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

The impact of oat ß-glucan concentration and molecular weight (MW) on gel properties was investigated. Mixed MW gels/viscous solutions at 3, 4, and 5% ß-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 (TP) was highest for 0:100 gels and decreased with the addition of HMW ß-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 ß-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 ß-glucan gels can be manipulated by adjusting the ratios of molecular weight fractions or addition of sugar for different applications.

Increasing the viscosity of oat ß-glucan beverages by reducing solution volume does not reduce glycaemic responses.

The soluble fibre (1 → 3)(1 → 4)-ß-D-glucan attenuates postprandial glycaemic responses when administered in solution. This attenuating effect is strengthened when solution viscosity is increased by increasing the ß-glucan dose or molecular weight (MW). The effect of varying solution viscosity by changing solution volume, without changing the ß-glucan dose or MW, on glycaemic responses was determined. A total of fifteen healthy subjects received six 50 g oral glucose beverages prepared with or without 4 g of high-MW (HMW, 580,000 g/mol) or low-MW (LMW, 145,000 g/mol) ß-glucan, with a beverage volume of 250 or 600 ml. Postprandial plasma glucose concentration was measured over 2 h, and the peak blood glucose rise (PBGR) and the incremental area under the glycaemic response curve (AUC) were calculated. Subjects served as their own controls. The physico-chemical properties of the beverages were measured to examine their relationship with glycaemic response results. The HMW ß-glucan beverage was more viscous and achieved greater reductions in PBGR than the glucose beverage with LMW ß-glucan (P < 0·05). At the same MW, the 250 and 600 ml ß-glucan beverages differed in viscosity (>9-fold difference) but not in PBGR (P > 0·05). No differences in AUC were detected among the beverages (P = 0·147). The effects of ß-glucan on glycaemic response were altered by changes in beverage viscosity achieved through changes in MW but not in volume. Therefore, ß-glucan dose and MW are the most vital characteristics for optimising the bioactivity of ß-glucan solutions with respect to glycaemic response.

Attenuation of glycemic responses by oat ß-glucan solutions and viscoelastic gels is dependent on molecular weight distribution.

Oat ß-glucan attenuates postprandial glycemic responses when solubilized to form viscous solutions. High molecular weight (MW) ß-glucan is associated with high solution viscosity, which is in turn associated with lower glycemic responses. However, low MW ß-glucan is also able to form viscoelastic gels. The effect of low (145,000 g mol(-1)) and high (580,000 g mol(-1)) MW ß-glucan presented as liquid drinks and gels on glycemic responses was determined. Healthy subjects (n = 15) consumed 50 g glucose drinks with no ß-glucan; 4 g low MW; or 4 g high MW ß-glucan; and gels containing 4 g low MW; 2 g low plus 2 g high MW; or 3 g high plus 1 g low MW ß-glucan. Overall, ß-glucan solutions elicited lower glycemic responses than gels. For gels, peak blood glucose rise (PBGR) decreased with increasing dose of high MW ß-glucan (r(2) = 0.976, P > 0.05), and PBGR for the gel with 3 g high-MW was lower than for the control (P < 0.05). However, ß-glucan gels retained glucose better than solutions under in vitro analysis. Observed effects were found to be related to the rheological properties of the foods. ß-Glucan solutions and not gels effectively attenuated in vivo glycemic responses.