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How do saliva and salivary amylase begin the digestion of starch?

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USDA MyPlate dietary guidelines — human nutrition MyPlate, a revised set of dietary guidelines introduced by the U.S. Department of Agriculture (USDA) in 2011, divides the four basic food groups (fruits, grains, protein, and vegetables) into sections on a plate, the size of each section representing the relative dietary proportions of each food group. The small blue circle shown at the upper right illustrates the inclusion and recommended proportion of dairy products in the diet.

Human digestion begins in the mouth, where mechanical processing by teeth breaks down food to increase the surface area available for chemical action. During this process, food is mixed with saliva, a fluid secreted by the salivary glands that provides moisture and lubrication to facilitate swallowing.123

Saliva contains an enzyme known as amylase—specifically a type called ptyalin—which initiates the chemical digestion of starch. Starch is a complex carbohydrate consisting of long chains of glucose units. Amylase catalyzes the hydrolysis of these starch molecules, breaking the bonds between glucose units to produce smaller molecules, primarily the double sugar maltose.431

Although food remains in the mouth for only a short time, the digestive action of ptyalin continues after the food is swallowed and enters the [stomach]. This process persists until the food is thoroughly mixed with acidic gastric juices, which eventually inactivate the enzyme. Under optimal conditions, this initial phase can break down 30 to 40 percent of ingested starches into maltose.4