Reducing Beta‐Glucan Solubility in Oat Bran Muffins by Freeze‐Thaw Treatment Attenuates Its Hypoglycemic Effect

Abstract

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.

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

“…We modified the MW and solubility of oat b-glucan in extruded cereal products to provide a range of values consumed by subjects that we knew was large enough to elicit differences in glycemic response (21,27,28), and, thus, we believed would differentially affect serum cholesterol. We measured the viscosity of the b-glucan extracted from the test foods, but because viscosity is shear thinning (ie, the value decreases as the shear rate of measurement increases), measurement of the proportion of b-glucan solubilized (C) and its MW may be a more robust way to estimate bioactivity because MW and C are relatively insensitive to extrinsic factors.…”

“…We showed a role for viscosity in determining the blood glucose-lowering effect of soluble fibers in humans (20,25,26) and that food-processing methods that reduce the MW and solubility of oat b-glucan reduce its ability to lower blood glucose (21,27,28). Therefore, we also hypothesized that the LDL-lowering effect of oat b-glucan is related to its ability to increase the viscosity of the contents of the small intestine, which, in turn, is related to the MW and amount of b-glucan solubilized in the small intestine.…”

Oat β‐glucan increases postprandial cholecystokinin levels, decreases insulin response and extends subjective satiety in overweight subjects

“…However, b-glucan from barley, served as a hot cereal, produced a significant decrease in glucose with only 2 g of b-glucan in women [29]. All of the test meals here produced blunted glucose responses when compared to a similar study [30]. It was expected that the 43 g of available carbohydrate here would produce a greater elevation in blood glucose from baseline, particularly in the overweight/obese study sample.…”

Efectos del consumo del beta-glucano de la avena sobre el colesterol sanguíneo: una revisión

“…43 observaron que el almacenamiento por congelación de unas magdalenas con salvado de avena redujo más de un 50% la solubilidad del beta-glucano, lo que puede disminuir la solubilidad del mismo en el intestino y sus efectos bioactivos. Un reciente estudio ha mostrado que someter a unas magdalenas con beta-glucano de avena a una serie de ciclos de congelación (14 horas a -18 ºC) y descongelación (10 horas a temperatura ambiente) reduce progresivamente la solubilidad del beta-glucano, de forma que tras cuatro ciclos ésta puede disminuir en un 50% 44 .…”