What Is the Benefit of Oat Beta Glucan Powder?

Oats belong to the annual herbaceous plants of the genus Avena in the family Gramineae. They are a special type of crop that is used for food, cosmetics, animal feed, medicine and industrial raw materials. Oats are rich in minerals, vitamins, a good balance of amino acids, unsaturated fatty acids and unique water-soluble dietary fibre[1]. Among them, the most studied and applied is the non-starch water-soluble dietary fiber, oat β-glucan, which is mainly found in the cell walls of the aleurone layer and subaleurone layer of oat grains. Its basic structure is a high-molecular, unbranched, linear mucopolysaccharide formed by β(1 → 3) glycosidic bonds and β(1 → 4) glycosidic bonds linked to β-D-glucopyranose units. It is a kind of short-chain glucan with a relatively small molecular weight and belongs to the oligosaccharide category[2]. Oat β-glucan has the highest content of β-glucan among cereal crops.

Oat β-glucan has a variety of beneficial biological functions, and has become a research hotspot at home and abroad, as well as attracting the attention of consumers. In particular, in the 1990s, the US Food and Drug Administration (FDA) pointed out that consuming more than 3 g of beta-glucan per day in the diet or eating low-fat oats can lower blood lipid levels and reduce the incidence of cardiovascular disease [3], which has further promoted the rapid development of scientific research and product applications of oat beta-glucan. A large number of studies have confirmed that oat β-glucan also has the effects of lowering blood sugar, improving intestinal flora, anti-oxidation and enhancing immunity. It has been widely used in the production of high-fibre drinks, pasta, pastries and cooked meat products[4] . For this reason, this paper, based on a review of a large number of domestic and foreign literature, provides an in-depth analysis and discussion of the structural characteristics, content, biological functions and application of oat β-glucan in foods, with the expectation of providing a scientific basis for the in-depth development and utilization of oat β-glucan as a functional food factor.

1 Molecular structural characteristics of oat β-glucan

The beneficial biological value of oat β-glucan is constantly being explored, and the exploration of the basic structure, content and distribution of oat β-glucan is also becoming more and more in-depth. The research results show that the various beneficial functions of β-glucan are affected by its structural characteristics, molecular weight, content, chain type and other factors[5] . The chemical structure of β-glucan in the seeds of different cereal crops is similar, with only a slight difference in the ratio of β(1→4) glycosidic bonds to β(1→3) glycosidic bonds in the molecule [6]. The basic structure of oat β-glucan is a linear polymer composed of β(1 → 3) glycosidic bonds and β(1 → 4) glycosidic bonds linked to β-D-glucopyranose units, and the β(1 → 3) bonds give β-glucan a certain degree of flexibility [7]. Zhang Juan et al. showed that the structural distribution of oat β-glucan, which is composed of β(1 → 4) and β(1 → 3), is not completely ordered, but also not a completely disordered arrangement [8]. About 90% of the glucose units are arranged in β(1→3) linked fiber trisaccharide and fiber tetrasaccharide units, and the rest of the structure is longer cellulose segments [9].

The physicochemical properties of oat β-glucan at the molecular scale, in particular its weight-average molecular weight, largely determine its solubility, viscosity, dispersibility and gelling properties[10], while the molecular weight-dependent solubility and viscosity are believed to be related to the biological functions produced by oat β-glucan[11]. Since the molecular weight of oat β-glucan is affected by the different processing methods used, the quality of the oats, agronomic measures, food shape, etc., its biological activity is also affected to varying degrees accordingly (see Table 1). Relevant studies have shown that different processing methods, such as excessive particle size, high temperatures, pressure, production environment and enzymatic catalysis, can affect the molecular weight and thus the content and biological activity of β-glucan in oats [1 2]. The molecular weights of β-glucans in different grains such as rye, barley, oats and wheat range from 2.1 × 103 to 1.1 × 103 g/mol, 3.1 × 103 to 2.7 × 103 g/mol, 65×103 ~3100×103 g/mol, 2 0 9 × 1 0 3 ~4 8 7 × 1 0 3 g/mol[1 3] . The molecular weight of β-glucan in oats is relatively large, which may be closely related to its various biological effects.

2. Beta-glucan content in oats

The beta-glucan content of oats is a starting point for the nutritional evaluation of oat foods, and requirements for its content have become an integral part of oat products and a trend [15]. The content of oat β-glucan is affected by several factors, such as the growing region, variety, and year. Among these factors, the variety has the greatest influence, followed by the growing region, and the year has the least influence [16]. In addition, the content of oat β-glucan can also be changed through certain agronomic measures. From the perspective of the few known factors that can affect the content of oat β-glucan, it is very instructive to increase the content of oat β-glucan by cultivating new varieties. Tian Zhi-fang and others found that the β-glucan content of new varieties of oats is higher, and that the β-glucan content of more oat varieties is between 3. 0% ~ 5.0% [17]. Current domestic and international research shows that there are significant differences in the β-glucan content of oat resources, and that there are also differences in the β-glucan content of oat resources in different ecological regions, planting areas and years (see Table 2). Zhang Haifang et al. found that different oat varieties and regional effects have a significant effect on oat β-glucan content, with a range of 4.75% to 7.12%, while the β-glucan content of oats in the same region does not vary greatly [18]. Therefore 75% ~ 7.12%, while the β-glucan content of oats in the same region does not vary greatly[18]. Therefore, developing oat varieties with high β-glucan content is also the direction of future development.

3 Biological functions of oat β-glucan

3.1 Cholesterol reduction

Ho et al. found that an average dose of oat β-glucan in the diet of 3.5 g/d can significantly lower LDL-C, non-HDL cholesterol and apolipoprotein B levels. They also found that the effect of oat β-glucan on LDL-C is related to the experimental design and intervention time. A large data analysis confirmed that the regulation of LDL-C by oat beta-glucan is inversely related to the baseline LDL-C level, but this is not the case for non-HDL cholesterol and apolipoprotein B. The mechanism by which oat β-glucan lowers cholesterol may be to limit the absorption of dietary cholesterol in the small intestine and the reabsorption of bile by forming a viscous substance in the small intestine, thereby reducing the concentration of TC and LDL-C in the blood serum [2 1] . Studies have also found that the mechanism by which oat β-glucan lowers blood lipids also includes up-regulating the activity of cholesterol 7-α-hydroxylase, thereby accelerating cholesterol degradation. At the same time, comparing the lipid-lowering effects of oatmeal and oat β-glucan, it was found that the oatmeal and extract with the best lipid-lowering effect are not from the same species, indicating that oats may also contain other substances with lipid-lowering properties[2 2] . For middle-aged men without a history of cardiovascular events and a 10-year risk of coronary heart disease of ≥5%, β-glucan may be cost-effective for preventing coronary heart disease events. Maintaining a daily intake of 3 g of oat β-glucan can reduce the incidence of myocardial infarction and first fatal coronary heart disease event[23].

3.2 Antioxidant

Du B et al. proposed that oat β-glucan has the ability to scavenge free radicals and reduce inflammation, and has a significant protective effect against severe oxidant-induced lipid peroxidation in blood or plasma [24]. Suchecka et al. found that in rats with LPS-induced colitis, those supplemented with oat β-glucan showed antioxidant activity in liver and gastric tissue, resulting in a reduction in ROS products [25]. Oat β-glucan has an indirect antioxidant effect in rats with 2,4,6-trinitrobenzenesulfonic acid-induced colitis [26]. In a study on rats fed a high-fat diet, oat beta-glucan was found to significantly reduce serum malondialdehyde levels, indicating that oat beta-glucan has a certain lipid antioxidant effect; and the serum superoxide dismutase (SOD) enzyme activity of rats in the high-fat group was significantly lower than that of the control group. experiments have shown that oat β-glucan can significantly increase the SOD activity of rats, thereby maintaining a dynamic balance between the body's oxidation and anti-oxidation systems, reducing the toxic side effects of free radicals, and protecting tissues and cells from damage caused by free radicals [2 7].

3.3 Hypoglycemic

In 1977, the US Food and Drug Administration (FDA) issued a statement that consuming oat foods for a certain period of time and reaching a threshold of oat β-glucan will have a hypoglycemic effect [28]. A meta-analysis found that T2DM patients who consumed 2.5 to 3.5 g of oats per day for 3 to 8 weeks could significantly lower fasting plasma glucose (FPG) and glycated hemoglobin levels, but had no significant effect on fasting plasma insulin (FPI) levels [29]. g for 3 to 8 weeks can significantly lower fasting plasma glucose (FPG) and glycosylated hemoglobin levels, but has no significant effect on fasting plasma insulin (FPI) levels [29]. Consuming bread enriched with 3 g/d of oat beta-glucan for 3 weeks can reduce insulin resistance in patients with T2DM.

A dose of about 0.6 g/d for more than 4 weeks can improve blood glucose levels in diabetic patients, and consumption of a low dose of oat beta-glucan for 12 weeks also has a metabolic promoting effect [30]. However, some studies have found that an 8-week intake of 3. 9 g of oat β-glucan-rich meals for 8 weeks had no diet-related effect on FPG, FPI or insulin resistance in T2 DM patients. The reason for this difference may be that the high viscosity of oat β-glucan is related to the attenuation of postprandial blood glucose and insulin response in T2 DM patients. Some studies have confirmed that Oat β-glucan exerts its hypoglycemic effect by forming a highly viscous environment in the intestines. High viscosity can delay gastric emptying, slow intestinal peristalsis, and slow the absorption of glucose in the small intestine. The viscosity of different oat β-glucans also varies greatly [3 1].

3.4 Modulating the intestinal flora

Oat beta-glucan has been shown to modulate the intestinal microbiota in humans, animals and in vitro fermentation systems, typically with a relative increase in bifidobacteria and lactobacilli [32]. The composition of the intestinal microbiota is now considered to be an important regulator of cholesterol and bile acid metabolism in the host. Oat β-glucan has an effect on the host intestinal flora, thereby affecting bile acid signaling, short-chain fatty acid signaling, and other cholesterol homeostasis regulatory factors, which is one of the mechanisms that plays an important role in maintaining cholesterol homeostasis in the body [33].

Zhang Wei et al. also found that oat β-glucan can significantly increase the abundance and diversity of the intestinal flora, as well as the ratio of the Firmicutes and Bacteroidetes phyla, in rats with diabetic nephropathy, which may be one of the mechanisms by which it delays diabetic nephropathy [34]. Some studies have shown that endogenous 1, 3 (4)-polyglucosanase treatment improves the fermentability of oat β-glucan. Oat β-glucan treated with the enzyme has similar effects to breast milk oligosaccharides. As a prebiotic, it stimulates the immune system, increases the relative abundance of immature dendritic cells and eosinophils, and reduces the production of pro-inflammatory cytokines [3 5]. Enzyme-treated oat beta-glucan has a beneficial effect on the composition of the microbiome in infants and is highly compatible with infant formula. Although it has not yet been used in infant formula, it may be used for supplementation.

4 Application of oat beta-glucan in foods

Singh Mukti et al. [3 6] mainly aimed to develop functional yoghurt. By blending 0 %, 0.1 %, 0.2 %, 0.3 %, 0.4 % and 0. 5% pure oat β-glucan powder  was added to the yogurt mixture. It was found that the addition of β-glucan could be as high as 0.3%, which is in line with nutritional guidelines and can also increase nutritional benefits without affecting the characteristics of the yogurt.

Rosburg Valerie et al. [37] found that β-glucan has a protective effect on bifidobacteria in yogurt when stored at low temperatures, and it also improves the mouthfeel and stability of yogurt. The use of oat β-glucan in gluten-free products has also been shown to have a positive effect, with good results in terms of texture, volume and sensory properties [38]. The use of oat beta-glucan in beverage products can not only increase the viscosity of the beverage, but also meet the health requirements approved by the FDA to reduce the risk of cardiovascular disease [39]. In addition, high-molecular β-glucan can also be used in cosmetics and has a variety of skin protection effects such as anti-wrinkle, anti-aging, and reducing external stimuli[40]. Oat β-glucan can also be added to sausages to improve their elasticity and chewiness, enhance their texture and nutrition[41].

5 Prospects

This paper describes the characteristics and biological activity of oat β-glucan from the molecular structure, content, and its various biological effects such as lowering cholesterol, reducing blood sugar, anti-oxidation, and regulating intestinal flora. It is hoped that it can provide a scientific basis for the development and exploration of a variety of new oat foods in the future. As scientific research on oat β-glucan deepens, it is expected to have better commercial prospects as a new functional food ingredient.

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