I assume that by DNS reagent you mean an alkaline solution of Rochelle's salt (potassium sodium tartrate) and dinitrosalicylic acid (+other ingredients). Since you're lowering the pH of your sample I would assume that the tartrate dianion gets protonated and thusly potassium bitartrate precipitates. 

One should search for the role of Rochelle's salt in the DNS reagent and try to achieve the same role with another compound.

I think you mean dinitrosalicylic acid, as it is an acid, it will be a salt in basic and neutral media and therefore soluble but in acid, it becomes protonated and so it precipitates. You need to perform your reaction in  basic media. Maybe you could use a buffer or you will need to look for an alternative in acidic media.

Dear Preshanthan,

I think you need to adjust the pH using buffer such as sodium acetate.

Find in attached Research Article on:

Comparison of Two Methods for Assaying Reducing Sugars in the Determination of Carbohydrase Activities

Alexander V. Gusakov,1 Elena G. Kondratyeva,2 and Arkady P. Sinitsyn1, 2

International Journal of Analytical Chemistry

Volume 2011, Article ID 283658, 4 pages

doi:10.1155/2011/283658

You'll find in:

DNS Assay. An aliquot of the substrate stock solution (0.3 mL, 10mg/mL in 0.1M Na-acetate buffer) was mixed with 0.3mL of the enzyme solution (both solutions were preheated at 50◦C for 5min). After 10min of incubation at 50◦C, 0.9mL of the DNS reagent was added to the test tube and the mixture was incubated in a boiling water bath for 5min. After cooling to room temperature, the absorbance

of the supernatant at 540 nm was measured. The A540 values for the substrate and enzyme blanks were subtracted from the A540 value for the analyzed sample. The substrate and enzyme blanks were prepared in the same way as the analyzed

sample except that 0.3mL of the acetate buffer was added to the substrate (enzyme) solution instead of the enzyme (substrate) solution

Best wishes