2.3.1. Dinitrosalicylic Acid Method (DNS)

DNS reagent was prepared by dissolving dinitrosalicylic acid (0.2 g, 0.88 mmol), phenol (0.04 g, 0.42 mmol), sodium thiosulfate (0.01 g, 0.04 mmol) and sodium-potassium tartrate (4.0 g, 14.2 mmol) in 10 mL of NaOH 2% (W/V). Distilled water was added to this solution to a final volume of 20 mL.

For determination of reducing sugars, 2 mL of DNS reagent and 500 µL of distilled water were added to 500 µL of enzymatic reaction sample. The mixture was brought to a boil for 5 min and left to cool at RT. The absorbance was measured at 540 nm in a Shimadzu UV-1601 spectrophotometer.

The concentration of reducing sugars produced was calculated by comparison with the previously constructed calibration curve.
