Carbohydrates digestion

Carbohydrates digestion is very easy to understand but first, you have to understand which types of carbs are present in our diets.

Dietary carbohydrates contain polysaccharides, disaccharides, and monosaccharides. Polysaccharides present in our diets are starch and glycogen. Starch comes from plant sources while glycogen comes from animal sources.

Disaccharides present in dietary carbohydrates are maltose, lactose, and sucrose.

Monosaccharides present in our diet are fructose, pentoses, etc.

Digestion of carbs in mouth

Liquid substances pass directly into the stomach and escape digestion while solid foods are masticated in the mouth.

Digestion of carbohydrates in the mouth begins when it comes in contact with saliva. Saliva contains an enzyme that is known as salivary amylase.  Salivary amylase is also known as ptyalin.

The salivary amylase enzyme is an alpha-amylase that needs chlorine ions for activation. The optimum PH (PH at which enzymes show maximum activity. The PH value is different for different enzymes) is 6. 7.
This enzyme hydrolyzes alpha 1-4 glycosidic linkage. Salivary amylase becomes deactivates when it reaches the stomach.

In the mouth, some carbs are broke down into monosaccharides but most of them pass into the stomach.

Digestion in stomach

In the stomach, carbohydrates splitting enzymes are not present in the gastric juice however some of the sucrose presents in our diets are broken down into glucose and fructose by the action of HCL.

Digestion of carbohydrates in the duodenum

Foods from the stomach enter into the duodenum where it comes in contact with pancreatic juice which contains an enzyme known as pancreatic amylase. Pancreatic amylase is also known as amylopsin.

Pancreatic amylase enzyme is an alpha-amylase that breakdown alpha 1-4 glycosidic linkage. The optimum PH for this enzyme is 7.1.

Digestion in the small intestine

In the small intestine, the carbohydrates present in our foods come in contact with intestinal juices which consist of following enzymes

1. Intestinal amylase
2. Lactase
3. Isomaltase
4. Maltase
5. Sucrase

Intestinal amylase

This enzyme-like other amylases such as salivary and pancreatic amylases also hydrolyze alpha 1-4 glycosidic linkage but the difference is that this enzyme works only on the terminal alpha 1-4 glycosidic linkage.


Lactase is a beta-galactoside.
It is an enzyme that breaks down lactose. Lactose is a disaccharide which on hydrolysis yields glucose and galactose. The optimum ph for this enzyme ranges from 5.4 to 6.

The Isomaltase

This enzyme hydrolyzes alpha 1-6 glycosidic linkage. This enzyme split dextrin at a branching point and produces maltose + glucose.


Maltase is enzymes that hydrolyze alpha 1-4 glycosidic linkages in maltoses and produce glucose molecules. The optimum PH for this enzyme ranges from 5.8 to 6.2.


Sucrase is an enzyme that hydrolyzes sucrose. Sucrose is a disaccharide which on hydrolysis yields glucose and fructose. The optimum PH for enzyme sucrase ranges from 5 to 7.

Point to be noted

There are 5 types of maltases been identified.  Among these types maltase V acts as isomaltase while maltase III and maltase IV act as sucrase enzymes.