Beta Glucan What Is It?

Dextran is a homopolymer composed of glucose as the monosaccharide. The glucose units are linked by glycosidic bonds and are divided into α-dextran and β-dextran. Among them, cereal β-glucan is a linear homopolymer of D-glucopyranose residues linked by β-(1-3) and β-(1-4) bonds, consisting of fibrous fragments, i.e. β-(1-4)-oligoglucan, which are linked by β-(1-3) bonds. As a functional polysaccharide, cereal β-glucan is mainly extracted from the aleurone layer and endosperm cell walls of cereals such as oats, wheat, barley and rye. In oats and barley, β-glucan is distributed throughout the starch endosperm.

Oats and barley are commonly used as animal feed, in brewing and as a meal replacement. In vivo and in vitro experiments have shown that β-glucan has a variety of biological activities [1], including increasing the viscosity of digestive juices in the gastrointestinal tract, slowing gastric emptying, delaying carbohydrate absorption, and significantly inhibiting and preventing diabetes; reducing blood cholesterol levels, LDL levels, and increasing HDL levels; promote intestinal peristalsis, absorb harmful substances in the intestine, increase the production of short-chain fatty acids, and promote the activation of useful bacteria in the intestine; enhance the activity and phagocytic ability of macrophages, which further has an anti-cancer effect; and have a certain effect on the secretion of cytokines, phagocytosis and cytotoxicity of immune cells and the activation of the complement system.

This article reviews the functions of oat and barley β-glucan in lowering blood sugar and blood lipids, improving intestinal health, preventing tumors and regulating immunity.

1 Physiological functions of cereal β-glucan

1.1 Hypoglycemic effect

The β-glucan molecules are cross-linked into a network structure, thereby hindering contact between food and digestive enzymes. β-Glucan is a polysaccharide with high viscosity. By increasing the viscosity of the upper gastrointestinal tract contents, it forms mucus in the gastrointestinal tract, prolongs gastric emptying time, reduces starch digestibility, promotes insulin secretion, thereby reducing glucose absorption and reducing the risk of type II diabetes.

Regand et al. [2] found that as the viscosity of the in vitro extract of oat β-glucan increased, the in vitro starch digestibility decreased and the glucose response decreased. When the mass ratio of β-glucan to starch was 1. 6:10, β-glucan showed a better effect in reducing the peak blood glucose response and the incremental area under the curve. LIU et al. [3] found that oat β-glucan can improve the blood glucose levels and hepatic glucose metabolism induced by streptozotocin-nicotinamide in mice, significantly repairing and improving the integrity of pancreatic β-cells and tissues.

A study of non-diabetic men aged 18 to 60 (n = 16) and non-pregnant women (n = 12) found that adding instant oatmeal containing 4 g of oat beta-glucan significantly reduced the area under the blood glucose and insulin curves and delayed gastric emptying. and the response to postprandial peptide tyrosine and gastric hunger hormone was similar to that after a normal meal when 2 and 4 g oat β-glucan were included in the diet [4]. Barley β-glucan can reduce liver weight and liver lipid concentration in rats with type II diabetes, and reduce the area under the glucose curve, suggesting that barley β-glucan can effectively improve hyperglycemic symptoms [5]. MATSUOKA et al. [6] found in a study of 23 healthy young Japanese people that consumption of refined barley flour bread containing β-glucan can lower postprandial blood glucose concentrations compared to consumption of refined wheat flour bread containing β-glucan.

1.2 Lipid-lowering effect

The ability of β-glucan to lower serum cholesterol depends on its ability to lower cholesterol, which is mainly achieved by increasing the viscosity of the intestinal contents.

Shen Ruiling et al. [7] found in a study of rats with hypercholesterolemia that oat β-glucan can significantly reduce fasting plasma total cholesterol and low-density lipoprotein levels in rats, and this is time- and dose-dependent. It was also found that after adding β-glucan to the feed, the body weight and food intake of the rats showed a clear downward trend, indicating that oat β-glucan has a good cholesterol-lowering effect. An in vitro lipid digestion test found that the time of lipolysis does not directly depend on the concentration of oat β-glucan released into the solution. Maintaining the structural integrity of the oat tissue matrix is important for reducing the rate and extent of lipolysis, and is related to the physical form in which oat β-glucan is delivered for digestion [8].

The results of a study by TONG et al. [9] showed that consumption of beta-glucan from hulless barley can promote the excretion of fecal lipids, regulate the activities of 3-hydroxy-3-methylglutaryl-coenzyme A and cholesterol 7-a hydroxylase in the liver of high cholesterol hamsters, and reduce the concentration of plasma low-density lipoprotein cholesterol. WANG et al. [10] found that the cholesterol-lowering effect of barley β-glucan may be related to enhanced bile acid synthesis due to individual consumption of high-viscosity β-glucan, rather than inhibition of cholesterol absorption or synthesis. XIAO et al. [11] showed that, compared with barley β-glucan, fermented barley β-glucan has better inhibitory activity against α-amylase, α-glucosidase and lipase, as well as cholesterol adsorption capacity under acidic conditions.

1.3 Improving intestinal health

In the stomach and small intestine, soluble dietary fibre β-glucan mainly functions by increasing the viscosity of gastric and intestinal contents, and this effect is mediated by a neurohormonal system involving endocrine and gastrointestinal hormones. In the colon, the main function of β-glucan is as a substrate that is conducive to the production of butyric acid. It has been shown that oligosaccharides produced by β-glucan act as selectins that are conducive to the growth of some known probiotic strains, thereby protecting intestinal health [12].

Shen Ruiling et al. [13] studied the effect of oat β-glucan on the colonic flora and its function in mice and found that with an increase in the time of gavage, oat β-glucan can increase the proliferation of bifidobacteria and lactobacilli in the mouse intestine and feces, while reducing the number of Escherichia coli. DONG et al. [14] found that β-glucan in different oat products increased the intestinal milk viscosity, delayed gastric emptying, promoted intestinal motility, reduced the activities of amylase, trypsin, lipase and Na +, K +-ATPase, and promoted the secretion of plasma cholecystokinin (CCK) and motilin (MOT).

MIYAMOTO et al. [15] used a mouse model of obesity induced by a high-fat diet to show that feeding mice with high-barley-β-glucan content increased the secretion of the intestinal hormones peptide YY and glucagon-like peptide-1, which in turn reduced food intake and improved insulin sensitivity by altering the intestinal flora and increasing short-chain fatty acids (especially butyrate). Studies have shown that taking barley β-glucan significantly increased the total short-chain fatty acid concentration in the daily stool of 30 subjects with mild hypercholesterolemia but otherwise healthy, as measured by the concentration of bile acids, neutral sterols and short-chain fatty acids excreted in the stool.

1.4 Tumor prevention and immunomodulatory effects

The anti-tumor and immune-enhancing effects of β-glucan are based on its ability to activate white blood cells by stimulating their phagocytic activity and the production of inflammatory cytokines (e.g. TNFα). β-Glucan interacts with the Dectin-1 receptor on the cell surface and is expressed on macrophages, neutrophils, dendritic cells, natural killer cells and T lymphocyte subsets, thereby preventing tumors and regulating immunity.

CHOROMANSKA et al. [17] observed in cancer cells that with increasing incubation time and β-glucan concentration, the survival rate of cancer cells decreased significantly, indicating that low-molecular-weight oat β-glucan has strong antitumor properties and is not toxic to normal cells. ES-TRADA et al. [18] found that oat β-glucan can stimulate macrophages to release IL-1 and TNF-α, and enhance the ability of nonspecific resistance to bacterial attack in mice, indicating that oat β-glucan can stimulate immune function and regulate immune activity in vivo and in vitro. HONG et al. [19] showed that oral administration of barley β-glucan can enhance the activity of anti-tumor monoclonal antibodies, leading to tumor regression and improved survival rates.

1.5 Blood pressure lowering effect

Insulin resistance is associated with the development of hypertension. β-glucan may affect blood pressure by regulating insulin metabolism. The reduction in plasma cholesterol levels is also associated with endothelium-mediated vasodilation and blood pressure reduction.

MAKI et al. [20] found that foods containing oat β-glucan had a positive effect on carbohydrate metabolism and blood pressure in obese subjects, with both systolic and diastolic blood pressures lower than those in the control group. WANG et al. [21] found that after 35 days of dietary intervention with barley β-glucan, daily intake of 3 g of high molecular weight barley β-glucan could significantly increase the number of Bifidobacteria, and the increase in Bifidobacteria was negatively correlated with blood pressure. However, the potential hypotensive mechanism of β-glucan has not yet been elucidated, and more research is needed to fully demonstrate the mechanism by which β-glucan has a positive effect on hypertension and related diseases.

2 Prospects

In recent years, the physiological functions of β-glucan extracted from oats and barley, such as lowering blood sugar and blood lipids, improving intestinal health, and anti-tumor, have been extensively studied by scholars at home and abroad. Strengthening research on the isolation and extraction, physicochemical properties, and functional characteristics of β-glucan, and developing a series of β-glucan health foods and high value-added β-glucan products, has a relatively broad market and development prospects.

Reference:

［ 1 ］BRENNAN C S，CLEARY L J.  The potential use ofcere- al ( 1→3，1→4) -β-D-glucans as functional food  ingredi- ents［J］.  Journal of Cereal Science，2005，42( 1) :   1 - 13.

［ 2 ］REGAND A，CHOWDHURY Z，TOSH S M，et al.  The  molecular weight，solubility and viscosity of oat beta-glu- can affect  human  glycemic  response  by modifying starch  digestibility［J］.  Food Chemistry，2011，129( 2) :  297 -  304.

［ 3 ］LIU M，ZHANG Y，ZHANG H，et al.  The anti-diabetic  activity  of  oat   β-D-glucan  in  streptozotocin-nicotinamide  induced diabetic  mice［J］.   International  Journal  of  Bio- logical Macromolecules，2016，91:  1170 - 1176.

［ 4 ］WOLEVER T M S，TOSH S M，SPRUILL S E，et al.   Increasing  oat   β-glucan   viscosity  in  a  breakfast  meal  slows gastric  emptying  and  reduces glycemic and insu- linemic responses but has no effect on appetite，food in- take，or  plasma  ghrelin  and  PYY responses in healthy  humans:   A   randomized ， placebo-controlled ， crossover  trial［J］.   The  American  Journal  of  Clinical  Nutrition， 2020，111( 2) :  319 - 328 .

［ 5 ］ BROCKMAN D A ，CHEN X ，GALLAHER D D.  Con- sumption of a high β-glucan barley flour improves glucose  control and fatty liver and increases muscle acylcarnitines  in the Zucker diabetic fatty rat［J］.  European Journal of Nutrition，2013，52( 7) :  1743 - 1753.

［ 6 ］MATSUOKA T，TSUCHIDA A，YAMAJI A，et al.  Con- sumption of a meal containing refined barley flour bread is  associated with a lower postprandial blood glucose concen- tration after a  second  meal  compared  with  one  containing  refined wheat flour bread in healthy Japanese:  A random- ized control trial［J］.  Nutrition，2019，72:  110637.

[7] Shen Ruiling, Wang Zhirui, Li Hongquan, et al. Effect of oat β-glucan on blood lipids and growth in rats with hypercholesterolemia [J]. Chinese Journal of Cereals, Oils and Foodstuffs, 2009, 24(1): 44-48.

［ 8 ］GRUNDY M M L，QUINT J，RIEDER A，et al.  The im- pact of oat structure and  β-glucan on in vitro lipid diges- tion［J］.  Journal of Functional  Foods，2017，38( Pt  A) :378 - 388.

［ 9 ］TONG L T，ZHONG K，LIU L，et al.  Effects of dietary  hull-less barley β-glucan on the cholesterol metabolism of  hypercholesterolemic   hamsters ［J］.     Food    Chemistry， 2015，169:  344 - 349.

［10］ WANG Y，HARDING S V，THANDAPILLY S J，et al.  Barley β-glucan reduces blood cholesterol levels via inter- rupting bile acid metabolism［J］.  British Journal of Nutri- tion，2017，118( 10) :  822 - 829.

［11］ XIAO X，TAN C，SUN X J，et al.  Effects of fermentation  on structural characteristics and in vitro physiological ac- tivities of barley  β-glucan［J］.   Carbohydrate Polymers， 2020，231:  115685.

［12 ］ REILLY  P ，SWEENEY T ，O’SHEAK  C ，et  al.   The  effect of cereal-derived  β-glucans  and  exogenous enzyme  supplementation on intestinal microflora，nutrient digesti- bility，mineral metabolism and volatile fatty acid concen- trations in  finisher  pigs［J］.   Animal  Feed Science and  Technology，2010，158( 3 /4) :  165 - 176.

[13] Shen Ruiling, Wang Zhangcun, Yao Huiyuan. The effect of oat β-glucan on the intestinal flora of mice [J]. Food Science, 2005, 26(2): 208-212.

［14］ DONG J L，ZHANG W L，LIN J，et al.  The gastrointesti- nal  metabolic   effects  of  oat  product  based-β-glucan  in  mice［J］.  Food Science &Biotechnology，2014，23 ( 3) :917 - 924.

［15］ MIYAMOTO J，WATANABE K，TAIRA S，et al.  Barley  β-glucan improves metabolic condition via short-chain fat- ty acids produced by gut microbial fermentation in high fat  diet fed mice［J］.  The Public Library of Science，2018， 13( 4) :  e0196579 .

［16］THANDAPILLY S J，NDOU S P，WANG Y，et al.  Bar- ley β-glucan increases fecal bile acid excretion and short  chain fatty acid levels in mildly hypercholesterolemic indi- viduals［J］.  Food & Function，2018，9( 6) :  3092 - 3096.

［17］ CHOROMANSKA A ，KULBACKA J ，REMBIALKOWS- KA  N ， et   al.   Anticancer   properties   of  low   molecular  weight oat beta-glucan-An in vitro study［J］.  Internation- alJournal of Biological Macromolecules，2015，80:  23 -   28.

［18］ ESTRADA A，YUN C H，VAN K A，et al.  Immunomodu- latory activities of oat beta-glucan in vitro and in vivo［J］.  Microbiology & Immunology，2013，41( 12) :  991 - 998.

［19］ HONG  F ，YAN J ，BARAN J T ，et  al.   Mechanism  by  which orally  administered  beta-1，3-glucans  enhance  the  tumoricidal activity of antitumor monoclonal antibodies in  murine tumor models［J］.  Journal of Immunology，2004， 173( 2) : 797 - 806.

［20］ MAKI K C，GALANT R，SAMUEL P，et al.  Effects of consuming foods containing oat beta-glucan on blood pres- sure，carbohydrate metabolism and biomarkers of oxidative  stress in men and women with elevated blood pressure［J］.  European Journal of Clinical Nutrition，2007，61( 6) :786 - 795 .

［21］ WANG Y A，AMES N P，TUN H M，et al.  High molecu- lar weight barley β-Glucan alters gut microbiota toward re- duced cardiovascular disease risk［J］.  Frontiers in Micro- biology，2016，7 :  129.