Question

Raffinose is a
A. trisaccharide
B. monosaccharide
C. disaccharide
D. none of the above

Answer 1

Hint: Raffinose having molecular formula ${{C}_{18}}{{H}_{32}}{{O}_{16}}$ is an oligosaccharides which contain more than one sugar unit. Raffinose is made up of galactose, glucose and fructose and thus contains three units of monosaccharides. It is a sugar which is present in cotton seed, sugar beet and many cereals.

Complete answer:
From your chemistry lesson you have learnt about the carbohydrates and on the basis of the number of units sugar can be classified as monosaccharides, disaccharides, oligosaccharides and polysaccharides.
The basic unit of all types of sugar is monosaccharides. If there are two units of monosaccharides then that type of sugar is known as disaccharide and if the sugar contains 2-10 monosaccharides then it is known as oligosaccharide.
Here we are going to deal with oligosaccharides because raffinose contains 3 units of monosaccharides. And the sugars which contain 3 units of monosaccharides are known as trisaccharides and they are also called oligosaccharides.
Raffinose (${{C}_{18}}{{H}_{32}}{{O}_{16}}$) is a type of trisaccharides which contains three different monosaccharides units on hydrolysis, that are one molecule of fructose, one molecule of glucose and one molecule of galactose.
\[{{C}_{18}}{{H}_{32}}{{O}_{16}}\to Glu\cos e+Fructose+Galactose\]
Raffinose is a non-reducing sugar due to the absence of free aldehyde and ketonic group and the structure of raffinose is:

Raffinose is a sugar found in cotton seed, sugar beet and cereals and some important sources of raffinose are cabbage, bean and asparagus.

Thus the correct option will be (A).

Note:
The enzyme which is necessary for the breakdown of raffinose is not present in humans and thus it is not digestible in humans. In our stomach and small intestine there is no digestion of raffinose but some amount of fermentation and breakdown of raffinose takes place in the large intestine because the bacteria present there possess the enzyme.