The fluid that our mouths produce (saliva) is not just a lubricant. Researchers are discovering that it plays an active role in how we perceive flavors and may influence what we choose to eat.
At first glance, saliva may seem like a rather mundane substance, simply a liquid that moistens our food. But the reality is quite different; saliva interacts with everything that enters our mouths. Although 99% of saliva is water, it has a profound effect on the flavor — and our enjoyment — of what we eat and drink.
Saliva interacts with everything that enters the mouth.
“It is a liquid, but it is not just a liquid,” said oral biologist Guy Carpenter from King’s College London.
Scientists have long understood some functions of saliva: it protects teeth, aids in speaking, and creates a conducive environment for food to enter the mouth.
However, researchers are now discovering that saliva also acts as a mediator that influences how food moves through the mouth and how it stimulates our senses. New evidence suggests that the interaction between saliva and food may even help shape the types of foods we prefer.
This substance is not very salty, so eaters can perceive the saltiness of potato chips. It is not very acidic, which is why a little lemon can be very stimulating.
The water and proteins in saliva lubricate each bite of food, and its enzymes, such as amylase and lipase, kickstart the digestion process. This wetting also dissolves the chemical components of flavors, also known as flavor compounds, into the saliva so they can move to and interact with taste buds.
Jianshe Chen, a food scientist at Zhejiang Gongshang University in Hangzhou, China, stated that through saliva, “we can detect the chemical information of food: aroma, taste.”
Chen coined the term “oral food processing” in 2009 to describe the interdisciplinary field based on food science, the physics of food ingredients, and the physiological and psychological responses of the body to food…
Chen explains that when people eat, they are not actually tasting the food but rather a mixture of food combined with saliva. For example, a person can only perceive a sweet or sour molecule in a bite of food if that molecule can reach the taste buds — and for that to happen, it must pass through the layer of saliva covering the tongue.
However, it has been noted that even with the same amount of sugar, regular soda tastes sweeter than diet soda. Researchers have suggested this is because the carbon dioxide bubbles in fresh soda create a level of acidity that distracts the brain from the sweetness.
But when Carpenter and his colleagues studied this process in the lab using a type of artificial mouth, they found that saliva prevents soda bubbles from flowing between the tongue and the roof of the mouth. Carpenter believes these bubbles may block sugar from reaching the taste sensory organs on the tongue.
Saliva influences how food moves through the mouth.
Saliva can also affect aroma — which is responsible for most of our perception of flavor — that arises from food in the mouth. When we chew, some flavor molecules in the food dissolve in the saliva, but those molecules cannot enter the nasal cavity to be sensed by the numerous receptors there.
Therefore, people with different saliva flow rates or different saliva compositions — particularly a protein called mucin — may have very different flavor experiences from the same food or beverage.
For example, Spanish researchers measured the saliva flow of 10 volunteers tasting wines enhanced with fruity esters. They found that volunteers who produced more saliva tended to perceive the flavors as more intense, possibly because they swallowed more often and pushed more aromas into the nasal passage.
Saliva also plays an important role in our perception of texture. Take astringency, the dry feeling that occurs in the mouth when drinking red wine or eating unripe fruit, as an example. Wine doesn’t actually make your mouth drier. Instead, molecules called tannins in wine can cause proteins to precipitate from saliva, making it less effective as a lubricant.
Saliva can also affect aroma.
Saliva also helps us perceive differences between high-fat and low-fat foods. Anwesha Sarkar, a food scientist at the University of Leeds in the UK, noted that even if two yogurts look the same and have the same ingredients, the low-fat version will make us feel drier in the mouth.
Sarkar stated, “What you are trying to understand is not the properties of the food, but how the food interacts with the surfaces.” She explained that the fat in milk can combine with saliva to create a droplet layer on the surface of the mouth that can mask astringency and add a creamier sensation to yogurt.
Sarkar’s research uses a mechanical tongue, immersed in artificial saliva, as a way to simulate what happens when food moves through the mouth and how that affects sensory experiences while eating.
Sarkar expressed that fully understanding these interactions between saliva, food, and the mouth — and how information is transmitted to the brain — could lead to the design of healthier food products. She envisions developing a type of “color-changing food” that could include enough sugar on the outside of the food to dissolve in saliva to provide a sweet sensation while having lower concentrations and calorie levels throughout the food. She mentioned that a similar conceptual approach could help reduce fat in foods.
However, understanding these interactions to develop such food products will not be easy, as individuals will have different saliva compositions and perceptions throughout the day and among different people. Generally, saliva flow is slower in the morning and fastest in the early afternoon. And the components of any individual’s saliva — such as the level of certain proteins — will change throughout the day.
