Distribution of Free and Bound Phenolic Compounds in Buckwheat Milling Fractions

Abstract

Buckwheat is a rich source of phenolic compounds that have shown to possess beneficial effect to reduce some diseases due to their antioxidant power. Phenolic compounds are present in the free and in the bound form to the cell wall that are concentrated mainly in the outer layer (hull and bran). Hull is removed before the milling of buckwheat to obtain flours. In order to evaluate the phenolic composition in dehulled buckwheat milling fractions, it was carried out a determination of free and bound phenolic compounds in dehulled whole buckwheat flour, light flour, bran flour, and middling flour by high-performance liquid chromatography-mass spectrometry (HPLC-MS). The most abundant free phenolic compounds were rutin and epiafzelchin-epicatechin-O-dimethylgallate, whereas the most abundant bound phenolic compounds were catechin and epicatechin in all buckwheat flours. Besides, the highest content of free phenolic compounds was obtained in bran flour (1249.49 mg/kg d.w.), whereas the greatest bound phenolic content was in middling (704.47 mg/kg d.w.) and bran flours (689.81 mg/kg d.w.). Thus, middling and bran flours are naturally enriched flours in phenolic compounds that could be used to develop functional foods.Phenolic compounds in buckwheat are present in the free and in the bound form to cell wall [11], however, the majority of phenolic compounds are present in the free form, which has a distribution and concentration that is different in each part of the grain: pericarp (hull, husk), coat, endosperm, embryo with axis, and two cotyledons [12]; phenolic compounds are concentrated in the outer layers (hull and bran) of buckwheat grain [2]. Nevertheless, during buckwheat seeds processing into flour, the hull (17-20% of buckwheat grain) is removed by stone dehuller. The resulting product, called groat (intact achene), is milled into bran flour (10-24%), which is a by-product that it is not commonly used in foods, and light flour (55-70%), which consists principally of endosperm and is used in human nutrition [13]. In addition, middling is a by-product from buckwheat milling that is not a flour that comprises different fractions and it includes 12% of the original grain, consisting of fractions of endosperm, bran, and germ [14]. Milling techniques used in the food industry employ mechanical force to break the grains into smaller fragments or fine particles. [15]. Previous studies reported the use of roller milling process in dehulled whole buckwheat to obtain a flour and the separation of this flour into various fractions from outer to inner parts [2,16]. These studies have shown that outer layers are richer in protein, lipid, dietary fiber, and ash content than the inner layers. Also, the antioxidant capacity in flour fractions in the outer layers is higher than that in the inner layers by the increase of phenolic compounds from bran [2,16]. In addition, it has reported that milling fractions that contain outer layers possess a higher concentration of phenolic compounds than whole grain and groat flour fractions [...

Polyphenol profile of buckwheat honey, nectar and pollen

“…Of 21 phenolic compounds found in the pollen, only myricetin ( m/z 317), which is a pollen-nectar-derived flavonoid [ 51 ], was common to pollen and honey from Serbia. The presence of myricetin in buckwheat honey has been reported [ 35 , 45 ] and also in buckwheat flours (in a bound form) [ 15 ]. Furthermore, myricetin has been proposed as a chemical marker of the authenticity of heather honey [ 7 ].…”

“…Phenolic compounds that were present only in the pollen sample were mostly (epi)catechin units, its galloylated derivatives and procyanidin dimers, which have already been considered as buckwheat markers [12][13][14][15][16][17]29]. Potential health effects have been reported of procyanidins B type with their content being higher in buckwheat than in cereals (barley and spelt) [17].…”

“…7: 201576 Ölschläger et al [13] reported the presence of galloylated flavan 3-ols in buckwheat seeds, underscoring their absence in other crops. The presence of epicatechin (m/z 289) and (epi)catechin gallate (m/z 441) is characteristic for buckwheat [12][13][14][15][16][17]29]. Their presence in pollen has been confirmed among many other components, in particular methyl-B type prodelphinidin dimer (m/z 607), methyl-(epi)gallocatechin gallate (m/z 471) and B type procyanidin dimer gallate (m/z 745) with its two isomers (m/z 729).…”

Treasure from garden: Bioactive compounds of buckwheat

“…Buckwheat is the most abundant source of d - chiro -inositol. Farinetta is a specific type of buckwheat flour that contains high levels of d - chiro -inositol when it milled especially ( Martin-Garcia et al, 2019 ). Fagopyritols are an important derivative of d - chiro -inositol which accumulates mainly in aleurone tissue and embryo of buckwheat seeds.…”

Ultrasound Treatment of Buckwheat Grains Impacts Important Functional Properties of Resulting Flour

“…Rutin (quercetin-3-rhamnosyglucoside) is a glycoside flavonol that can reduce capillary fragility associated with hypertensive disorders [ 18 ]. Several researchers were studying the amount [ 20 , 21 ] and characteristics [ 22 , 23 ] of antioxidants from buckwheat fractions, especially grains [ 24 ]. Both common buckwheat and Tartary buckwheat can serve as an excellent source of polyphenols compounds, and many studies explore the extraction of buckwheat grain with different solvents and techniques, primarily assisted by ultrasound [ 25 ].…”