The secrets inside your saliva

At first glance, saliva seems like pretty boring stuff, merely a convenient way to moisten our food. But the reality is quite different, as scientists are beginning to understand. The fluid interacts with everything that enters the mouth, and even though it is 99% water, it has a profound influence on the flavours – and our enjoyment – of what we eat and drink.

“It is a liquid, but it’s not just a liquid,” says oral biologist Guy Carpenter of King’s College London.

Scientists have long understood some of saliva’s functions: it protects the teeth, makes speech easier and establishes a welcoming environment for foods to enter the mouth. But researchers are now finding that saliva is also a mediator and a translator, influencing how food moves through the mouth and how it sparks our senses. Emerging evidence suggests that interactions between saliva and food may even help to shape 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 spritz of lemon can be so stimulating. The fluid’s water and salivary proteins lubricate each mouthful of food, and its enzymes such as amylase and lipase kickstart the process of digestion.

This wetting also dissolves the chemical components of taste, or tastants, into saliva so 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 of food: the flavour, the taste.”

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Chen coined the term “food oral processing” in 2009 to describe the multidisciplinary field that draws on food science, the physics of food materials, the body’s physiological and psychological responses to food, and more, a subject he wrote about in the 2022 Annual Review of Food Science and Technology. When people eat, he explains, they don’t actually savour the food itself, but a mixture of the food plus saliva. For example, an eater can perceive a sweet or sour-tasting molecule in a bite of food only if that molecule can reach the taste buds – and for that to happen, it must pass through the layer of saliva that coats the tongue.

That’s not a given, says Carpenter, who points to how flat soda tastes sweeter than fizzy soda. Researchers had assumed this was because bursting bubbles of carbon dioxide in fresh soda provided 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 sort of artificial mouth, they found that saliva prevented the soda’s bubbles from flowing between tongue and palate. Carpenter thinks these backed-up bubbles could physically block the sugars from reaching the taste receptors on the tongue. With flat soda, no bubbles build up to block the sweet taste.