Unlocking the Hidden Mysteries: The Surprising Power of Saliva
Saliva is more than just a means of keeping your mouth lubricated.
Scientists are discovering that the x-factor behind the flavors we taste is a cocktail of substances.
At first glance, saliva appears to be pretty mundane, just a convenient way to moisten our food.
However, as scientists are learning, the reality is quite different.
The fluid interacts with everything that enters the mouth, and despite being 99% water, it has a significant impact on the flavors – and thus our enjoyment – of what we eat and drink.
“It’s a liquid, but it’s not just a liquid,” says Guy Carpenter, an oral biologist at King’s College London.
Scientists have long known that saliva protects teeth, facilitates speech, and creates an inviting environment for foods to enter the mouth.
Saliva, however, is now being discovered to be a mediator and translator, influencing how food moves through the mouth and how it stimulates our senses.
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Emerging evidence suggests that saliva-food interactions may even influence which foods we prefer to eat.
Because the substance is not very salty, people can taste the saltiness of a potato chip.
Because it’s not very acidic, a spritz of lemon can be very stimulating.
The fluid’s water and salivary proteins lubricate each mouthful of food, and enzymes like amylase and lipase begin the digestion process.
This wetting also dissolves taste chemicals, or tastants, into saliva, allowing them to travel to and interact with taste buds.
“We detect chemical information of food: the flavor, the taste,” says Jianshe Chen, a food scientist at Zhejiang Gongshang University in Hangzhou, China.
Chen coined the term “food oral processing” in 2009 to describe the multidisciplinary field that incorporates food science, the physics of food materials, the body’s physiological and psychological responses to food, and other topics, which he discussed in the 2022 Annual Review of Food Science and Technology.
He explains that when people eat, they savor a mixture of the food and saliva rather than the food itself.
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An eater, for example, can perceive a sweet or sour-tasting molecule in a bite of food only if that molecule can reach the taste buds – and that molecule must pass through the layer of saliva that coats the tongue for that to happen.
That isn’t a given, according to Carpenter, who points out that flat soda tastes sweeter than fizzy soda.
Researchers assumed this was because bursting carbon dioxide bubbles in fresh soda provided an acidic hit that distracted the brain from the sweetness.
Carpenter and his colleagues discovered that saliva prevented the soda’s bubbles from flowing between the tongue and palate when they studied the process in the lab in a sort of artificial mouth.
Carpenter believes that the backed-up bubbles may physically prevent sugars from reaching taste receptors on the tongue.
There are no bubbles to obstruct the sweet taste of flat soda.
Saliva can also influence the aromas produced by food in the mouth, which account for the vast majority of our perception of flavor.
Some flavor molecules in food dissolve in saliva as we chew, but those that do not can waft up into the nasal cavity and be sensed by the myriad receptors there.
As a result, people with different salivary flow rates or saliva composition – particularly of proteins known as mucins – may have very different flavor experiences when eating or drinking the same food or beverage.
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For example, Spanish researchers measured the flow of saliva in 10 volunteers who rated wine flavored with fruity esters.
The scientists discovered that volunteers who produced more saliva rated the flavors as more intense, possibly because they swallowed more frequently and thus forced more aromas into their nasal passages.
Wine enthusiasts who are proud of their ability to detect aroma nuances may have their spit to thank, at least in part.
Saliva is also important in our perception of texture.
Consider astringency, the dry sensation that occurs in the mouth after drinking red wine or eating unripe fruit.
The wine does not dry out your mouth.
Instead, tannins in wine can cause proteins to precipitate out of the saliva, causing it to no longer lubricate as well.
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Saliva also assists us in distinguishing between high-fat and low-fat foods.
Even if two yogurts look and pour the same, a low-fat version feels drier in the mouth, according to Anwesha Sarkar, a food scientist at the University of Leeds in the United Kingdom.
“You’re trying to understand how the food interacts with the surface [of the mouth], not the property of the food,” Sarkar says.
According to her, milk fat can combine with saliva to form a layer of droplets that can mask astringency and add richness to the yogurt.
Sarkar’s study employs a mechanical tongue bathed in artificial saliva to simulate what happens as food moves through the mouth and how this affects the sensory experience of eating.
A low-fat smoothie may appear creamy at first glance, but it lacks the textural luxuriousness that fat provides when mixed with saliva, according to Sarkar.
According to Sarkar, fully understanding the interactions between saliva, food, and the mouth, as well as how the information is transferred to the brain, could lead to the development of healthier foods.
She hopes to create a “gradient food” with enough sugar on the outside of the food to dissolve in saliva and give a sense of sweetness, but at a lower concentration and calorie level in the whole food. She believes that a similar conceptual approach could aid in the reduction of fat in foods.
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However, understanding these interactions well enough to develop such foods will be difficult because saliva and perception vary throughout the day and between individuals.
Saliva flows slowly in the morning and quickly in the early afternoon.
And the components of any individual’s saliva, for example, the amounts of certain proteins, will vary throughout the day and in the presence or absence of stimuli such as enticing aromas.
Elsa Lamy, an oral biochemist at the University of Évora in Portugal, investigated this by blindfolding volunteers and allowing them to smell a piece of bread for four minutes while monitoring their saliva for changes.
She discovered that two types of protein, starch-digesting amylases and cystatins, which have been linked to taste sensitivity and perception, increased after bread exposure.
Lamy’s group conducted similar experiments with vanilla and lemons and discovered changes in saliva protein levels in all cases, though the specific changes depended on the food presented.
Her team is now investigating what purpose this could serve.
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Saliva composition varies from person to person, and this is influenced in part by an individual’s previous food choices, according to Ann-Marie Torregrossa, a behavioral neuroscientist at the University at Buffalo.
Torregrossa observed significant increases in multiple categories of saliva proteins when she fed bitter-tasting additives to rats.
Rats became more likely to accept bitterness in their food as those changes occurred.
“We think of it this way: if you eat broccoli all the time, broccoli doesn’t taste bad to you,” Torregrossa says.
Torregrossa used catheters in another experiment to transfer saliva collected from rats used to eating bitter diets into the mouths of rats that were not.
Despite their lack of experience, the naive animals became more tolerant of bitter foods.
However, control animals that were not given the bitterness-tolerant saliva proteins still rejected the bitter food.
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Torregrossa and her colleagues have yet to determine which proteins are responsible for this tolerance.
Proline-rich proteins and protease inhibitors are two possible candidates, but there could be others.
They need to know which proteins are involved before they can assess how the mouth and brain respond to bitter flavors.
Of course, rats aren’t people, but researchers have discovered hints that saliva affects taste perception in humans, though the picture is more complicated.
“There are a lot of other things in human diets and experiences that are influencing our day-to-day experience, particularly with foods and flavors, that rodents simply do not have to deal with,” says Lissa Davis, a Purdue University sensory and nutrition scientist who studies taste and behavior.
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However, if these patterns can be decoded and understood, the potential is enormous, according to Lamy. If you could give kids an additive that causes changes in their saliva and thus makes their experience with a bitter vegetable more enjoyable, you could encourage healthier eating.
“Probably they will associate a good experience with that vegetable,” she says if their first experience with new food isn’t accompanied by a high level of bitterness.
More broadly, developing a better understanding of how saliva influences taste – and how diet, in turn, influences the composition of saliva – could open up a slew of new avenues for nudging dietary preferences toward often-vilified healthy foods. “How can we convert the haters into people who love these foods?” asks Torregrossa. That’s what I’m preoccupied with.”
