Question

One mole of stachyose on hydrolysis yields:
A.1 mole of glucose + 1 mole of fructose + 2 mole of galactose
B.2 mole of glucose + 1 mole of fructose + 1 mole of galactose
C.1 mole of glucose + 2 mole of fructose + 1 mole of galactose
D.2 mole of glucose + 2 mole of fructose

Answer 1

Hint:
 A tetrasaccharide is a saccharide or carbohydrate which upon hydrolysis gives four molecules of the same monosaccharide or different monosaccharides. The general formula of tetrasaccharides is ${{\text{C}}_{{\text{24}}}}{{\text{H}}_{{\text{42}}}}{{\text{O}}_{{\text{21}}}}$ . The monosaccharides are the simplest carbohydrates which cannot be hydrolyzed further to smaller molecules. Their general formula is ${\left( {{\text{C}}{{\text{H}}_{\text{2}}}{\text{O}}} \right)_{\text{n}}}$ where n is equal to 3-7.

Complete step by step answer:
Stachyose is an example of a tetrasaccharide. It gives four molecules of different monosaccharides on complete hydrolysis. These four molecules are one molecule of glucose, one molecule of fructose and two molecules of galactose. Thus, stachyose consists of two ${\text{alpha }}$ - D - galactose units, one ${\text{alpha }}$ - D - glucose unit and one ${\text{beta }}$ - D - fructose unit. Thus, option A is the correct answer. The structure of stachyose is shown below.

The hydrolysis of a polysaccharide results in the breakage of the glycosidic linkage formed between two monosaccharide monomer units when the polysaccharide is formed. The hydrolysis of the oligosaccharide sucrose gives glucose and fructose.
The other options are not correct as there are no particular tetrasaccharides known to give any of the three combinations which are 2 mole of glucose, 1 mole of fructose, 1 mole of galactose or 1 mole of glucose, 2 mole of fructose, 1 mole of galactose or 2 mole of glucose, 2 mole of fructose. Also, the hydrolysis of stachyose does not result in these monosaccharides. Hence, the options B, C, D are not correct.

Hence option A is correct.

Note:
The carbohydrates which upon hydrolysis give two molecules of the same or different monosaccharides are called disaccharides. For example, sucrose gives glucose and fructose, maltose gives 2 molecules of glucose and lactose gives glucose and galactose. Similarly, trisaccharides give 3 molecules of the same or different monosaccharides. For example, raffinose gives one molecule each of glucose, fructose and galactose on hydrolysis.