What Is the Extraction Method of Oat Beta Glucan Powder?

Dextran is a type of high-molecular compound made up of D-glucopyranosyl residues linked by α or β glycosidic bonds. It includes linear, branched and cyclic structures, and most of it is soluble in water, while some types are insoluble (such as bacterial gel polysaccharides). The properties of glucans vary depending on the chain conformation, isomer configuration, sequential arrangement of bonds, branch length and main chain structure. According to the configuration of glucan, it can be divided into α-glucan and β-glucan [1]. In terms of stereochemistry, the α-glucosidic bond is located along the axis, while the β-glucosidic bond is located at the equator in the chair conformation [2]. Beta-glucan is mainly derived from cereal grains (barley, oats, wheat, etc.), yeast, fungi, bacteria, corn husks, brown algae, cedar bark, etc. It also contains some beta-glucan, and its molecular weight is 2.1 × 103 ~ 2 × 106 Da [3].

It is estimated that the market value of β-glucan will reach 1.03 billion US dollars by 2024 [1], of which cereal β-glucan will reach 476.5 million US dollars (nearly 50%) [4]. Oat β-glucan is generally found in the subaleurone layer and endosperm cell walls of the grain. Among them, oat β-glucan (3% to 7%) is mostly found in the aleurone layer, especially the subaleurone layer, and the starch endosperm contains very little [5]. The excellent quality characteristics of oat β-glucan have made it a research hotspot at home and abroad. This paper briefly describes the quality characteristics of oat β-glucan and provides a detailed description and summary of the extraction and purification process of oat β-glucan over the years, with the aim of providing a scientific basis for in-depth research and comprehensive development of oat β-glucan.

1 Quality characteristics

Oat β-glucan is a high-molecular, unbranched, non-starch polysaccharide composed of glucosyl units linked β-(1→4) every 2 to 3 units by a β-(1→3) link. which contains about 70% β-(1→4 ) bonds and 30% β-( 1 → 3 ) bonds, with a molar ratio of 1.5 to 2.1 and a molecular mass of 6.5 × 104 to 3.1 × 106 Da. Its special molecular structure determines its good quality characteristics. as a soluble dietary fiber, has a good health effect on the human body [6-7]. Oat β-glucan is widely used in food and medicine due to its good water solubility, high viscosity, gelling and other functional properties. It is also stable under heat, acid and alkali conditions, and is often used as an emulsifier, thickener, stabilizer and natural preservative in the development of corresponding foods.

Studies have shown that high-purity oat β-glucan, as a structural modifier, has a significant effect on the physical, chemical and sensory properties of gluten-free yeast-fermented cakes. When used at a dosage of 66.12%, it can improve the specific volume, brightness, color difference and hardness of the cake [8]. A gel made from oat hulls rich in β-glucan can be used as a fat substitute to make high-quality low-fat beef burgers with a high β-glucan content [9]. Experiments have shown that adding 80 g/kg oat β-glucan fiber powder can make pasta have better water absorption and adhesion during cooking, and the color is similar to that of untreated cooked pasta [10]. In addition, oat β-glucan can also be used in the development of foods such as wheat bread, porridge, wheat noodles, low-fat beef patties, dairy products, and egg white pasta.

With consumers pursuing nutrition and health, the physiological health effects of oat beta-glucan, in addition to its quality improver properties, have gradually attracted the attention of researchers, and the corresponding physiological activities and mechanisms of action have gradually been proposed. Studies have shown that oat beta-glucan can stimulate the expansion of the population of micro-organisms with a worm-like shape, thereby exerting a probiotic effect on the cecum microflora. Oat β-glucan can also significantly promote lipid metabolism, reduce the proportion of plaques in the main artery, and regulate and improve the negative effects associated with high-fat/cholesterol-induced atherosclerosis [11].

It has been reported that oat beta-glucan has a significant effect in lowering low-density lipoprotein cholesterol and improving other cardiovascular disease risk factors [12]. At the same time, β-glucan can regulate postprandial blood glucose and insulin levels and can be used to prevent diabetes [13]. In addition, oat β-glucan also has good anti-cancer effects, anti-inflammatory effects, lowers cholesterol levels, regulates lipid metabolism, weight loss and treatment of obesity, lowers blood pressure, improves intestinal health, treats chronic kidney disease, prebiotic effects, antioxidant and antibacterial activity and other physiological activities.

2 Extraction process

Due to the good quality characteristics of oat β-glucan, a lot of work has been done on the extraction, separation and purification of oat β-glucan. With the advancement of technology, the pretreatment, extraction and purification processes of oat β-glucan have also been continuously updated (see Figure 1). From the treatment of materials, there are roughly two extraction methods: the dry method and the wet method. The dry extraction method mainly includes grinding and sieving to achieve the separation and concentration of glucan, but it requires a large number of separation steps, and the yield is usually low.

SIBAK-OV et al. [14] used ultra-fine grinding and electrostatic separation to obtain an oat enrichment with a β-glucan content of up to 56.2%, which is significantly higher than that of the traditional grinding and sieving method. Therefore, compared with traditional dry extraction, electrostatic separation may be a method to improve the yield of glucan. Wet extraction, i.e., solvent extraction, can be divided into (hot) water extraction, alkali extraction, enzymatic extraction, and subcritical extraction. These techniques can be used alone, in combination, or with auxiliary extraction, such as ultrasound, microwaves, or pulsed electric fields. Compared with the dry method, wet extraction has more influencing factors, such as the type and concentration of the solvent, temperature, time, pH, stirring, particle size, and various ingredients in the raw material.

2.1 Pretreatment

In order to improve the extraction rate of β-glucan, it is usually necessary to pretreat the raw material. Dry grinding and sieving can be used as a pretreatment process for wet extraction. In addition, pretreatments such as roasting, steaming, baking, extrusion, and homogenization can also affect the extraction rate of oat β-glucan. Studies have shown that compared with untreated samples, the extraction rate of oat β-glucan is highest after extrusion, followed by steaming and baking [15]. Wet extraction also requires degreasing and enzyme inactivation to further improve the extraction rate and purity. Commonly used degreasing solvents include petroleum ether, ether, ethanol, isopropanol, etc. In the process of degreasing with ethanol, controlling the temperature at 80 °C can rapidly inactivate endogenous β-glucanase, and also remove small molecular sugars, proteins and fat-soluble substances.

2. 2 Water extraction

Oat β-glucan is insoluble in organic solvents such as alcohol, ether or ketone, but is soluble in water, so it can be extracted with hot water. A study used hot water to extract β-glucan from oat bran, and the highest yield of β-glucan was obtained after drying, which was (5.3 ± 0.3)%. while the β-glucan yields from enzymatic, acid and alkaline methods were relatively low [16]. WANG et al. [17] used an aqueous extraction method to extract β-glucan from oat bran concentrate. The conventional aqueous extraction process produced a product containing 66% β-glucan, acidification (pH 3) before ethanol precipitation contains 69%, and the β-glucan content reaches 72.7% after phytate removal.

Wu Jia et al. [18] used hot water extraction-freeze-thaw cycle to extract oat β-glucan, without inactivating endogenous enzymes, extracted at 55 °C for 2 h, the extract was concentrated to a β-glucan mass fraction of 1%, and then frozen and thawed 3 times. The yield of β-glucan was 1.5%, and the purity was 92%.

It can be seen that although the extraction conditions of the water extraction method are relatively mild, the long extraction time leads to an increase in time costs, the large amount of extraction solvent used and the need for recovery leads to high energy consumption, and most importantly, the purity and yield of the product from simple water extraction are low, so it is often used only as a basic extraction method.

2. 3 Alkali extraction

Some acidic or high molecular weight β-glucans are not easily soluble in hot water but are soluble in dilute alkali solutions. Therefore, can be extracted with a certain concentration of NaOH solution or Na2 CO3 solution. CHAIYASUT et al. [19] used 1.0 mol/L NaOH solution to extract total glucan from oat samples, and the total glucan content in the obtained extract was (89 ± 4)%, of which β-glucan was (84 ± 4)%. RIMSTEN et al. [20] extracted β-glucan from oats and oat bran using carbonate (60 °C), 0.05 mol/L NaOH (room temperature), and hot water containing heat-resistant α-amylase (100 °C), the extraction rates of the two alkali β-glucans were 86%-98%, while those of the hot water extracts were 36% and 28%, respectively. One study used a dilute alkali solution for extraction. Under the optimal extraction conditions of an extraction solution with a pH of 10.9, a time of 1.9 h, a material-to-liquid ratio of 1:21 (g:mL), and a temperature of 85 °C, the yield of β-glucan was 4.36% [21].

Alkaline extraction has received relatively little research in recent years. Although the extraction yield is relatively high, it is accompanied by partial depolymerization of the molecule, which reduces the molecular weight of the β-glucan. In addition, alkaline extraction can cause increased contamination of the extract with protein and starch, which darkens the color and is not conducive to subsequent purification and decolorization.

2. 4 Enzyme extraction

Enzyme extraction uses the specificity of enzymes to decompose and remove impurities in the extract. It has been reported that the yield of oat gum using the enzyme method, alkali method and acid method is 3.74% to 5.14%, with the enzyme method having the highest yield (5.14%); The extraction rate of β-glucan was 82.1% to 86.8%, with the highest rate (86.8%) obtained by the enzymatic method and the lowest by the alkaline method, which may be due to the high removal rate of enzymes for starch and protein [22]. Similar research found that enzymatically extracted β-glucan has a high molecular weight, a high yield, good colloidal stability, and minimal protein content. The yield of β-glucan was 13.9%, while the yields of acidic and alkaline extraction were 6.97% and 5%, respectively [23]. NEHA et al. [24] used alkaline, acid, hot water method and enzyme method to separate β-glucan, of which the highest extraction rate was the enzymatic method using heat-resistant α-amylase and protease (86.7%), and it had the highest antioxidant and antibacterial activity.

Enzyme extraction is safer than chemical reagent extraction, does not pollute the environment, has a higher purity of the final product, and can replace some chemical reactions to make the extraction more efficient. The use of enzymes is often found in other extraction processes to further improve the yield and purity, so the use of biological enzymes for the extraction of oat β-glucan has good application prospects.

2. 5 Ultrasonic-assisted extraction method

Ultrasonic-assisted extraction makes use of its cavitation effect to cause local high temperature and high pressure in the extraction solution. In addition, the mechanical agitation effect of the ultrasonic waves is added to reduce the mass transfer resistance between the solid and liquid phases, thereby shortening the extraction time, increasing the extraction rate, and not damaging the activity of β-glucan. Some studies have optimized the process of extracting oat bran β-glucan by combining ultrasound and enzymatic methods. The conditions are a material-to-liquid ratio of 1:10 (g:mL), a water bath heating temperature of 75 °C, a heating time of 4 h, enzyme addition 1. 5%, enzymatic hydrolysis time 30 min, ultrasonic power 400 W, ultrasonic temperature 50 ℃, ultrasonic time 30 min, the yield of β-glucan was 5. 09% [25].

Su Chang et al. [26] studied the ultrasonic-assisted hot alkali water extraction of β-glucan from naked oats. The optimal process parameters were 5% naked oat slurry, 360 W ultrasonic pretreatment for 6 min, pH 8, and 50 ℃ water bath extraction for 60 min. The β-glucan content in the extract can reach 1153 μg/mL. Huang Yuyan et al. [27] used ultrasonic extraction, evaporation concentration, and repeated freezing and thawing to extract β-glucan from oat bran. When the liquid-to-material ratio was 1:20 (g:mL), the ultrasonic power was 500 W, the extraction temperature was 55 °C, time 50 min, the extraction solution was evaporated and concentrated to 4.0% by volume, and the β-glucan yield from oat bran was 6.0% after being frozen and thawed twice, with a purity of up to 82.3%. Liu Shaojuan et al. [28] determined that the optimal extraction process conditions for oat bran polysaccharides are: ultrasonic temperature 66 °C, pH 9.2, ultrasonic time 21 min, power 401 W. Under these process parameters, the average yield of polysaccharides is (7.48 ± 2.6)%.

Ultrasonic-assisted extraction is milder than traditional hot water extraction in terms of extraction conditions, with lower extraction temperatures, less water used, shorter times, and higher yields. However, it processes relatively little raw material, and too much raw material may result in excessive ultrasonic energy consumption and insufficient processing of the raw material.

2. 6 Microwave-assisted extraction

Microwaves can penetrate the interior of the grain to form an internal heat source. The selectivity of this heating causes the aleurone layer, subaleurone layer and endosperm cell walls to crack and split, shortening the extraction time of β-glucan while increasing its yield. Wang Shangyu et al. [29] optimized the microwave-assisted extraction process of oat bran β-glucan: the liquid-to-material ratio was 1:15 (g:mL), the microwave time was 4 min, the power was 640 W, and the temperature was 80 °C. The yield of β-glucan was 5.1%. Shen Ruiling et al. [30] extracted β-glucan from naked oat bran by microwave, and the yield of β-glucan was 8.31% under the conditions of a material-to-liquid ratio of 1:12 (g:mL), a microwave power of 720 W, an extraction time of 9 min, and a pH of 10.

Microwave-assisted extraction not only greatly shortens the extraction time and reduces solvent consumption, but also has a higher β-glucan extraction rate than traditional hot water extraction. However, the internal heating operation of microwaves is not easy to control, which can easily damage β-glucan and thus relatively reduce the extraction rate.

2. 7 Subcritical water extraction method

Subcritical extraction is an extraction technique using subcritical water as a solvent. subcritical water exhibits lower viscosity and higher diffusion coefficient than water, thereby increasing the diffusion rate into the sample matrix and accelerating the extraction of β-glucan [31]. Yoo et al. [32] extracted β-glucan from oat flour: extraction temperature 200 °C, solvent pH 4.0, extraction time 10 min, particle size 425 ~ 850 μm, the yield of β-glucan was (6. 98 ± 1. 17)%, and the extraction rate was 88. 08%, which was significantly higher than the hot water extraction rate (36. 62% ); the optimal process conditions for the pilot scale were: temperature 210 ℃, time 10 min,  the yield of β-glucan was (3.01 ± 0.27)%, and the extraction rate was 76.36%. DU et al. [33] used accelerated solvent extraction technology to extract β-glucan from bran, and the optimal extraction process parameters were: extraction time 9 min, extraction temperature 70 °C, 4 cycles, extraction pressure 10 MPa, and the yield of β-glucan under these conditions was (16.39 ± 0.3)%.

Compared with traditional solvent extraction, subcritical extraction of β-glucan has a higher yield, the extraction system and solvent system are more environmentally friendly, the extraction time is shorter, and the degradation loss of β-glucan is small, which is conducive to the development of industrial extraction processes.

2. 8 Fermentation method

The fermentation method for extracting oat β-glucan involves inoculating a bacterial solution into an oat culture medium, fermenting under suitable conditions, and then centrifuging the fermentation liquid to extract the β-glucan. Wu Di et al. [34] used three medicinal fungi (yellow umbrella, big cup umbrella, and grey tree mushroom) to extract oat β-glucan through two-way fermentation. and the yield is higher than that of unfermented oats.

Among them, the yield of the yellow umbrella fungus and oats is the highest (289 μg/mL) under the optimal conditions of two-way fermentation at a fermentation temperature of 28 °C, a liquid-to-feed ratio of 1:20 (g:mL), a pH of 5, and a fermentation time of 48 h. Liu Xinqi et al. [35] optimized the fermentation process for the extraction of β-glucan. The optimal process parameters were: a liquid-to-feed ratio of 1:6 (g:mL), inoculation with 0.05% highly active dry yeast, and fermentation at 32°C for 34 h, with a yield of (5.21 ± 0.02)%. compared with the traditional water extraction method, not only the yield is increased by 60.8%, but also it contains less protein. 97.81% can be removed by activated carbon adsorption, and the purity of β-glucan is as high as 91.21%, with an average molecular weight of 1.366 × 105 Da. Gu Feiyan [36] reported that the optimal fermentation conditions for the extraction of β-glucan from active dry yeast are: a liquid-to-feed ratio of 1:6 (g:mL), an inoculum of 0.05%, a fermentation time of 34 h, temperature 32 ℃, the yield of β-glucan was 5. 21%, and the yield and purity were 94. 96% and 91. 20%.

Compared with the traditional water extraction method, the fermentation method has higher β-glucan extraction rate and purity, and is relatively economical. However, the advantages of the fermentation strain screening and the separation and purification of oat β-glucan from the obtained mixed β-glucan all increase the extraction workload.

2. 9 Other

In addition to the above extraction methods, there are also some relatively less researched extraction methods and combined process technologies. KUREK et al. [37] used natural flocculants (chitosan, guar gum and gelatin) to extract and purify β-glucan from oats. The use of flocculants has relatively reduced the total amount of the extract, but it can effectively remove impurities such as protein and ash, and improve the purity of the extract. When the concentration of chitosan is 0.6%, the β-glucan content in the extract is the highest, at (79.0 ± 0.19)%. You Maolan et al. [38] used an ultrasonic-microwave synergistic method to extract β-glucan, and the optimal process parameters were as follows: ultrasonic power 250 W, ultrasonic time 20 min, microwave power 800 W, microwave time 3 min, liquid-to-solid ratio 1:25 (g:mL), the yield of β-glucan was 2.29%, which was 120.19%, 57.93% and 18.65% higher than that obtained by water extraction, ultrasonic extraction and microwave extraction, respectively.

Wang Chong et al. [39] used a synergistic method of ultra-high pressure and ultrasound to improve the yield of β-glucan. Under the conditions of an ultrasound power of 300 W, an ultrasound time of 15 min, an ultra-high pressure of 300 MPa, an ultra-high pressure time of 4 min, an aqueous extraction pH of 10, and a liquid-to-solid ratio of 1:18 (g:mL), the yield of glucan was 1.66%, which was 159.38%, 43.10% and 23.88% higher than the water extraction method, ultrasonic method and ultra-high pressure method, respectively. The above shows that the synergistic extraction process can not only significantly shorten the extraction time and improve the extraction efficiency, but also effectively improve the yield and purity.

From existing research, it is known that different extraction processes have a significant impact on the extraction rate, yield and purity of oat β-glucan. In addition, different oat varieties, qualities, growing environments, and pretreatment processes will also affect the β-glucan extraction rate, yield and purity to a certain extent. Therefore, it is necessary to comprehensively consider the relevant influencing factors in order to maximize the yield and purity.

3 Purification process

The β-glucan obtained from oats often contains components such as starch, protein, heteropolysaccharides, pigments and small molecules. Due to insufficient purity, it does not meet the requirements for actual production and use, so it is generally necessary to remove impurities to improve purity.

3.1 Removal of starch and protein

Most of the existing extraction processes for oat β-glucan (water extraction, alkali extraction, subcritical extraction) are carried out at relatively high temperatures, causing the starch to gelatinize and be extracted together with β-glucan, thus affecting the purity of β-glucan. In actual production, α-amylase is generally used to hydrolyze the starch into small molecules of dextrin, which are then hydrolyzed into small molecules of glucose by glucanase and removed by dialysis. PAPAGEORGIOU et al. [40] used heat-resistant α-amylase for treatment (90 °C, 3 h, pH 4.5), and almost no starch was detected in the final product.

In the crude β-glucan extract, protein is another major type of impurity besides starch. Compared to the removal of starch, there are more methods for removing protein, such as the Sevag method, the trifluoro-trichloroethane method, the trichloroacetic acid method, the enzyme method, the isoelectric point method, the enzyme-Sevag method, and the enzyme-isoelectric point method. Luo Yan [41] compared three protein removal methods for crude β-glucan (trichloroacetic acid method, Sevag method and papain method) and found that the papain method was the most effective, with a protein removal rate of up to 88.6% and a β-glucan retention rate of up to 91.3%.

HARASYM et al. [42] used an alkaline extraction method to obtain high and low molecular weight β-glucan components with contents of 76.7% and 87.1%, respectively. Proteins and starch impurities were removed by trypsin, heat-resistant α-amylase and isoelectric point precipitation (pH 4.5), and both components could be purified up to 97%; If the impurities are removed in succession by trypsin, heat-resistant α-amylase, amyloglucosidase and papain, the β-glucan content can be increased to 97.5% and 99.25%, respectively. Wang Zhenqiang et al. [43] used heat-resistant α-amylase (6 U, 40 min) to remove starch from the extract, and isoelectric precipitation (pH 4.5) to remove protein. The sugar content in the final product was 60.518%, and the residual protein content was 3.584%.

Starch and protein are the main impurities in the crude oat β-glucan extract. Among them, amylase deamylates starch and trypsin-isoelectric point method deproteinizes, which are often used in primary purification methods in domestic and foreign research. Compared with other methods, this method also has the highest removal rate and glucan retention rate.

3.2 Removal of pigments and small molecular substances

Pigments in the extract can affect the quality of the product, so decolorization is required. Activated carbon adsorption is often used to remove pigments, which can also remove proteins, and is not only effective but also simple to operate. In addition, diatomaceous earth, cellulose, H2 O2, macroporous adsorption resin, macroporous adsorption resin-activated carbon, ion exchange column (DEAE-cellulose), etc. can also be used. Among them, compared with activated carbon decolorization, the decolorization of β-glucan by macroporous adsorption resin has a higher retention rate. Jia Ying et al. [44] optimized the optimal decolorization process of D-201 resin for glucan: the temperature of the sample solution is 40 °C, pH 5, flow rate 0.5 mL/min, and the decolorization rate under these conditions is 67.8%, the loss rate of β-glucan is about 25%; the optimal decolorization process for XAD-7 resin is: sample solution temperature 40 °C, pH 6, flow rate 0.5 mL/min, decolorization rate up to 72.9%, β-glucan loss rate 4.3%. Considering both the decolorization effect and the β-glucan retention rate, the macroporous adsorption resin is the best for decolorization.

Small molecular substances and heteropolysaccharides in the extract can be removed by precipitation and membrane separation techniques. Organic solvents such as ethanol, acetone, isopropanol and ammonium sulfate are commonly used as precipitants. RYU et al. [5] used a Na2 CO3 solution (pH 10. 0) at 45 °C to extract oat β-glucan, The crude extract was then purified using 300 g/L (NH4)2SO4 and 50% (v/v) isopropanol, and the yield of β-glucan was 1.9%, with a purity of 78.8%. It has been reported that when extracted with water at a temperature slightly lower than the gelatinization temperature of starch, followed by enzymatic hydrolysis of the starch, the pH is adjusted to 4.0 to 4.5 to remove the protein, and finally precipitated with 80% (volume fraction) ethanol, the purity of the oat β-glucan obtained is 90.4% to 93.7%, with a molecular weight of (0.44 to 1. 10) × 105 Da [40]. Overall, ethanol precipitation has the best purification effect compared to several other precipitants. It not only effectively enriches glucan molecules, but also has the ability to deproteinize, degrease, and decolor.

Liu Huanyun et al. [45] obtained β-glucan powder with a yield of 6.25% and a purity of 75.56% from crude oat bran by water extraction, heat-resistant α-amylase deamylation, isoelectric point protein precipitation, and alcohol precipitation. Then ammonium sulfate was used for stepwise purification to remove the remaining heteropolysaccharides, and the purity of the final product could reach 90.66%. Dong Xingye [46] determined the optimal extraction method in an experiment analyzing the effect of water extraction and ultrasonic extraction on the yield of oat β-glucan. The average yield was (4.09 ± 0.04)%; the purification process was amylase to remove starch, trypsin-isoelectric point method to remove protein, AB-8 resin depigmentation, 60% ethanol precipitation of β-glucan, and the final total sugar content was 95.25%, of which β-glucan was 91.10%. It is proposed to further purify it by chromatography.

After the primary purification process, the purity of the oat β-glucan extract has reached a high level. In order to obtain a completely purified and single-component glucan preparation, methods such as chromatography are often required.

3. 3  Gradual purification

In order to obtain a highly pure, single-component β-glucan, the β-glucan extract obtained after primary purification must also be gradually purified in stages, most often using chromatography.

Yuan Jian et al. [47] used ammonium sulfate precipitation, DEAE Sepharose CL-6B anion exchange column chromatography, and Sepharose CL-4B gel filtration chromatography to purify β-glucan, obtaining two single components (free of nucleic acids, pigments, protein), with molecular masses of 4. 87 × 105 Da (purity 98. 57%) and 6. 13 × 104 Da (purity 97. 03%), respectively. Xie Haoyu et al. [48] used the alkali extraction and alcohol precipitation method to extract β-glucan. The crude extract was gradually purified by ammonium sulfate precipitation, anion exchange, and gel chromatography. The total sugar content and β-glucan content of the product were 96.88% and 94.91%, respectively. Wang Haibo et al. [49] obtained a semi-pure product of oat β-glucan (yield of about 1.8%) by deproteinization at isoelectric point, decolorization with an activated carbon column, removal of starch with α-amylase, and ethanol precipitation. The semi-pure product was then separated and purified by polyamide column chromatography and multiple ethanol precipitations to obtain a pure β-glucan product with a single component.

After purification, oat β-glucan meets the requirements of a single-component glucan preparation and can meet the high purity standards of food and pharmaceutical preparations. However, the consumption of chromatography columns or filter membranes during the purification process has also become an obstacle to large-scale industrial production.

4 Conclusion and outlook

As research into the properties and physiological activity of oat β-glucan intensifies, it is being increasingly used in food, cosmetics and medicine. However, the challenge of meeting the high purity requirements of β-glucan in food and especially in the pharmaceutical field must be addressed. Although there have been many reports on the extraction and purification of β-glucan, further research is needed in the following areas: (1) Most extraction and purification processes remain at the laboratory scale and lack industrial production processes.

It is recommended that a series of studies be carried out around the scale-up of existing processes; (2) Existing studies have shown that appropriate pretreatment can effectively improve the extraction rate, it is recommended that research be carried out to optimize the pretreatment process; (3) there are already some auxiliary or combined processes and emerging technologies, but they are still in their infancy, and it is recommended that emphasis be placed on developing combined processes and emerging technological methods (such as auxiliary methods such as microwaves, ultrasound, and pulsed electric fields, and emerging methods such as subcritical and supercritical). In addition, when optimizing the original process, all influencing factors should be considered as much as possible to obtain the best process parameters. Since more enzymatic methods are used in the separation and purification process, immobilized enzyme technology can be considered to extend the service life of the enzyme, reduce enzyme consumption and the separation process of the enzyme from the product, and minimize resource consumption. Achieving large-scale production with high yield and purity on an industrial scale is of great significance for improving the deep processing of oats and their by-products (oat bran, oat rice residue) and for the research and development of functional foods and medicines.

Reference:

[1]  VENKATACHALAMG ,ARUMUGAM S ,DOBLE M. Industrial pro- duction and applications of α/ β linear and branched glucans[J] . In- dian Chemical Engineer ,2020 :1 - 15.

[2]  KAGIMURA F Y ,DA CUNHA M A A ,BARBOSA A M ,et al. Bio- logical activities of derivatized D-glucans:A review [J] . International Journal of Biological Macromolecules ,2015 ,72 :588 - 598.

[3]  ZHU F M ,DU B ,XU B J. A critical review on production and indus- trial applications of beta-glucans [J] . Food Hydrocolloids ,2016 ,52 : 275 - 288.

[4]  BAI J Y , REN Y Y , LI Y , et al. Physiological functionalities and mechanisms of β-glucans[J] . Trends in Food Science & Technolo- gy ,2019 ,88 :57 - 66.

[5]  RYU J H ,LEE S ,YOU S ,et al. Effects of barley and oat β-glucan structures on their rheological and thermal characteristics[J] . Carbo- hydrate Polymers ,2012 ,89(4) :1 238 - 1 243.

[6 ]  CHANG S C ,SALDIVAR R K ,LIANG P H ,et al. Structures ,biosynthesis ,and physiological functions of ( 1 ,3 ; 1 ,4 ) -β-D-glucans [J] . Cells ,2021 ,10 (3 ) . DOI :10. 3390/cells 10030510.

[7 ]  MEJIA S M V ,DE FRANCISCO A ,BOHRER B. A comprehensive review on cereal β-glucan:extraction ,characterization ,causes of deg- radation ,and food application [ J] . Critical Review in Food Science Nutrition ,2020 ,60 (21 ) :3 693 - 3 704.

[8 ]  KARP S ,WYRWISZ J ,KUREK M A. The impact of different levels of oat β-glucan and water on gluten-free cake rheology and physico- chemical characterisation[J] . Journal of Food Science and Technolo- gy,2020 ,57 (10 ) :3 628 - 3 638.

[9 ]  SUMMO C , DE ANGELIS D , DIFONZO G , et al. Effectiveness of oat-hull-based ingredient as fat replacer to produce low fat burger with high β-glucans content[J] . Foods ,2020 ,9 (8 ) :1057.

[10 ]  PIWINSKAM ,WYRWISZ J ,KUREK M ,et al. Effect of oat β-glucan fiber powder and vacuum-drying on cooking quality and physi- cal properties of pasta [ J ] . CyTA-Journal of Food ,2016 , 14 ( 1 ) :101 - 108.

[11 ]  RYAN P M ,LONDON L E E ,BJORNDAHL T C ,et al. Microbiome and metabolome modifying effects of several cardiovascular disease interventions in apo-E - / - mice[J] . Microbiome ,2017 ,5 (1 ) :30.

[12 ]  HO H V ,SIEVENPIPER J L ,ZURBAU A ,et al. The effect of oat beta-glucan on LDL-cholesterol ,non-HDL-cholesterol and apoB for CVD risk reduction :a systematic review and meta-analysis of ran- domised-controlled trials [ J ] . The Beritish Journal of Nutrition , 2016 ,116 (8 ) :1 369 - 1 382.

[13 ]  BOZBULUT R , SANLIER N. Promising effects of β-glucans on glyceamic control in diabetes[J] . Trends in Food Science & Tech- nology ,2019 ,83 :159 - 166.

[14 ]  SIBAKOV J ,ABECASSIS J ,BARRON C ,et al. Electrostatic separation combined with ultra-fine grinding to produce β-glucan en- riched ingredients from oat bran[J] . Innovative Food Science & E- merging Technologies ,2014 ,26 :445 - 455.

[15 ]  KHAN M A ,AMIR R M ,AMEER K ,et al. Characterization of oat bran β-glucan with special reference to efficacy study to elucidate its health claims for diabetic patients[J] . Food Science and Tech- nology ,2021 ,41 (1 ) :105 - 112.

[16 ]  CLIMOVA A ,IBRAHIM M N G ,SALAMAHINA A ,et al. Application of extracted β-glucan from oat for β-carotene encapsulation [J] . Journal of Food Science and Technology,2021 ,58(7) :2 641 - 2 650.

[17 ]  WANG Y J , YANG L X , SONTAG-STROHM T. Co-migration of phytate with cereal β-glucan and its role in starch hydrolysis in- vitro[J] . Journal of Cereal Science ,2020 ,93 :6 :102933.

[18 ] WU J ,LIN X Y ,HUANG D H ,et al. Extraction of oat β-glucan by freeze-thaw method and structure characterization of the product [J] . Journal of Chinese Institute of Food Science and Technology , 2011 ,11 (4 ) :48 - 54.

[19 ]  CHAIYASUT C ,PENGKUMSRI N ,SIVAMARUTHI B S ,et al. Ex-

traction of β-glucan of Hericium erinaceus ,Avena sativa L. , and Saccharomyces cerevisiae and in vivo evaluation of their immunomod- ulatory effects [ J ] . Food Science and Technology ,2018 ,38 ( 1 ) :138 - 146.

[20 ]  RIMSTEN L ,STENBERG T ,ANDERSSON R ,et al. Determination of β-glucan molecular weight using SEC with calcofluor detection in cereal extracts[J] . Cereal Chemistry,2003 ,80 (4 ) :485 - 490.

[21 ]  LI N ,YAN Z C ,SUN Y L ,et al. Study on extraction technology and physicochemical properties of naked oat β-glucan [ J ] . Food Re- search and Development ,2021 ,42 (8 ) :81 - 86.

[22 ]  AHMAD A ,ANJUM F M ,ZAHOOR T ,et al. Extraction and characterization of beta-D-glucan from oat for industrial utilization[J] . International Journal of Biological Macromolecules ,2010 ,46 ( 3 ) :304 - 309.

[23 ]  LEKSHMI. R. BABU. Green extraction techniques ,structural analysis and antioxidant activites of β-glucan present in oats[ J] . Inter- national Journal of Latest Trends in Engineering and Technology , 2015 ,5 (4 ) .

[24 ]  NEHA M ,NEETU M ,PRAGYA M. Influence of different extraction methods on physiochemical and biological properties of β-glucan from Indian barley varieties[J] . Carpathian Journal of Food Science and Technology,2020 ,12 (1 ) :27 - 39.

[25 ]  LI M Z ,LU W X ,LI M L ,et al. Optimization on extraction process of oat bran β-glucan by ultrasonic combined with enzymatic method [J] . Guizhou Agricultural Sciences ,2020 ,48 (11 ) :91 - 95.

[26 ]  SU C , LIU B N , LIN Q. Extraction of β-glucan from hulless oat [J] . The Food Industry,2016 ,37 (8 ) :1 - 2.

[27 ]  HUANG Y Y ,CHAI X Y ,HE J ,et al. Ultrasonic assisted freeze- thaw extraction of β-glucan from oat bran [J] . Food Research and Development ,2021 ,42 (3 ) :68 - 72.

[28 ] LIU S J ,LIU H P ,ZHAO F ,et al. Optimization of ultrasonic-assis- ted extraction process of oat bran polysaccharide based on response surface methodology [ J] . Food Research and Development ,2017 , 38 (22 ) :70 - 75.

[29 ]  WANG S Y ,SHU J ,XIA W S. Microwave-assisted extraction of β - glucan from oat bran[J] . Science & Technology of Food Industry , 2005 ,26 (12 ) :143 - 144 ;171.

[30 ]  SHEN R L ,DONG J L ,WANG Z C. The Study of the microwave- assisted extraction of naked oat bran β-glucan [ J] . Chinese Agri- cultural Science Bulletin ,2006 (10 ) :316 - 320.

[31 ]  ZHANG J X ,WEN C T ,ZHANG H H ,et al. Recent advances in the extraction of bioactive compounds with subcritical water :A review [J] . Trends in Food Science & Technology,2020 ,95 :183 - 195.

[32 ]  YOO H U ,KO M J ,CHUNG M S. Hydrolysis of beta-glucan in oat flour during subcritical-water extraction [ J ] . Food Chem , 2020 , 308 :125670.

[33 ]  DU B ,ZHU F M ,XU B J. β-Glucan extraction from bran of hullless barley by accelerated solvent extraction combined with response surface methodology[J] . Journal of Cereal Science ,2014 ,59 ( 1 ) :

95 - 100.

[34 ]  WU D ,BING X ,WANG C T ,et al. Bidirectional fermentation of oat β-glucan and research of physical and chemical properties [ J ] . Food Research and Development ,2019 ,40(1) :184 - 193.

[35] LIU X Q ,HE X Z ,LIU J C ,et al. Study on optimization of extrac- tion process of barley bran β-glucan by fermentation and its physi- cochemical properties[J] . Science and Technology of Food Indus- try,2020 ,41(7) :49 - 54.

[36]  GU F Y. Extraction of β -glucan from highland barley and its appli- cation in cosmetics[ D ] . Shanghai :Shanghai Institute of Technolo- gy ,2018.

[37]  KUREK M A , KARP S ,STELMASIAK A ,et al. Effect of natural flocculants on purity and properties of β-glucan extracted from bar- ley and oat[J] . Carbohydrate Polymers ,2018 ,188 :60 - 67.

[38]  YOU M L ,QIN X L ,DUAN J J ,et al. Ultrasonic-microwave syner- gistic extraction of β-glucan from hull-less barley [ J ] . Food and Fermentation Industries ,2019 ,45(8) :178 - 183.

[39]  WANG C ,ZOU J W ,CHEN H J ,et al. Extraction of quinoa β-glu- can by an ultra-high pressure - ultrasonic wave synergy method [J] . Journal of the Chinese Cereals and Oils Association ,2020 ,35(6) :39 - 44.

[40]  PAPAGEORGIOU M ,LAKHDARA N ,LAZARIDOU A ,et al. Wa- ter extractable (1→3 ,1→4) -β-D-glucans from barley and oats:An intervarietal study on their structural features and rheological be- haviour[J] . Journal of Cereal Science ,2005 ,42(2) :213 - 224.

[41]  LUO Y P ,LI J L ,ZHANG X F. Optimization of microwave-assisted extraction technology of β-glucan from barleys [ J] . Farm Products Processing,2016(14) :35 - 38.

[42]  HARASYM J , ZYLA E , DZIENDZIKOWSKA K , et al. Protein- aceous residue removal from oat -glucan extracts obtained by alka- line water extraction[J] . Molecules ,2019 ,24(9) :16 :1729.

[43]  WANG Z Q ,JIA J W ,WANG H. Optimization and purification of oat gum extracted from oat bran and purity determination[J] . Food Research and Development ,2019 ,40(3) :125 - 130.

[44]  JIA Y ,CHANG Y N ,YU J Y ,et al. Study on decolorization technol- ogy of β-glucan from highland barley bran [ J ] . Food Industry , 2013 ,34(8) :107 - 110.

[45]  LIU H Y ,LI H L ,WEN Z Y. Optimization of process conditions of extracting β-glucan from naked oat bran [ J] . Food Science ,2008 , 29(3) :237 - 240.

[46]  DONG X Y. Study on extraction ,purification and properties of β - glucan from oat [ D ] . Harbin : Northeast Agricultural University , 2014.

[47]  YUAN J ,FAN Z ,WANG Y , et al. The isolation ,purification and composition analysis of β-glucan from wheat bran [ J] . Science & Technology of Food Industry,2014 ,35(15) :90 - 94.

[48]  XIE H Y ,HE S Y ,JIA D Y ,et al. Isolation ,purification and physi- co-chemical properties of highland barley beta-glucan [ J ] . Food Science and Technology,2016 ,41(1) :142 - 146.

[49]  WANG H B ,LIU D C ,WANG H Y ,et al. Study on advanced mo- lecular chain structure and solution behavior of oat beta-glucan [J] . Food Science ,2008 ,29(10) :80 - 84.