Question

Describe the digestion of starch.

Answer 1

Digestion of starch:

1. Digestion of starch takes place in the mouth (oral cavity) and in the small intestine.
2. About 40% of starch that is a carbohydrate is partially digested by ptyalin (salivary amylase) while the remaining 60% starch is digested by pancreatic amylase secretion of the pancreas.

Digestion of starch in the oral cavity:

1. In the mouth, food is mixed with saliva.
2. Salivary amylase or ptyalin converts starch into maltose and isomaltose.

$\mathrm{Starch}\stackrel{\mathrm{Salivary}\mathrm{amylase}}{\to }\mathrm{Maltose}+\mathrm{Isomaltose}$

Digestion of starch in the small intestine:

1. Small intestine receives the secretion from the liver and pancreas.
2. Pancreas secretes pancreatic juice which has enzymes to digest starch.

$\mathrm{Starch}\stackrel{\mathrm{Pancreatic}\mathrm{amylase}}{\to }\mathrm{Maltose}+\mathrm{Isomaltose}$

3.The enzymes of intestinal juice act as given below-

$\mathrm{Maltose}\stackrel{\mathrm{Maltase}}{\to }\mathrm{Glucose}$

$\mathrm{Isomaltose}\stackrel{\mathrm{Isomaltase}}{\to }\mathrm{Glucose}$

$\mathrm{Sucrose}\stackrel{\mathrm{Sucrase}}{\to }\mathrm{Glucose}+\mathrm{Fructose}$

$\mathrm{Lactose}\stackrel{\mathrm{Lacltase}}{\to }\mathrm{Glucose}+\mathrm{Galactose}$

4. Humans can't digest cellulose as they don't have cellulase enzymes.