Buckwheat (Fagopyrum esculentum Moench) is a dicotyledonous crop belonging to Polygonaceae family taxonomically unrelated to wheat (Heffler et al., 2014). It is popular in the mountainous regions of China and in other countries at the northern hemisphere. It can be grown at high altitudes and has a short growing span (Zhou et al., 2012).Buckwheat has been a culture of secondary importance, however it is produced in almost all countries where cereals are grown (Campbell, 1997).

The crop is not a cereal, but the seeds (achenes) are usually classified among the cereals grains because of its similar usage. The grain is generally used as human food and as animal feed. The dehulled groats can be cooked as porridge and the flour can be used in the preparation of pancakes, biscuits, noodles, cereals, among others (Campbell, 1997). Buckwheat contains proteins with high biological value and balanced amino acid composition, presenting relatively high content of fibre, Zn, Cu, Mn and Se (Ahmed et al., 2014).

Currently, China, Russian Federation, Kazakhstan and Ukraine are the leading producers of buckwheat, with production in other countries of different continents, according to Table 1, which shows the current leading producers of buckwheat, area harvested and yield in 2013. The leading continents producers are Europe and Asia (FAOSTAT, 2013). So, the aim of this study was to identify different buckwheat forms of use and benefits in agriculture and human nutrition.

Fagopyrum esculentum Moench  is common buckwheat, widely cultivated over the Northern and to some extent the Southern hemisphere. There are many cultivars or landraces in this species and their achene forms can vary, some of them being winged on the angles. It is an annual crop, branched, glabrous, and reaching up to 1 m tall (Campbell, 1997).

The leaves are petiolate, blades are ovate-triangular to triangular, 2 to 8 cm long, with acuminate tips, bases are cordate or approximately hastate; upper leaves are smaller,  sessile.  The   inflorescences   are  terminal  and auxiliary, branch in dense corymbose or paniculate cyme. Flowers are white or pink, 6 mm in diameter; pedicel is 2 to 3 mm long, articulate; perianths are 3 mm long; 8 nectaries are yellow, alternating with stamens; being heterostyly, capitate stigma (Campbell, 1997). The achenes are triquetrous, acute angle, longer than 5 mm, more than twice the persistent perianths lenght, brown or black-brown, lucid (Campbell, 1997). Details of buckwheat are presented in Figure 1.

Buckwheat can be used as a cover crop (green manure) by having high tolerance to acidity and good ability to grow in poor soils. It can reach 30 Mg ha^-1 of green mass and dry mass up to 7 Mg ha^-1 with a height up to 1.30 m at 72 days after sowing (DAS). Klein et al. (2010) found higher concentration of potassium and nitrogen and micronutrients zinc, manganese and iron, showing good ability to recycle nutrients from the soil (Table 2). In alfafa (Medicago sativa), green manure crops (like buckwheat) may provide benefits in production systems by increasing pathogen antagonists (Samac et al., 2013). Other benefits of using green manures include reduction on the dependence on mineral fertilizers, maintenance of organic matter in the soil providing nutrients for plant growth (Yadav et al., 2000) and increase of size and activity of soil microbial communities (Kautz et al., 2004; Manici et al., 2004; Tejada et al., 2008). However, the positive effects of green manure are affected by the crops chosen for this purpose (Mancinelli et al., 2013).

The crop is known to increase beneficial insects which are predators of common insects pests and can help to reduce their populations. The increase in population is due to the food source provided to the insect in the plant flowering. As examples, can be mentioned hover flies, predatory wasps, minute pirate bugs, insidious flower bugs,  tachinid  flies,  and  lady  beetles  (Valenzuela  and Smith, 2002).

Buckwheat should not be grown in fields with presence of root lesion nematodes (Pratylenchus penetrans) and root-knot nematodes, because the crop is suscetible to these nematodes (Valenzuela and Smith, 2002). In a previous trial work, buckwheat showed promising as a nematode suppressant, significantly reducing Pratylenchuszeae numbers in comparison to sugarcane (Berry and Rhodes, 2006). In addition, may have ability to increase the population of beneficial soil nematodes to crops, like Helicotylenchus (Rhodes et al., 2014). The use of buckwheat can be an option to reduce the use of chemical control, because in general, nematode control has traditionally relied to this kind of control (e.g. aldicarb in South African sugar industry) (Berry and Ramouthar, 2012).

Though producing low amounts of biomass, buckwheat grows and flowers in a short time period. For sugarcane growers, it can be ideal due to pressing circumstances, may need to include only a short fallow in their sugarcane cycle (Rhodes et al., 2014).

With regard of nutritional value for animals, crude protein is particularly concentrated in leaves, followed by flowers, whereas stems are characteristically high in fiber. Leiber et al. (2012) found 620 g of non-NDF carbohydrates/kg DM in buckwheat grains, and leaves also were rich in non-NDF carbohydrates. In comparison with ryegrass (Lolium multiflorum), the entire aerial part of the buckwheat herb contained less crude protein, ether extract and fibre, but more non-fibre carbohydrates (e.g. starch, oligosaccharides and sugars) and almost six times more total extractable phenols (Leiber et al., 2012).

Buckwheat is an important ingredient of traditional dishes of Asia (e.g. Japanese and Korean noodles and jellies), Russia (e.g. pancakes or a sort of porridge called “kasha”), and Europa (e.g. French pancakes, Dutch “poffertjes” and Northern Italian hot porridge and pasta). Hulls are also used to fill pillows. It is used to obtain dark gluten-free flour which can be used as supplement for patients with celiac (or coeliac) disease (also known as celiac sprue and gluten-sensitive enteropathy), one of the most common food intolerances in the world (Heffler et al., 2014). Therefore, buckwheat has the potential to be used as natural means of fortification and enrichment in gluten-free, allergen-free foods and to benefit these individuals (Omary et al., 2014).

The composition of buckwheat is similar to other cereals and pseudo-cereals consumed around the world. The comparison of buckwheat and wheat flour is shown in Table 4. The bran contains fagopyritols and rutin, compounds which may be useful medicinally. However, it also contains large amounts of phytic acid, a major anti-nutritional factor in common wheat (Triticum aestivum (Steadman et al., 2001).

Buckwheat grains hulls have some components with biological activity, e.g. flavonoids and flavones, phenolic acids, condensed tannins, phytosterols, fagopyrins, RS, dietary fibre, lignans, plant sterols, vitamins and minerals (Ahmed et al., 2014).

The protein content in buckwheat is significantly higher than important grasses such rice, wheat, sorghum, millet and maize, being the second highest after oat flour. Buckwheat has a well-balanced amino acid profile with a high quality of lysine, limiting amino acid in grasses such wheat (Table 5). The crop has one of the highest amino acid scores among plant sources (Ikeda et al., 2002). The buckwheat flour is a good source of many essential minerals, contains higher levels of Zn, Cu and Mn (Ikeda et al., 1999; Steadman et al., 2001) (Table 6). The content of these essential minerals is higher in comparison with other cereal flours (Ikeda   et   al., 2006).  Buckwheat grains contain higher levels of vitamin B1 (thiamine), B2 (riboflavin), E (tocopherol) and B3 (niacin and niacinamide) compared with most cereals. The vitamin content of buckwheat are presented in Table 6 (Wijngaard and Arendt, 2006).

In breads supplemented with 40% seed mixture of buckwheat and quinoa, it was shown potential to improve nutritional characteristics with 2.5% higher protein, 2% higher fat as well as two-fold higher fiber content and higher Ca and P contents. The sensory characteristics of evaluated breads were excellent even at the level of 40% supplementation level and the addition of quinoa and buckwheat seeds also influenced the rheological characteristics of dough. The inclusion of such high levels of seed in bread was possible by modification in technological procedure of seed preparation, and it could enable the development of a range of new baking products with enhanced nutritive value (Demin et al., 2013).

Buckwheat allergy

Buckwheat allergy is already seen in Asia, Europe and USA. In Europe, since the crop was introduced in popular food sectors. Failure to recognize buckwheat allergy can expose people to a risk to health. Allergy to buckwheat is typically IgE mediated and it is often associated to severe anaphylaxis (Wieslander and Norbäck, 2001). Although various buckwheat allergens have been identified, the proteins 24 kDa (Fag e 1), 26 kDa and 67-70 kDa have been suggested as important (Tohgi et al., 2011). In all patients with allergies to buckwheat, the protein Fag e 1, which is homologous to 11S or 12S globulin, has reacted with all of the serum IgE. The protein 16 KDa is resistant to digestion and has been identified as a major buckwheat allergen in Japanese and Korean patients with allergy (Park et al., 2000).

Over the past decades, many studies on buckwheat allergy have been published (Smith, 1909; Wieslander and Norbäck, 2001; Heffler et al., 2014). The first study was published in 1909, a case about patients who suffered from dyspnoea, acute rhinitis, urticaria and mucosal angioedema after the ingestion of buckwheat flour (Smith, 1909). Failure to recognize buckwheat allergy can expose people to a risk to health. It is recommended to clinician’s suspect and test allergy to buckwheat in patients with symptoms of food allergy, when have the consumption of food produced with this plant in the composition (Heffler et al., 2014).

Buckwheat is a crop with potential in agriculture, livestock and human nutrition. In agriculture, it can be used as green manure, to increase predators of common insect pests helping reduce their populations etc. In livestock, it can be used to feed cattle, sheep, pigs, goats and poultry. The plant could act as functional forage to manipulate ruminal fermentation and the presence of tannins can positively influence the health of small ruminants. In human nutrition, buckwheat is an important food, which contains balanced amino acid composition, relatively high fiber content, high contents of available Zn, Cu and Mn and dietary Se. Therefore, it is a culture that should be further explored, as it promotes many benefits and is easily adaptable to various areas, which can be grown in different regions of the world.

The authors have not declared any conflict of interests.

The authors thank Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Fundação Araucária (Paraná, Brasil), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and the following ministries: Ministério da Agricultura, Pecuária e Abastecimento (MAPA), Ministério da Ciência, Tecnologia e Inovação (MCTI), Ministério do Desenvolvimento Agrário (MDA), Ministério da Educação and Ministério da Pesca e Aquicultura for the support and granted scholarships.