Reducing beta-glucan solubility in oat bran muffins by freeze-thaw treatment attenuates its hypoglycemic effect

The viscosity of soluble fibers such as beta-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 beta-glucan, and its physiological effectiveness in lowering postprandial blood glucose response. A controlled range of P-glucan solubility was achieved by subjecting oat bran muffins containing two levels of beta-glucan to repeated freeze-thaw temperature cycling. (beta-Glucan solubilized by in vitro digestion extraction was measured by flow-injection analysis. MW distributions of P-glucan were analyzed using size-exclusion chromatography. beta-Glucan solubility decreased as the number of freeze-thaw cycles increased, while MW distribution of beta-glucan decreased slightly. Peak blood glucose rise (PBGR) after fresh muffins (8 and 12 g of (beta-glucan/serving) was significantly lower than that after muffins (8 and 12 g of beta-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 (beta-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 P-glucan and PBGR (r(2) = 0.85, P = 0.01), and AUC (r(2) = 0.71, P = 0.03). The results show that reduction of P-glucan solubility in foods attenuates its physiological effectiveness in lowering postprandial glycemia.