Please perform some literature searches to learn about the method, including its limitations.

It is an old, relatively simple chemical end-point analysis based method where aldehyde group of reducing sugar is oxidized in the presence of dinitrosalicylic acid. As the aldehyde group, in case of glucose, changes to carboxylic group at elevated temp, one nitro group of DNS is converted to amino group - giving you a reddish-brown color, which can be measured.

Here's a useful reference:

http://onlinelibrary.wiley.com/store/10.1002/bit.260260727/asset/260260727_ftp.pdf;jsessionid=8DD8F1AA9457B76E75EEA8060141EB82.f02t02?v=1&t=iu8nvqmb&s=6a2d6828e21e27b82c0a31cbf86c0ea471081da5

Thanks a lot Tausif, ur answer is very helpful =)