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Buckwheat as a Functional Food and its effects on Health – a Comprehensive Review Henryk Zielinski, and Juan Antonio Gimenez Bastida J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.5b02498 • Publication Date (Web): 13 Aug 2015 Downloaded from http://pubs.acs.org on August 20, 2015
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Buckwheat as a Functional Food and its effects on Health – a Comprehensive Review
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Juan Antonio Giménez-Bastida, Henryk Zieliński*
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Division of Food Science, Institute of Animal Reproduction and Food Research of the Polish
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Academy of Sciences, Tuwima 10, P.O. Box 55, 10-748 Olsztyn 5, Poland
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*Corresponding author: Tel.: +48 89 523 46 82. Fax: +48 89 524 01 24.
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E-mail:
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ABSTRACT
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Buckwheat (BW) is a gluten-free pseudocereal that belongs to the Polygonaceae family. BW
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grain is a highly nutritional food component that has been shown to provide a wide range of
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beneficial effects. Health benefits attributed to BW include plasma cholesterol levels´ reduction,
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neuroprotection, anticancer, anti-inflammatory, antidiabetic effects, and improvement of
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hypertension conditions. In addition, BW has been reported to possess prebiotic and antioxidant
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activities. In vitro and animal studies suggest that BW´s bioactive compounds, such as D-chiro-
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inositol (DCI), BW proteins (BWP) and BW flavonoids (mainly rutin and quercetin) may be
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partially responsible for the observed effects. Bearing this in mind, the purpose of this paper is to
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review the recent research regarding the health benefits of BW, in vitro and in vivo, focusing on
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the specific the role of its bioactive compounds and on the mechanisms by which these effects
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are exerted.
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KEYWORDS: Common buckwheat; bioactive compounds; Fagopyrum; rutin; buckwheat
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protein
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INTRODUCTION The family Polygonaceae is a group of plants composed by 1200 species approximately1.
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BW, which belongs to this family, is found almost everywhere but grows mainly in the northern
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hemisphere. Russia and China are the main producers of BW in the world2. Furthermore, the
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consumption of this product has become increasingly popular in United States, Canada and
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Europe3. Among the main nine species with agricultural meaning, common BW (Fagopyrum
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esculentum Moench) and tartary BW (F. tataricum Gaertn) are the most widely grown species.
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Tartary BW is cultivated in some mountain regions, whereas common BW is grown from
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temperate Europe to Japan4.
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BW seeds are the main form of consumption of this pseudocereal. Dehulled seeds (raw
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groats) are principally used for human consumption as breakfast cereals, or as processed flour for
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making different bakery products (bread, cookies, snacks and noodles) enriched with BW flour
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(0.3 – 60%), and BW-enhanced non-bakery products (tea, honey, tarhana, and sprouts)5. Since
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BW is a gluten-free pseudoceral, these products may be included in gluten-free diets for patients
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suffering gluten intolerance6.
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BW is recognized as a good source of nutritionally valuable protein, lipid, dietary fiber
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and minerals, and in combination with other health-promoting components, such as phenolic
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compounds and sterols, it has received increasing attention as a potential functional food7.
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Functional foods are those that exert a scientifically proven specific health benefit (health claim)
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beyond their nutritional properties, although the consumption of its specific formulation is not
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essential for human life8.It has been described that the consumption of BW and BW-enriched
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products is related to a wide range of biological and healthy activities: hypocholesterolemic,
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hypoglucemic, anticancer, and anti-inflammatory. Buckwheat proteins (BWPs) and phenolic 3 ACS Paragon Plus Environment
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compounds are presumed to be responsible, at least in part, for these benefits4. It has been
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recognized that some of these effects may be related to the antioxidant capacity of these
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compounds, but newly discovered mechanisms of action may be also responsible for the
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observed healthy effects9, 10. The purpose of this paper is to review the recent literature addressing the health benefits
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of BW, its proteins and phytochemicals, and to describe the mechanisms underlying the
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beneficial effects attributed to these compounds.
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BIOACTIVE COMPOUNDS IN BUCKWHEAT
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BW is presently considered a food component of high nutritional value. BW seed is the
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main form of consumption, although the consumption of BW sprouts is increasingly popular in
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North America and other parts of the world. The general composition of sprouts and dehulled,
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unroasted BW seeds or groats from common and tartary BW is described in tables 1A7, 11-15 and
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1B16.
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Fagopyritols are mono-, di-, and trigalactosyl derivatives of DCI termed fagopyritols B1,
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B2, and B3, respectively. Fagopyritols A1, A2 and A3 have also been identified as isomers of
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B1, B2, and B3, respectively13, 17, 18. Fagopyritols are concentrated in aleurone and embryo cells
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of the seed being the most abundant the fagopyritol B1 (0.392 mg g-1 d.m. of whole common
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BW groats)13. DCI, the free form, is present in lower concentration (0.21 – 0.42 mg g-1 dry
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matter –d.m.-)12. The role of DCI and fagopyritols as molecules exerting insulin-like activity has
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been previously reported 12, 19, 20. Chemically synthesized DCI has shown to reduce elevated
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plasma glucose level in an important number of studies21, 22. Although studies investigating the
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effect of DCI and fagopyritols in humans have not been conducted so far, these compounds may
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have positive effects in diabetes treatment. D-fagomine is a minor component detected in
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common BW groats (1 – 25 mg kg-1 in common BW-based foodstuffs) that exhibits a glucose-
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lowering effect23, 24. The anthraquinone emodin is present in BW at concentrations between 1.72
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– 2.71 mg kg-1 d.m. 25. Due to the broad spectrum of biological activities exerted by emodin, it
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may be an important bioactive factor in BW26.
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BWPs have a high biological value due to a well-balanced amino acid composition. They
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are rich in lysine, which is generally the first limiting amino acid in other plant proteins, and
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arginine. However, the content in glutamine and proline is much lower than in wheat27, and
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threonine and methionine are the first and the second limiting amino acids, respectively.
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Thiamin-binding proteins isolated from BW may be used in the care of people who suffer from
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the lack of thiamin7. Furthermore, many researchers reported that the low digestibility of BWPs
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and lysine/arginine and methionine/glycine rates are critical factors in determining the
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cholesterol-lowering effects of the plant proteins7, 28.
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The contents and composition of flavonoids are dissimilar in different BW species.
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Generally, the flavonoid content in F. tataricum (40 mg g-1) is higher than in F. esculentum (10
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mg g-1) reaching concentrations of 100 mg g-1 in tartary BW flowers, leaves and stems2. BW
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seeds (groats and hull) and sprouts are important sources of rutin (quercetin-3-rutinoside) and
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their content depends on the variety and growth conditions29, 30. Tartary BW groats (BWG)
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contain more rutin (80.94 mg g-1 d.m.) than common BW (0.20 mg g-1 d.m.)31, 32, while tartary
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BW sprouts (BWS) possess 2.2 fold-time rutin than common BWS33. Rutin has attracted
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increasing attention mainly due to its numerous beneficial effects observed in vitro and in vivo:
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anti-inflammatory, antidiabetic, hypocholesterolemic, anti-atherosclerotic, and
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anticarcinogenic34. Its activity has been associated with its antioxidant capacity, although the
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precise mechanism of protection is not known. Quercitrin (quercetin-3-rhamnoside) is another
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glycoside present in BW at concentrations ranging from 0.01 – 0.05% d.m. in tartary BW, and
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from 0.54 – 1.80% d.m. in common BW31, 35. Isoquercetin (quercetin-3-glucoside) is present in
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BW hypocotyls (1.4 µM g-1 d.m.)36, and it has been shown to exert antidiabetic and anticancer
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activity37-39. The aglycone quercetin is present in BWG (0.001 mg g-1 d.m.) and BW hull (0.009
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– 0.029 mg g-1 d.m.) at lower concentration than rutin12, 32. The flavone C-glycosides present in
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BW seedlings (vitexin, isovitexin, orientin and homoorientin), the content of anthocyanins and
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proanthocyanins36, and the presence of squalene, epicatechin and vitamin E (tocopherols)40 make
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BW a good antioxidant source in human diet.
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Phenolic acids of BW also contribute to its antioxidant capacity. 4-hydroxybenzoic (p-
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Hydroxybenzoic), 3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid (ferulic) and 3,4-
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dihydroxybenzoic (protocatechuic) acids are prominent in the seeds of different cultivars of
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tartary BW, and other phenolics, including 4-hydroxycinnamic (p-coumaric), 3,4,5-
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trihydroxybenzoic (gallic), 3,4-dihydroxycinnamic (caffeic), 4-hydroxy-3-methoxybenzoic
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(vanillic) and 3,5-dimethoxy-4-hydroxybenzoic (syringic) acids have been detected41. Several
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phenolic acids were described in the inflorescences of different varieties of BW: 3-(3,4-
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dihydroxycinnamoyl)quinic (chlorogenic), 4-methoxybenzoic (p-anisic), 2-hydroxybenzoic
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(salicylic) and methoxycinnamic acid42. The most abundant phytosterol in BW flour (BWF) is β-
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sitosterol (0.86 mg g-1 d.m.) followed by campesterol (0.11 mg g-1 d.m.) and stigmasterol (0.02
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mg g-1 d.m.)43.
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BW is also an important source of vitamins. Total vitamin B content, including B1
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(thiamin, 2.2 – 3.3 µg g-1 d.m.), B2 (riboflavin, 10.6 µg g-1 d.m.), B3 (niacin, 18 µg g-1), B5
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(pantothenic acid, 11 µg g-1) and B6 (piridoxine, 1.5 µg g-1), is higher in tartary BW than in 6 ACS Paragon Plus Environment
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common BW, and the levels of vitamic C have been reported as 50 µg g-1 d.m., reaching up to
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250 µg g-1 d.m. in sprouts5, 44, 45. Along with vitamins, other compounds such as glutathione
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(1.10 mmol g-1 d.m. in BWG), phytic acid (35 - 38 mg g-1 d.m. in BW bran), carotenoids (2.10
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mg g-1 d.m. in BW seeds), and melatonin (470 pg g-1 d.m. in BWG) have been detected and may
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contribute to the antioxidant activity of BW4, 32.
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Recently, γ-aminobutyric acid (GABA) and 2”-hydroxynicotianamine (2HN) have been found to
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serve as functional compounds in BW. Seeds and sprouts contain GABA, while 2HN has been
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recently identified in BWF. These compounds have been reported to reduce blood pressure in
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humans, and to inhibit the angiotensin I converting enzyme (ACE) activity46-48.
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HEALTH BENEFITS AND BUCKWHEAT
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Antioxidant activity
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Increasing appreciation of the nutritional and functional properties of BW has also
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encouraged some investigations about its antioxidant properties. The antioxidant features of BW
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pseudocereals appear reflected in human intervention studies. There have been reported increases
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in the total antioxidant capacity of plasma samples from healthy donors after consuming 1.5 g of
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BW honey kg-1 (single dose, n=37)49, or when BW honey was added to water or black tea (160 g
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honey L-1, n=25)50 as well as after BW-enriched wheat bread consumption51.
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The biological antioxidant capacity of BW is further supported by in vivo experimental models
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fed a BWH-containing diet (0.75% in diet, 14 days)52, a BW by-product-enriched diet (15% for 4
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weeks)53 and 100 and 200 mg of BW kg-1 day-1 for 20 days54. The results showed increased
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activity of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT),
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gluthatione peroxidase (GSH-Px), reduced lipid peroxidation parameters such as thiobarbituric
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acid reactive substances (TBARS), malondialdehyde (MDA), and fluorescent substance (FLS) in
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plasma samples, red blood cells, and several different organs (heart, kidney, liver and brain). In
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contrast, total plasma antioxidant status and the activities of SOD and GSH-Px were unaltered in
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healthy rats fed a normal diet containing 30% expanded BW seeds or 5% of BWS for 4 weeks55.
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In vitro antioxidant activity of BW has been assessed in relation to its phenolic content and
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composition41, 42, 56-59 and compared to that of other cereals and pseudocereals60-63. In this sense,
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Zieliński and Kozłowska established the following hierarchy of antioxidant activity: BW >
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barley > oat > wheat ~ rye64. The high antioxidant capacity of BW is connected with high
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polyphenol content, especially rutin65, 66. Liu et al. described the antioxidant effects of BWS in
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human hepatoma HepG2 cells, revealing that tartary and common BW had a positive effect on
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the production of intracellular peroxide and superoxide anions. Tartary BW was more effective
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than common BW and this effect was associated with the higher concentration of rutin16. Studies
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by Zhou et al. also reported that BW honey showed protective effects on hydroxyl radicals-
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induced DNA damage through is antioxidant activity67. These studies seem to indicate that BW
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may exert its beneficial effects through its antioxidant activity.
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Hypocholesterolemic activity
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Increased cholesterol intake can induce oxidative stress and cause an increase in blood
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cholesterol level, leading to the up-regulation of low density lipoproteins (LDL) and oxidized
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LDL (oxLDL), contributing to the development of chronic diseases such as atheroclerosis68. In
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vitro and in vivo studies have proposed that BW’s protective effect against cardiovascular
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diseases may come from its ability to modulate cholesterol (Ch) level.
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The number of studies investigating the cholesterol-lowering activity of BW in humans is
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scarce (Table 2). The investigation carried out by Zhang et al. in 2007 is one of the biggest
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studies in relation to the consumption of BW and health. 3542 Mongolians in two adjacent
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countries of Inner Mongolia (China) were randomly sampled in a cross-sectional study to assess
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the association of hypertension, dyslipidaemia, and hyperglycaemia with lifetime consumption of
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BW seed as a staple food. The authors described a reduction of total cholesterol (TCh) (4%;
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p0.05) and LDL (9.05%; p
