CROPS AND SOILS REVIEW

Phytochemicals and biofunctional properties of buckwheat:a review

A. AHMED1, N. KHALID2*, A. AHMAD1, N. A. ABBASI3, M. S. Z. LATIF4 AND M. A. RANDHAWA5

1Department of Food Technology, Pir Mehr Ali Shah, Arid Agriculture University, Rawalpindi 46300, Pakistan2Department of Global Agricultural Sciences, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1,Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan3Department of Horticulture, Pir Mehr Ali Shah, Arid Agriculture University, Rawalpindi 46300, Pakistan4Department of Biochemistry, Khawaja Muhammad Safdar Medical College, Sialkot, Pakistan5National Institute of Food Science and Technology, University of Agriculture, Faisalabad-38040, Pakistan

(Received 27 June 2012; revised 18 February 2013; accepted 1 March 2013;first published online 27 March 2013)

SUMMARY

A growing trend for nutraceutical and gluten-free cereal-based products highlights the need for development ofnew products. Buckwheat is one of the potential candidates for such products and the present paper reviews thefunctional and nutraceutical compounds present in common buckwheat (Fagopyrum esculentum) and tartarybuckwheat (Fagopyrum tataricum). The vital functional substances in buckwheat are flavonoids, phytosterols,fagopyrins, fagopyritols, phenolic compounds, resistant starch, dietary fibre, lignans, vitamins, minerals andantioxidants, which make it a highly active biological pseudocereal. Cholesterol-lowering effects that lessen theproblems of constipation and obesity are important health benefits that can be achieved through the functionalsubstances of buckwheat.

INTRODUCTION

Buckwheat (Fagopryum esculentum Monch) is derivedfrom the Anglo-Saxon boc (beech) and whoet (wheat)because it resembles the beech nut (Edwardson 1995).It is classified as a pseudocereal because of thesimilarity to conventional cereals in its use andchemical composition (Campbell 1997). Historically,it was a very popular food during the 17th–19thcenturies, although it was later neglected duringthe 20th century in Western countries because ofcompetition from wheat (Cawoy et al. 2008). Yet itis well recognized as a potential functional foodsource in some countries, such as China, Japan andTaiwan.Buckwheat has a powerful ecological adaptability

that allows the plant to grow in almost all kindsof extreme environments (Li & Zhang 2001). Majorcultivation areas are located in Asia and particularly insoutheast Asia, where crops are grown on marginaland fairly unproductive land. In these areas, it is often

cultivated as a subsistence crop with barley, oftenat higher altitudes. Tartary and common buckwheatexhibit different growth behaviours: tartary buckwheatis a frost-tolerant crop and is generally grown at higheraltitudes, whereas common buckwheat is grown atlower altitudes. In many areas, the trend is for thereplacement of common buckwheat, which has alower yielding ability and lacks frost tolerance, withfinger millet or other crops (Campbell 1997).

Buckwheat is a dicotyledon and belongs to thefamily Polygonaceae. Its seeds are brown in colour,irregularly shaped and have four triangular surfaces.Buckwheat seeds are smaller than soybean seeds byabout a factor of ten (thousand grain weight of 20 and200 g, respectively). The seeds germinate and emergerapidly when planted in warm soil, typically in 3–4days. Plants grow rapidly, producing small heart-shaped leaves with slender, hollow stems. Floweringbegins c. 3 weeks after planting and is prolific for afew weeks, before gradually tapering off as the plantmatures. At the peak of flowering, a buckwheat fieldis a striking sea of white petals. After a flower ispollinated, a full-sized seed will form within 10 days,

* To whom all correspondence should be addressed. Email:nauman_khalid120@yahoo.com

Journal of Agricultural Science (2014), 152, 349–369. © Cambridge University Press 2013doi:10.1017/S0021859613000166

although that seed will need another 1–2 weeks toreach maturity. Seeds appear and mature earlier on thelower stem, with seed development continuing up thestem as the plant matures. Plant height and speed ofmaturity depend on planting date. If planted early inthe summer and given good fertility, plants will usuallybe at least 1 m tall, and may take 11–12 weeks tomature. If planted in the latter part of July, buckwheatwill mature in c. 9–10 weeks and will be shorter,c. 0·76 m on good soils and 0·61m tall, or less, on poorsoils. A hot, dry period during plant development willlimit the vigour and size of the crop. Buckwheat growsbest on soils that are neither too compacted, nor toocoarse or sandy. It can tolerate wet soils to a slightdegree, but will generally fair better on soils wheredrainage is adequate. Buckwheat does not requirehighly fertile soils, but it benefits from having modestlevels of nitrogen (N) fertility (Ye & Guo 1992; Ohnishi& Matsuoka 1996; Campbell 1997). The cultivation ofbuckwheat has numerous advantages, such as beingeasy to cultivate, having a short growing period(70–90 days) and a longer storage time withoutalteration due to its phenolic and antioxidant proper-ties. The major disadvantages of buckwheat cultiva-tion include lower grain yield, as its seeds ripen moreasynchronously, and as a result there are many moretechnical harvesting problems compared with cereals.Similarly, buckwheat sets seed quickly and may, ifallowed to go to seed, become a weed problem insubsequent crops.

Many species of buckwheat are grown aroundthe world; however, only nine have agricultural andnutritional value (Krkoskova & Mrazova 2005). Outof these, only two species are used as food aroundthe world; common buckwheat (F. esculentum) andtartary buckwheat (F. tataricum). Detailed classifi-cation is presented in Fig. 1. China, the RussianFederation, Ukraine and Kazakhstan are the leadingproducers of common buckwheat (Li & Zhang 2001;Bonafaccia et al. 2003b) with production also inSlovenia, Poland, Hungary and Brazil (Kreft et al.1999).The current leading producers of buckwheat,

together with yield and area harvested are presented inTable 1 (FAOSTAT 2013).

There is interest in buckwheat for the production ofnutraceutical preparations (He et al. 1995) with thepotential for functional food development that mayprovide health benefits beyond basic nutrition (Li &Zhang 2001; Bonafaccia et al. 2003a, b). The presentreview collates and synthesizes the available infor-mation on important aspects related to the functionalpotential of buckwheat that is being produced inmost parts of Asia. The emphasis is on exploiting theimportance of buckwheat as a potential functionalfood and for utilization in the prevention and treatmentof human diseases.

Vernacular names in major languages

Buckwheat has been named by many people duringthe history of its development. According to someresearchers, the ancient Yi people of the Yunnanprovince called buckwheat er, common buckwheat erchi, and tartary buckwheat er ka (Li & Zhang 2001).Buckwheat names are important in order to trace itsmigration through Europe and Asia. Today, commonbuckwheat is called ogal in India, mite phapar inNepal, soba (traditional noodles) in Japan, jawas inPakistan, tian qiao mai in Mandarin, jare in Bhutan,grecicha kul’furnaja in Russia and tatarka gryka orpoganka in Poland. In French, it is called sarrasin,ble noir, renouee or bouquette, in Italy fagopiro,grano saraceno, Sarasin or faggina and in Germany

Fig. 1. Classification of buckwheat.

Table 1. World’s largest producers of buckwheat(production year 2011) (FAOSTAT 2013)

CountriesProduction(tonnes)

Yield(t/ha) Area (ha)

RussianFederation

800380 0·949 843200

China 720000* 0·962 7 48000*Poland 92985 1·227 75768France 91000 2·935 31000USA 79554† 1·029 77244†Brazil 57000* 1·239 46000*Belarus 44456 1·091 40734Kazakhstan 37400 1·274 66780Japan 32000 0·567 56400Lithuania 26000 0·955 27200World total 2294178‡ 0·885 2327409‡

* FAO estimates.† Data based on imputation methodology.‡ Aggregate data (official, semi-official and estimated).

350 A. Ahmed et al.

Buchweizen or Heidekorn (Hammer 1986; Campbell1997).Tartary buckwheat is called phapar in India, tite

phapar in Nepal, bjo in Bhutan and brow in Pakistan.It is of interest to note that in both China and Nepal,common buckwheat is referred to as sweet buckwheat,while tartary buckwheat is called bitter buckwheat(Ohnishi 1993).

CHEMISTRY OF BUCKWHEAT

Chemical composition of buckwheat

Buckwheat contains a variety of nutrients in its grains.The main compounds are proteins, rutin, polysacchar-ides, dietary fibre, lipids, polyphenols and micronutrients (minerals and vitamins) (Kim et al. 2004;Qin et al. 2010). The total content of these componentsdepends on different factors, such as the species andthe environment (Barta et al. 2004; Qin et al. 2010).Whole buckwheat groats (the hulled seeds) contain550mg/g starch, 120 mg/g protein, 70 mg/g totaldietary fibre (TDF), 40 mg/g lipid, 20 mg/g solublecarbohydrates and 180mg/g other components suchas organic acids, phenolic compounds, tannins, phos-phorylated sugars, nucleotides and nucleic acids

(Im et al. 2003; Bonafaccia et al. 2003b). Detailedcomposition of buckwheat flour in comparison withwheat flour is presented in Table 2.

Buckwheat flour is mostly derived from the endo-sperm consisting of 700–750mg/g starch, 60–100mg/gproteins, 20–240mg/g TDF, 10–30mg/g lipids and130mg/g other components, while bran with littlecentral endosperm consists of 360 mg/g proteins,180 mg/g starch, 150mg/g TDF, 110mg/g lipids,60 mg/g soluble carbohydrates and 70mg/g othercomponents (Bonafaccia et al. 2003a; Skrabanjaet al. 2004; Alvarez-Jubete et al. 2009; Lin et al.2009;Qin et al. 2010). Buckwheat bran is a rich sourceof dietary fibre, and in particular bran with hullfragments contains 400mg/g TDF, of which 250mg/gis soluble dietary fibre (SDF), while bran without hullfragments contains 160mg/g TDF, of which 750mg/gis soluble. Bran fractions also contain the highestconcentration of protein among all milling fractions(Steadman et al. 2001b; Krkoskova & Mrazova 2005).The proximate composition of buckwheat is well inline with other cereals and pseudocereals consumedall over the world (Table 3). It is important to notethat buckwheat fibre is free of phytic acid, a majoranti-nutritional factor in common wheat (Steadmanet al. 2001a). Soluble dietary fibre concentration

Table 2. Proximate composition (mg/g DW) of buckwheat flour, wheat flour and quinoa flour (Ogungbenle2003; Lin et al. 2009; Qin et al. 2010)

Proximate

Huskedbuckwheatflour

Unhuskedbuckwheatflour

Tartarybuckwheatflour

Commonbuck wheatflour

Wheatflour

Quinoaflour

Carbohydrates 616 770 702 737 835 583Crude ash 17 16 22 22 12 12Crude fat 22 22 28 28 26 63Crude fibre 238 103 26 23 20 95Crude protein 107 90 105 103 106 135

Table 3. Comparison of buckwheat flour composition (m/g DW) with other commonly used cereals andpseudo-cereals (Bonafaccia & Fabjan 2003; Czerwinski et al. 2004; Vega-Gálvez et al. 2010)

Crop Protein Ash Lipid Soluble fibre Insoluble fibre Total fibre

Wheat 115 17 10 10 15 24Common buckwheat 110 26 34 12 53 65Tartary buckwheat 103 18 25 5 58 63Oats 126 18 71 33 49 82Rye 117 15 18 36 100 136Quinoa 165 38 61 43 96 139Amaranth 139 21 73 63 82 145

Nutritional profile of buckwheat 351

(77–92mg/g) in buckwheat bran is higher whencompared with wheat bran (43 mg/g), or even oatbran (72mg/g). In uncooked buckwheat groats, starchresistant to digestion comprises 303–380 g/100 g oftotal starch, but after cooking RS is 70–100mg/g(Skrabanja & Kreft 1998; Steadman et al. 2001b). It wasobserved that soluble carbohydrates are concentratedin the embryo, with a low concentration in theendosperm but higher in the bran. Since starch isconcentrated in the central endosperm, light-colouredflour, grits and whole groats are mostly composed ofstarch (Steadman et al. 2001b).

Fatty acid composition in buckwheat

The lipids in whole buckwheat, buckwheat flour,steamed and stored buckwheat have been reviewed byseveral researchers (Pomeranz & Lorenz 1983). Seedsof common buckwheat contain 15–37mg/g total lipids(Campbell 1997). The highest concentration is inthe embryo at 70–140mg/g and the lowest is in thehull at 4–9mg/g. Groats or dehulled seeds of Mancan,Tokyo and Manor buckwheat contain 21–26mg/gtotal lipids, of which 810–850mg/g are neutral lipids,80–110mg/g are phospholipids and 30–550mg/g areglycolipids (Campbell 1997). The major fatty acidsof common buckwheat are palmitic, oleic, linoleic,stearic, linolenic, arachidic, behenic and lignoceric(Table 4). The long-chain acids arachidic, behenic andlignoceric, which represent c. 80 mg/g of the totalacids in buckwheat, are only minor components orare not present in cereals. Buckwheat contains aboutthe same amount of total lipids as wheat rye (Becker2008). In buckwheat, the neutral lipids constitute810–850mg/g of the total lipids, compared with

c. 350mg/g in wheat and rye. The major classes offatty acids of all cultivars and lipid classes werepalmitic (16 :0), oleic (18 :1) and linoleic (18 :2).

In buckwheat, lipids are also concentrated in theembryo, making the bran the most lipid-rich fractionduring milling. Triacylglycerides are the main com-ponent of the lipid fraction; linoleic, oleic and palmiticaccount for 880 mg/g of total fatty acids (Horbowicz &Obendorf 1992). Buckwheat is nutritionally superior infatty acid composition to cereal grains with 800mg/gunsaturated fatty acids, out of which 40mg/g of fattyacids are polyunsaturated (Steadman et al. 2001a).In another study by Kim et al. (2001) total saturatedfatty acid was 200mg/g, while unsaturated fatty acidwas 790mg/g, with a major fraction of 460mg/glinoleic acid.

Proteins and amino acids in buckwheat

In buckwheat seeds, the protein content ranges from85·1 to 188·7mg/g depending on the variety (Aubrecht& Biacs 2001; Li & Zhang 2001; Krkoskova &Mrazova2005). The buckwheat proteins include albumin,globulin, prolamin and glutelin (Ikeda et al. 1999;Ikeda & Asami 2000), but the relative content ofthese individual protein fractions show considerablevariation and are dependent on variety. Buckwheatprotein consists of 180 mg/g albumin, 430mg/gglobulin, 8 mg/g prolamin, 230mg/g glutelin and50mg/g other nitrogen residues (Javornik & Kreft1984; Ikeda et al. 1991; Ikeda & Asami 2000). It isgenerally recognized that albumin and globulin arethe major storage proteins in buckwheat seeds, andprolamin and glutelin content are very low (Guo& Yao2006). The major storage proteins from commonbuckwheat seeds, including 8S and 13S globulins,and 2S albumins, have been characterized (Radovicet al. 1996, 1999; Fujino et al. 2001;Milisavljevic et al.2004). Salt-soluble 13S globulin has a hexamericstructure with disulphide-bonded subunits composedof acidic and basic polypeptides with molecularmasses between 43 and 68, 57 and 58 and 26 and36 kDa (Radovic et al. 1996); 2S albumins are com-posed of polypeptides of molecular mass from 8to 16 kDa (Radovic et al. 1999). Buckwheat proteinisolate (BPI) is composed mainly of globulin andalbumin fractions. Tang & Wang (2010) studied theconformational properties of globulin and albuminfractions from common buckwheat seeds and com-pared them with those of BPI; they concluded thatalbumin from buckwheat seed had a higher content

Table 4. Fatty acid profile (mg/g) of tartary andcommon buckwheat (Mazza 1988; Tsuzuki et al.1991; Becker 2008; Gulpinar et al. 2011)

Fattyacids

Tartarybuckwheat

Commonbuckwheat

C16:0 171 186C18:0 21 19C18:1 367 359C18:2 369 344C18:3 16 22C20:0 11 14C20:1 21 30C22:0 11 14C22:1 5 2C24:0 6 9

352 A. Ahmed et al.

of uncharged polar amino acids, but lower acidicamino acids than globulin. Due to the well-balancedamino acid composition, buckwheat proteins have ahigh biological value, and the main disadvantageof buckwheat is its low protein digestibility (79·9%)(Ikeda & Kishida 1993). Similarly, proteins of thealbumin family with disulphide bonds appear to beresponsible for the allergic response that is induced bybuckwheat products (Satoh et al. 2008).The protein content in buckwheat is significantly

higher than in rice, wheat, sorghum, millet and maize.Similarly, its protein content is the second highest afteroat flour. Buckwheat has a well-balanced amino acidprofile with a good quality of lysine which is generallyrecognized as the first limiting amino acid in wheatand barley and arginine (Table 5). The quality ofprotein can be judged by the fact that buckwheat flourhas an amino acid score of 100, which is one of thehighest amino acid scores among plant sources (Ikeda2002). No or low gluten types have been identified inbuckwheat, thus contributing as an ingredient in thegluten-free diet for people suffering from coeliacdisease.The major problem with buckwheat protein is low

digestibility in both humans and animals (Farrell 1978;Javornik et al. 1981). The low digestibility is because ofanti-nutritional factors present in common buckwheat,including protease inhibitors (such as trypsin inhibi-tors) and tannins (Ikeda et al. 1986, 1991). Trypsininhibitors in buckwheat seeds are resistant to thermal

processing, especially at elevated temperatures anddue to acidic conditions (Ikeda et al. 1986, 1991).Germination of buckwheat seeds considerably re-duces the activity of protease inhibitors; thereforeseedlings and buckwheat plants are a source of foodwith improved utilization of proteins (Kreft 1983;Ookubo 1992).

‘Resistant proteins’ such as those in buckwheat arealso effective in lowering blood cholesterol (Kayashitaet al. 1996; Iwami 1998; Tomotake et al. 2000). Huff &Carroll (1980) reported that ratios of lysine/arginine(Lys/Arg) and methionine/glycine (Met/Gly) are thekey factors in determining the cholesterol loweringproperties of proteins. The ratios of Lys/Arg andMet/Gly in buckwheat are significantly lower than inthe other plant proteins. Similarly, nutritional studieshave shown that buckwheat proteins have the highestcholesterol-lowering properties among the plantproteins known to science so far (Huff & Carroll1980). The amino acids in buckwheat regulate thehepatic low-density lipoprotein (LDL) receptors, andthus lower the serum cholesterol, resulting indirectlyin the prevention of arteriosclerosis. Moreover,Kayashita et al. (1995) identified that the BPI wasmore efficient in cholesterol lowering than soybeanprotein isolates and other plant isolates. They alsoshowed that weight gain of BPI-fed rats was notnegatively affected when compared with casein-fedrats, suggesting that buckwheat proteins were suffi-ciently digested and absorbed to provide adequate

Table 5. Essential amino acid composition (mg/g protein) of buckwheat, cereals, pseudo-cereals and egg(Radovic et al. 1999; Mendonça et al. 2009; Tang & Wang 2010; Vega-Gálvez et al. 2010)

Amino acid Buckwheat Barley Wheat Maize Quinoa Amaranth Egg*

Lysine 51 37 25 28 61 62 60Methionine 19 18 18 24 48 20 38Cystine 22 23 18 22 48 20 24Threonine 35 36 28 39 38 33 43Valine 47 53 45 50 45 44 72Isoleucine 35 37 34 38 44 37 59Leucine 61 71 68 105 66 61 84Phenylalanine 42 49 44 45 73 46 61Histidine 22 22 23 24 32 26 22Tryptophan 16 11 10 6 12 33 15TD (%) 79·9 84·3 92·4 93·2 – – 99·0BV (%) 93·1 76·3 62·5 64·3 – – 100·0NPU (%) 74·4 64·3 57·8 59·9 – – 94·0UP (%) 9·1 7·3 7·3 6·0 – – 12·2

TD, true protein digestibility; BV, biological value (based on amino acid composition); NPU, net protein utilization; UP,utilizable protein (protein×NPU/100).* For whole egg.

Nutritional profile of buckwheat 353

amount of amino acids for growth. The BPI was shownto be more effective in lowering ‘bad cholesterol’,LDL and very low-density lipoproteins (VLDL), whencompared with other plant and animal proteins (Saekiet al. 1990).

Buckwheat protein isolates can also be used as afunctional food ingredient to treat hypertension,obesity and constipation. These proteins lower theactivity of angiotensin converting enzyme (ACE) anddirectly control hypertension (Kato et al. 2001;Tomotake et al. 2001, 2002). Rat feeding experimentsshowed that high-fat diets and overeating did not affectthe body weight of the animals when buckwheatprotein hydrolysate was included in the diet. Thisprotective effect was much weaker for soybean proteinhydrolysates (Tomotake et al. 2001).

Mitsunaga et al. (1986) reported the presence ofthiamine-binding protein (TBP) in buckwheat seeds.After ingestion, this complex is digested by proteasesand thiamine is released and absorbed. The proteinmoiety in the TBP complex improves the stability ofthiamine during storage and processing and enhancesits bioavailability (Mitsunaga et al. 1986).

Buckwheat protein, together with dietary fibre, canameliorate constipation (Kayashita et al. 1995). Severalepidemiological studies have shown that buckwheatproteins, like dietary fibre, can suppress the develop-ment of colon cancer (Cassidy et al. 1994; Lipkin et al.1999). Hard to digest proteins interact with RS and arethe main source of short chain fatty acids (SCFA),known to positively affect the tissues and physiology ofthe colon (Scheppach et al. 1992; Morishita et al.1998). Liu et al. (2001) utilized buckwheat proteinextract containing c. 730mg/g buckwheat protein toassess its effect on induced colon tumours in rats.It was shown that dietary buckwheat protein reduced

the incidence of colonic adenocarcinomas by 47%.Buckwheat protein also reduced carcinoma cellproliferation and expression in colonic epithelium.The results clearly suggest that buckwheat proteinshave a protective effect against colon carcinogenesis.

Minerals in buckwheat

The nutritional functions of essential minerals inbuckwheat and foods prepared from it have beenstudied by many scientists (Ikeda & Yamashita 1994;Ikeda et al. 2001, 2002, 2003, 2004, 2005). All ofthese studies concluded that buckwheat seeds are agood source of many essential minerals (Table 6). Incomparison with other cereals such as rice, wheat flouror maize, buckwheat contains higher levels of zinc(Zn), copper (Cu) and manganese (Mn) (Ikeda et al.1999; Steadman et al. 2001b) (Table 7).

The bioavailability of Zn, Cu and potassium (K) frombuckwheat is especially high. It has been determinedthat 100 g of buckwheat flour can provide c. 13–89%of the recommended dietary allowance (RDA) for Zn,Cu, magnesium (Mg) and Mn. A major quantity ofthese minerals exists in bran portions, followed byendosperm. Buckwheat flour contains relatively highlevels of Zn, Cu, Mn and Mg, with a slightly lowercontent of calcium (Ca) in comparison with otherflours, especially wheat (Bonafaccia et al. 2003b).

Recently, Ikeda et al. (2006) compared the compo-sition of eight essential minerals, i.e. Fe, Zn, Cu, Mn,Ca, Mg, K and phosphorus (P), of buckwheat flour tothose of cereal flours by using an in vitro enzymaticdigestion technique. The results showed a highercontent of essential minerals in buckwheat flour incomparison with other cereal flours. Further enzymaticdigestion proved that a larger portion of the Zn, Cu andK were released in soluble form from the buckwheatflour, relative to that in cereal flours.

Vitamins in buckwheat

Vitamins are a group of organic compounds that areessential in very small amounts for the normalfunctioning of the human body. They vary widely intheir chemical and physiological functions and arebroadly distributed in natural food sources (Wijngaard& Arendt 2006). Vitamin content of common buck-wheat groats are presented in Table 8. Buckwheatgrains contain higher levels of vitamin B1 (thiamine),B2 (riboflavin), E (tocopherol) and B3 (niacin andniacinamide) compared with most cereals. Generally,

Table 6. Mineral concentrations (mg/g) inbuckwheat and milling fractions (Steadman et al.2001b; Ikeda et al. 2006)

Minerals Whole groats Flour Bran

Potassium 5·6500 5·0030 14·1630Phosphorus 4·9000 4·1670 13·5330Magnesium 2·6760 2·5300 5·9910Calcium 0·1970 0·3000 0·3330Iron 0·0303 0·0340 0·0604Zinc 0·0292 0·0283 0·0726Manganese 0·0164 0·0180 0·0462Boron 0·0067 0·0066 0·0241Copper 0·0071 0·0070 0·0104

354 A. Ahmed et al.

tartary buckwheat has more vitamin B1, B2 and B3, butless vitamin E than common buckwheat (Bonafacciaet al. 2003b; Ikeda et al. 2006).Thiamine (vitamin B1) is known to adhere strongly

to TBPs in buckwheat seeds (Mitsunaga et al. 1986;Rapala-Kozik et al. 1999). In general, tartary buckwheathas higher levels of vitamin B than common buck-wheat (Pomeranz & Lorenz 1983; Bonafaccia &Fabjan 2003). Thiamine-binding proteins can improvethe stability of thiamine during storage and improve thebioavailability of thiamine (Li & Zhang 2001). Levels ofvitamin C and the sum of vitamin B1 and B6 can beincreased by germinating buckwheat. The level ofvitamin C can be increased by up to 0·25mg/g inbuckwheat sprouts (Lintschinger et al. 1997; Kim et al.2004). Wheat, barley, oat, rye and buckwheat groatsexhibit the same maximum level of tocopherols, withγ-tocopherol being the main one (Zielinski et al. 2001;Kim et al. 2002), while Przybylski et al. (1998) reportedα-tocopherol as the major tocopherol in buckwheat.Differences in tocopherol forms have been attributedto different cultivars of common buckwheat (Przybylskiet al. 1998; Zielinski et al. 2001; Kim et al. 2002).Tartary buckwheat contains higher levels of tocopherolsthan common buckwheat (Kim et al. 2002).

Iminosugars in buckwheat

Polyhydroxylated piperidines (azasugars or imino-sugars) have gained increasing synthetic interestdue to their high biological activity as glycosidaseinhibitors (Zechel & Withers 2000). Koyama &Sakamura (1974) isolated 1 and 2-dideoxy-azasugarssuch as D-fagomine and its stereoisomers from theseeds of Japanese buckwheat Fagopyrum esculentumaustrale Moench. If used as a dietary supplement orfunctional food component, D-fagomine may reducethe risks of developing insulin resistance, becomingoverweight and suffering from an excess of potentiallypathogenic bacteria (Amézqueta et al. 2012). Theseazasugars are potential therapeutic agents for thetreatment of a wide range of diseases, including dia-betes, cancer, AIDS, viral infections and many more(Butters et al. 2000). Fagomine itself has stronginhibitory activity towards mammalian α-glucosidase,β-galactosidase (Kato et al. 1997) and has also beenfound to have a potent anti-hyperglycaemic effect instreptozocin-induced diabetic mice and a potentiationof glucose-induced insulin secretion (Nojima et al.1998).

Amézqueta et al. (2012) determined D-fagomine andits diastereomer, 3,4-di-epi-fagomine in buckwheatgroats, bran and leaves, and also in buckwheat flour.The highest content of D-fagomine and 3·4-di-epi-fagomine was present in groats (44 and 43mg/kg,respectively). Fagopyrum tataricum seeds containedless D-fagomine than F. esculentum (Amézqueta et al.2012).

NEUTRACEUTICAL AND FUNCTIONALCOMPONENTS OF BUCKWHEAT

Buckwheat grains and hulls consist of some com-ponents that have biological activity, i.e. flavonoids

Table 7. Comparison of mineral composition (mg/g) of buckwheat flour with maize meal, semolina, wheatflour, soybean flour, quinoa flour and raw amaranth (Ranhotra et al. 1993; Edwardson 1995)

Products Ca Fe Mg K Na Zn Cu Mn

Buckwheat flour 410 40 2510 3370 0 31 0·9 0·9Maize meal 60 34 1270 2410 350 18 1·9 4·9Semolina 170 12 470 1360 10 11 1·9 6·1Wheat flour 150 12 220 1080 20 7 1·4 6·8Soybean flour 2060 64 4290 4940 130 39 29·2 22·7Quinoa flour 700–860 26–63 1610–2320 7140–8550 27–930 32–38 7–76 35·0Raw amaranth 1590 76 2480 5080 40 28 5·3 33·3

Ca, calcium; Fe, iron; Mg, magnesium; K, potassium; Na, sodium; Zn, zinc; Cu, copper; Mn, manganese.

Table 8. Vitamin composition of commonbuckwheat (Wijngaard & Arendt 2006)

Vitamins Level (mg/g)

A (β-carotene) 2·1B1 (thiamine) 4·6B2 (riboflavin) 1·4B3 (niacin) 18·0B5 (pantothenic acid) 10·5B6 (pyridoxine) 7·3C (ascorbic acid) 50·0E (tocopherols) 54·6

Nutritional profile of buckwheat 355

and flavones, phenolic acids, condensed tannins,phytosterols, fagopyrins, RS, dietary fibre, lignans,plant sterols, vitamins and minerals.

Dietary fibre

Dietary fibre is a nutrient used for the proper digestionof foods, proper functioning of the digestive tract atlarge and for adding bulk to food. It also gives a feelingof satiety and helps in losing weight. A low intakeof fibre can lead to constipation, haemorrhoids andelevated levels of cholesterol and sugar in the blood.Conversely, an excess of fibre can sometimes leadto bowel obstruction, diarrhoea or even dehydration(Anderson et al. 2009).

The amount of TDF in buckwheat varies withdifferences in genetic and environmental factors. Themajor components of TDF are cellulose, non-starchpolysaccharides and lignin. These are concentrated inthe cell walls of starchy endosperm, aleurone, seedcoats and hulls (Joshi & Rana 1995; Zheng et al. 1998;Steadman et al. 2001b; Izydorczyk et al. 2002).A considerable portion of buckwheat dietary fibreis soluble. Soluble non-starch polysaccharides ofbuckwheat contain xylose, mannose, galactose andglucuronic acid (Asano et al. 1970). Bran fractionsobtained by the milling of buckwheat are especiallyrich in dietary fibre (130–160mg/g), but buckwheatflours contain considerably lower amounts of fibre(17–85mg/g) (Steadman et al. 2001a).

For nutritional purposes, TDF is classified into SDFand insoluble dietary fibre (IDF). Insoluble dietary fibre(IDF) decreases transit time in the stomach, smallintestine and colon and increases faecal mass. It iscommonly used as a bulking agent to prevent or treatconstipation. Soluble dietary fibre, due to its highviscosity, slows gastric emptying, reduces the adsorp-tion of certain nutrients and increases transit time in thesmall intestine by slowing down glucose absorption.Soluble dietary fibre and to a lesser extent IDF arefermented by microflora in the digestive systemto produce SCFA, implicated in serum cholesteroland colon cancer reduction (Elleuch et al. 2011).A considerable portion of buckwheat dietary fibreis soluble (Joshi & Rana 1995; Zheng et al. 1998;Steadman et al. 2001b; Izydorczyk et al. 2002).However, relatively little is known about the compo-sition and properties of SDF in buckwheat. Asano et al.(1970) isolated water soluble non-starch polysacchar-ides from buckwheat and reported that they consistedof xylose, mannose, galactose and glucuronic acid.

It was postulated that the main chain of thesepolysaccharides consisted of glucuronic acid, man-nose and galactose. More recently, arabinose andglucose residues have also been identified in water-extractable buckwheat polysaccharides (Izydorczyket al. 2002). One of the most important characteristicsof buckwheat water soluble non-starch polysac-charides is their very high molecular weight; as aconsequence they can form very viscous solutionswhen dissolved in water.

Buckwheat bran containing hulls has c. 400mg/gfibre, including 250mg/g soluble fibre, while ‘pure’bran without hulls contains c. 160 mg/g fibre, in-cluding 750mg/g soluble fibre (Górecka et al. 2010;Dziedzic et al. 2012). Depending on the type oftechnological processes applied in the production ofbuckwheat groats, the level and fraction compositionof dietary fibre affects the functional properties(Górecka et al. 2009, 2010; Dziedzic et al. 2012). Inbuckwheat grains, dietary fibre constitutes 50–110mg/g,and the soluble fibre content is 30–70mg/g, whilethe amount of the insoluble fibre is 20–40mg/g(Krkoskova & Mrazova 2005). Soluble fibre reducesblood cholesterol levels, the risk of incidence ofischaemic heart disease and postprandial glycaemia(Brown et al. 1999). Functional properties of dietaryfibre, such as water holding capacity and cationbinding, play a significant role in the prevention ofdiet-dependent diseases, e.g. obesity, atherosclerosisand colon cancer (Esposito et al. 2005; Górecka et al.2005; Mehta 2005).

Dziedzic et al. (2012) examined the influence of thetechnological process of buckwheat groat productionon dietary fibre content and its fraction with theabsorption of selected bile acids by buckwheat groatsand products such as buckwheat grains, buckwheatgrains after roasting, buckwheat hull, buckwheat bran,whole buckwheat groats, broken buckwheat groatsand buckwheat waste. They recorded the highestcontent of TDF in hulls, while the lowest was in wholeand broken buckwheat groats. Buckwheat hullscontain higher lignin and cellulose fractions, whilethe hemicellulose fraction predominated in brokengroats. Similarly, roasting of buckwheat grains resultedin an increase in the content of dietary fibre and the allfractions dietary fibre (Dziedzic et al. 2012).

Resistant starch

The term ‘resistant starch’ (RS) was first coined byEnglyst et al. (1982) to describe a small fraction of

356 A. Ahmed et al.

starch that was resistant to hydrolysis by exhaustiveamylase and pullulanase treatment in vitro. Resistantstarch is the starch that is not hydrolysed after 120minof incubation at 37 °C (Englyst et al. 1992). However,starch reaching the large intestine may be more or lessfermented by the gut microflora.Starch is the major component of buckwheat

(Skrabanja & Kreft 1998). Buckwheat flour contains700–910mg/g of starch depending on the flour types,and the starch consists of c. 250mg/g amylose and750mg/g amylopectin (Qin et al. 2010; Takahama &Hirota 2010). Scanning electron microscope (SEM)studies showed granules of buckwheat starch (Fig. 2) tobe polygonal and of irregular shape (Christa et al.2009). Buckwheat starch particles range from 2 to9 μm in diameter (Lorenz & Dilsaver 1982; Soral-Smietana et al. 1984; Acquistucci & Fornal 1997). Thebuckwheat starch has small granules as particles ofgrain cotyledons and they are smaller than those ofmaize starch (12·2 μm), tapioca starch (18 μm) andpotato starch (30·5 μm) (Mishra & Rai 2006).It has been found that the consumption of boiled

buckwheat groats or bread baked using 0·50

buckwheat flour induced significantly lowered post-prandial blood glucose and insulin responses com-pared with white wheat bread (Skrabanja et al. 2001).Buckwheat products may provide an important sourceof retrograded starch and RS (Christa & Soral-Smietana2008). The in vitro rate of starch hydrolysis and RSformation in boiled and baked buckwheat indicatedthe highest concentration of RS in boiled buckwheatgroats (60 mg/g total starch basis), while the RS levelin bread products based on different proportions ofbuckwheat flour and groats varies from 90 to 40mg/g.The rate of in vitro amylolysis was significantly lower(P<0·05) in all buckwheat products in comparisonwith white flour bread (Skrabanja et al. 2001).

The inclusion of 30 g buckwheat in the daily diet hasbeen sufficient to produce clinically relevant reduc-tions in serum total and LDL-cholesterol, triglyceridesand increases in HDL-cholesterol, thus reducingthe risk of cardiovascular diseases (CVD) (He et al.1995). Their results support the view that buckwheatproteins and RS could have beneficial effects onvarious diseases, including hyperlipidemia. Similarly,He et al. (1995) demonstrated that the inclusion

Fig. 2. Buckwheat starch micrographs from different origins adopted from Qian & Kuhn (1999).

Nutritional profile of buckwheat 357

of buckwheat in the diet of non-independent insulindiabetes mellitus (NIDDM) led to a significantreduction in their fasting and post-prandial bloodglucose levels since it is rich in D-chiro-inositol, whichcontributes to the improvement of insulin resistance byenhancing the action of insulin.

Antioxidant activity

Antioxidant activity is the fundamental prophylacticproperty which is important for humans. A variety ofbiological functions such as antimutagenic, anti-carcinogenic and antiaging originated from an anti-oxidant property (Holasova et al. 2002). Condensedcatechins and phenolic acids, including hydrobenzoicacids, synigric, p-hydroxy-benzoic, vanillic andp-coumaric acids that have antioxidant properties arepresent in the bran-aleurone layer of buckwheat grains(Przybylski et al. 1998). The primary antioxidants inbuckwheat are rutin, quercetin and hyperin (Morishitaet al. 2007). Buckwheat bran and hulls have 2–7 timeshigher antioxidant activity than barley, triticale andoats (Holasova et al. 2002; Zdunczyk et al. 2006).Zielinski & Kozlowska (2000) established the follow-ing hierarchy of antioxidant activity for 80% metha-nolic extracts which originated from different wholegrains: buckwheat>barley>oat>wheat>rye.

The antioxidant activities of buckwheat arecomparable to butylated hydroxyanisole (BHA),butylated hydroxytoluene (BHT) and tertiary butylhy-droquinone (TBHQ), as determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay and the Rancimatmethod (Sun & Ho 2005). Fabjan et al. (2003)extracted tartary buckwheat seeds (F. tataricumGaertn.) with methanol and found that tartary buck-wheat seeds contained more rutin (8–17mg/g dryweight (DW)) than commonbuckwheat seeds (0·1mg/gDW). For buckwheat, 80% methanol was foundto extract 64 times more phenolic compoundsand four times the antioxidant activity than water(Zielinski & Kozlowska 2000). Important componentsinclude rutin, rutin aglycone, quercetin, epicatechin,catechin 7-O-β-D-glucopyranoside, epicatechin, 3-O-p-hydroxybezoate and epicatechin 3-O(3,4-di-O-methyl)-gallate that were extracted with ethanolfrom buckwheat groats (F. esculentum Moench) byWatanabe (1998), while the presence of proanthocya-nidins in flour (1·59 mg/g DW) was confirmed byQuettier-Deleu et al. (2000).

Inglett et al. (2010, 2011) studied the antioxidantactivity in buckwheat with water, 0·50 aqueous

ethanol, or total ethanol using microwave irradiationor a water bath for 15min at various temperatures(23–150 °C). They found the highest antioxidantactivity of 5·61–5·73 μmol Trolox equivalents/g intotal ethanol extract at 100 and 150 °C, independent ofthe heat source. Lin et al. (2009) proved antioxidantactivity by reducing power and DPPH radical scaven-ging ability in buckwheat enhanced wheat bread.Similarly, Sedej et al. (2011) proved that buckwheatflours exhibited significantly higher (P<0·05) anti-radical activity on hydroxyl (.OH), superoxide anion(O2.) and DPPH radicals, antioxidant activity andreducing power in comparison with wheat fractions.

Flavonoids in buckwheat

Flavonoids are polyphenolic compounds that areubiquitous in plants and are a group of more than4000 polyphenolic compounds that occur naturally infoods of plant origin. They have been shown to possessa variety of biological activities at non-toxic concen-trations in organisms. These compounds possess acommon phenylbenzopyrone structure (C6-C3-C6)and they are categorized according to the saturationlevel and opening of the central pyran ring, mainly intoflavones, flavanols, isoflavones, flavonols, flavanonesand flavanonols (Ren et al. 2003). Phenolic com-pounds in buckwheat also possess antioxidant activity(Holasova et al. 2002; Sun & Ho 2005; Sensoy et al.2006). Four flavonol glycosides including rutin,quercetin, kaemferol-3-rutinoside and a trace amountof a flavonol triglycoside were found in the methanolextract of buckwheat (Tian et al. 2002). Tartarybuckwheat has been shown to contain a highercontent of flavonoids (19·02 mg/g) in comparisonwith common buckwheat (0·28 mg/g) (Jiang et al.2007).

Buckwheat contains more rutin compared withother grain crops. This is a quercetin-3-rutinosidewith antioxidant, anti-inflammatory and anticarcino-genic properties, and it can also reduce the fragility ofblood vessels related to haemorrhagic disease andhypertension in humans (Oomah & Mazza 1996;Baumgertel et al. 2003). It has been found that wholebuckwheat contains 2–5 times more phenolic com-pounds than oats or barley, while buckwheat bran andhulls have 2–7 times higher antioxidant activity thanbarley, triticale and oats (Holasova et al. 2002;Zdunczyk et al. 2006). Buckwheat contains a majorityof phenolic compounds present in the free form anddistributed throughout the entire grain (Hung & Morita

358 A. Ahmed et al.

2008). Recently, 2-hydroxy-3-O-β-D-glucopyranosil-benzoicacid,1-O-caffeoyl-6-O-alpha-rhamnopyranosyl-β-glycopyranoside and epicatechin-3-(3′′-O-methyl)gallate were identified in buckwheat by reversephase high performance liquid chromatography–electrospray ionisation-mass spectrometry (Tian et al.2002), and then again with reverse phase highperformance liquid chromatography–electrosprayionization-time of flight-mass spectrometry (Verardoet al. 2011).The flavonoid content and composition in seeds

vary between different buckwheat species and devel-opment phases. Flavonoid content in F. tataricumis generally higher than that in F. esculentum. InF. tataricum seeds, the flavonoid content is c. 40mg/g,while that of F. esculentum seeds is c. 10 mg/g (Li &Zhang 2001). In F. tataricum flowers, leaves andstems, the flavonoid content can exceed 100mg/g.Buckwheat tissues can serve as very useful resourcesfor high-quality flavonoids, though flavonoid con-tent varies with development and is significantly

influenced by the contents of phenylalanine andtyrosine and the activity of kinetin in the issuesalong with different existing forms of nitrogen in thesoil (Li & Zhang 2001).

Six flavonoids (Fig. 3) have been isolated andidentified in buckwheat grain. All six flavonoids(rutin, quercetin, orientin, vitexin, isovitexin andisoorientin) have been found in buckwheat hulls(Dietrych-Szostak & Oleszek 1999; Kreft et al. 1999;Tian et al. 2002). Epidemiological studies havesuggested a protective role of dietary flavonoidsagainst coronary heart diseases and possibly cancer(Chao et al. 2002). In recent years, flavonoids haveattracted increasing interest because they have variousbeneficial health effects such as anti-allergic, antiviral,anticancer and anti-oxidation properties (Fotsis et al.1997; Chao et al. 2002). The flavonoid content intartary buckwheat (c. 40 mg/g) is higher than that incommon buckwheat (10mg/g) (Li & Zhang 2001).

Flavonoids are known for their effectiveness inreducing cholesterol levels in the blood, keeping

Fig. 3. Important phenolic compounds in buckwheat: A, isorientin; B, orientin; C, rutin; D, vitexin (Verardo et al. 2011).

Nutritional profile of buckwheat 359

capillaries and arteries strong and flexible, reducinghigh blood pressure and reducing the risk of arterio-sclerosis (Li & Zhang 2001; Fabjan et al. 2003).Verardo et al. (2011) quantified 32 free and 24 boundphenolic compounds in buckwheat flour and buck-wheat spaghetti, with two new compounds, i.e.protochatechuic-4-O-glucoside acid and procyanidinproving the further phenolic potential of buckwheat.Kim et al. (2011) reported the effect of methyljasmonate on phytochemical production in buck-wheat sprouts cultivated in dark conditions, andtheir findings proved that isoorientin, orientin, rutinand vitexin were the main flavonoids in buckwheatsprouts. Similarly, buckwheat flour (476·3 and618·9 mg GAE/g extract) contain polyphenolic con-tents four times higher than wheat flour (37·1 and137·2 mg GAE/g extract) (Sedej et al. 2010).

Rutin content

Rutin (quercetin-3-beta-D-rutinoside) is an importanttherapeutic substance that favourably influences theincrease of blood vessel elasticity (Mukasa et al. 2009),the treatment of circulatory disorders and athero-sclerosis, the reduction of blood pressure, andstimulates the utilization of vitamin C (Yildizoglu-Ariet al. 1991). Rutin is widely present in plants, but isrelatively rare in their edible parts. It was first detectedin Ruta graveolens, which gave the common name tothis pharmaceutically important substance (Chen et al.2001). No rutin has been found in cereals orpseudocereals except buckwheat, which can be usedas a good source of dietary rutin (Ohsawa & Tsutsumi1995; Watanabe 1998; Kreft et al. 1999; Park et al.2000; Jiang et al. 2007). The content of rutin is

dependent on the buckwheat genotype, growingconditions, developmental phase, plant part and yearof harvest (Table 9) (Lachmann & Adachi 1990).Different cultivars of buckwheat may have differentcontents of rutin (Ohsawa & Tsutsumi 1995) withpotential variation also in different plant parts. Mostrutin is accumulated in the inflorescence (up to0·12 mg/g DW), in stalks (0·004–0·01mg/g DW),upper leaves (0·08–0·10mg/g DW) (Hagels 1999)and 0·12–0·36mg/g DW in grains depending on thevariety and growth conditions (Kitabayashi et al. 1995;Brunori et al. 2010; Park et al. 2011). The highestquantity of rutin is found in leaves immediately beforeflowering (Michalova et al. 1998) therefore providingthe opportunity for utilizing buckwheat tops for thenatural fortification of food with rutin. Among fruits,vegetables and grain crops, grapes and buckwheat arethe most important rutin-containing foods. Ecologicalfactors such as ultra-violet (UV) irradiation may alsohave a great influence on rutin content (Kreft et al.2002).

In a research report by Park et al. (2004), rutincontent in 50 seeds and plants of different tartarybuckwheat strains from all over the world wascompared. These 50 strains were collected fromChina (27 strains), India (5 strains), Nepal (9 strains),Bhutan (3 strains), Pakistan (1 strain), Slovenia(3 strains) and Japan (2 strains). They found the rutincontent in seed and plant parts of tartary buckwheat tobe higher than that of F. esculentum and F. cymosum(Park et al. 2004). Similar results were obtained byJiang et al. (2007) and Brunori et al. (2010). The rutincontent of tartary buckwheat was c. 3·2 times higher inthe flower, c. 3·1 times in the stem and c. 65 timeshigher in the seed compared with F. esculentum

Table 9. Rutin content (mg/g DW) in different partsof buckwheat (Park et al. 2004; Paulícková et al.2004)

Plant part Rutin

Hulled grains 126Unhulled grains 178Hulled germinated grains 366Root 436Germ 1692Stalk 5634Flower 12726Young plants 17920Tops 23374Leaves 40011

Table 10. Comparison of rutin content in leaves,stems and seeds of tartary buckwheat of differentorigins (Park et al. 2004)

Rutin content (mg/g)

Region Leaves Stems Seeds

Bhutan 53200 8646 21397China 41000 5347 15115India 42596 5518 11994Japan 36074 4091 12749Nepal 39000 6828 13360Pakistan 23315 2522 14672Slovenia 30537 2064 19382

Total 38537 5519 15893

360 A. Ahmed et al.

(Park et al. 2004). Similarly, rutin content in buck-wheat varied with cultivation region (Table 10). Rutincontent in the leaf, stem and seed of the strainscollected from the Bhutan area were higher than in thestrains collected from Slovenia and Pakistan (Park et al.2004).Rutin has desirable physiological and biological

properties, such as anti-oxidation, anti-inflammation,anti-hypertension, vasoconstrictive, spasmolitic and apositive inotropic effect (Kuntic et al. 2011; Landberget al. 2011). Rutin also provides protection againstgastric lesions, improves sight and hearing, protectsagainst UV light, lowers plasma cholesterol, protectsfrom oxidative stress (Gong et al. 2010), causes musclehypertrophy (Gaberscik et al. 2002) and also sup-presses gallstone formation and cholesterol levels(Kuntic et al. 2011). Guo et al. (2007) concluded thatadding rutin to the digestion mixture in the flourcaused a significant increase in pepsin digestibility.

Fagopyrins and fagopyritols

Fagopyrin is a photo-sensitive substance found inbuckwheat plants, belonging to the naphthodian-thrones and structurally related to hypericin (Kreft &Germ 2008). The fagopyrins found in buckwheatgrains are unique, but the concentration is very lowand isolation is difficult. In buckwheat, some anthra-noides have also been found in concentrations which

could cause very small laxative effects (Hagels 2007).The fagopyrins found in buckwheat can be utilized inthe treatment of type II diabetes (Krkoskova &Mrazova2005).

Buckwheat seeds accumulate the soluble carbo-hydrates sucrose and fagopyritols in the embryo andaleurone tissues. Fagopyritols are carbohydrate com-pounds which were first identified in buckwheat andare ex-galactosyl derivatives (mono, di and trigalacto-syl derivatives) of D-chiro-inositol (Horbowicz et al.1998).

Six fagopyritols (Figs 4 and 5), representing twodistinct series differing in bonding positions, have beenfound in buckwheat seeds (Horbowicz et al. 1998;Szczecinski et al. 1998; Obendorf et al. 2000;Steadman et al. 2000, 2001c). These are fagopyritolA1 (α-D-galactopyranosyl-(1?3)-1D-chiro-inositol),fagopyritol A2 (α-D-galactopyranosyl-(1?6)-α-D-ga-lactopyranosyl-(1?3)-1D-chiro-inositol), fagopyritolA3(α-D-galactopyranosyl-(1?6)-α-D-galactopyranosyl-(1?6)-α-D-galactopyranosyl-(1?3)-1D–chiro-inositol),fagopyritol B1(α-D-galactopyranosyl-(1?2)-1D-chiro-inositol), fagopyritol B2(α-D-galactopyranosyl-(1?6)-α-D-galactopyranosyl-(1?2)-1D-chiro-inositol) andfagopyritol B3 (α-D-galactopyranosyl-(1?6)-α-D-ga-lactopyranosyl-(1?6)-α-D-galactopyranosyl (1?2)-1D-chiro-inositol) (Obendorf 1997; Ueda et al. 2005).

Fagopyritol B1 and A1 (Obendorf et al. 2000, 2008)are the major fagopyritols accumulated in buckwheat

Fig. 4. Fagopyritol A series present in buckwheat (Horbowicz et al. 1998).

Nutritional profile of buckwheat 361

seeds (Horbowicz et al. 1998), and these constitute0·50 of the total soluble carbohydrates of buckwheatembryos (Cid et al. 2004). Fagopyritols accumulatein the dicotyledonous embryo of buckwheat seeds,mostly in the cotyledons (Horbowicz et al. 1998).Recently, Obendorf et al. (2008) determined themolecular structure of fagopyritol A1 as O-α-D-galactopyranosyl-(1-3)-D-chiro-inositol by 1H and 13CNMR and concluded that fagopyritol A1 is a positionalisomer of fagopyritol B1 (O-α-D-galactopyranosyl-(1-2)-D-chiro-inositol, which has a positive effect onblood glucose levels and insulin activity (Fonteles et al.2000).

Buckwheat is the richest source of these carbo-hydrates. The bran milling fractions may contain26mg of fagopyritols per g DW, whereas dark andlight buckwheat flours contain 7 and 3mg/g DW,respectively (Fonteles et al. 2000).

Buckwheat is being studied for use in treating type IIdiabetes (Kawa et al. 2003) and can also help tocontrol the development of polycystic ovaries (Nestleret al. 1999): it contains D-chiro-inositol, a componentof the secondary messenger pathway for insulin signal

transduction found to be deficient in type II diabetesand polycystic ovary syndrome (PCOS). Researchon D-chiro-inositol and PCOS has shown promisingresults (Nestler et al. 1999). A buckwheat protein hasbeen found to bind cholesterol tightly, thus reducingplasma cholesterol in people with hyperlipidemia(Tomotake et al. 2001). D-chiro-inositol is a com-ponent of galactosamine D-chiro-inositol, a putativeinsulin mediator (Larner et al. 1988) believed to bedeficient in subjects with NIDDM (Asplin et al. 1993)because of an abnormal D-chiro-inositol metabolism.Adding D-chiro-inositol as a dietary supplementappeared to be effective in reducing the symptoms ofNIDDM and PCOS (Ortmeyer et al. 1995; Fonteleset al. 2000). Several research groups are developingsources for natural and synthetic supplies of D-chiro-inositol (Kennington et al. 1990). One natural source ofD-chiro-inositol (in free form and as galactosides,predominantly fagopyritol A1 and fagopyritol B1) isin buckwheat seed. During dry milling, fragments ofthe outer cotyledon adhere to the bran (Steadman et al.2001c). Therefore, the bran milling fraction frombuckwheat seed (Steadman et al. 2000, 2001c) can

Fig. 5. Fagopyritol B series present in buckwheat (Horbowicz et al. 1998).

362 A. Ahmed et al.

be used for the isolation and preparation of fagopyr-itols and can free D-chiro-inositol for the production ofnutraceuticals and pharmaceuticals (Obendorf et al.2000, 2008; Steadman et al. 2000; Kawa et al. 2003).

ALLERGIES TO BUCKWHEAT

Allergy to buckwheat was first reported in the literaturein 1909 (Smith 1909), and it is mostly an immediateIgE-mediated reaction that can cause a severe allergicreaction similar to that caused by peanut allergy (Aseroet al. 2009). Several buckwheat allergens have beenidentified, of which the 24 kDa (Fag e 1), 26 kDa and67–70 kDa proteins have been suggested to be ofimportance (Tohgi et al. 2011). Fag e 1, which ishomologous to 11S or 12S globulin, has reacted withthe serum IgE of all buckwheat allergy patients. The16 kDa protein (Fag e 2), which is resistant to digestion,has been identified as a major buckwheat allergen inJapanese and Korean patients with buckwheat allergy(Park et al. 2000).

CONCLUSION

Buckwheat is an important food, as it contains proteinswith high biological value and balanced amino acidcomposition, relatively high fibre content, high con-tents of available Zn, Cu and Mn and dietary Se. Thenutraceutical potential of buckwheat and its use infood products emphasizes the need to further exploitthe use of bioactive compounds and precious func-tional ingredients which are well researched andestablished by various studies in the related area.This will not only help in the prevention and treatmentof various human diseases, it will also be helpful inimproving various traditional and local buckwheatfoods and better use of the by-products of buckwheat.Proper utilization of buckwheat will also promote foodindustries in the development of new functional foods.

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