Question 9: How are polysaccharides and disaccharides digested?
Answer:
The digestion of carbohydrates starts in the mouth and completes in the small intestine region of the alimentary canal. The enzymes that act on carbohydrates are collectively known as carbohydrases.
Digestion in the mouth:
As food enters the mouth, it gets mixed with saliva. Saliva – secreted by the salivary glands – contains a digestive enzyme called salivary amylase; also called as Ptyalin. This enzyme breaks down starch into sugar at pH 6.8.
Starch
Maltose + Isomaltose + Limit dextrins
Salivary amylase continues to act in the oesophagus, but its action stops in the stomach as the contents become acidic. Hence, carbohydrate-digestion stops in the stomach.
Digestion in the small intestine:
Carbohydrate-digestion is resumed in the small intestine. Here, the food gets mixed with the pancreatic juice and the intestinal juice. Pancreatic juice contains the pancreatic amylase that hydrolyses the polysaccharides into disaccharides.
Starch
Disaccharides
(Polysaccharides)
Similarly, the intestinal juice contains a variety of enzymes (disaccharidases such as maltase, lactase, sucrase, etc.). These disaccharidases help in the digestion of disaccharides. The digestion of carbohydrates is completed in the small intestine.
Maltose
2Glucose
Lactose
Glucose + Galactose
Sucrose 
Glucose + Fructose
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