To construct standard maltose curve by DNS Method.

Maltose is a reducing sugar as it can reduce Fehling's and Benedict's reagents Maltose can be used as a standard for estimating reducing sugar in unknown samples.The standard curve for maltose is usually constructed using 3, 5-Dinitro salicylic acid (DNS) as the reagent. Maltose reduces the pale yellow coloured alkaline 3,5-Dinitro salicylic acid (DNS) to the orange- red coloured, 3 amino,5 nitro salicylic acid. Wave length is set to 540 nm because it is the region where orange-red colour absorbs. A series of solutions containing varying concentrations of maltose are prepared in test tubes and a known quantity of DNS is added to each. These test tubes are then heated on a water bath for few minutes and their optical densities are measured using a colorimeter. A graph is then plotted with amount of maltose on X axis and the observed optical density at Y axis. The plot thus obtained is called a standard maltose curve.

4. Steps for experiment : 

1. Pipette out standard maltose solution in the range of 0.2, 0.4, 0.6, 0.8 and 1 ml, into 5 separate test tubes.

2. Prepare a test tube containing blank solution also.

3. Add distilled water to each test tube and bring the volume up to 2ml.(including the test tube containing the blank solution)

4. Add 1 mL of DNS reagent to each tube and cover the test tubes with aluminum foil.

5. Heat the contents in the test tubes in a boiling water bath for 5 minutes.

6. After taking out the test tubes from water bath cool them to room temperature.

7. Then add 9ml distilled water to each test tube and mix well.

8. Take 1ml from each test tube into different cuvettes and place each cuvette in a calorimeter and record the intensity of dark orange red colour at 540 nm as the absorbance or OD.

9. Plot a graph with the amount of maltose on X axis Vs OD at 540nm on Y axis.

5. Observations : We get the maltose calibration curve as a straight line passing through the origin.