Β-glucan Fractions Research Articles

Effect of the β-glucan from Lentinus edodes on colitis-associated colorectal cancer and gut microbiota

Colorectal cancer is the third most common cancer in the world, and therapies with safety are in great need. In this study, the β-glucan isolated from Lentinus edodes was successfully fractionated into three fractions with different weight-average molecular weight (Mw) by ultrasonic degradation and used for the treatment of colorectal cancer. In our findings, the β-glucan was successfully degraded with the Mw decreased from 2.56 × 106 Da to 1.41 × 106 Da, exhibiting the triple helix structure without conformation disruption. The in vitro results indicate that β-glucan fractions inhibited colon cancer cell proliferation, induced colon cancer cell apoptosis, and reduced inflammation. The in vivo results based on Azoxymethane (AOM)/dextran sulfate sodium (DSS) mouse model demonstrate that the lower-molecular weight β-glucan fraction showed stronger anti-inflammatory and anti-colon cancer activities by reconstructing intestinal mucosal barrier, increasing short chain fatty acids (SCFAs) content, regulating metabolism of gut microbiota, and rebuilding the gut microbiota structure with the increased Bacteroides and the decreased Proteobacteria at the phylum level, as well as with the decreased Helicobacter and the increased Muribaculum at the genus level. These findings provide scientific basis for using the β-glucan to regulate gut microbiota as an alternative strategy in the clinical treatment of colon cancer.

Food By-Products and Agro-Industrial Wastes as a Source of β-Glucans for the Formulation of Novel Nutraceuticals.

Food and agro-industrial by-products provoke a great environmental and economic impact that must be minimized by adding value to these wastes within the framework of circular economy. The relevance of β-glucans obtained from natural sources (cereals, mushrooms, yeasts, algae, etc.), in terms of their interesting biological activities (hypocholesterolemic, hypoglycemic, immune-modulatory, antioxidant, etc.), has been validated by many scientific publications. Since most of these by-products contain high levels of these polysaccharides or can serve as a substrate of β-glucan-producing species, this work reviewed the scientific literature, searching for studies that utilized food and agro-industrial wastes to obtain β-glucan fractions, attending to the applied procedures for extraction and/or purification, the characterization of the glucans and the tested biological activities. Although the results related to β-glucan production or extraction using wastes are promising, it can be concluded that further research on the glucans' characterization, and particularly on the biological activities in vitro and in vivo (apart from antioxidant capacity), is required to reach the final goal of formulating novel nutraceuticals based on these molecules and these raw materials.

New insight into the structure-dependent two-way immunomodulatory effects of water-soluble yeast β-glucan in macrophages

The immunomodulatory effects and signalling pathways of five water-soluble yeast β-glucan fractions (WYG1–5) with different molecular weights (Mw) and chain conformations were investigated in RAW264.7 macrophages. All five WYG fractions were shown to increase nitric oxide (NO) production, phagocytosis activity and cytokine secretion compared with the normal group. The incubation of cells with WYG for 2 h and then with lipopolysaccharide (LPS) for 24 h showed an inhibition of NO production, phagocytosis activity, cytokine secretion, and the expression of inducible nitric oxide synthase (iNOS) and cytokine mRNA compared with the LPS group. The results showed a two-way immunomodulatory effect of WYG on inflammatory factors, with the best effect for WYG-2 having a Mw of 2830 × 103 g/mol and spherical conformation. Furthermore, both mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-κB) signalling pathways were triggered in the two-way immunomodulation. This study reveals the structure-activity relationship and provides a pharmacological basis for controlling inflammatory disorders with WYG.

Different molecular sizes and chain conformations of water-soluble yeast β-glucan fractions and their interactions with receptor Dectin-1

Although β-glucan could bind to Dectin-1 to exert bioactivity, the influence of molecular size and chain conformation of β-glucan on its interaction with Dectin-1 is still unclear. This work investigated the molecular sizes and chain conformations of five water-soluble yeast β-glucan (WYG1–5) fractions as well as their interactions with Dectin-1 by fluorescence spectroscopy and microscale thermophoresis. Results revealed a spherical conformation for higher molecular weight WYG and a stiff chain conformation for smaller molecular weight WYG. The WYG and Dectin-1 interactions were in the order of WYG-2 > WYG-1 > WYG-3 > WYG-4 > WYG-5. The spherical WYG-2 exhibited the largest binding constant of 7.91 × 105 M1 and the lowest dissociation constant of 22.1 nM to Dectin-1. Additionally, the underlying interaction mechanism showed that it may be easier for spherical WYG with longer side chains to interact with receptor Dectin-1.

Influence of Yeast Products on Modulating Metabolism and Immunity in Cattle and Swine.

Simple SummaryDietary supplementation has been used in order to improve animal growth and health, and reduce the risk of disease for many years. Yeast and yeast products are a group of supplements that have broad applications in livestock production. These benefits include improving milk production, weight gain, and immunity. Recent studies suggest that yeast can have impacts beyond growth and health and may impact metabolism. Available energy is important for immune activation, and therefore any change in metabolism and energy availability may affect immune responses. This paper explores the effects of yeast on energy metabolism and how these changes may influence immune responses in cattle and swine.Nutritional supplementation has been used by livestock producers for many years in order to increase animal performance, improve animal health, and reduce negative effects associated with enteric and/or respiratory pathogens. Supplements such as yeast and yeast-based products have broad applications across many livestock production systems, including poultry, aquaculture, cattle, and swine and have been shown to benefit animal production at various stages. These benefits include improvement in milk production, weight gain and feed conversion, as well as immune function. Initial research into the mode of action for these effects has focused on stimulation of the immune system by the β-glucan fractions of yeast. However, emerging studies have revealed that some of the beneficial effects of yeast products may stem from altering metabolism, including the availability of glucose and fatty acids. These changes in metabolism, and potentially energy availability, may partially explain differences in immune function observed in yeast-supplemented livestock, as the energy demands of an activated immune system are extremely high. Thus, this paper explores the influence of yeast products on metabolism in cattle and swine, and how changes in metabolism and energy availability may contribute to improvements in immune function in supplemented animals.

Purified β-glucans of Different Molecular Weights Enhance Growth Performance of LPS-challenged Piglets via Improved Gut Barrier Function and Microbiota.

Simple SummaryBeta-glucan is currently under consideration as an alternative to in-feed antibiotics for the sustainable pig production industry in China. Modulating intestinal function by β-glucan treatment in young pigs is one potential way of decreasing disease susceptibility and presumably increasing growth performance. In the present study, as a newly developed commercial product, β-glucans have proved to modulate gut function, and have improved growth performance in lipopolysaccharide (LPS)-challenged piglets. The present study aimed to determine the mechanisms involved inβ-glucan of low and high molecular weight mediated growth alterations in weaned piglets. The results confirmed that β-glucans isolated from Agrobacterium sp. ZX09 could improve growth performance in weaned piglets and they showed intestinal modulatory properties via different mechanisms in regulating the mucosal barrier function and microbial populations between two different molecular weight β-glucans.This study investigated β-glucan derived from Agrobacterium sp. ZX09 with high (2000 kDa) and low (300 kDa) molecular weight (MW) to compare their effects on growth performance and gut function in LPS-induced weaned piglets. Changes in jejunal morphology, mucosal barrier function, microbial populations, and fermentation in the piglets were determined. Data showed that β-glucan prevented body weight loss in LPS challenged piglets. Supplementation with both β-glucan fractions improved jejunal morphology. Compared to low MW, β-glucan of high MW generally up-regulated transcripts of ZO-1, MUC1, and MUC2 in jejunal mucosa to a lesser extent. Mucosal D-lactate, diamine oxidase, and anti-oxidation index were effectively resumed in β-glucan treatment. Both β-glucan diets provoked the emergence of a balanced microbiota and a richer concentration of volatile fatty acids in the colon. The richest community of bifidobacterium and concentration of butyrate emerged after feeding β-glucan with high MW. Results suggested that the effect of Agrobacterium sp. ZX09 β-glucans on the gut-modulatory function is largely linked to their MW. Low MW β-glucan mainly improved the mucosal barrier function in the jejunum, while high MW β-glucan had profound effects on the microbial community and fermentation in the hindgut of piglets.

Proteinaceous Residue Removal from Oat β-Glucan Extracts Obtained by Alkaline Water Extraction.

Background: Wet methods of 1-3, 1-4 -β-D-glucan isolation from cereals differ mainly in the type of grain fraction used as raw material, the solid-liquid ratio of β-glucan in raw material vs. solvent used, and the type of aqueous solvent modification (alkali, neutral or acidic). All these factors impact the characterization of the residues finally found in extracts. Oat bran is a rich source of globulin fraction which can be transferred into the extracts, especially when a high pH is employed. Methods: A multi-stage (enzymatic and acidic) purification procedure was performed to remove the residues, especially starch and protein, from β-glucan isolates from oat of different molar mass. Pancreatin, thermostable α-amylase, amyloglucosidase, and papain were used for consecutive residue removal. Three levels of low pH = 4.5, 3.5 and 3.0 were also tested for effective protein precipitation. Results: The starch hydrolysis and liquefaction significantly facilitate the proteinaceous matter removal although papain usage showed an intensive unfavorable impact on β-glucan molar mass. Soluble protein content was significantly decreased after pancreatin and α-amylase treatment, while the significant reduction of amine nitrogen was noted after complete starch hydrolysis and a second acidification step. Conclusions: A complex procedure employing different enzymes is needed to successfully reduce the possibly bioactive residues in isolated oat β-glucan fractions.

Structure analysis of β-glucan in barley and effects of wheat β-glucanase

In this study, β-glucan in samples of sifted flour from six barley varieties was sequentially extracted with water and NaOH obtaining three fractions: water-extractable (WE), NaOH- extractable (NaE) and residual (Res). β-Glucan isolates were incubated with lichenase and oligomers released were analysed with high performance anion exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD). A higher ratio of 3-O-β-cellobiosyl-D-glucose (DP3) to 3-O-β-cellotriosyl-D-glucose (DP4) is reported in WE, NaE and Res fractions in variety SLU 7 (shrunken endosperm) compared to the other varieties, suggesting a more packed β-glucan structure. Water-extractable and water-unextractable β-glucan fractions were incubated with wheat extract and effects of wheat β-glucanase on the structure was assessed after lichenase digestion and analysis with HPAEC-PAD. Findings suggest that wheat β-glucanase manifests a selective hydrolysis towards β-glucan with lower DP3/DP4 ratio and that β-glucan of SLU 7 is composed of a population with higher DP3/DP4 ratio and hence with a more tighten structure which may be more resistant to enzymic action. Overall, the results obtained are of interest to characterise barleys differing in starch and dietary fibre composition, specifically shrunken endosperm barley SLU 7 in the perspective of its inclusion in the production of β-glucan enriched foods.

In vitro fermentation of oat β-glucan and hydrolysates by fecal microbiota and selected probiotic strains.

Emerging evidence suggested that the prebiotic ability of β-glucan was intimately related to its molecular weight (Mw ). However, the effect of oat β-glucan with differing Mw on gut homeostasis was inconsistent. Importantly, knowledge of the fermentation properties of oat β-glucan fractions was still limited. The present study aimed to evaluate the prebiotic potential of raw and hydrolyzed oat β-glucan during in vitro fermentation by fecal microbiota and selected probiotic strains. The results obtained showed that both oat β-glucan (OG) and hydrolysates (OGH) comparably promoted the growth of fecal Lactobacillus counts (P < 0.05). Importantly, OGH revealed greater fermentability compared to OG as denoted by lower pH value and higher short-chain fatty acid concentration (P < 0.05). Moreover, OGH was found to be more favorable to provide growth substrates for Lactobacillus helveticus R389 (LR389), Lactobacillus rhamnosus GG ATCC 53103 (LGG) and Bifidobacterium longum BB536 (BB536) than OG, and was preferentially utilized by LR389, LGG and BB536 as the sole carbon source. The results of the present study indicate that oat β-glucan hydrolysates could serve as a more promising material for developing novel symbiotic foods. © 2017 Society of Chemical Industry.

Immunomodulatory properties of oat and barley β-glucan populations on bone marrow derived dendritic cells

Specific structures of oat and barley β(1,3)(1,4)-glucans induced different in vitro immunomodulatory effects in bone marrow derived dendritic cells (BMDC) from TLR2/4 knock out mice. All barley β-glucan fractions induced larger amounts of cytokines in BMDCs than their oat equivalents. The particulate fractions of both glucans induced high amounts of cytokines, especially after sample homogenisation. The small particulate barley β-glucans induced more cytokines than the equivalent oat fraction, hence there are more features influencing the immunomodulatory properties of β-glucans than only the particle size. The soluble glucan fraction and heated suspension induced only low amounts of cytokines, but were different for the two β-glucans, indicating that molecular specificity matters for immunomodulation. Immunomodulatory activity is influenced by the insolubility of β-glucans, to which characteristics as particle size, granule conformation and particulate homogeneity are related. Consequently, sample preparation influences the immunomodulatory activity of β-glucans.

Purification, characterization and physiological significance of a chitinase from the pilei of Coprinopsis cinerea fruiting bodies.

We purified a chitinase from pilei extractions of Coprinopsis cinerea fruiting bodies by ammonium sulfate precipitation and CM Sepharose cation exchange chromatography. MALDI-TOF/TOF MS analysis characterized this purified chitinase as a putative class V chitinase, ChiB1. ChiB1 hydrolyzed colloidal chitin and chitosan, whereas it did not hydrolyze chitin powder. ChiB1 cleaved only pNP-(GlcNAc)2, rather than pNP-GlcNAc or pNP-(Glc-NAc)3, to release nitrophenol. ChiB1 preferably and progressively released (GlcNAc)2 from (GlcNAc)6 and digested (GlcNAc)6 to two molecules of (GlcNAc)3 in a small proportion, but did not split (GlcNAc)2, so it is an exochitinase. ChiB1 has an optimum temperature range of 35°C to 40°C and an optimum pH of 5.0. ChiB1 exhibited Km and Vmax values of 2.63 mgml(-1) and 2.31 μmolmin(-1)mgprotein(-1) for colloidal chitin, respectively. The ChiB1 gene, along with another putative endochitinase (class III chitinase gene), was expressed dominantly among eight predicted chitinase genes in the genome, and its expression level increased with the maturation of fruiting bodies. ChiB1 incubation released a large amount of soluble β-glucan fractions from alkali-insoluble cell wall fractions of C. cinerea fruiting bodies, thereby it may promote the degradation of cell walls in synergy with the β-1,3-glucanases during pileus autolysis.

Electrostatic separation combined with ultra-fine grinding to produce β-glucan enriched ingredients from oat bran

Electrostatic separation was studied in a dry fractionation diagram to obtain β-glucan-enriched fractions from oat bran preparations. Ultra-fine grinding at ambient or cryogenic temperature was needed to achieve good dissociation between the macronutrients of oat bran particles. Particles rich in β-glucan and starch were by electrostatic separation separated from particles rich in arabinoxylan. β-Glucan was only little enriched in the non-defatted bran fractions from 19.6 to 25.0%. In contrast, preliminary defatting by super critical carbon dioxide significantly improved the dissociation of particles during grinding and allowed enrichment of β-glucan to 42.2 or 48.4% after one or two successive electrostatic separation steps. The twice separated positive fraction, containing 48.4% β-glucan, was further fractionated by a combination of jet-milling and air classification, yielding up to 56.2% β-glucan concentration. The results point out the good potential of using electrostatic separation as a bran-fractionation method to produce nutritionally interesting food ingredients. Oat β-glucan has a widely accepted health claim related to cholesterol lowering, and has a great industrial applicability in functional foods and nutraceuticals. The high concentrations of β-glucan obtained with defatted material are of major interest from an industrial point of view, since this kind of ingredients can be used in applications where normal oat bran preparations cannot provide β-glucan at high enough concentration. In addition, the obtained β-glucan fractions retained their original molecular weight. The high β-glucan fractions had an appealing white colour and were well solubilised in hot water and in 0.1 M NaOH compared to their low β-glucan counter-fractions. Supercritical carbon dioxide extraction is a relatively costly method due to the long processing time (several hours per batch), but there are existing factories offering contract manufacturing. Lipid extraction and fractionation process can be economically feasible, especially when the fractions obtained are used in high-value applications. Ultra-fine grinding and electrostatic separation are energy intensive methods, but they enable enrichment of components without any liquids or solvents. These methods can be used to produce unique fractions which are not possible to obtain with conventional fractionation methods such as sieving and air classification. • Oat bran was fractionated into higher value components. • Defatting by super critical CO 2 improved the dissociation of particles in grinding. • Particles rich in β-glucan were separated from particles rich in arabinoxylan. • β-Glucan was enriched up to 48.4% in electrostatic separation. • Up to 56.2% β-glucan was obtained by jet-milling and air classification.

Integration of β-Glucan Fibre Rich Fractions from Barley and Mushrooms to Form Healthy Extruded Snacks

β-glucan is a commonly researched plant cell wall component that when incorporated into food products has been associated with cholesterol and glycaemic response reductions. This study focusses on β-glucan rich fractions from barley and mushroom used in the production of extruded ready to eat snacks. Inclusion of barley β-glucan rich fractions and mushroom β-glucan fractions at 10% levels increased the total dietary fibre content of extrudates compared to the control (P < 0.05). Product expansion increased with the introduction of both barley and mushroom fraction (P < 0.05) which in turn resulted in a reduction in product hardness (P < 0.05). In vitro digestion protocol illustrated that inclusion of barley and mushroom β-glucan rich fractions manipulated the starch digestibility profile and hence rate of glucose release during digestion compared to the control sample. This in turn resulted in a significant (P < 0.05) reduction in potential glycaemic response of the samples of between 20and 25% for barley β-glucan rich fractions and between 17 and 25% for mushroom β-glucan rich fractions. We conclude that the inclusion of these fractions could be utilised by the food industry to manipulate the glycaemic response of extruded snack products.

Modulation of Intestinal Inflammation by Yeasts and Cell Wall Extracts: Strain Dependence and Unexpected Anti-Inflammatory Role of Glucan Fractions

Yeasts and their glycan components can have a beneficial or adverse effect on intestinal inflammation. Previous research has shown that the presence of Saccharomyces cerevisiae var. boulardii (Sb) reduces intestinal inflammation and colonization by Candida albicans. The aim of this study was to identify dietary yeasts, which have comparable effects to the anti-C. albicans and anti-inflammatory properties of Sb and to assess the capabilities of yeast cell wall components to modulate intestinal inflammation. Mice received a single oral challenge of C. albicans and were then given 1.5% dextran-sulphate-sodium (DSS) for 2 weeks followed by a 3-day restitution period. S. cerevisiae strains (Sb, Sc1 to Sc4), as well as mannoprotein (MP) and β-glucan crude fractions prepared from Sc2 and highly purified β-glucans prepared from C. albicans were used in this curative model, starting 3 days after C. albicans challenge. Mice were assessed for the clinical, histological and inflammatory responses related to DSS administration. Strain Sc1-1 gave the same level of protection against C. albicans as Sb when assessed by mortality, clinical scores, colonization levels, reduction of TNFα and increase in IL-10 transcription. When Sc1-1 was compared with the other S. cerevisiae strains, the preparation process had a strong influence on biological activity. Interestingly, some S. cerevisiae strains dramatically increased mortality and clinical scores. Strain Sc4 and MP fraction favoured C. albicans colonization and inflammation, whereas β-glucan fraction was protective against both. Surprisingly, purified β-glucans from C. albicans had the same protective effect. Thus, some yeasts appear to be strong modulators of intestinal inflammation. These effects are dependent on the strain, species, preparation process and cell wall fraction. It was striking that β-glucan fractions or pure β-glucans from C. albicans displayed the most potent anti-inflammatory effect in the DSS model.

Cell Wall Polysaccharides of Candida albicans Induce Mast Cell Degranulation in the Gut.

We investigated Candida albicans-induced mast cell degranulation in vitro and in vivo. Cell wall fraction but not culture supernatant and cell membrane fraction prepared from hyphally grown C. albicans induced β-hexosaminidase release in RBL-2H3 cells. Cell wall mannan and soluble β-glucan fractions also induced β-hexosaminidase release. Histological examination of mouse forestomach showed that C. albicans gut colonization induces mast cell degranulation. However, intragastric administration of cell wall fraction failed to induce mast cell degranulation. We propose that cell wall polysaccharides are responsible for mast cell degranulation in the C. albicans-colonized gut.

Optimizing the Molecular Weight of Oat β-Glucan for in Vitro Bile Acid Binding and Fermentation

A previous study showed β-glucan with low molecular weight (MW, 1.56×10(5) g/mol) bound more bile acid and produced greater amounts of short-chain fatty acids (SCFA) than did β-glucan with high MW (Mn=6.87×10(5) g/mol). In the current study, β-glucan extracted from oat flour was fractionated into six different MW levels (high MW, 7.09×10(5); low level 1 (L1), 3.48×10(5); L2, 2.42×10(5); L3, 1.61×10(5); L4, 0.87×10(5); and L5, 0.46×10(5) g/mol) and evaluated to find the optimum MW affecting in vitro bile acid binding and fermentation. The β-glucan fractions with 2.42×10(5)-1.61×10(5) g/mol (L2 and L3) bound the greatest amounts of bile acid. After 24 h of fermentation, no differences were found in total SCFA formation among L1, L2, L3, and L4 fractions; however, the high MW and L5 MW fractions produced lower amounts of total SCFA. Thus, the optimum MW of β-glucan to affect both hypocholesterolemic and antitumorigenic in vitro effects was in the range of 2.42×10(5)-1.61×10(5) g/mol. This MW range also was the most water-soluble among the MWs evaluated.

In Vitro Bile-Acid Binding and Fermentation of High, Medium, and Low Molecular Weight β-Glucan

The impact of beta-glucan molecular weight (MW) on in vitro bile-acid binding and in vitro fermentation with human fecal flora was evaluated. beta-Glucan extracted from oat line 'N979-5-4' was treated with lichenase (1,3-1,4-beta-D-glucanase) to yield high (6.87x10(5) g/mol), medium (3.71x10(5) g/mol), and low (1.56x10(5) g/mol) MW fractions. The low MW beta-glucan bound more bile acid than did the high MW beta-glucan (p<0.05). If the positive control, cholestyramine, was considered to bind bile acid at 100%, the relative bile-acid binding of the original oat flour and the extracted beta-glucan with high, medium, and low MW was 15, 27, 24, and 21%, respectively. Significant effects of high, medium, and low MW beta-glucans on total SCFA were observed compared to the blank without substrate (p<0.05). There were no differences in pH changes and total gas production among high, medium, and low MW beta-glucans, and lactulose. The low MW beta-glucan produced greater amounts of SCFA than the high MW after 24 h of fermentation. Among the major SCFA, more propionate was produced from all MW fractions of extracted beta-glucans than from lactulose. In vitro fermentation of extracted beta-glucan fractions with different MW lowered pH and produced SCFA, providing potential biological function.

β-Glucan Fractions from Barley and Oats Are Similarly Antiatherogenic in Hypercholesterolemic Syrian Golden Hamsters

The cholesterol-lowering activities of oats and barley are commonly attributed to the beta-glucan fractions. Although beta-glucan is present in both grains and appears to be chemically similar, the effect of source on cholesterol-lowering activity has not been evaluated. In the present study, the antiatherogenic properties of beta-glucan concentrates from oats and barley were evaluated in Syrian golden F(1)B hamsters consuming a semipurified hypercholesterolemic diet (HCD) containing cholesterol (0.15 g/100 g), hydrogenated coconut oil (20 g/100 g) and cellulose (15 g/100 g). After a 2-wk lead-in period, control hamsters were fed the HCD, whereas experimental hamsters consumed HCD formulated to include beta-glucan (2, 4, or 8 g/100 g) by addition of beta-glucan concentrate prepared from oats or barley at the expense of cellulose. Compared with control hamsters, dose-dependent decreases that were similar in magnitude in plasma total and LDL cholesterol concentrations were observed in hamsters fed beta-glucan from either source at wk 3, 6 and 9. Compared with controls, liver cholesterol concentrations were also reduced (P < 0.05) in hamsters consuming 8 g/100 g oat or barley beta-glucan. In agreement with previously proposed mechanisms, total fecal neutral sterol concentrations were significantly increased (P < 0.05) in hamsters consuming 8 g/100 g barley or oat beta-glucan. Aortic cholesterol ester concentrations were significantly reduced (P < 0.05) in hamsters fed 8 g/100 g beta-glucan from barley or oats. Although aortic total cholesterol and cholesterol ester concentrations were significantly correlated with LDL cholesterol (r = 0.565, P < 0.004 and r = 0.706, P < 0.0001, respectively), this association could explain only half of the variability. This study demonstrated that the cholesterol-lowering potency of beta-glucan is approximately identical whether its origin was oats or barley.

Fractionation of Oat (1→3), (1→4)-β-D-Glucans and Characterisation of the Fractions

A commercial sample of oat β-glucan was fractionated through stepwise precipitation with ammonium sulphate to yield four fractions. These were analysed for apparent viscosity values, relative molecular weights using high-performance size-exclusion chromatography, and chemical structure by methylation analysis and analysis of water-soluble fragments released from the fractions by lichenase. Fractions exhibiting lower molecular size and decreased limiting viscosity values were precipitated at higher concentrations of ammonium sulphate. Methylation analysis indicated that in all fractions β-(1→3) and β-(1→4) linkages represented more than 90% of all linkages present. The β-(1→3) to β-(1→4) ratio in the fractions decreased with molecular size. β-glucan fractions with distinct physical and structural characteristics were obtained with the ammonium sulphate fractional precipitation technique.

Fractionation and viscometric characterization of a (1→3), (1→4)-β- d-glucan from oat, and universal calibration of a high-performance size-exclusion chromatographic system by the use of fractionated β-glucans, alginates and pullulans

A polydisperse sample of mixed-linkage (1→3), (1→4)-β- D-glucans from oat aleurone was fractionated by conventional size exclusion chromatography on semipreparative columns of Sepharose CL 4B and 6B to produce fractions of low polydispersity. The fractions were characterized by their intrinsic viscosities and their number-average molecular weight. The HPSEC-chromatograms of the β-glucan fractions suggested very narrow molecular weight distributions in all fractionated samples. From knowledge of the relative weights of the fractions and by assuming that each fraction was strictly monodisperse, the weight and number-average molecular weight of the unfractionated sample of β-glucan were determined to be 71 900 and 49 000, respectively, in reasonable agreement with the number-average molecular weight determined by osmometry (55 000). The Mark-Houwink-Sakurada viscosity equation for monodisperse β-glucans was determined for samples having molecular weights from 26 × 10 3 to 137 × 10 3 g/mol as [ η ] = 6.7 × 10 − 2 M ¯ n 0.75 (in ml/g) (20°C, 0.1 mol/dm 3 NaCl). The β-glucan fractions were further characterized by high-performance size-exclusion chromatography, and compared with commercially prepared pullulan fractions of low polydispersity and alginate fractions obtained in another study in this laboratory. The validity of the universal calibration procedure was tested with the three different polysaccharides, showing the same linear relationship between hydrodynamic volume ([η] × M) and elution volume for all three polysaccharides. The commercial pullulan samples seemed well-suited for calibration purposes.