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

In vitro assessment of oat β-glucans nutritional properties: An inter-laboratory methodology evaluation

The purpose of this inter-laboratory study was to test the repeatability and reproducibility of an in vitro method aimed at analyzing the physicochemical properties under physiological conditions of β-glucans from foods. After evaluating β-glucans molar mass and quantification methods using five β-glucan controls, four laboratories ran six oat-based products through in vitro digestion, measured β-glucans solubility and viscosity and molar mass of solubilized β-glucans. The determination of the molar mass of β-glucan controls, their viscosity in solution and β-glucans content in food samples exhibited relative standard reproducibility of 20.9-40.9%, 10.2-40.9% and 2.3-14.8%, respectively. After in vitro digestion, relative standard reproducibility ranged 12.1-60.0%, 12.2-64.3% and 9.7-36.3% for molar mass of extracted β-glucans, their viscosity and their solubility, respectively. Although the characterization methods were satisfactory within the limits of current technology, the in vitro extraction contributed significantly to the uncertainty of final characterization.

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.

Dietary fibre-rich oat-based products affect serum lipids, microbiota, formation of short-chain fatty acids and steroids in rats

Wistar rats (ten per group) were fed either an oat-free control diet or a dietary fibre-rich test diet containing 500 g oat-based products/kg for 6 weeks. The oat-based products, containing 4–128 g/kg resistant starch, 30–92 g/kg β-glucan and 122–304 g/kg total dietary fibre, were oat flour extrudate, flour/Novelose (commercial resistant starch) extrudate (80:20 w/w), oat bran, bran/Novelose extrudate (80:20 w/w) and autoclaved oat flour. Serum total cholesterol decreased in the groups fed flour, flour/Novelose and bran/Novelose (P<0·05). In most of the test groups, count numbers of bifidobacteria were higher (P<0·001) and of coliforms were lower (P<0·05). The mass of the caecum walls and contents was greater in groups fed Novelose- and bran-containing diets (P<0·005). In all the test groups, pH values were lower in the intestinal contents (P<0·001), and caecal concentrations of acetate (P<0·001), propionate (P<0·05), butyrate (P<0·005) and total SCFA (P<0·001) were higher. The lowest concentrations of steroids were found in rats fed the autoclaved flour. In the other test groups, more bile acids appeared in the caecal (P<0·001) and colonic contents (P<0·005), as well as in the faeces, at week 6 (P<0·001). The highest bile acid excretion was found after feeding bran-containing diets. In the intestinal contents of all the test groups, more primary bile acids (P<0·001) appeared than in the control group. The excretion of steroids increased within the experimental period. Using extrusion technology, dietary fibre-rich oat-based products, which have beneficial physiological effects in rats, can be produced. Oat flour and bran are excellent sources for the preparation of directly edible oat products. Their nutritional properties can be further improved by the addition of resistant starch.

Solution and conformational properties of wheat beta-D-glucans studied by light scattering and viscometry

The solution properties of wheat beta-glucan were investigated by light scattering and viscometric methods. The hydrodynamic radius (R(h)), weight average molecular weight (M(w)), radius of gyration (R(g)), and the second virial coefficient (A(2)) of wheat beta-glucan were determined by both dynamic and static light scattering methods, whereas the critical concentrations (c) of the solution were derived from [eta] via viscometric method. The structure sensitive parameters, rho (1.52-1.62), the conformation parameter nu (0.62), and the Mark-Houwink-Sakurada exponents alpha (0.78) confirmed the random coil conformation of wheat beta-glucan in 0.5 M NaOH solution. The characteristic ratio (4.97) was obtained by the random flight model, and the statistical segment length (8.83 nm) was derived from the wormlike cylinder model. It was found that the wormlike cylinder model could explain the chain stiffness better than the random flight model, which suggested an extended random coil conformation of wheat beta-glucan in 0.5 M NaOH solution. The study also revealed that the structure feature of wheat beta-glucan; that is, the higher trisaccharide-to-tetrasaccharide ratio contributed to the stiffer chain conformation compared with other cereal beta-glucans.

Size-exclusion chromatographic determination of beta-glucan with postcolumn reaction detection

Using the specific interaction of beta-glucan with calcofluor dye as a detection method for size-exclusion chromatographic analysis, very simple direct extractions can be used for sample preparation. Either fluorescence or UV detection is employed. The calibration graphs are linear between 200 and 20 mg/l, although much more sensitive analyses are possible. The response remained independent of relative molecular mass in the range studied (1.7 x 10(6)-1.85 x 10(5)). Results for barley and malt show good correlation with those obtained by flow-injection analysis using calcofluor.