Salivary amylase, also known as ptyalin, is a digestive enzyme present in human saliva that initiates the chemical breakdown of starches as soon as food enters the mouth. This protein acts as an alpha-amylase, meaning it specifically targets the complex carbohydrate molecules that form the structure of starch. Its purpose is to begin converting large, complex starches into smaller, simpler sugars, preparing them for further processing later in the digestive tract. This enzyme allows the body to immediately begin extracting energy from starchy foods like potatoes, rice, and bread during chewing.
Where Salivary Amylase is Produced
Salivary amylase originates in the exocrine glands located around the oral cavity, which produce and secrete saliva. Humans have three major pairs of salivary glands: the parotid, submandibular, and sublingual glands. The largest of these, the parotid glands, are the primary contributors to the total amount of amylase found in saliva.
The enzyme is released into the mouth as a component of saliva, a watery fluid that also contains mucus, electrolytes, and other proteins. Saliva serves multiple functions, including lubricating food to aid in swallowing and beginning the chemical digestion of carbohydrates. The concentration of amylase can vary significantly among individuals, linked to differing dietary habits and starch consumption levels.
How Amylase Breaks Down Starch
The function of salivary amylase is to begin the hydrolysis of starch, which chemically breaks down the large starch molecule. Starch is a polysaccharide, a long chain made up of hundreds of glucose units linked together. This complex structure is too large to be directly absorbed by the body.
Amylase acts as a catalyst to break the internal alpha-1,4-glycosidic bonds within the starch chain. This specific action is known as endo-glycosidase activity, meaning it cleaves bonds located randomly along the length of the molecule. The breakdown is called hydrolysis because a molecule of water is used to split the chemical bond.
The result of this initial breakdown is not immediate glucose, but a mix of smaller carbohydrate fragments. The main products are dextrins, which are shorter segments of the original starch, along with the disaccharide maltose and the trisaccharide maltotriose. Maltose is a sugar composed of two glucose units, and it often gives starchy foods a subtle sweet taste when chewed for a long time. These smaller sugars are then ready for subsequent digestion by other enzymes further down the digestive system.
The Limits of Salivary Amylase
The activity of salivary amylase is temporary, limited by the changing environment of the upper digestive tract. The enzyme works optimally at a neutral pH, typically between 6.7 and 7.0, which is the normal pH range of saliva. This environment allows the enzyme to efficiently bind to starch and catalyze its breakdown.
Once the food bolus is swallowed, the enzyme travels into the stomach, which presents a hostile environment for amylase. The stomach secretes strong gastric acid, resulting in a highly acidic pH that can drop as low as 1.5 to 3.0. This shift in pH causes the amylase protein to rapidly lose its three-dimensional structure, a process known as denaturation.
Denaturation permanently inactivates the enzyme, halting its ability to continue breaking down starch. While some activity may persist briefly in the center of the swallowed food mass, the majority of the enzyme is deactivated quickly. Complete carbohydrate digestion is paused until the partially processed food moves into the small intestine, where pancreatic amylase takes over the task of breaking down the remaining starch.