Dextranase

The content of soluble dextran produced during fermentation by W. cibaria P9 was determined by an enzyme-assisted method using a mixture of dextranase (Sigma-Aldrich, Darmstadt, Germany) and α-glucosidase (Megazyme, Bray, Ireland) according to the method reported by Katina et al. [37 (link)]. dextranase from Chaetomium erraticum and α-glucosidase from Aspergillus niger were purchased from Sigma-Aldrich (Germany). About 100 mg of freeze-dried dough was placed in 10 mL centrifuge tubes with 3 mL of water/ethanol (50:50 v/v) solution at 100 °C for 5 min. Another 3 mL of aqueous ethanol solution was added; then, the mixture was centrifuged at 10,000× g for 10 min. A further sample cleaning was made by re-suspending and centrifuging the pellet in 5 mL aqueous–ethanol solution. The pellet was re-suspended in 4.5 mL of sodium citrate buffer 0.05 M (pH 5.5) and kept at 100 °C for 5 min, vigorously vortexing after 2 min. The solutions cooled before the addition of a mixture of dextranase (100 nkat/mL) and α-glucosidase (10 nkat/mL), reaching the final volume of 5 mL with a hydrolysis temperature of 30 °C for 48 h. The reaction was stopped by keeping the samples in a boiling water bath for 10 min, after which the glucose formed was quantified using a K-GLUC glucose kit (Megazyme, Bray, Ireland).