Salivary proteins may be part of a feedback loop that influences how food tastes and, by extension, what foods people are willing to eat, according to researchers at Purdue University, who believe their findings could one day help consumers stick to a healthier diet.
For example, many healthy foods like broccoli and dark chocolate taste bitter. The researchers, then, set out to see if eating bitter foods could help people overcome an aversion to bitter compounds so 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,” said Cordelia A. Running, MS, PhD, assistant professor in the Department of Nutrition Science at the Purdue University College of Health and Human Sciences and principal investigator of the study.
While saliva consists almost entirely of water, it also includes 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,” said Running.
Previous work by the researchers found that a bitter diet altered the expression of proteins in 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 this work, the researchers then decided to see if the same thing would happen in people.
The researchers carried out sensory evaluation tests in which they asked participants to drink chocolate almond milk three times a day for a week and rate its bitterness and astringency. 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,” Running said.
The findings support the idea that “saliva modifies flavor, which in turn modifies dietary choices,” Running said.
“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,” Running said.
The researchers plan to investigate the particular compounds in food that elicit changes in salivary proteins. In chocolate, for example, they want to know what concentration of bitter polyphenols is necessary to affect expression of salivary proteins. They also want to assess how long it takes to reduce the bitter taste of any given food and whether mimics for salivary proteins could someday be added to food to improve its flavor.
The results of the study were presented at the 256th National Meeting & Exposition of the American Chemical Society, August 20, in Boston.