Nutritional and bioactive characteristics of buckwheat, and its potential for developing gluten‐free products: An updated overview

Abstract In the present era, food scientists are concerned about exploiting functional crops with nutraceutical properties. Buckwheat is one of the functional pseudocereals with nutraceutical components used in the treatment of health‐related diseases, malnutrition, and celiac diseases. As a preferred diet as a gluten‐free product for celiac diseases, buckwheat is a good source of nutrients, bioactive components, phytochemicals, and antioxidants. The general characteristics and better nutritional profile of buckwheat than other cereal family crops were highlighted by previous investigations. In buckwheats, bioactive components like peptides, flavonoids, phenolic acids, d‐fagomine, fagopyritols, and fagopyrins are posing significant health benefits. This study highlights the current knowledge about buckwheat and its characteristics, nutritional constituents, bioactive components, and their potential for developing gluten‐free products to target celiac people (1.4% of the world population) and other health‐related diseases.


| INTRODUC TI ON
In recent years, the consumption of functional food with bioactive ingredients has increased in consumers' diets. These functional foods provide nutritional as well as health benefits to end-use consumers. Among the health-related foods, pseudocereals are among the functional foods with numerous health benefits (Astrini et al., 2020;Mir et al., 2018;Xu et al., 2022). However, pseudocereals are taxonomically different; they show similar characteristics to the Poaceae family (wheat, rice, and barley) due to endospermrich starch components. The main pseudocereals with healthrelated benefits are buckwheat, amaranth, and quinoa (Ferreira et al., 2022). Buckwheat is one of the pseudocereals, belongs to the family of Polygonaceae, and is commonly used in the cold region of the world. The buckwheat cultivars are mainly found in mountain regions, especially Russia and China (Begemann et al., 2021;Yilmaz et al., 2020;Zou et al., 2021). The world production of buckwheat is about 3.8 million tons, and Russia ranked at the top position with 1.5 million tons, followed by China with 0.9 million tons (FAO STAT data, 2019). Buckwheat is also cultivated in France (8.3%), the USA (5.7%), Poland (5.4%), Brazil (3.5%), and Japan (1.0%). Buckwheat seeds are mainly used as breakfast cereals in the form of groats, flour for bakery products, and other enriched products such as bread, tea, honey, and sprouts (Giménez- Bastida et al., 2015;Małgorzata et al., 2018). The various health-related benefits (hypocholesterolemic, hypoglycemic, anticancer, and anti-inflammatory) were associated with buckwheat and its byproducts which enhance their potential for functional food formulation (Mondal et al., 2021) and increase their agricultural, industrial, and pharmaceutical uses (Fotschki et al., 2020).
The biological values of buckwheat proteins are outstanding, but antinutritional factors (tannins and proteases) associated with buckwheat proteins lower their protein digestibility (Mattila et al., 2018).
Polyphenolic compounds (flavonoids and phenolic acids) are bioactive ingredients in buckwheat and increase the nutraceutical potential of buckwheat. Buckwheat is a rich source of flavonoids such as rutin, isoorientin, quercetin, isovitexin, vitexin, and orientin (Raguindin et al., 2021). Among all pseudocereals, rutin is only present in buckwheat, with higher antioxidant, anti-inflammation, and anticancer properties (Zhu, 2016). The flavonoid compounds in buckwheat impart pharmaceutical and other health-related benefits (Lee et al., 2016). Buckwheat is also a good source of resistant starch, tannins, plant sterols, and fagopyrins (Ahmed et al., 2014).
There are two well-known disorders linked to gluten exposure: celiac disease and IgE-mediated wheat allergy. Genetic susceptibility factors play a significant role in the development of celiac disease, an autoimmune condition that may cause significant intestine damage. In the general community, celiac disease affects 0.5% to 1% of people (Giménez- Bastida et al., 2015;Manikantan et al., 2022;Rafiq et al., 2021). Contrarily, gluten sensitivity and/or other wheat proteins is caused by IgE antibodies that identify epitopes from certain proteins, known as allergens, setting off a chain of events that results in allergic inflammation. Wheat allergy is present in between 0.33% and 1.17% of the population (Ballini et al., 2021;Brand et al., 2022;Srisuwatchari et al., 2020). A rigorous, gluten-free diet for the rest of one's life is only suggested for those diagnosed with celiac disease.
Similar restrictions apply to those who have been diagnosed with IgE-mediated wheat allergy. In that context, nonceliac gluten sensitivity, a third illness marked by discomfort after ingestion of gluten and in which neither celiac disease nor IgE-mediated allergy plays a role, has received more attention in recent years (Aksoy et al., 2021;Srisuwatchari et al., 2020;Vassilopoulou et al., 2021). Various products without gluten protein are available on the market, but most products lack acceptance by celiac patients (Mir et al., 2014).
Products free from gluten are available in the market with low protein, dietary fiber, and vitamins compared to gluten-containing food products. So, designing through fortification or supplementation of nutrient-dense ingredients is the novel approach for enhancing the nutritional profile of gluten-free products. Buckwheat is a nutrientdense pseudocereal, free from gluten protein, and the preferred diet for celiac patients (Morales et al., 2021). This study highlights the current knowledge about buckwheat and its characteristics, nutritional constituents, bioactive components, and potential for developing gluten-free products.

| D IVER S IT Y AND G ROWING A S PEC TS OF BUCK WHE AT
Buckwheat is an annual herbaceous plant adaptable to all environmental conditions, including infertile land unsuitable for other crops (Rodríguez et al., 2020). The origin of buckwheat is China and Central Asia . Buckwheat is derived from beech and wheat due to its similarity with beechnut and wheat. Buckwheat has been grouped into annual and multiannual types of species. The annual species include Fagopyrum tataricum L, Fagopyrum giganteum Krotov, and Fagopyrum esculentum Moench, whereas Fagopyrum suffruticosum Fr. Schmidt, Fagopyrum ciliatum Jaegt, and Fagopyrum cymosum Meissn are multiennual types (Jing et al., 2016). The The buckwheat has a diversified crop ecology depending upon season and climate. Buckwheat is a mostly adapted crop of the Himalayas at different altitudes, such as low hills, mid-hills, and high hills. The most commonly grown buckwheat is adapted to low hills and is a winter crop, while tartary buckwheat is suitable for mid-and high hills and is a spring-growing crop (Koirala, 2020). Buckwheat is a dicot with irregular and triangular seeds (Ahmed et al., 2014). The seed contains brown-to-black color hulls covering the whole kernel, F I G U R E 1 Different lines/selections of buckwheat (a), buckwheat at harvesting stage (b), and seeds from different lines from buckwheat (c).
colored white to light green. The color and hardness of buckwheat hull are related to different cultivars of buckwheat (Roy et al., 2019).
The buckwheat seed germinates in soil (3-4 days), flowering after 3 weeks of planting with white petals, and after pollination by wind, seed formation starts within 10 days. The buckwheat seed needs more than 1 week to attain full maturity after seed formation. The buckwheat seed for growth requires low-fertility soil with a moderate nitrogen content (Gairhe et al., 2015). The cultivation period of buckwheat is a short growing period of 70-90 days and good storage periods due to its chemical constituents. The harvesting of buckwheat seeds has technical problems due to their uneven ripening pattern. So modern techniques and harvesting equipment need to be adopted to tackle the problems and issues related to the harvesting of buckwheat.

| NUTRITIONAL CONS TITUENTS OF B U CK WH E AT
Buckwheat is a nutrient-dense grain with an excellent nutrient profile to target malnutrition and the celiac population. The buckwheat type pseudocereal is preferred for formulating food products through supplementation with cereal crops to enhance nutritive value or replace cereal grains with gluten-free product formulation.
The nutritional composition of buckwheat is presented in Table 1.

| Proteins
Buckwheat is an important source of protein content (8.5%-18.8%), depending on the cultivar, source, and climate conditions (Dziadek et al., 2016). The protein concentration in buckwheat grains is higher than in cereal grains (Bobkov, 2016). The proteins in buckwheat are composed of globulins (43.3%-64.5%), albumins (12.5%-18.2%), prolamins (0.8%-2.9%), and glutelins (8.0%-22.7%), and 15% of residual proteins (Chrungoo et al., 2016). The prolamine content in buckwheat proteins is very low, and proteins responsible for celiac diseases (30 kDa prolamins) are absent in buckwheat as observed from gel electrophoresis and enzyme-linked immunosorbent method by Petr et al. (2003). The 2 S albumins, 8 S, and 13 S globulins in buckwheat proteins are similar to the storage proteins of legumin (Bobkov, 2016). Among the globulin proteins, 13 S globulins are the main storage protein having a hexameric structure with acidic (32-43 kDa) and basic (23-25 kDa) polypeptide subunits bonded by disulfide bonding (Taylor et al., 2016). The compositions of amino acids are well balanced in buckwheat proteins and are rich in arginine, lysine, and aspartic acids (Bhinder et al., 2020). The presence of tannins and protease inhibitors decreases the protein digestibility of buckwheat. However, the presence of lysine amino acid in buckwheat protein increases the protein digestibility-corrected amino acid scores of proteins in buckwheat than the cereals .

| Carbohydrates
Starch is the available carbohydrate source in buckwheat grains that varies from 60% to 70% (Vojtiskova et al., 2012). The amylose and amylopectin are in the ratio of 25 and 75%, respectively, present in the starch of buckwheat . Buckwheat starch granules are small in size, smooth surfaced, polygonal in shape and size (3-10 μm), and are similar to tuber and cereal starch (Yang et al., 2019).
Buckwheat is also a good source of resistant starch (33.5%) as Yang et al. (2019) reported in buckwheat groats. Different processes, such as autoclaving, cooking, or boiling, affect buckwheat-resistant starch content (Bobkov, 2016). Buckwheat contains more starch content than the other pseudo cereals, and the calorie content (343 cal/100 gm) of buckwheat is similar to cereal and legumes (Mir et al., 2014). The buckwheat embryo is a storehouse of soluble carbohydrates in the form of d-chiro-inositol, besides sucrose. The dchiro-inositol in the embryo of buckwheat is stored in the form of fagopyritols which is galactosyl derivative of d-chiro-inositol, and

TA B L E 1 Nutritional composition of buckwheat
their concentration varied from 20.7 to 41.7 mg 100/g, out of which 71% is concentrated in buckwheat embryo (Zieliński et al., 2019).
The maximum concentrations of fagopyritols are reported in Tartary buckwheat than in the common cultivars. Another soluble carbohydrate has been identified from tartary buckwheat as rhamnosyl glucoside (31%) (Dębski et al., 2016).

| Dietary fiber
The and also induce adverse effects such as mineral and protein unavailability (Zhu, 2020).

| Lipids
The lipids in buckwheat are low but have shown good importance in various physiological activities, with lipid content ranging from 1.5% to 3.7% (Ruan et al., 2020). The lipids in buckwheat are classified into neutral lipids at 81-85%, phospholipids at 8%-11%, and glycolipids at 3%-5% (Bobkov, 2016). Buckwheat is a rich source of unsaturated fatty acids (74.5%-79.3%), which have health benefits against heart diseases, cancer, inflammation, and diabetes (Ruan et al., 2020). The unsaturated fatty acids are concentrated in the embryo of buckwheat seed, and palmitic, oleic, and linoleic are the most common type of fatty acids, representing 87.3%-88% in buckwheat seeds (Gulpinar et al., 2012).

| Vitamins and minerals
Vitamins and minerals are leading in physiological processes in the human body. The buckwheat grain is a rich source of vitamin A, vitamin B complexes, and vitamins C and E (Zhu, 2016 (Zhou, Hao, et al., 2015;Zhou, Wen, et al., 2015). Vitamin B1 of buckwheat is associated with thiamine-binding proteins and increases their bioavailability and stability during storage conditions (Wronkowska, Zielinska, et al., 2010;Wronkowska, Soral-Śmietana, et al., 2010). Zhou, Hao et al. (2015) and Zhou, Wen et al. (2015) reported a vitamin C content of 5 mg/100 g in buckwheat, and after germination, the vitamin C levels rose to 25 mg/100 g. Buckwheat grains are mineral sources of both macro-and micronutrients.
Macronutrients like phosphorus, potassium, magnesium, and calcium are at reasonable levels, whereas iron, manganese, and zinc are at lower concentrations in buckwheat (Zhu, 2016). The micronutrients in buckwheat are higher than in cereal grains, and their concentration is mainly confined to the seed coat, hull, and aleurone layers (Orožen et al., 2012). The minerals like zinc, copper, and potassium become readily available for absorption after enzymatic digestion into a soluble form (Klepacka et al., 2020). The diet available for gluten-free consumers is low in vitamins and minerals, and the incorporation of buckwheat in gluten-free diets increases the concentration of vitamins and essential minerals in their diet (Mir et al., 2014).

| B I OAC TIVE COMP OUNDS IN B U CK WH E AT
Buckwheat is a dense nutritive pseudocereal with various bioactive compounds such as bioactive peptides, flavonoids, fagopyrins, fagopyritols, d-fagomine, and phenolic acids (Table 2), and their chemical structure is presented in Figure 2. The bioactive compound of buckwheat grains enhances its healing effect against health-related diseases.

| Bioactive peptides
Buckwheat grains are a good source of protein higher than cereal crops (Bobkov, 2016). The protein content in buckwheat has wellbalanced amino acids with a nutritive value similar to milk and egg solids (Gimenez- Zhou, Hao, et al., 2015;Zhou, Wen, et al., 2015). According to Clare and Swaisgood (2000), bioactive peptides have pharmacological activity. The pharmacological activities associated with bioactive peptides are antioxidant, antimicrobial properties, cholesterol-lowering ability, hypoglycemic effect, and antitumor activity (Nasri, 2016). The peptide generally contains 3 to 50 amino acid residues, with their activity depending on their sequence, composition, structure, charge, and hydrophobicity (Saadi et al., 2015). Bioactive peptides are either naturally available or prepared through enzymatic hydrolysis (Aiello et al., 2017).
Buckwheat-based protein extracts have also been effective against dimethylhydrazine-induced mammary and colon cancer in rats (Liu et al., 2001).
Buckwheat hypotensive peptides contain 2-5 amino acid residues (Zhou, Hao, et al., 2015;Zhou, Wen, et al., 2015). The hypotensive peptides inhibit the angiotensin I-converting enzyme and lower blood pressure (Zieliński et al., 2020). The hypotensive peptides with amino acids (proline, tyrosine, tryptophan, tyrosine, proline, and phenylalanine) at the carboxyl and terminal end have a great affinity for inhibiting the activity of the angiotensin Iconverting enzyme (Ma et al., 2006). The inhibitors of angiotensin I-converting enzyme isolated from protein hydrolysates of buckwheat were FY, YQ, AY, LF, YQY, YV, VK, PSY, LGI, ITF, and INSQ (Li et al., 2002). The inhibitors such as DVWY, FDART, FQ, VAE, VVG, and WTFR were also reported by Koyam et al. (2013) in fermented buckwheat sprouts with hypotensive activity. The buckwheat protein extracts have been reported as the antidiabetic property (Zhou, Hao, et al., 2015;Zhou, Wen, et al., 2015). The reactive oxygen species generated during metabolic processes damage the pancreatic islets' cell membrane, which is one of the reasons for diabetes (Fakhruddin et al., 2017). The damage of pancreatic islets can be reduced by the intake of buckwheat proteins containing antioxidant enzymes and reactive oxygen species scavenging activity (Liu et al., 2009). Buckwheat proteins maintain the balance of glucose levels in diabetic people (Zhou, Hao, et al., 2015;Zhou, Wen, et al., 2015). Buckwheat-digested proteins produce antioxidant peptides (WPL, VPW, VFPW, and PW) with a strong scavenging capacity of reactive oxygen species (Zhou, Hao, et al., 2015;Zhou, Wen, et al., 2015). Buckwheat proteins are an effective supplement for people suffering from high cholesterol levels and obesity. Buckwheat protein extracts can bind with bile acids in the gastrointestinal tract, which increase the neutral sterols excretion through feces (El-Sayed et al., 2020). The binding affinity of buckwheat protein extract with bile acid increases the secretion of liver bile acid from cholesterol and lowers the liver cholesterol level (Zhou, Hao, et al., 2015;Zhou, Wen, et al., 2015). The maximum level of rutin content is present in leaves (0·08-0·10 mg/g), and in buckwheat seeds, it varied from 0·12-0·36 mg/g (Brunori et al., 2010;Park et al., 2008).

| Fagopyrins
Fagopyrin is a photosensitive polyphenol compound present in buckwheat seeds. The fagopyrins have a naphthodianthrone skeleton with a structure similar to hypericin compounds (Kim & Hwang, 2020). Fagopyrins are considered a toxic polyphenol due to their photosensitization and allergy reaction present in seeds and leaves of buckwheat. They are difficult to isolate due to their lower content in buckwheat (Ahmed et al., 2014). The fagopyrins in buckwheat have laxative, antibiotic, and antiviral effects and treatment for diabetes (Hagels, 2007).

| Fagopyritols
Fagopyritols are d-chiro-inositol with galactosyl derivatives present in bran fraction and higher concentration in buckwheat embryos.

| Phenolic acids
Buckwheat is the richest source of phenolic acids available in free or bound form . The phenolic acid in buckwheat is mostly benzoic acid and cinnamic acid derivatives (Mir et al., 2018).
Phenolic acids in buckwheat are associated with antioxidant activity (Gimenez-  and prevent the buckwheat seed from chemical degradation during prolonged storage (Antoniewska et al., 2018). Phenolic acids are natural antioxidants, effective against reactive oxygen species, reducing cardiovascular diseases, cancer, and age-related processes (Forni et al., 2019;Wani et al., 2022). The phenolic acids from buckwheat bran have biological activity against liver cancer cells, as tested in vitro by Li et al. (2016).

| HE ALTH -PROMOTING AT TRIBUTE S OF B U CK WH E AT
Buckwheat is a potentially promising herb used in ancient times to treat health-related diseases (Cai et al., 2016). Buckwheat is pseudocereal rich in protein and starch content, with a rich source of minerals and vitamins (Khalid et al., 2020). The unique nature, structure, and bioactive compounds of buckwheat have a vast potential to support nutraceutical potential to human health (Zhu, 2016).
Buckwheat provides a good source of nutrients and bioactive components, resulting in the enhancement of the therapeutic potential of buckwheat. The therapeutic potential of buckwheat is as follows:

| Antioxidant activity
The antioxidant activity of buckwheat is due to the presence of polyphenolic compounds, particularly rutin content. Due to the generation of reactive oxygen species in human metabolism, free radicals are responsible for cancer, cardiovascular disease, aging, cerebrovascular disease, and degenerative diseases. Additionally, it has been shown that naturally occurring polyphenolic antioxidants decreased the ROS in antigen-IgE-activated mast cells and concurrently suppressed the release of histamine by these activated mast cells. Therefore, it may be hypothesized that buckwheat's antiallergic effects are partially a result of its polyphenolic components' antioxidant properties (Ahmed et al., 2014;Papadopoulou et al., 2021;Ünsal et al., 2021). However, more research must be done to determine how buckwheat and its components affect allergic responses.
Buckwheat flavonoids can act as scavengers against free radicals due to their ease of oxidation (Zhou et al., 2018). Buckwheat flavonoids have a molecular structure that supports the concept of an active phenolic hydroxyl group capable of scavenging free radicals and preventing cancer, cardiovascular disease, aging, and cerebrovascular and degenerative diseases (Li et al., 2017;Shahbaz et al., 2022).

| Anticancer activity
Due to their lifestyle, cancer is the leading cause of death in developed and developing countries (Jemal et al., 2011). One of the century's major global problems is the formulation of functional foods to prevent chronic diseases, including cancer. It was found that eating a variety of foods, including buckwheat in diet, was reported to have a lower risk of lung cancer (Shen et al., 2008). Flavonoids and polysaccharides (Zhu, 2020); lectins (Bai et al., 2015); and phenylpropanoids Zheng et al., 2012)

| Hepatoprotective activity
Reactive oxygen and nitrogen species, as well as a variety of chemicals, damaged the liver in mice and rats. Lee et al. (2017) reported that buckwheat-based flavonoids and their extract from the tartary cultivar protect the liver against carbon tetrachloride and ethanol-induced damage. On a molecular level, the buckwheat flavonoids reduced serum aspartate transaminase activities. They increased superoxide dismutase enzyme activity, decreased liver dysfunction and hepatic inflammation, and improved the antioxidative and anti-inflammatory functions for hepatoprotection . The hepatoprotective effects of buckwheat were related to polyphenols such as rutin (Ruan et al., 2020). Buckwheat-

| Antidiabetic activity
Diabetes is a severe public health problem today, affecting over 300 million people (Zhang et al., 2011). Buckwheat helps avoid diabetes and its complications by reducing fasting blood sugar, increasing insulin levels, lowering glycosylated hemoglobin and glycosylated serum protein, and suppressing blood sugar levels .
Buckwheat-based products have significantly reduced blood sugar concentration and a lower risk of diabetes mellitus. Buckwheat should be cultivated more extensively as a grain crop due to its ability to effectively reduce the diabetes mellitus rate in people more prone to it. Both digested and undigested buckwheat flavonoids have improved glucose consumption and glycogen amount (Ruan et al., 2020). Rutin inhibits the glucosidases and amylase enzymes and thus reduces the glucose uptake in the small intestine by a decrease in carbohydrate digestion (Jadhav & Puchchakayala, 2012).
Buckwheat starch has a greater sensitivity to digestive enzymes because of the structure and compactness of its granules (Zhu, 2016).
Polyphenolic compounds, dietary fiber, and other nonstarch elements lead to the food matrix effects and lower the glycemic index of buckwheat-based products (Singh et al., 2010). Fagopyritols are a special active ingredient of buckwheat-soluble carbohydrates, used as a treatment for people with diabetes, noninsulin dependence, and polycystic ovarian syndrome.

| Anti-inflammatory and Antifatigue effects
Inflammation is a natural biological reaction to tissue damage, microbial pathogens, and chemical irritants (Pan et al., 2010), and their chronic stage is related to cancer development (Chen et al., 2018). An extract of buckwheat can lower inflammatory mediators, including interleukin-6, monocyte chemoattractant protein-1, tumor necrosis factor, and inducible nitric oxide synthase, as well as nitric oxide resulting in its inhibiting inflammation reaction (Li et al., 2017;Nam et al., 2017;Zhang et al., 2018). Different phenolic acids, such as feluric and p-coumaric, in buckwheat decreased lipopolysaccharideinduced inflammation activity (Hole et al., 2009). Fatigue is a term that encompasses a wide range of medical disorders related to pathology, general health, and physical activity. Exercising for a long time at a high intensity induces fatigue. Buckwheat protein significantly increased climbing, swimming time, and liver glycogen level, effectively reducing the blood lactate and serum urea contents (Jin & Wei, 2011). in blood vessels . Bran extract from buckwheat can also lower the lipid in the blood and liver, boosts antioxidants, and prevents peroxides in the blood (Ruan et al., 2020).

| Antihypertensive activity
Hypertension affects approximately 1 billion people in the global population and is expected to be 1.56 billion by 2025 (Devos & Menard, 2019). The biological system of renin-angiotensin maintains blood pressure. The system involves the conversion of angiotensinogen into angiotensin I and then converted into angiotensin II by angiotensin I-converting enzyme (ACE), resulting in hypertension (Jao et al., 2012). The presence of ACE inhibitors blocks the conversion reaction of ACE I to ACE II and hence results in lowering the pressure in blood vessels. The hypotensive effect of buckwheat was also supported both in in vitro and in vivo conditions as ACE inhibition (Jin et al., 2022). The buckwheat-based flavonoids, particularly rutin, prevent blood vessel hardening, boost microcirculation, detoxify the blood, improve blood circulation, remove toxins, and lower blood and urine sugar levels (Hou et al., 2017). By assisting in regulating vasoconstriction and diastole, buckwheat extract helps lower blood pressure with quercetin as the key active component in minimizing oxidative stress of blood vessels and restoring vasodilation in clinical trials (Gimeńez-Bastida et al., 2015).

| Antineurodegenerative effect
Accumulating excessive protein (amyloid-b protein) aggregation contributes to oxidative stress in the central nervous system, leading to neurodegenerative disorders (Citron, 2004 (Gulpinar et al., 2012). Recent research suggests that neuroprotective effects in the buckwheat parts and their extracts were attributed to rutin (Choi et al., 2015).

| Antigenotoxicity
Genotoxicity is a term used to describe a negative impact on the integrity of a cell's genetic material (DNA and RNA). Buckwheat extracts showed good protection against DNA damage induced by hydroxyl radicals under in vitro chemical assays. The use of buckwheat extract to repair the DNA damage was found to repair by over 50% owing to higher levels of phytochemicals and their ability to scavenge hydroxyl radicals and chelate iron (Cao et al., 2008). The DNA-protective properties of buckwheat using a human hepatoma cell line reported that inhibition of DNA damage in the body was related to antioxidants from buckwheat extract containing rutin and quercetin (Vogrincic et al., 2013). The presence of rutin and quercetin components in buckwheat extracts works synergistically to protect against DNA damage (Wang & Zhu, 2015).

| DE VELOPMENT OF G LUTEN -FREE PRODUC TS FROM BUCK WHE AT
Gluten intolerance is an autoimmune disease caused by the consumption of cereal-based gluten proteins that leads to mucosa damage in the small intestines through interaction among celiac patients, gluten diet, and response from the immunological system (Mir et al., 2018). Celiac disease involves loss of intestinal villi, incomplete digestion, and absorption of nutrients, affecting the overall function of the human body (Kreutz et al., 2020).

| Challenges and achievements in the technology of gluten-free products
Buckwheat's utilization in developing gluten-free products enhances its valorization in the gluten-free market. It mitigates various diet-related diseases and alternates gluten-free diets to feed 1.4% of the world population . The promising health ingredients and absence of gluten proteins in buckwheat focused on its use in food processing for various global gluten free buckwheat products (Małgorzata et al., 2018). There is an increased demand for gluten-free products since the incidence of celiac diseases or other gluten intolerance or allergies. People with celiac disease have to restrict their diet of gluten proteins and shift their diet to gluten-free products (Rosida et al., 2022). To reduce the prevalence of celiac disease and ensure customer-acceptable quality, cutting out gluten from the diet presents technological obstacles. Gluten is the abundant structural protein complex found in wheat and exhibits the technofunctional properties of TA B L E 3 Buckwheat-based gluten-free products and their biologically active compounds and chemical structure wheat-based products (Allai et al., 2022;Sapone et al., 2012). The elimination of gluten in food products results in defects that appear in the form of quality attributes, nutritional characteristics, and consumer acceptance. Hence, the development of glutenfree products for celiac patients is unrealistic to mimic the overall qualities of gluten products. Different approaches and technologies were adopted to overcome gluten-free products' defects and make them acceptable to celiac patients. Incorporating nutritional ingredients, hydrocolloids, and enzymes to modify and mitigate the defects and problems of gluten-free products (Alvarez-Jubete et al., 2009;Hamada et al., 2013;Ronda et al., 2015). Other than altering formulations, technologies like high pressure, extrusion, and sourdough fermentation acting directly on the product's base material also bring a promising result, mimicking the gluten product qualities.

| Use of buckwheat in the technology of gluten-free products
The buckwheat was used to prepare different gluten-free products such as bakery products (bread, biscuits, and cookies), noodle making, tea preparation, and extruded products with good organoleptic quality and consumer acceptability.

| Gluten-free bakery products
In the bakery industry, there is a great scope to create innovative and health-promising products by utilizing bioactive-rich ingredients to produce functional bakery products. The buckwheat flour with bioactive-rich components positively impacted human health . Subsequently, the exploration of bakery products (bread and biscuits) from different functional ingredients, modification, advancement in final product functionality, and composite flour-based bakery products (bread, biscuits, and snacks) increases the consumer demand for these products. Buckwheat-based ingredients in enriching bakery products are a new gluten-free food with nutraceutical attention. The incorporation of buckwheat flour ingredient in bread development enhances the nutritional quality of bread with an increase in nutrients such as protein and mineral content (Wronkowska et al., 2013). The addition of buckwheat flour in product development leads to a technological problem in bread development due to its viscoelastic properties, lower baking quality, and acceptability by consumers (Hager et al., 2012;Saturni et al., 2010). The characteristics of gluten-free bread, such as loaf volume and crumb texture, improved significantly with the incorporation of buckwheat as compared to control gluten (Alvarez-Jubetea et al., 2010). Besides nutritional quality, the incorporation of buckwheat in bread enhances the antioxidant activity, low glycemic index, and functional properties of bread (Wolter et al., 2013;Wronkowska, Zielinska, et al., 2010;Wronkowska, Soral-Śmietana, et al., 2010). The sensory and quality of buckwheat-based bread were improved by incorporating other nonbuckwheat-based ingredients such as starch, corn flour, and rice (Torbica et al., 2010;Wronkowska et al., 2013). The development of bread from buckwheat needs more effort in terms of technological and formulation aspects to enhance the overall quality and alternate targets for celiac diseases with high consumer acceptability. The buckwheat flour incorporation for the development of gluten-free products  (Suzuki et al., 2020). The increase in buckwheat flour the bread development increased their rutin and antioxidant activity (Vogrincic et al., 2013). The gluten-freebased buckwheat bread reported a high level of protein, phenolic content, and antioxidant activity compared to amaranth and quinoa flour-enriched gluten-free bread (Chlopicka et al., 2012). The buckwheat, along with other pseudocereals, is considered an alternative to gluten protein-based bread, with an increased nutritional profile and phenolic content (Schoenlechner et al., 2010). Wronkowska, Soral-Śmietana et al. (2010) and Wronkowska, Zielinska et al. (2010) formulated a buckwheat-based gluten-free bread with corn starch as the base material. They showed increased activity of antioxidants, minerals, proteins, and vitamins compared to control bread without buckwheat flour. Furthermore, bread containing whole-grain buckwheat flour expressed higher antioxidant and phenolic compounds . However, the addition of buckwheat in bread development, besides the increase in nutritional content and functionality, is restricted due to their low baking quality and consumer acceptability (Saturni et al., 2010).
Cookies and biscuits from buckwheat are bakery products with health-promising functional ingredients for gluten-intolerant people . Cookies made from buckwheat proved to have excellent product quality and acceptability by consumers by up to 20% (Torbica et al., 2010). Gluten-free cookies from buckwheat with added chickpea flour enhance nutritional value and organoleptic properties compared to control wheat-based cookies (Yamsaengsung et al., 2012). The area of gluten-free cookies needs much more studies for the optimization process to enhance the quality and sensory properties for targeting celiac patients as a diet to control the impact of celiac diseases.
The buckwheat-enriched snacks, not less than 30 percent buckwheat flour with corn flour, showed good acceptability as an attractive appetizer with high nutritional properties (Wojtowicz et al., 2013). The biscuits prepared by incorporating buckwheat changed the physicochemical and organoleptic properties and increased spread, hardness, and fracturability (Filipcev et al., 2011).
The incorporation of buckwheat from 20% to 50% enhances the sensory attributes, biofunctional properties, protein, fiber, micronutrients, polyphenolic content, and antioxidant activity (Baljeet et al., 2010;Filipcev et al., 2011). The cookies from buckwheat are also gluten-free products with broad consumer acceptability and nutraceutical properties. The cookies made from buckwheat flour were more protein and fiber rich than those from wheat flour . The protein content of the cookies formulated from buckwheat flour was in the range 4.34%-5.45%, fat (18.81%-20.04%) and the fiber content 0.39%-0.68%, with better cookie qualities (Altındag et al., 2015).

| Gluten-free noodles and pasta
The noodles are convenient, easy to prepare, acceptable by consumers, and nutritionally rich products (Sofi et al., 2019). These noodles and pasta properties would be acceptable for celiac patients to develop gluten-free products. The buckwheat noodles, commonly called soba noodles, are prepared by substituting with cereal flour or with buckwheat flour only (Hatcher et al., 2011). Buckwheat noodles were prepared with other ingredients such as green tea powder, mushroom, or seaweed to enhance sensory and texture quality (Yoon et al., 2007). The textural properties of noodles are an important quality parameter for judging the sensory score of the noodle and are dependent upon the amount of starch, protein, and fiber content present in noodles (Hatcher et al., 2011). The demand for noodles has increased from buckwheat due to its nutraceutical potential, but consumers' sensory quality is only partially acceptable due to a lack of a viscoelastic network (Han et al., 2012). Recent studies on noodles prepared from buckwheat were done to improve texture, sensory, and noodle quality to make acceptable noodles for gluten-intolerant people (Bouasla & Wójtowicz, 2019).
Buckwheat-based noodles are known as soba-type noodles, with 35% buckwheat flour having good texture and cooking qualities (Hatcher et al., 2011). Buckwheat-based noodles also contain 60%-100% of buckwheat flour for preparing soba noodles with good consumer acceptability (Sun et al., 2019). Buckwheat noodles have been added with functional ingredients such as green tea, shiitake mushroom, or seaweed powder to enhance their nutraceutical potential (Yoon et al., 2007). The increase in demand for buckwheatbased noodles is an alternative product for gluten-intolerant people with a good source of nutrients. However, the nongluten protein in noodle dough does not produce a cohesive structure that affects the textural qualities (Hatcher et al., 2011). The buckwheat flour incorporation in gluten-free noodle development increased the mineral and nutritional composition. However, buckwheat addition to noodles reduced the cooking quality and color parameters. The noodles produced from the fermented buckwheat increase the amount of amino acids and minerals, whereas reduce the allergenic proteins and phytic acid (Bilgicli, 2009).

| Other gluten-free products
The buckwheat, rich in bioactive compounds, can also be processed into tea, beer, and extruded products to enhance the valorization of buckwheat beyond bakery products. The process of tea formation from buckwheat involves many steps to minimize the bioactive compound degradations. The process involves soaking, steaming, and drying of buckwheat seeds, and then dehulled seeds are roasted and powdered into tea development . The effects of this thermal processing on the nutrient composition and polyphenolic content depend upon the cultivars and processing time. The thermal stability of chemical constituents such as proteins in buckwheat tea is related to the proportion of lipid content in the buckwheat seed (Jin et al., 2022). The alternate method of retaining the nutrients, polyphenols, and antioxidants is using microwave heating for buckwheat tea preparation . With a nutraceutical potential, Buckwheat tea is used in most Asian and European countries (Zielinska et al., 2013). The presence of rutin in buckwheat plant parts such as flowers and leaves was used for the preparation of tea, and the processing of these buckwheat-rich rutin plant parts into tea showed a slight change in rutin content during boiling (Xu et al., 2019). Moreover, buckwheat's byproduct, such as hulls rich in flavonoids, was used to prepare infusions or teas (Zielinska et al., 2013). Buckwheat has been used in the production of malt as a basis of a mash for the development of beer suitable for celiac sufferers or others sensitive to specific glycoproteins (Agu et al., 2012).
Buckwheat has been shown as an alternative source of glutenfree beer due to its dense nutritional profile (Brasil et al., 2020).
In recent years, the investigation into the use of buckwheat in the production of beer has increased to avoid gluten-based grains for Extrusion technology in food processing is used to produce food products with broad diversification, product quality, and consumer acceptability. The extruded products include pasta, modified flours, textural vegetable protein, meat analogs, snacks, and starch-based food (Leonard et al., 2020). The extruded products have good digestibility and consumer acceptability and are available in various shapes and sizes due to the extruder's high pressure, mixing, and shear operations (Alam et al., 2016). The end-user consumers' preference for healthy foods focuses on the extrusion technology industry to shift functional extruded products with added fiber, resistant starch, antioxidants, and vitamins (Chillo et al., 2010;Leonard et al., 2020). The buckwheat pseudocereal with nutritive dense, rich ingredients focused the researchers on formulating extruded products from buckwheat and was reported as prebiotic and maintains gut microbiota and reduced cholesterol level (Petrova & Petrov, 2020). The extruded products from buckwheat maintain nutrients during extrusion processing with higher antioxidant activity than roasted buckwheat. The protein digestibility, dietary fiber, and polyphenols in extruded buckwheat products are retained in higher amount, suggesting the addition of buckwheat flour as a functional supplement for the production of functional extruded products (Klepacka & Najda, 2021). The pasta produced from extrusion technology is an easy-to-prepare and available food product in the market with high acceptability by consumers. Buckwheat flour used in pasta maintains good-quality dough and texture without affecting the cooking qualities of gluten-free pasta (Schoenlechner et al., 2010). Optimization for the development of gluten-free pasta from buckwheat flour was used to produce better firmness, a good structural network, and improved cooking and sensory quality Verardo et al., 2011).

| CON CLUS ION
Buckwheat is the main pseudocereal with an excellent nutritional profile, rich in phytochemicals, vitamins, and minerals. Buckwheat is a cheap source of protein, with protein content higher than cereals would be an approach to mitigating protein-related malnutrition in developing countries. The buckwheat associated with bioactive components has health and nutraceutical significance. The bioactive components isolated from buckwheat can be used in the pharmaceutical industry to treat various health-related diseases. Nowadays most attractive trend in the food industry is the formulation of functional food with health benefits. In recent years, buckwheat-related food products with good sensory and technofunctional qualities attract the food market with health benefits and are suitable food for people with gluten intolerance. However, more research and development are needed to improve gluten-free buckwheat products' organoleptic.

ACK N OWLED G EM ENT
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CO N FLI C T O F I NTE R E S T
The authors declare no conflict of interest

DATA AVA I L A B I L I T Y S TAT E M E N T
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E TH I C A L A PPROVA L
The study involved no experimentation with human subjects.

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