.2.7. Analysis methods
Enzyme from koji was extracted with 50 volumes of water at room temperature for 6 h and filtered. The enzyme extract was centrifuged at 4000 rpm for 10 min, and the clear supernatant was used for enzyme assay. Filter paper activity and cellobiase activity were determined according to standard International Union of Pure and Applied Chemistry (IUPAC) procedures (Ghose, 1987). Filter paper activity was assayed by incubating a reaction mixture containing a strip of Whatman no. 1 filter paper (1×6 cm) immersed in 1 ml of 0.05 M citrate buffer and 0.5 ml of appropriately diluted enzyme solution at 50 °C for 30 min. One unit of filter paper activity (FPU) is defined as the amount of enzyme that forms 1 μmol glucose (reducing sugar as glucose) per minute under the assay conditions. Cellobiase activity was assayed in a reaction mixture containing 1 ml of 15 mM cellobiose solution (prepared in 0.05 M citrate buffer, pH 4.8) and 1 ml of appropriately diluted enzyme solution at 50 °C for 30 min. One unit of cellobiase activity (CBU) is the amount of enzyme that forms 2 μmol glucose per minute from cellobiose.
The reducing sugar was determined using the 3,5-dinitrosalicylic acid (DNS) method (Ghose, 1987). Glucose, xylose, cellobiose, arabinose, ethanol and glycerol were analyzed by HPLC (Syltech model 500 pump, USA) with an organic acid column (TRANSGENOMIC ICSep ICE-COREGEL 87H3 Column). Purified water was used as the mobile phase at a flow rate of 0.5 ml/min. The column temperature was fixed at 60 °C. The eluate was detected by a refractive index detector (Spectra-Physics 6040 XR RI detector).
The yield of enzymatic hydrolysis was calculated as follows:
Hydrolysis yield (%)=reducing sugar×0.9×100/polysaccharide in substrate.
At least three parallel samples were used in all analytical determinations, and data are presented as the mean of three replicates.