Why amylase breaks down starch into maltose instead of glucose directly?

Answer 1

Remember that digestion of starch, the most common carbohydrate in the human diet, begins with the secretion of alpha-amylase from salivary glands in the mouth. Salivary alpha-amylase breaks all the alpha(1-4) glucosidic bonds of starch except those next to branches or its outermost bonds. However, by the time the chewed food reaches the stomach, the acidic conditions into it inactivate the salivary alpha-amylase. In that time, the average lenght of starch has been reduced from several thousands to only eight glucose units. It will be until the food continues in the small intestine when the starch remnants continue it digestion. Then, pancreatic alpha-amylase continues the hydrolisis to produce a mixture of: a) the disaccharide maltose (glucopyranosyl alpha(1-4) glucopyranoside, or alpha-amylose unit); b) the trisaccharide maltotriose (three glucose residues linked with alpha(1-4) bonds; and c) dextrins (oligosaccharides containing alpha(1-6) branches. Finally, specifc enzymes (e.g., alpha-glucosidase, alpha-dextrinase or debranching enzyme, sucrase, and, in infants, lactase), in the brush border membranes of the intestinal mucosa, will finish to break the remnant bonds to hydrolize the oligosaccharides and produce their component monosaccharides.

From this point of view, only pancreatic alpha-amylase produces maltose units during the time the food is in the small intestine. The final hydrolisis, where monosaccharides are produced, takes place in the intestinal mucosa.

Answer 2

Amylase breaks down starch into maltose because of its specific enzymatic activity. Amylase catalyzes the hydrolytic breakdown of starch by specifically targeting the glycosidic bonds between glucose monomers in starch polysaccharides, resulting in the formation of maltose as an intermediate product. Maltose is then further broken down into glucose by another enzyme, maltase.