Digestion is a complex process that begins even before food enters the stomach. It involves various chemical reactions facilitated by specialized proteins called enzymes, which break down food into smaller molecules the body can absorb. This initial phase of digestion, particularly for carbohydrates, starts immediately in the mouth.
What is Salivary Amylase?
Salivary amylase, also known as ptyalin, is a specific digestive enzyme produced primarily by the salivary glands, including the parotid, submandibular, and sublingual glands. This enzyme belongs to the alpha-amylase family, which are glycoside hydrolases. Its role is to initiate the chemical breakdown of certain food components in the oral cavity.
The Initial Breakdown of Starches
Salivary amylase begins the digestion of complex carbohydrates, specifically starches. Starches are large polysaccharide molecules, long chains of many glucose units. Common foods like potatoes, bread, rice, and corn contain starch. Salivary amylase breaks these long starch chains into smaller carbohydrate molecules, such as dextrins and maltose.
The breakdown of starches by salivary amylase contributes to a change in taste perception. As starches, which are generally tasteless, are broken down into smaller sugar molecules like maltose, a slight sweetness can be detected. This enzymatic action also helps in transforming the gelatinous texture of starch into a semi-liquid form. This change prepares the food for its journey through the digestive tract.
How Salivary Amylase Works
Salivary amylase breaks specific chemical bonds within starch molecules. It targets the alpha-1,4-glycosidic linkages found in starch through a process called hydrolysis. Hydrolysis involves adding water to break these chemical bonds, effectively cleaving the large starch polymers into smaller units.
The enzyme has an active site where the starch molecules bind. This binding allows efficient catalysis of the hydrolysis reaction. Salivary amylase works optimally at a neutral to slightly alkaline pH, between 6.7 and 7.0, which matches the pH of saliva in the mouth.
Its Journey Through the Digestive System
After food is chewed and mixed with saliva, it is swallowed and moves from the mouth through the esophagus and into the stomach. While salivary amylase begins starch digestion in the mouth, its activity is affected by the highly acidic environment of the stomach. The stomach’s gastric juice has a pH of about 1.0 to 3.0, too acidic for salivary amylase to function effectively.
Upon reaching the stomach, the low pH causes the salivary amylase to denature, meaning it loses its three-dimensional structure and, consequently, its ability to break down starch. Although some limited activity might persist within larger food particles in the upper part of the stomach, the majority of its digestive action ceases. Starch digestion continues and completes in the small intestine by pancreatic amylase, an enzyme produced by the pancreas.