Biomolecules Test - 5

Maltose can be produced from starch by hydrolysis in the presence of the  enzyme  diastase. It can be broken down into two glucose  molecules  by  hydrolysis. In living  organisms, the enzyme maltase can achieve this very rapidly. In the laboratory, heating with a strong acid for several minutes will produce the same result.

Sucrose or cane sugar is the commonest of the disaccharides. It has the molecular formula C₁₂ H₂₂ O₁₁ . It does not form a phenylhydrazone or exhibit carbonyl properties. On hydrolysis with dilute acids, it yields one molecule of D-(+)-glucose and one molecule of D-(—)-fructose. It is not a reducing sugar. 

Glucose and fructose are functional isomers of each other Because they have same molecular formula that is C₆ H₁₂ O₆ But different functional group in their chemical formula. Glucose has aldehyde group while fructose has ketone as functional group.

Lactose : The sugar found naturally in milk, it is a disaccharide composed of one galactose unit and one glucose unit; sometimes called milk sugar.

Because it is the chemical property of aliphatic aldehyde to give red precipitate with fehling solution.

RCHO + 2 CuO ----------->Cu₂ O. + RCOOH

Fehling reagents is aq. alkaline CuSO₄ solution along with Rochelle salt Na-K tartrate.
And glucose molecule consists of aldehydic group at first position and hence it is also a aldehyde and thus give this characteristic test.

Fructose is an important ketohexose. It is obtained along with glucose by the hydrolysis of disaccharide, sucrose. The two monosaccharides are joined together by an oxide linkage formed by the loss of a water molecule. Such a linkage between two monosaccharide units through oxygen atom is called Glycosidic Linkage.

Glucose gives silver mirror test with Tollens reagent. It shows the presence of aldehyde group.
Also, mild oxidation of glucose with bromine water gives gluconic acid which shows the presence of aldehyde group.

Fehling 's solution to make difference between carbohydrate and ketone functional grp and also used for differentiate reducing and non reducing sugar and as u know glucose is a reducing sugar so it will give red colour with fehling 's solution (all monosachharides are reducing sugar).

• Disaccharides on hydrolysis with dilute acids  or enzymes yield two molecules of either the  same or different monosaccharides.
• The two monosaccharides are joined together  by an oxide linkage formed by the loss of a  water molecule. Such a linkage between two  monosaccharide units through oxygen atom  is called  glycosidic linkage.