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.