What kind of sugar is maltose Name a different test to detec

What kind of sugar is maltose? Name a different test to detect the presence of maltose. Do you expect the same result if you use sucrose instead of maltose in the DNS assay?

Solution

Maltose or malt sugar is present in germinating grains, in corn syrup, and is a partial hydrolysis product of starch. It is a disaccharide consisting of two glucose residues joined by a -1,4- glycosidic bond. It is a reducing sugar having a free aldehyde or keto group and can reduce Fehling\'s and Benedict\'s reagents.

Benedict\'s test give brick red precipitate in the presence of maltose, indicating that the carbohydrate is a reducing sugar. In case of presence of sucrose, no colour change results.

Osazone test is a confirmatory test for maltose. The solution of reducing sugar heated with phenyl hydrazine produces definite crystalline structures depending on the type of reducing sugar present. The reducing sugar maltose, gives sunflower shaped crystals of maltosazone, which can be observed under microscope. Sucrose, which is a non-reducing sugar does not form osazone crystals.

3,5-Dinitro salicylic acid (DNS) binds only to reducing sugars and cannot bind to non reducing sugars like sucrose. However, if sucrose is first hydrolyzed in an acid solution to glucose and fructose, this method,which is a modification of the original DNS method gives positive result.

Maltose, a reducing sugar, reduces the pale yellow coloured alkaline DNS to the orange- red coloured, 3- amino,5- nitro salicylic acid. The intensity of the colour depends on the concentration of maltose in the solution and is measured using a colorimeter at absorbance of 540nm wavelength.