In vitro starch digestibility

In vitro starch digestibility of the barley flours (non-heated and heated) of six different varieties and the eight different mixtures of potato starch with β-glucans were determined [19]. The enzyme for digestion was prepared with 0.9 g of pancreatin (Sigma-Aldrich) in 8 mL of distilled water and centrifuged at 1500×g for 10 min. The supernatant (5.4 mL) was mixed with 0.8 mL of diluted amyloglucosidase (89 U/mL, Megazyme International Co.). The enzyme solution was added with 0.5 mL of distilled water.

The six different barley flours (non-heated and heated), the mixtures of potato starch with β-glucans (heated), potato starch without β-glucan (non-heated and heated), and white bread (control) were digested as following: the sample was mixed with 10 glass beads (5 mm diameter), 2 mL of 0.05 M hydrochloric acid, and 10 mg of pepsin in 50 mL tube. The samples were incubated at 37 °C in a shaking water bath for 30 min. Four milliliter of sodium acetate buffer (0.5 M, pH 5.2) and 1 mL of enzyme solution were added to the tube at 1 min interval while the samples were incubated at 37 °C in a shaking water bath. Aliquots (100 µL) from the tube were taken at 0, 10, 20, 30, 60, 90, 120, and 180 min and 1 mL of 50% ethanol was added to each tube. These tubes were centrifuged at 800×g for 5 min. The glucose concentration of the supernatants (100 µL) was measured using d-glucose assay kit (Megazyme International Co.). Total starch hydrolysis was calculated as following: Total starch hydrolysis (%) = ((released glucose weight × 160/182)/(total starch weight in prepared solutions)) × 100.