**1. Introduction**

Buckwheat is an annual herbaceous plant that botanically belongs to the order *Polygonales*, family *Polygonaceae*, genus *Fagopyrum* [1], but in terms of processing, similar use, chemical composition, and the seed structure itself, it is similar to cereals. It is therefore often classified as a pseudocereal [2, 3]. In the genus *Fagopyrum*, 15 species were discovered and described, among which nine have agricultural and nutritional value. However, only two species are most commonly grown: common (*Fagopyrum esculentum* Moench) and Tartary buckwheat (*Fagopyrum Tataricum* L.). Common buckwheat is the most common and cultivated species from temperate Europe to Japan, while Tartary buckwheat is grown in some mountainous areas [4].

Buckwheat grains are the main form of consumption of this pseudocereal. Hulled grains are mostly used for human consumption in the form of breakfast cereals or

as flour for the production of various bakery products (bread, cakes, snacks) and noodles enriched with buckwheat flour (0.3–60%), buckwheat-improved nonbakery products (tea, honey, and tarhana) [5] and products made of buckwheat husks such as pillows, quilts, mattresses, collars, eye masks, and children's toys [6]. In addition to flour and groats, buckwheat sprouts are increasingly used to improve bakery products [5, 7].

Since buckwheat is gluten-free, these products can be included in a gluten-free diet for patients with gluten intolerance [8, 9].

The addition of buckwheat into bakery products is of particular importance. This pseudocereal is gaining increasing attention as potentially functional food [4, 10]. Namely, buckwheat is recognized as a good source of nutritious proteins, lipids, dietary fiber and minerals and, in combination with other components that have a positive impact on health such as phenolic components and sterols, it is attracting increasing attention as a functional food. *In vitro* and *in vivo* studies have shown that the consumption of buckwheat and products enriched with this pseudocereal is associated with a wide range of biological and health activities: hypocholesterolemic, hypoglycaemic, anticancer, and anti-inflammatory. According to the recent phytochemical and pharmacological researches polysaccharides of buckwheat present also important bioactive components with numerous biological activities [11].

Buckwheat is the only pseudocereal that contains rutin, which has shown anti-inflammatory, anticancer, antiatherogenic, and antioxidant activity [4, 12]. Buckwheat protein extracts are associated with anticancer and cholesterol-lowering effects in animals [13, 14]. Apparently, the incorporation of buckwheat into bread results in significantly lower blood glucose and insulin responses compared to white wheat bread [15]. Buckwheat grain contains very rare D-*chiro*-inositol, which has been associated with reducing the symptoms of type 2 diabetes mellitus (non-insulindependent diabetes mellitus) [16].

#### **2. Bioactive components in buckwheat**

#### **2.1 Proteins**

Buckwheat proteins have a high biological value thanks to a well-balanced amino acid composition. The protein content of buckwheat is relatively lower than the protein content of legumes. However, the amino acid score of buckwheat protein is 100 and the content of essential amino acids corresponds to the recommended amino acid intake for children and adults [17].

They are rich in lysine, which is the first limiting amino acid of plant proteins, and arginine [18, 19]. However, the content of glutamine and proline is much lower compared to wheat [20], and threonine and methionine are the first and second limiting acids in buckwheat. Furthermore, Giménez-Bastida et al. [5] stated that buckwheat proteins are rich in albumin and globulin and that they are very poor in prolamin and gluten. Therefore, buckwheat flour is suitable for use in the diet of people with celiac disease due to its low non-toxic prolamin content [21]. The protein content in buckwheat flour is significantly higher compared to rice, wheat, corn, millet, and sorghum flour. While it is lower only compared to the protein content of oat flour [19]. Guo et al. [22] pointed out that the average protein content in buckwheat is 12.94%.

The digestibility of buckwheat proteins is about 80%, which is lower compared to proteins of animal origin such as hemoglobin and ovalbumin. However, it is higher

#### *The Importance of Buckwheat as a Pseudocereal: Content and Stability of Its Main Bioactive… DOI: http://dx.doi.org/10.5772/intechopen.102570*

than cereal proteins (e.g., sorghum 55–59%; corn 66–75%) and has a value approximate to rice bran (89%) and wheat germ (77–93%). Despite the balanced composition of essential amino acids, the bioavailability of buckwheat protein after digestion is not complete. Relatively low digestibility is attributed to the molecular structure of buckwheat protein and the presence of antinutritive factors in flour and protein isolates [17].

Buckwheat, along with other pseudocereals such as quinoa and amaranth, is recommended for use in creating new value-added bakery products because it can provide high levels of essential amino acids in the human diet [23].

The literature states that buckwheat proteins have many unique physiological functions, such as treating chronic diseases in humans, reducing serum cholesterol, suppressing gallstones and tumors, inhibiting angiotensin I-converting enzyme (ACE), and so on [17, 24, 25]. An ACE inhibitory tripeptide (Gly-Pro-Pro) was isolated and identified from common buckwheat [26]. In humans, buckwheat consumption has also been associated with a lower prevalence of hyperglycemia and improved glucose tolerance in people with diabetes [27]. Since many health benefits of buckwheat are inherently related to peptide radical binding activity from digested proteins, it is hypothesized that buckwheat protein hydrolysis may release peptide fragments capable of stabilizing reactive oxygen kinds and inhibiting lipid oxidation. By in vitro digestion of buckwheat protein six peptide fractions were obtained, whereas LC-MS/MS identified Trp-Pro-Leu, Val-Pro-Trp, and Val-Phe-Pro-Trp (IV), Pro-Trp (V), and tryptophan (VI) as the prominent peptides/amino acid in these fractions [28]. Six peptides DVWY (H-Asp-Val-Trp-Tyr-OH), FDART (H-Phe-Asp-Ala-Arg-Thr-OH), FQ (H-Phe-Gln-OH), VAE (H-Val-Ala-Glu-OH), VVG (H-Val-Val-Gly-OH), and WTFR (H-Trp-Thr-Phe-Arg-OH) identified from buckwheat sprouts fermented with *Lac*tobacillus Plantarum revealed significant blood pressure-lowering effect, thereby the most potent were DVWY, FQ, and VVG [29]. From the seeds of common buckwheat were purified two peptides (Fa-AMP1 and Fa-AMP2) which have antimicrobial properties [30]. Studies have shown that buckwheat protein extracts show anticancer activity, activity of lowering cholesterol, as well as anticonstipation and anti-obesity activities in animals [13, 17, 24]. An unusual antitumor protein TBWSP31 isolated from water-soluble Tartary buckwheat extracts was also examined [31].

#### **2.2 Phenolic components**

Many health benefits of buckwheat are attributed to the high content of phenolic components and high antioxidant activity [18]. Whole grain buckwheat was found to contain 2–5 times more phenolic components than barley and oats, while the husk and bran of buckwheat have 2–7 times higher antioxidant activity compared to barley, triticale, and oats [32, 33]. The research by Begić et al. [34] showed that Tartary buckwheat contains about 20 times more total phenol content and that it shows antioxidant activity nine times higher than common buckwheat.

Among the polyphenolic components present in buckwheat, those from the group of flavonoids, and among them rutin, are the most important ones.

#### *2.2.1 Flavonoids*

The presence and amount of flavonoids in buckwheat grain make it specific compared to cereals, which contain small amounts of flavonoids. This group of polyphenolic components is the basic antioxidant of buckwheat [35, 36]. Buckwheat is considered to be one of the best dietary sources of rutin [36]. The content and composition of flavonoids are different in different types of buckwheat. In general, the flavonoid content in *F. Tataricum* (40 mg/g) is higher than in *F. esculentum* (10 mg/g), reaching concentrations of 100 mg/g in flowers, leaves, and stems [37]. The content of flavonoids in Tartary buckwheat can be up to 7% [38].

Flavonoids demonstrate a protective effect in lipid oxidation in vitro as "scavengers" of free radicals and metal chelators [39]. They generally occur as O-glycosides in which one or more hydroxyl groups are bound to sugars.

Six flavonoids were isolated and identified from whole buckwheat grains: rutin, quercetin, orientin, isoorientin, vitexin, and isovitexin. The presence of rutin and isovitexin was found in hulled grain while buckwheat husk contained all 6 flavonoids [40, 41]. Buckwheat is the only pseudocereal that contains rutin and is, therefore, a useful source of this flavonoid [25]. Except in buckwheat, rutin has not been detected in cereals and pseudocereals [41, 42]. Rutin (quercetin-3-O-β-rutinoside), a secondary metabolite present in buckwheat, is the best-known glycoside derived from flavonol quercetin. Buckwheat is considered the best source of dietary rutin. Buckwheat grains (groats and husk) and sprouts are important sources of rutin and their content depends on the type and conditions of growth [43, 44]. It is important to develop new well-adaptive varieties with a high content of rutin, and improved biological value of the proteins [45].

Tartary buckwheat groats contain more rutin—80.94 mg/g dry matter (DM) than common buckwheat groats—0.20 mg/g DM [46, 47] while Tartary buckwheat sprouts have 2,2 times more rutin than common buckwheat sprouts [48]. Li et al. [49] stated that Tartary buckwheat can contain up to 100 times more rutin than common buckwheat.

Rutin has attracted much attention mainly because of its many health benefits observed in vitro and in vivo: anti-inflammatory, antidiabetic, hypocholesterolemic, antiatherogenic, antiatherosclerotic, and anticancer ones [4, 12, 36, 50–53] and its activity are related to antioxidant capacity [54]. Furthermore, rutin may be effective in preventing the toxic effects of methotrexate on the kidneys [55].

Rutin has relaxing effects on smooth muscles and is effective in preventing capillary apoplexy and retinal bleeding, lowers high blood pressure and shows antioxidant activity and lipid peroxidation activity. It also has lipid-lowering activity by reducing dietary cholesterol absorption, as well as reducing plasma and liver cholesterol [56, 57]. In addition, possibilities of rutin as a new strategy for the prevention of type 2 diabetes are noted [58]. Alkaline luminol chemiluminescence and electron spin resonance analysis revealed the formation of the rutin-ovalbumin complex which significantly increases the radical-binding activity in rutin. Rutin has also demonstrated antioxidant activity against hydroxyl radicals in a DNA protection test [59].

Quercetin (quercetin-3-ramnoside) is another glycoside present in buckwheat in concentrations ranging from 0.01 to 0.05% DM in Tartary and from 0.54 to 1.80% DM in common buckwheat [46, 60]. Isoquercetin (quercetin-3-glucoside) is present in buckwheat hypocotyl (1.4 μM/g DM) [61] and has been shown to exhibit antidiabetic and anticancer activity [36, 49, 62, 63]. Quercetin, an aglycone of rutin, is present in hulled grain (semolina) of buckwheat (0.001 mg/g DM) and husk (0.009–0.029 mg/g DM) in lower concentrations than rutin [18, 47]. Quercetin is the most studied flavonoid, primarily due to its pronounced antioxidant activity, as well as significant absorption in the digestive tract. It is predominantly in the form of glycoside as rutin (quercetin-3-O-beta-rutinoside). In addition to this, kaempferol-3-Orutinoside and quercetin 3-O-rutinoside-3'-O-β glucopyranoside have been found in buckwheat seeds [49, 64].

*The Importance of Buckwheat as a Pseudocereal: Content and Stability of Its Main Bioactive… DOI: http://dx.doi.org/10.5772/intechopen.102570*

Three flavonoids from Tartary buckwheat bran: quercetin, isoquercetin and rutin were evaluated as R-glucosidase inhibitors (controlling blood glucose) using fluorescence spectroscopy and enzyme kinetics. The R-glucosidase activity was clearly influenced by extractives (mostly rutin) and their hydrolysis products (a mixture of quercetin, isoquercetin, and rutin) from buckwheat bran [65].

Recent research relating to the examination of the antiviral activity of rutin in the treatment of patients with COVID-19 symptoms have been topical [66, 67].

In addition to rutin, catechins, the antioxidant activity of which is higher than the antioxidant activity of rutin, were isolated from ethanol extracts of buckwheat groats. Four catechins were isolated and their structures were determined as: (−)-epicatechin, (+)-catechin-7-O-β-D-glucopyranoside, (−)-epicatechin 3-O-p-hydroxybenzoate, and (−)-epicatechin 3-O-(3,4-di-O-methyl)gallate [68]. The following components from the catechin group were identified in buckwheat: catechin, epicatechin, catechin glucoside (A or B isomers), catechin gallate, epicatechin gallate, epicatechin-O-3,4-dimethylgallate, epiaphzelchin-(4─8) epicatechin-3,4-O- dimethylgallate, while catechin-3,4-O- dimethylgallate was identified in thermally treated buckwheat and epiaphzelchin- (4─6) -epicatechin was identified in green buckwheat [69].

These ingredients in plant tissue are influenced by numerous environmental factors such as ultraviolet (UV) radiation, harvest time and damage caused by pests, and genetic and aging-related factors. Studies have shown significant positive correlations between the mean altitude of the growth site and the amount of individual phenolic antioxidants [70, 71]. Buckwheat, as a source of rutin, can be successfully grown in Mediterranean conditions, too [72]. Flavon-3-glycosides present in buckwheat (vitexin, isovitexin, orientin, and homoorientin), anthocyanin and proanthocyanin content [61] and the presence of squalene, epicatechin, and vitamin E [73] make buckwheat a good antioxidant source in the human diet.

#### *2.2.2 Phenolic acids*

Phenolic acids in buckwheat also contribute to its antioxidant activity. In the grain of different varieties of Tartary buckwheat, p-hydroxybenzoic, ferulic and protocatechuic stand out, and other acids, including p-coumaric, gallic, caffeic, vanillic, and syringic acid, were also detected [74]. Several phenolic acids have been described during the flowering of different varieties of buckwheat: chlorogenic, p-anisic, salicylic, and methoxycinnamic [75].

#### **2.3 Vitamins**

Buckwheat is also an important source of vitamins, especially those of the B group. The total content of B vitamins, including B1 (thiamine, 2.2–3.3 μg/g DM), B2 (riboflavin, 10.6 μg/g DM), B3 (niacin, 18 μg/g), B5 (pantothenic acid, 11 μg/g) and B6 (pyridoxine, 1.5 μg/g) is higher in Tartary buckwheat compared to common buckwheat. The levels of vitamin C indicated for it in the literature go as high as 50 μg/g DM while its content, as well as the total amount of vitamins B1 and B6, increases by germination of buckwheat and, consequently, the content of vitamin C in buckwheat sprouts reaches 250 μg/g DM [4, 54, 76, 77]. Vitamin B1 is found in thiamine-binding proteins of buckwheat grains, which, according to Li and Zhang [37] increases the availability of vitamin B1 and improves its stability during storage. The content of vitamin E (tocopherols) in buckwheat is higher compared to wheat, barley, oats, and

rye [18]. The most common tocopherol in buckwheat is γ-tocopherol. In addition to γ-tocopherol, α- and δ-tocopherol have also been identified in buckwheat [78]. The concentration of total tocopherols in buckwheat grains ranges from 14.3 to 21.7 mg/kg [79]. Tocopherols, along with the other components mentioned above, make buckwheat a good antioxidant source in the human diet. Tocotrienols were not detected in buckwheat [80, 81], while Piironen et al. [82] identified traces of tocotrienols in whole buckwheat grains. High levels of vitamin E intake are associated with a reduction in cardiovascular disease, a reduction in the risk of Alzheimer's disease, and an improvement in the immune system [73].
