Carbohydrates in the diet provide the major exogenous source for glucose, which is the primary energy source for cells.
Carbohydrates are hydrophilic and require a series of reactions to digest them to monosaccharides which are absorbed in the small intestine. Carbohydrates consist of three main groups, simple carbohydrates (monosaccharides), disaccharides and complex carbohydrates (starch, glycogen, and fiber).The common monosaccharides include glucose, fructose, galactose, xylose and ribose.
Starch, the major food polysaccharide, consists of 85% amylopectin and 15% amylose. Amylose is composed of straight chains of glucose molecules linked through1:4-α bond where as amylopectin, in addition to chains of 1:4- α linked glucose molecules, also has 1:6- α links between glucose molecules in adjacent chains forming bridges.
When the person eat carbohydrates, such as a bowl of pasta or some vegetables, the digestive system breaks the carbohydrates down into simple sugars such as glucose, which travel into and through the bloodstream to nourish and energize cell.
The digestion process of polysaccharides such as starch will begin in the mouth where it is hydrolysed by salivary amylase. Chewing, also known as mastication, crumbles the carbohydrate foods into smaller and smaller pieces. The salivary glands in the oral cavity secrete saliva that coats the food particles. Salivary amylase breaks the bonds between the monomeric sugar units of disaccharides, oligosaccharides, and starches. The salivary amylase breaks down amylose and amylopectin into smaller chains of glucose, called dextrins and maltose.
The goal of carbohydrate digestion is to break down all disaccharides and complex carbohydrates into monosaccharides for absorption, although not all are completely absorbed in the small intestine (e.g.,fiber).
Fructose is absorbed by facilitated diffusion while glucose and galactose are actively transported. Glucose, at low concentrations is transported through the mucosal lining into the epithelial cells of the intestine by active transport, via a sodium dependant transporter. The first organ to receive glucose, fructose, and galactose is the liver. The liver takes them up and converts galactose to glucose, breaks fructose into even smaller carbon-containing units, and either stores glucose as glycogen or exports it back to the blood.
Digestion of carbohydrate
