At first glance, saliva seems like pretty boring stuff, just a handy way to moisten our food. But the reality is very different, as scientists are beginning to understand. The liquid interacts with everything that enters the mouth, and although it is 99% water, it has a major impact on the flavors – and our enjoyment – of what we eat and drink.
“It’s a liquid, but it’s not just any liquid,” says oral biologist Guy Carpenter of King’s College London.
Scientists have long understood a number of functions of saliva: it protects the teeth, makes speech easier and provides an inviting environment for food to enter the mouth. But researchers are now discovering that saliva is also a mediator and translator, influencing how food moves through the mouth and how it stimulates our senses. Emerging evidence suggests that interactions between saliva and food may even help determine which foods we like to eat.
The substance is not very salty, which allows people to taste the saltiness of a potato chip. It’s not very acidic, which is why a squeeze of lemon can be so energizing. The liquid’s water and salivary proteins lubricate each bite of food, and enzymes such as amylase and lipase kick-start the digestion process.
This wetting also dissolves the chemical components of taste, or flavourings, in saliva so that they can travel to and interact with the taste buds. Through saliva, says Jianshe Chen, a food scientist at Zhejiang Gongshang University in Hangzhou, China, “we detect chemical information from food: the flavor, the flavor.”
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Chen coined the term “oral food processing” in 2009 to describe the multidisciplinary field based on nutritional science, the physics of food materials, the body’s physiological and psychological responses to food, and more, a topic he wrote about in the Annual Review 2022 of Food Science and Technology. When people eat, he explains, they don’t actually enjoy the food itself, but a mixture of the food plus saliva. For example, an eater can only perceive a sweet- or sour-tasting molecule in a bite of food if that molecule can reach the taste buds – and for that to happen it has to pass through the layer of saliva that covers the tongue.
That’s not a given, says Carpenter, who points out that flat soda tastes sweeter than carbonated soda. Researchers had assumed this was because popping bubbles of carbon dioxide in fresh soda delivered an acidic hit that essentially distracted the brain from the sweetness. But when Carpenter and his colleagues studied the process in the lab in a kind of artificial mouth, they found that saliva prevented the soda’s bubbles from flowing between tongue and palate. Carpenter thinks these accumulated bubbles may physically prevent the sugars from reaching the taste receptors on the tongue. With flat soda, no air bubbles build up to block the sweet taste.