The process of digestion starts the moment food enters your mouth. The mouth and esophagus themselves don’t make any enzymes, but saliva, produced in the salivary glands and excreted into the mouth, and down into the esophagus, contains several important enzymes such as amylase, lysozyme and lingual lipase. Saliva is mixed with food as you chew, and acts as a lubricant to start the digestion process. The enzymes in saliva start to break down nutrients, while some also help protect you from bacteria and support the body's immune system.
As a primary enzyme in saliva, amylase starts to break down starches in the food you eat. Starches are long chains of sugars attached to each other, and amylase breaks the bonds along the chain to release maltose sugar molecules. To experience amylase in action, chew on a cracker for a minute and you will find that it starts to taste sweet. Amylase functions in a neutral to slightly basic environment, which is definitely not to be found in the acid bath that is your stomach.
Secreted in your tears, the mucus in your nose, human breast milk and your saliva, lysozyme isn’t there to digest your food, it is there to protect you from any harmful bacteria that came with it. Lysozyme breaks down the polysaccharides – a type of carbohydrate – in the cell walls of many bacteria. Once the cell wall has been broken down, a bacterium dies, bursting like a water balloon. In scientific terms, cell death by popping is known as lysis, so the enzyme that accomplishes the task is called lysozyme.
Lingual lipase is an enzyme that breaks down fatty acids, specifically triacylglycerols. Excreted as part of saliva, it doesn’t finish its job until it gets to the stomach. The amount of lingual lipase in your saliva decreases as you get older, and gastric and pancreatic lipase lower down in your digestive system take over the job of digesting fats. Lingual lipase is very important for infants because it helps them digest the fats in milk, making digestion much easier for their immature systems.
Kallikrein is the name for a group of proteases, enzymes that break down proteins, which are found throughout the body, including trace amounts in the saliva. The function of salivary kallikrein is not to digest the proteins you consume, as salivary kallikrein breaks down very specific proteins with a high molecular weight to produce bradykinin, a protein that helps blood vessels dilate. Changes to kallikrein enzymes have also been linked to certain cancers.
- Biology Online: Digestive Enzymes
- Colorado State University: Salivary Glands and Saliva
- Tufts University: Structure and Function in Lysozyme
- Advanced Nutrition and Human Metabolism; Sareen Gropper and Jack Smith
- Klinische Wochenschrift: Salivary Kallikrein Excretion in Hypertension
- Roger Lundblad Consulting: Kallikrein in Human Saliva [PDF]
- Stockbyte/Stockbyte/Getty Images