Salivary amylase is a digestive protein released into the mouth, initiating the chemical process that breaks down food. This enzyme is also known as Ptyalin. Its presence ensures that chemical digestion begins instantly upon eating, coordinating with the mechanical action of chewing. This initial enzymatic activity prepares food for the later stages of processing deeper within the digestive tract.
Where the Enzyme Comes From
Salivary amylase is produced primarily by the three major pairs of salivary glands: the parotid, the submandibular, and the sublingual glands. The parotid glands, located near the ears, secrete the largest volume of this enzyme-rich fluid. While these glands work constantly, secretion increases sharply in response to the sight, smell, or taste of food.
The enzyme is delivered into the oral cavity within saliva, which provides the precise chemical environment for its function. Saliva maintains a pH that is slightly acidic to neutral, with the optimal range for amylase activity typically falling between pH 6.7 and 7.0. This narrow pH window allows the enzyme to operate at its highest capacity, launching the initial phase of carbohydrate digestion while the food remains in the mouth.
The Chemical Process of Starch Breakdown
The sole target of salivary amylase is starch, a complex carbohydrate consisting of long chains of glucose molecules. Starch is a large molecule found in foods like potatoes, bread, and rice, and it cannot be absorbed by the body in its original form. The enzyme initiates hydrolysis, a chemical reaction that uses water to break specific bonds within the starch structure.
Salivary amylase is categorized as an alpha-amylase because it specifically cleaves the alpha-1,4 glycosidic bonds found along the straight chain of the starch molecule. It acts randomly along the interior of the chain, quickly reducing the large starch polymers into much smaller fragments. This rapid fragmentation is why starchy foods often begin to taste slightly sweet after prolonged chewing.
The products resulting from this initial hydrolysis are not absorbable simple sugars, but smaller carbohydrate fragments. These fragments include the disaccharide maltose, composed of two glucose units, and the trisaccharide maltotriose. Various shorter, branched polysaccharide chains, collectively known as dextrins, are also generated during this process.
Digestion is incomplete at this stage, as salivary amylase only has a short time to act while the food is in the mouth. Only a fraction of the total starch in a meal is broken down before the food is swallowed. The enzyme initiates the process, converting large molecules into intermediate fragments that require further enzymatic action later in the gut.
What Happens After Swallowing
Once the partially digested food bolus is swallowed, it descends into the stomach, immediately impacting the activity of salivary amylase. The stomach is a highly acidic environment due to the secretion of hydrochloric acid, which lowers the pH to a range between 1.5 and 3.5. This drastic change in environment is unsuitable for the enzyme.
Salivary amylase is a protein, and its structure is sensitive to extreme changes in pH. When exposed to the stomach’s low pH, the enzyme undergoes denaturation. This means its complex structure unravels, and it loses its ability to function. The enzyme’s digestive activity halts almost completely as the acid fully permeates the food mass.
This inactivation ensures that carbohydrate digestion stops momentarily in the stomach, which instead focuses on protein breakdown. The partially broken-down starch fragments continue their journey toward the small intestine. There, carbohydrate digestion is fully resumed by pancreatic amylase, a separate enzyme that completes the conversion of the remaining starch and dextrins into absorbable glucose units.