salicylaldehyde is the most characteristic compound of common buckwheat, and it
has not been found in Tartary buckwheat. The aroma of Tartary buckwheat significantly
differs from the aroma of common buckwheat; indeed, as salicylaldehyde is a volatile
compound, it can be used as a marker for detection of contamination of Tartary buckwheat
with common buckwheat [43,44]. Tartary buckwheat also contains naphthalene [44].
6. Conclusions
Foods made from the grain of Tartary buckwheat have shown preventive effects
against several chronic diseases, including obesity, cardiovascular diseases, gallstone formation, and hypertension. The effects are mainly attributed to the resistant starch, protein
and phenolic substances in the grain, and to the interactions among these constituents.
Polyphenols have an impact on protein digestibility after hydrothermal treatment. Their interaction reduces the digestion of protein through the small and large intestines. Microbial
processes in the colon enhance the digestibility of the grain protein and starch, which are
otherwise blocked by polyphenols in hydrothermally processed buckwheat. Among the
polyphenols, fagopyrin appears to pose a health threat when the green parts of the plants
are consumed, and especially in summer by people with a light skin color. Consuming
buckwheat grain and grain products has been shown to be safe.
Buckwheat protein can reduce serum cholesterol levels through increased fecal excretion of steroids, which is induced by the binding of steroids to undigested protein.
Digestion-resistant peptides are largely responsible for bile acid elimination. As buckwheat
does not contain the gluten proteins, it is used as food for people with celiac disease. The
balanced amino-acid composition of buckwheat proteins represents an important source
of dietary protein for people who maintain vegetarian or vegan diets. An increase in
Plants 2021, 10, 700
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digestion-resistant starch is obtained by cooking buckwheat groats, and by cold plasma
treatments and quercetin complexation, which all result in modifications to the Tartary
buckwheat grain starch. Resistant starch acts as a dietary fiber, and has a function as a
prebiotic. Tartary buckwheat is a crop that is traditionally used as a food in mountain areas
in Asia and Europe. Based on its origin, Tartary buckwheat is a low input plant. Due to its
content of flavonoids and other phenolic substances, Tartary buckwheat is resistant to plant
diseases, pests, and damage by UV-B radiation. This makes Tartary buckwheat feasible
to be grown as an organic and ecological crop, with little need for addition of artificial
fertilizers, or of chemical treatments.
Last but not least, Tartary buckwheat reminds many consumers of the “good old
days”, whereby Tartary buckwheat dishes have been rising in popularity, especially among
food quality-conscious people in Asia and Europe. This provides the possibility now
to develop new, more “modern”, food products based on old culinary traditions, with
re-evaluation through contemporary scientific knowledge of the quality and potential of
Tartary buckwheat.
Author Contributions: Conceptualization, Z.L., M.G., B.V., I.K.; data curation, A.G., M.G.; validation,
writing original draft preparation, review and editing, all authors equally responsible; visualization,
A.G.; supervision, I.K.; project administration and funding acquisition, Z.L., M.G. All authors have
read and agreed to the published version of the manuscript.
Funding: This publication was supported by the operational program Integrated Infrastructure
within the project: Demand-driven research for the sustainable and innovative food, Drive4SIFood
313011V336, cofinanced by the European Regional Development Fund and the result of a study
financed by the Slovenian Research Agency, through programs P1-0212 “Biology of Plants” and
P3-0395 “Nutrition and Public Health”, and the applied project L4-9305, co-financed by the Ministry
of Agriculture, Forestry and Food, Republic of Slovenia.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Acknowledgments: The authors are grateful for the collaboration with Christian Zewen, Luxemburg,
and to Christopher Berrie for revising the English text.
Conflicts of Interest: The authors declare that they have no conflicts of interest.
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