Dilute and semi-dilute solution properties of (1→3), (1→4)-β-d-glucan, the endosperm cell wall polysaccharide of oats (Avena sativa L.)

Effect of hydrocolloids on starch digestion: A review

Rapidly digestible starch can increase postprandial blood sugar rapidly, which can be overcome by hydrocolloids. The paper aims to review the effect of hydrocolloids on starch digestion. Hydrocolloids used to reduce starch digestibility are mostly polysaccharides like xanthan gum, pectin, β-glucan, and konjac glucomannan. Their effectiveness is related to their source and structure, mixing mode of hydrocolloid/starch, physical treatment, and starch processing. The mechanisms of hydrocolloid action include increased system viscosity, inhibition of enzymatic activity, and reduced starch accessibility to enzymes. Reduced starch accessibility to enzymes involves physical barrier and structural orderliness. In the future, physical treatments and intensity used for stabilizing hydrocolloid/starch complex, risks associated with different doses of hydrocolloids, and the development of related clinical trials should be focused on. Besides, investigating the effect of hydrocolloids on starch should be conducted in the context of practical commercial applications rather than limited to the laboratory level.

Extraction and characterization of waxy and normal barley β-glucans and their effects on waxy and normal barley starch pasting and degradation properties and mash filtration rate

Interactions between β-glucan and starch influence the health benefits of barley-based foods and barley brewing performance. Here, we characterized β-glucans from waxy and normal barley varieties and compared the effects of different β-glucans on the pasting and degradation of waxy and normal barley starches as well as the filterability of mashes from unmalted waxy and normal barley. Waxy barley Zangqing18 β-glucan displayed more compact micrographic features, higher molecular weight, larger particle size, higher thermal decomposition temperature and lower rheological viscosity than normal barley Zangqing2000 β-glucan. β-Glucan not only significantly decreased the pasting viscosities of waxy and normal starches but also lowered the pasting temperatures and peak times of normal starch, likely by inhibiting granule swelling and disrupting the integrity of the continuous phase. β-Glucan also decreased in vitro digestion extent of starch and increased the resistant starch. The unmalted waxy barley had a mash filtration rate much faster than normal barley because starch and β-glucan in waxy barley were rapidly and completely digested and formed more open filter passages. The effects of β-glucan on starch properties varied with the types and contents of β-glucans, whilst the types of starches showed more significant effects. CHEMICAL COMPOUNDS STUDIED: β-Glucan (Pubchem CID: 439262); Amylopectin (Pubchem CID: 439207); Starch (Pubchem CID: 156595876).

Study of Selected Beverages with Β-Glucan from Oats and Barley on Physical Properties, Sensory Perception, Glycemic Index and Satiety

Over recent years, more and more products with β-glucan have appeared in the market. This study was conducted to determine the physical, sensory evaluation and glycemic index (GI) of selected popular beverages with β-glucan in the Malaysian market, which were Biogrow Oat BG22 (from oats) and Biolife Barley BG25 (from barley). The physical parameters measured were colour, viscosity, and total suspended solid. Sensory analysis was conducted on 30 subjects using the 7-point hedonic scale. Attributes assessed were colour, aroma, viscosity, sweetness and overall acceptance. A total of 10 subjects were involved in the determination of GI value of these beverages. A total of 25 g glucose was used as the reference. Test meals also contained 25 g available carbohydrate and all beverages were mixed with 250 mL water. Blood samples (finger prick) were taken every 15 minutes (first hour) and 30 minutes (second hour) for the duration of 120 minutes after the food sample consumption. Test protocol was based on ISO26642:2010. Blood glucose values were determined using glucometer. A total of 30 subjects were chosen for the determination of satiety scores. Labelled magnitude satiety scale was used to measure satiety scores before and after test beverage consumption. Subjects were required to assess their perception of fullness or hunger by marking on the labelled magnitude satiety scale every 15 minutes for the first hour and 30 minutes for subsequent 2 hour for a total of 180 minutes. The colour analysis showed that BG25 and BG22 were slightly yellow due to positive b* value. The BG22 was more viscous and do not contain any sugar compared to BG25. Blood glucose level after glucose intake reached optimum level (9.9 mmol/L) at 30 minutes while BG25 and BG22 reached optimum level at 45 minutes with the value 7.9 mmol/L and 6.4 mmol/L respectively. Significant difference was found for attributes aroma, viscosity and overall acceptance of the two products. Our study found, BG22 from oats were has better physical attributes and is better accepted by the panelists. However, it is suggested that both products be taken together with milk or soy to improve the taste. The GI for BG25 was 79 (high GI) while BG22 was 32 (low GI). The BG22 with lower GI is significantly more satiating than BG25 and perhaps can be a choice of beverage for people who are managing diabetes and obesity.

The solution properties of galactomannan after simulated digestion of guar fortified bread predict the extent of postprandial insulin reduction in healthy adult overweight subjects

Coil overlap occurs when random coil polysaccharides such as cereal beta-glucan or galactomannan in solution are abundant enough and large enough to entangle with one another to form networks. It was recently shown that this concept applied to in vitro digested cereal-based foods could predict the efficacy of the food to reduce postprandial glycaemia. In the current study we further investigate the role of coil overlap for prediction of glycaemic and insulinaemic responses using four guar fortified breads (10-15% wheat flour replacement level) with galactomannans of different weight-average molecular weight (M_w). The breads, including a wheat flour control, were tested in a randomised crossover study in 12 overweight adults. Addition of guar reduced postprandial serum insulin, but not glucose responses. The extent of postprandial insulin reduction correlated with the solution properties of galactomannan after in vitro digestion. A significantly greater reduction in insulin response was observed for two of the breads where the galactomannan M_w and concentration in solution after in vitro digestion was above coil overlap, in contrast to two other breads, which resulted in digests containing galactomannan below coil overlap and a significantly lower reduction of postprandial insulin. Further in vitro digestion experiments focusing on amylolysis of starch with kinetic modelling showed a greater proportion of slowly digested starch in breads with galactomannan above coil overlap than below. A combination of the molecular weight of dietary fibre in a food and its soluble concentration are key parameters explaining its physiological efficiency in the upper gastrointestinal tract.

Characterization of acid hydrolysates from barley β-glucan concentrate for their physico-chemical and rheological properties

The present study was aimed at assessing the influence of acid hydrolysis on the physicochemical and rheological properties of β-glucan concentrate. Barley β-glucan concentrate was subjected to acid hydrolysis for 30 and 60 min. The molecular weight and viscosity were observed to be a function of hydrolysis time and decreased in a duration-based approach. Significant reduction in water binding capacity and swelling power was observed after acid hydrolysis. Acid hydrolysis dramatically altered the flow properties and a Newtonian behavior was observed for HBG₆₀. The oscillatory measurements revealed enhanced visco-elasticity for HBG₃₀ solutions in comparison to its native counterpart and were greatly reliant on molecular weight and concentration. DSC measurements showed reduced thermal stability of acid hydrolysates in comparison to native β-glucan concentrate. Overall, this study provides useful information on the hydration, thermal and rheological behavior of β-glucan concentrates and could be helpful in optimizing the concentration of β-glucan concentrates in food formulations.

Rheological and NMR Studies of Cellulose Dissolution in the Ionic Liquid BmimAc

Solutions of two types of cellulose in the ionic liquid 1-butyl-3-methyl-imidazolium acetate (BmimAc) have been analyzed using rheology and fast-field cycling nuclear magnetic resonance (NMR) spectroscopy, in order to analyze the macroscopic (bulk) and microscopic environments, respectively. The degree of polymerization (DP) was observed to have a significant effect on both the overlap (c*) and entanglement (c_e) concentrations and the intrinsic viscosity ([η]). For microcrystalline cellulose (MCC)/BmimAc solutions, [η] = 116 mL g^-1, which is comparable to that of MCC/1-ethyl-3-methyl-imidazolium acetate (EmimAc) solutions, while [η] = 350 mL g^-1 for the commercial cellulose (higher DP). Self-diffusion coefficients (D) obtained via the model-independent approach were found to decrease with cellulose concentration and increase with temperature, which can in part be explained by the changes in viscosity; however, ion interactions on a local level are also important. Both Stokes-Einstein and Stokes-Einstein-Debye analyses were carried out to directly compare rheological and relaxometry analyses. It was found that polymer entanglements affect the microscopic environment to a much lesser extent than for the macroscopic environment. Finally, the temperature dependencies of η, D, and relaxation time (T₁) could be well described by Arrhenius relationships, and thus, activation energies (E_a) for flow, diffusion, and relaxation were determined. We demonstrate that temperature and cellulose concentration have different effects on short- and long-range interactions.

Texture and mouthfeel perceptions of a model beverage system containing soluble and insoluble oat bran fibres

Dietary fibre fortified products have increased in popularity as health-conscious consumers seek convenient ways to increase fibre intake. Fibres from wholegrains are particularly desirable inclusions in food products because of their proven physiological health-benefits. When fortifying beverages with fibre, however, the insoluble dietary fibre components present in wholegrains often contribute to unpleasant gritty sensations making the products unpalatable. Consequently, designing wholegrain-fortified beverages with sufficient fibre-content to make health related fibre claims is a major challenge in the food manufacturing industry. This work aims to take a systematic approach in identifying the texture/mouthfeel related sensory impact and interaction between two commercial oat fibre ingredients (Oatwell28XF® and Milled Oats) when added to a model beverage system. Eighteen samples were prepared containing either or both the ingredients, at varying levels, and were assessed by a trained panel using conventional sensory descriptive techniques. The results indicate that the two different oat bran fibres produced distinct mouthfeel perceptions which could be attributed to the varying soluble and insoluble fibre content of the samples. Insoluble dietary fibre concentrations above 2% (w/w) resulted in particle-related sensory properties chalkiness, dryness and particle perception, which dominated the overall mouthfeel and textural sensory perception of the samples. Samples with predominantly soluble β-glucan, resulted in perceptions of smoothness, sliminess and stickiness residue, while thickness, mouthcoating and cloying sensations were driven by total fibre concentration, irrespective of fibre solubility. This work provides a solid foundation for food manufacturers aiming to rationally design and develop nutritionally superior fibre-fortified beverages and is relevant to fibre content concentrations required for labelling/nutrition claims for consumer products in many developed nations.

Influence of oat components on lipid digestion using an in vitro model: Impact of viscosity and depletion flocculation mechanism

Depletion flocculation is a well-known instability mechanism that can occur in oil-in-water emulsions when the concentration of non-adsorbed polysaccharide exceeds a certain level. This critical flocculation concentration depends on the molecular characteristics of the polysaccharide molecules, such as their molecular weight and hydrodynamic radius. In this study, a range of analytical methods (dynamic shear rheology, optical microscopy, and static light-scattering) were used to investigate the interaction between lipid droplets and polysaccharides (guar gum and β-glucans) of varying weight-average molecular weight and hydrodynamic radius, and concentration. The aim of this work was to see if the health benefits of soluble fibers like β-glucans could be explained by their influence on the structure and digestibility of lipid emulsions. The apparent viscosity of the emulsions increased with increasing polysaccharide concentration, molecular weight, and hydrodynamic radius. Droplet flocculation was observed in the emulsions only at certain polysaccharide concentrations, which was attributed to a depletion effect. In addition, the water-soluble components in oat flakes, flour, and bran were extracted using aqueous solutions, to examine their impact on emulsion stability and properties. Then, the rate and extent of lipolysis of a sunflower oil-in-water emulsion in the presence of these oat extracts were monitored using the pH-stat method. However, the inhibition of lipolysis was not linearly related to the viscosity of the oat solutions. The water-soluble extracts of β-glucan collected from oat flakes had a significant inhibitory effect on lipolysis. The results of this study increase our understanding of the possible mechanisms influencing the impact of oat constituents on lipid digestion. This work also highlights the importance of considering the molecular properties of polysaccharides, and not just their impact on solution viscosity.

The impact of oat structure and β-glucan on in vitro lipid digestion

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The structure of oat tissue is an important factor for determining its influence on (in vitro) lipid digestion.

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β-glucan release from oat cell walls during digestion was not complete.

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Processing of oats affects the rate and extent of lipolysis.

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Viscosity is not the only factor affecting lipolysis.

Oat β-glucan has been shown to play a positive role in influencing lipid and cholesterol metabolism. However, the mechanisms behind these beneficial effects are not fully understood.

The purpose of the current work was to investigate some of the possible mechanisms behind the cholesterol lowering effect of oat β-glucan, and how processing of oat modulates lipolysis. β-Glucan release, and the rate and extent of lipolysis measured in the presence of different sources of oat β-glucan, were investigated during gastrointestinal digestion.

Only a fraction of the original β-glucan content was released during digestion. Oat flakes and flour appeared to have a more significant effect on lipolysis than purified β-glucan.

These findings show that the positive action of β-glucan is likely to involve complex processes and interactions with the food matrix. This work also highlights the importance of considering the structure and physicochemical properties of foods, and not just the nutrient content.

Impact of hydrothermal and mechanical processing on dissolution kinetics and rheology of oat β-glucan

Oat mixed-linkage β-glucan has been shown to lower fasting blood cholesterol concentrations due notably to an increase in digesta viscosity in the proximal gut. To exert its action, the polysaccharide has to be released from the food matrix and hydrated. The dissolution kinetics of β-glucan from three oat materials, varying in their structure, composition and degree of processing, was investigated by incubating the oats at 37°C over multiple time points (up to 72h). The samples were analysed for β-glucan content, weight-average molecular weight and rheological behaviour. Regardless of the materials studied and the processing applied, the solubilisation of β-glucan was not complete. Mechanical and hydrothermal processing led to differences in the viscosity flow curves of the recovered solutions, with the presence of particulates having a marked effect. This study revealed that the structure and processing methods applied to oat materials resulted in varied and complex rheological properties, especially when particulates are present.

Oat β-glucan: physico-chemical characteristics in relation to its blood-glucose and cholesterol-lowering properties

The water-soluble, mixed-linkage β-glucan, a form of soluble dietary fibre, is considered the main biologically active component responsible for the capacity of many oat products to lower postprandial glycaemia and fasting plasma cholesterol in human subjects. The present review discusses the physical and chemical properties of oat β-glucan that are considered important predictors of these beneficial metabolic effects. In vitro modelling and animal and human studies have provided compelling evidence showing that the ability of oat β-glucan to increase the viscosity of digesta in the gastrointestinal tract (GIT) is a primary determinant of its blood-glucose and cholesterol-lowering properties. Therefore, the chemical structure, molecular weight (MW), the rate and extent of dissolution and solution rheology of oat β-glucan are key factors in determining the physiological function of oat-containing foods. The structure and properties of oat β-glucan vary between species and varieties of oats, and are also affected by the growing and storage conditions and processing of oat grain. In addition, the extraction and analysis methods may also contribute to the variations in the structure, MW, hydration and solution rheology of β-glucan obtained from different laboratories. Recent work has demonstrated that β-glucan solubility in foods depends on the source of the material and processing conditions; solubility may also be subject to changes during food preparation and storage (such as freezing). In conclusion, both the amount and MW of β-glucan that are solubilised in the GIT need to be considered when assessing the blood-glucose and cholesterol-lowering properties of oat-containing foods.

Textural and Rheological Properties of Oat Beta-Glucan Gels with Varying Molecular Weight Composition

The impact of oat β-glucan concentration and molecular weight (MW) on gel properties was investigated. Mixed MW gels/viscous solutions at 3, 4, and 5% β-glucan with high molecular weight (HMW):low molecular weight (LMW) ratios of 0:100, 25:75, 50:50, 75:25, and 100:0 were evaluated. The 100:0 and 50:50 gels had the lowest tan δ values. The 50:50 gels had the highest storage moduli (G'), whereas 100:0 solutions did not gel. Peak melting temperature (T_P) was highest for 0:100 gels and decreased with the addition of HMW β-glucan. Hardness, at 40% compression, increased with concentration, and 25:75 and 50:50 gels were hardest at each concentration. Ordered microstructure, apparent in 0:100 gels, diminished with HMW β-glucan addition. Glucose addition resulted in lower tan δ values and firmer, harder gels compared to gels without glucose. Thus, the textural properties and melting profiles of β-glucan gels can be manipulated by adjusting the ratios of molecular weight fractions or addition of sugar for different applications.

Review of human studies investigating the post-prandial blood-glucose lowering ability of oat and barley food products

Oat and barley foods have been shown to reduce human glycaemic response, compared to similar wheat foods or a glucose control. The strength of the evidence supporting the hypothesis that the soluble fibre, mixed linkage β-glucan, reduces glycaemic response was evaluated. A search of the literature was conducted to find clinical trials with acute glycaemic response as an end point using oat or barley products. Of the 76 human studies identified, 34 met the inclusion and exclusion criteria. Dose response and ratio of β-glucan to available carbohydrate as predictors of glycaemic response were assessed. Meals provided 0.3-12.1 g oat or barley β-glucan, and reduced glycaemic response by an average of 48 ± 33 mmol · min/l compared to a suitable control. Regression analysis on 119 treatments indicated that change in glycaemic response (expressed as incremental area under the post-prandial blood-glucose curve) was greater for intact grains than for processed foods. For processed foods, glycaemic response was more strongly related to the β-glucan dose alone (r(2)=0.48, P<0.0001) than to the ratio of β-glucan to the available carbohydrate (r(2)=0.25, P<0.0001). For processed foods containing 4 g of β-glucan, the linear model predicted a decrease in glycaemic response of 27 ± 3 mmol · min/l, and 76% of treatments significantly reduced glycaemic response. Thus, intact grains as well as a variety of processed oat and barley foods containing at least 4 g of β-glucan and 30-80 g available carbohydrate can significantly reduce post-prandial blood glucose.

Beta glucan: health benefits in obesity and metabolic syndrome

Despite the lack of international agreement regarding the definition and classification of fiber, there is established evidence on the role of dietary fibers in obesity and metabolic syndrome. Beta glucan (β-glucan) is a soluble fiber readily available from oat and barley grains that has been gaining interest due to its multiple functional and bioactive properties. Its beneficial role in insulin resistance, dyslipidemia, hypertension, and obesity is being continuously documented. The fermentability of β-glucans and their ability to form highly viscous solutions in the human gut may constitute the basis of their health benefits. Consequently, the applicability of β-glucan as a food ingredient is being widely considered with the dual purposes of increasing the fiber content of food products and enhancing their health properties. Therefore, this paper explores the role of β-glucans in the prevention and treatment of characteristics of the metabolic syndrome, their underlying mechanisms of action, and their potential in food applications.

Rheological and microstructural investigation of oat β-glucan isolates varying in molecular weight

The rheological properties and microstructure of aqueous oat β-glucan solutions varying in molecular weight were investigated. The structural features and molecular weights (MW) were characterized by (13)C NMR spectroscopy and high performance size-exclusion chromatography (HPSEC), respectively. The microstructure of the β-glucans dispersions was also examined by atomic force microscopy (AFM). The samples with β-glucan content between 78 and 86% on a dry weight basis had MW, intrinsic viscosity ([η]) and critical concentration (c*) in the range of 142-2800×10(3)g/mol, 1.7-7.2dl/g and 0.25-1.10g/dl, respectively. The flow and viscoelastic behaviour was highly dependent on MW and on the concentration of the β-glucans dispersions. Pseudoplastic behaviour was exhibited at high concentrations and Newtonian behaviour was evident at low concentrations. At the same concentration, the viscosity was higher for higher MW samples. The Cox-Merz rule was applicable for the lower molecular weight samples at higher concentrations whereas the high molecular weight sample deviated at concentrations greater than 1.0%, w/v. The mechanical spectra with variation of both MW and concentration were typical of entangled biopolymer solutions. AFM images revealed the formation of clusters or aggregates linked via individual polymer chains scattered heterogeneously throughout the system. The aggregate size increased with the molecular weight of the samples investigated and has been linked to the rheological behaviour of the samples.

Physicochemical properties of oat β-glucan influence its ability to reduce serum LDL cholesterol in humans: a randomized clinical trial

BACKGROUND

Consumption of 3 g oat β-glucan/d is considered sufficient to lower serum LDL cholesterol, but some studies have shown no effect. LDL cholesterol lowering by oat β-glucan may depend on viscosity, which is controlled by the molecular weight (MW) and amount of oat β-glucan solubilized in the intestine (C).

OBJECTIVES

Our 2 primary objectives were to determine whether consumption of 3 g high-MW oat β-glucan/d would reduce LDL cholesterol and whether LDL cholesterol lowering was related to the log(MW × C) of oat β-glucan.

DESIGN

In a double-blind, parallel-design, multicenter clinical trial, subjects with LDL cholesterol ≥3.0 and ≤5.0 mmol/L (n = 786 screened, n = 400 ineligible, n = 19 refused, n = 367 enrolled, and n = 345 completed) were randomly assigned to receive cereal containing wheat fiber (n = 87) or 3 g high-MW (2,210,000 g/mol, n = 86), 4 g medium-MW (850,000 g/mol, n = 67), 3 g medium-MW (530,000 g/mol, n = 64), or 4 g low-MW (210,000 g/mol, n = 63) oat β-glucan/d (divided doses, twice daily) for 4 wk.

RESULTS

LDL cholesterol was significantly less with 3 g high-MW, 4 g medium-MW, and 3 g medium-MW oat β-glucan cereals than with the wheat-fiber cereal by 0.21 (5.5%; 95% CI: -0.11, -0.30; P = 0.002), 0.26 (6.5%; 95% CI: -0.14, -0.37; P = 0.0007), and 0.19 (4.7%; 95% CI: -0.08, -0.30; P = 0.01) mmol/L, respectively. However, the effect of 4 g low-MW oat β-glucan/d (0.10 mmol/L) was not significant (2.3%; 95% CI: 0.02, -0.20). By analysis of covariance, log(MW × C) was a significant determinant of LDL cholesterol (P = 0.003). Treatment effects were not significantly influenced by age, sex, study center, or baseline LDL cholesterol.

CONCLUSIONS

The physicochemical properties of oat β-glucan should be considered when assessing the cholesterol-lowering ability of oat-containing products; an extruded breakfast cereal containing 3 g oat β-glucan/d with a high-MW (2,210,000 g/mol) or a medium-MW (530,000 g/mol) lowered LDL cholesterol similarly by ≈0.2 mmol/L (5%), but efficacy was reduced by 50% when MW was reduced to 210,000 g/mol. This trial was registered at www.clinicaltrials.gov as NCT00981981.

Processing affects the physicochemical properties of beta-glucan in oat bran cereal

The tendency of mixed linkage oat beta-glucan to form viscous solutions is generally assumed to be related to its ability to lower serum cholesterol levels in humans. However, the association has not been clearly demonstrated. To conduct a clinical trial showing the relationship between LDL-cholesterol levels and viscosity, a series of extruded oat bran cereals were prepared in which the beta-glucan had a range of molecular weights and modified solubility. An extraction protocol using physiological enzymes at 37 degrees C was used to estimate the effect that the cereals would have on gut viscosity. By reducing the molecular weight from 1,930,000 to 251,000 g/mol, the apparent viscosity in the physiological extract dropped from 2900 to 131 mPa.s (at 30 s(-1)). Microscopic examination showed that as the extrusion conditions were made more severe, to cause depolymerization, the integrity of the cell walls was lost and beta-glucan dispersed throughout the cereal. Differences in the hardness and density of the extruded cereals were also evident as the molecular weight was reduced.

Solution properties of the xyloglucan polymer from Afzelia africana

In this paper we describe the solution properties of a new xyloglucan polysaccharide extracted from the African legume Afzelia africana Se. Pers. The polysaccharide is of high weight-average molecular weight (Mw), but application of the "pressure cell" method enabled a range of Mw fractions to be prepared. Results from the light scattering/intrinsic viscosity measurements on these fractions suggest that like other xyloglucans from tamarind and detarium it occurs in solution as a polymeric coil, with a small amount of excluded volume. Measurement of dilute and semidilute solution rheology suggests that, like these polymers, and the related galactomannan series, it forms viscous solutions at higher concentrations via entanglements.