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Construction of Maltose Standard Curve by DNS Method




To construct a standard Maltose Curve.




 Maltose is a disaccharide made up of two subunits of glucose monomers. It is also called malt sugar. It is present in germinating grain, in a smaller amount  in corn syrup, and also is a product of the partial hydrolysis of starch. Maltose is considered as an important constituent in making fermented barley which is used to brew beer. Adding in a third unit of glucose produces a sugar known as maltotriose, while further units make it possible to produce maltodextrins.



α –D-glucopyranosyl,(1-4) D-glucopyranose


Maltose is a reducing sugar (those carbohydrates which have a free aldehyde or keto group can reduce Fehling's and Benedict's reagents are called reducing sugars). Maltose can be used as a standard for estimating reducing sugar in unknown samples. Constructing a standard curve / graph for maltose helps us to estimate concentration of reducing sugars present in an unknown sample and for determining the activity of amylase enzyme in forthcoming experiments.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.



The intensity of the colour is proportional to the concentration of maltose present in the solution [as per Beer Lambert's law (http://vlab.amrita.edu/?sub=3&brch=63&sim=156&cnt=1). This intensity change in colour is measured using a colorimeter as the absorbance at 540nm wavelength. 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.




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