Textural and Bile Acid-Binding Properties of Muffins Impacted by Oat β-glucan with Different Molecular Weights.
Sayar, S., Jannink, J. L. & White, P. J. (2011). Cereal Chemistry, 88(6), 564-569.
Water-soluble β-glucan (BG) extracted from a high-BG oat line was treated with different amounts of lichenase (1→3)(1→4)-β-D-glucanase) enzyme to yield three different molecular weight (MW) BG extracts. Low (LMW-BG, 157,000), medium (MMW-BG, 277,000), and high (HMW-BG, 560,000) MW BG extracts were added to plain muffin formulations at a level of 0.52% (0.42% in the batter, 0.52% in the resultant muffins) to investigate the effect of MW of BG on textural and bile acid (BA) binding properties of the muffins. In addition, treatments were prepared containing LMW-BG, MMW-BG, and HMW-BG extracts in amounts providing equivalent batter firmness as determined on a texture analyzer. Resultant BG concentrations (and per serving amounts) of these muffins were 1.36% (0.81 g/60 g muffin), 1.05% (0.63 g/60 g muffin), and 0.52% (0.31 g/60 g muffin), respectively; thus, the LMW treatment complied with a U.S. Food and Drug Administration health claim requiring 0.75 g of BG per serving. The firmness, springiness, and BA-binding capacity of the muffins were unaffected by the MW of BG. However, when added at the maximum limit for equivalent batter firmness, the LMW treatment was more firm and less springy than the HMW treatment. Furthermore, BA-binding capacities of LMW and MMW fractions tended to be greater than that of the HMW fraction when added at the maximum limit. These results add further evidence to the importance of fine-tuning BG structure to provide maximum health benefits while maintaining high product quality.
Impact of β-glucan and other oat flour components on physico‐chemical and sensory properties of extruded oat cereals.
Yao, N., White, P. J. & Alavi, S. (2011). International Journal of Food Science & Technology, 46(3), 651-660.
Whole oat flour, N979-5-2-4 (N979), IA95111 (IA95), ‘Jim’ and ‘Paul’ with β-glucan concentration of 8.6%, 7.6%, 5.3%, and 5.9%, respectively, was made into extruded breakfast cereal (EBC). EBC β-glucan had greater peak molecular weight than corresponding whole oat flour. Both whole oat flour and EBC from N979 and IA95 had greater peak viscosity (PV), as measured using a Rapid ViscoAnalyser, than that from Jim or Paul. Bile acid binding of EBC, correlated with total β-glucan concentrations and PV, was either similar or greater than that of corresponding whole oat flour. Jim EBC had the least expansion ratio, lowest brown colour and cereal aroma but greatest tooth packing values. Paul and N979 EBC, although different from each other in a few sensory attributes, had similar acceptability as judged from a consumer test, suggesting that oats with elevated β-glucan concentrations can be successfully incorporated into EBC with minimal processing alterations.
In vitro bile-acid binding and fermentation of high, medium, and low molecular weight β-glucan.
Kim, H. J. & White, P. J. (2010). Journal of Agricultural and Food Chemistry, 58(1), 628-634.
The impact of β-glucan molecular weight (MW) on in vitro bile-acid binding and in vitro fermentation with human fecal flora was evaluated. β-Glucan extracted from oat line ‘N979-5-4’ was treated with lichenase (1,3−1,4-β-D-glucanase) to yield high (6.87 × 105 g/mol), medium (3.71 × 105 g/mol), and low (1.56 × 105 g/mol) MW fractions. The low MW β-glucan bound more bile acid than did the high MW β-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 β-glucan with high, medium, and low MW was 15, 27, 24, and 21%, respectively. Significant effects of high, medium, and low MW β-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 β-glucans, and lactulose. The low MW β-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 β-glucans than from lactulose. In vitro fermentation of extracted β-glucan fractions with different MW lowered pH and produced SCFA, providing potential biological function.
Physicochemical properties and structural characterization by two-dimensional NMR spectroscopy of wheat β-D-glucan—comparison with other cereal β-D-glucans.
Cui, W., Wood, P. J., Blackwell, B. & Nikiforuk, J. (2000). Carbohydrate Polymers, 41(3), 249-258.
The first isolation, purification and characterization of a wheat β-D-glucan is reported. Alkaline extraction of wheat bran prepared by a novel pre-processing gave a non-starch polysaccharide fraction. Purification was carried out by hydrolyzing the arabinoxylans of this fraction with β-D-xylanase (T. Viride, EC 184.108.40.206), which had no effect on the molecular weight of the β-D-glucan. The structure of the purified wheat β-D-glucan was characterized by NMR spectroscopy, and additional structural detail was revealed by hydrolysis with (1→3)(1→4)-β-D-glucan-4-glucanohydrolase (lichenase, EC 220.127.116.11) and analysis of the oligosaccharide reaction products. Direct and long-range homo-(1H/1H) and hetero- (13C/1H) nuclear shift correlations were used to make complete assignments of both the 13C and 1H spectra as well as to confirm sequences and linkage sites. The 13C NMR spectrum of wheat β-D-glucan appeared identical to that of other cereal β-D-glucans, such as those from oat and barley. However, the ratio of 3-O-β-cellobiosyl- and 3-O-β-cellotriosyl-D-glucose obtained from wheat β-D-glucan by lichenase hydrolysis was significantly higher than ratios from other cereal β-D-glucans (approximately 4, 3 and 2 for wheat, barley and oat, respectively). The predominant molar proportion of trisaccharide (72.4%) from wheat β-D-glucan suggests that it will have a more regular structure than the other β-D-glucans, which might be responsible for its greater gelling ability and poorer solubility in water compared to other cereal β-D-glucans.
Macromolecular characterisation of three barley β-glucan standards by size-exclusion chromatography combined with light scattering and viscometry: an inter-laboratory study.
Christensen, B. E., Ulset, A. S., Beer, M. U., Knuckles, B. E., Williams, D. L., Fishman, M. L., Chau, H. K. & Wood, P. J. (2001). Carbohydrate Polymers, 45(1), 11-22.
Six (1→3)(1→4)-β-D-glucan standards (A–F) isolated from barley were analysed by size-exclusion chromatography (SEC) in five different laboratories with varying columns, solvent conditions and detector systems (low- and multi-angle light scattering and viscometry). Static (batch) measurements by capillary viscometry and laser light scattering were included. Fairly consistent results were obtained for the weight average molecular weights (Mw), radii of gyration (RG) and intrinsic viscosities [η], demonstrating that the β-glucans may serve as useful standards or reference materials in the study of cereal β-glucans. Average values for Mw were: A,E: 114,000 (±11%); B,C: 374,000 (±9%), D,F: 228,000 (±13%). Some inconsistencies regarding the polydispersity (Mw/Mn) could be ascribed to the influence of peak broadening in certain column/solvent systems. The study further demonstrated that individual researchers tended to use different processing parameters, especially refractive index increments (dn/dc), due to ambiguities in the literature or to differing experimental values. The need for consistent parameters and processing methods is clearly demonstrated.
Reducing beta-glucan solubility in oat bran muffins by freeze-thaw treatment attenuates its hypoglycemic effect.
Lan-Pidhainy, X., Brummer, Y., Tosh, S. M., Wolever, T. M. & Wood, P. J. (2007). Cereal Chemistry, 84(5), 512-517.
The viscosity of soluble fibers such as β-glucan depends on their concentration in solution and molecular weight (MW) distribution. We investigated whether freezing treatment of oat bran muffins affected the physicochemical properties of β-glucan, and its physiological effectiveness in lowering postprandial blood glucose response. A controlled range of β-glucan solubility was achieved by subjecting oat bran muffins containing two levels of β-glucan to repeated freeze-thaw temperature cycling. β-glucan solubilized by in vitro digestion extraction was measured by flow-injection analysis. MW distributions of β-glucan were analyzed using size-exclusion chromatography. β-glucan solubility decreased as the number of freeze-thaw cycles increased, while MW distribution of β-glucan decreased slightly. Peak blood glucose rise (PBGR) after fresh muffins (8 and 12 g of β-glucan/serving) was significantly lower than that after muffins (8 and 12 g of β-glucan/serving) treated with four freeze-thaw (FT) cycles (1.84 ± 0.2 vs. 2.31 ± 0.1 mmol/L, P = 0.007). Compared with the control whole wheat muffins, the reduction in incremental area under the glucose response curve (AUC) after fresh muffins (8 and 12 g of β-glucan/serving) was nearly twice that after 4 FT cycles (43.3 ± 4.4% vs. 27.0 ± 5.4%, P = 0.016). A significant inverse linear relationship was found between the log [concentration] of extractable β-glucan and PBGR (r2 = 0.85, P = 0.01), and AUC (r2 = 0.71, P = 0.03). The results show that reduction of β-glucan solubility in foods attenuates its physiological effectiveness in lowering postprandial glycemia.
In vitro fermentation of oat flours from typical and high β-glucan oat lines.
Kim, H. J. & White, P. J. (2009). Journal of Agricultural and Food Chemistry, 57(16), 7529-7536.
Two publicly available oat (Avena sativa) lines, “Jim” and “Paul” (5.17 and 5.31% β-glucan, respectively), and one experimental oat line “N979” (7.70% β-glucan), were used to study the effect of β-glucan levels in oat flours during simulated in vitro digestion and fermentation with human fecal flora obtained from different individuals. The oat flours were digested by using human digestion enzymes and fermented by batch fermentation under anaerobic conditions for 24 h. The fermentation progress was monitored by measuring pH, total gas, and short-chain fatty acid (SCFA) production. Significant effects of β-glucan on the formation of gas and total SCFA were observed compared to the blank without substrate (P < 0.05); however, there were no differences in pH changes, total gas, and total SCFA production among oat lines (P > 0.05). Acetate, propionate, and butyrate were the main SCFA produced from digested oat flours during fermentation. More propionate and less acetate were produced from digested oat flours compared to lactulose. Different human fecal floras obtained from three healthy individuals had similar patterns in the change of pH and the production of gas during fermentation. Total SCFA after 24 h of fermentation were not different, but the formation rates of total SCFA differed between individuals. In vitro fermentation of digested oat flours with β-glucan could provide favorable environmental conditions for the colon and these findings, thus, will help in developing oat-based food products with desirable health benefits.
Physicochemical properties of β-glucan in differently processed oat foods influence glycemic response.
Regand, A., Tosh, S. M., Wolever, T. M. & Wood, P. J. (2009). Journal of Agricultural and Food Chemistry, 57(19), 8831-8838.
To assess the effect of food processing on the capacity of oat β-glucan to attenuate postprandial glycemia, isocaloric crisp bread, granola, porridge, and pasta containing 4 g of β-glucan as well as control products with low β-glucan content were prepared. The physicochemical properties (viscosity, peak molecular weight (Mp), and concentration (C)) of β-glucan in in-vitro-digestion extracts were evaluated, and fasting and postprandial blood glucose concentrations were measured in human subjects. Porridge and granola had the highest efficacy in attenuating the peak blood glucose response (PBGR) because of their high Mp and viscosity. β-Glucan depolymerization in bread and pasta reduced β-glucan bioactivity. Pastas, known to have low glycemic responses, showed the lowest PBGR. The analyses of these products with previously reported data indicated that 73% of the bioactivity in reducing PBGR can be explained by Mp × C. Characterizing the physicochemical properties of β-glucan in bioactive foods aids functional food development.
Glycemic response to oat bran muffins treated to vary molecular weight of β-glucan.
Tosh, S. M., Brummer, Y., Wolever, T. M. & Wood, P. J. (2008). Cereal Chemistry, 85(2), 211-217.
Oat bran muffins, containing 4 or 8 g of β-glucan per two-muffin serving, were prepared with or without β-glucanase treatment to produce a range of β-glucan molecular weights from 130,000 to just over 2 million. Following an overnight fast, the glycemic responses elicited by the untreated and treated muffins was measured in 10 healthy subjects and compared with a control whole wheat muffin. Taken all together, the 4-g β-glucan/serving muffins reduced blood glucose peak rise (PBGR) by 15 ± 6% compared with the control. The 8-g β-glucan/serving muffins had a significantly greater effect (44 ± 5% reduction compared with the control, P < 0.05). The efficacy of the muffins decreased as the molecular weight was reduced from a 45 ± 6% reduction in PBGR (P < 0.05) for the untreated muffins (averaged of both serving sizes) to 15 ± 6% (P < 0.05) for muffins with the lowest molecular weight. As the molecular weight was reduced from 2,200,000 to 400,000, the solubility of the β-glucan increased from a mean of 44 to 57%, but as the molecular weight was further decreased to 120,000, solubility fell to 26%. There was a significant correlation (r2= 0.729, P < 0.001) between the peak blood glucose and the product of the extractable β-glucan content and the molecular weight of the β-glucan extracted.
Solution behavior of barley β-glucan as studied with asymmetrical flow field-flow fractionation.
Ulmius, M., Önning, G. & Nilsson, L. (2012). Food Hydrocolloids, 26(1), 175-180.
Physicochemical properties of cereal β-glucans, associated with beneficial health effects, are related to their solution behavior and possibly to their propensity to form aggregates. Such properties are often analyzed with methods that may influence the aggregates per se. In this paper, the effect of processing on solution behavior of pure barley β-glucan was studied using asymmetrical flow field-flow fractionation (AsFlFFF), a method which is capable of analyzing the present aggregates. Molar mass distributions were determined by in-line multi-angle light scattering and refractive index detectors. Unprocessed samples had a main fraction of aggregates with a weight-average molar mass of 2.8 × 106 g/mol. Microwave heating to 100°C reduced the largest aggregates, while heating to 121°C prominently decreased the molar mass. Frozen storage for 1 week did not influence the aggregation, but repeated freeze–thaw cycles changed the structure of aggregates in a way that suggests cryogelation. The influence of processing conditions on solution behavior might explain why differently processed food products containing β-glucan have given different health effects. Experiments with the aim to eliminate aggregates demonstrated that filtration (0.45 µm) prior to analysis resulted in disruption of the largest aggregates, indicating that these aggregates will not be detected when filtration is used. Dissolution in NaOH solution, one of few solvents reported to eliminate aggregates, resulted in retained molar mass. Using AsFlFFF to study the solution behavior of β-glucans is a gentle method to analyze subtle changes of physicochemical properties.