Saliva is necessary for digestion. It lubricates the throat to make swallowing easier and contains chemicals that break down food. It also assists with oral hygiene as it helps break down plaque. But Purdue University researcher Cordelia Running has now found that saliva may have another role: salivary proteins could be part of a feedback loop that influences how food tastes to people — and by extension, what foods they’re willing to eat.
Flavor influences diet, but diet may also influence saliva, which in turn may influence flavor. Image credit: Silvia Rita.
“Many healthy foods — like broccoli and dark chocolate — taste bitter,” Dr. Running said.
She set out to see if eating bitter foods would help people overcome an aversion to bitter compounds. Thus, they could eat more of these healthy foods without cringing.
“By changing your diet, you might be able to change your flavor experience of foods that at one point tasted nasty to you,” Dr. Running noted.
While saliva consists almost entirely of water, it also contains thousands of proteins released by salivary glands.
Some of these proteins are thought to bind to flavor compounds in food and also to taste receptor cells in the mouth.
Certain proteins may be responsible for the astringent sensations, such as dryness and roughness, that develop when eating some chocolates, red wine and other foods.
“If we can change the expression of these proteins, maybe we can make the ‘bad’ flavors like bitterness and astringency weaker,” Dr. Running said.
In prior work with rats, researchers showed that a bitter diet altered expression of proteins in the rodents’ saliva.
Those changes in protein composition correlated with the rats’ feeding behavior. After initially cutting back on bitter foods, the animals apparently experienced less bitterness and resumed normal eating levels.
Inspired by that work, Dr. Running decided to see if the same thing would happen in people.
The researcher carried out sensory evaluation tests in which she asked participants to drink chocolate almond milk three times a day for a week and rate its bitterness and astringency.
She found that the protein composition of the participants’ saliva changed during that week.
Several proline-rich proteins, which can bind the bitter/astringent compounds in chocolate, increased after drinking the chocolate almond milk.
The changes in these proteins corresponded to changes in sensory ratings: as these proteins shifted up, the sensory ratings for bitterness and astringency shifted down.
“We think the body adapts to reduce the negative sensation of these bitter compounds,” Dr. Running said.
“The findings to-date support the idea that saliva modifies flavor, which in turn modifies dietary choices.”
“Those choices then influence exposure to flavors, which over time may stimulate altered expression of saliva proteins, and the circle begins anew. Maybe this knowledge will help someone stick to a healthier diet long enough to adapt to like it.”
Dr. Running presented the results today at the 256th National Meeting & Exposition of the American Chemical Society in Boston, Massachusetts.
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Cordelia A. Running. 2018. Flavor influences diet, but diet may also influence saliva, which in turn may influence flavor. 256th ACS National Meeting & Exposition, abstract # AGFD 307
