DisplayTitle

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

¹University of Toronto, Department of Nutritional Sciences, Toronto, ON. ²Agriculture and Agri-Food Canada, Food Research Program, Guelph. ³Corresponding author. E-mail: toshs@agr.gc.ca

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.