Researchers in the nutrition science and food science departments keep a freezer full of boxes of frozen saliva in the basement of Stone Hall.
These researchers, professors and students alike, work in Purdue’s Saliva, Perception, Ingestion and Tongues Laboratory (SPIT Lab).
The SPIT Lab’s website states that its main purpose is to focus on the “sensations, secretions, and psychology of what happens in the mouth to try and make good food a reality for everyone—not just the young, the healthy, the wealthy and the culinary-inclined.”
The saliva kept in the SPIT Lab’s freezer is stored for use for various research purposes, most recently in a study exploring how certain proteins found in human saliva affect the way we perceive bitter flavors in our food.
According to Cordelia Running, professor in the department of nutrition science, head of the SPIT Lab and self-proclaimed “saliva enthusaist,” the lab is ready to move forward with the next stages of research.
“This is our first study going down this road, so we learned a lot about how we should do the research,” she said.
The first part of the study involved having 64 participants volunteer to drink cow milk and almond milk mixed with cocoa and rate the bitterness of the milk over the course of six weeks.
Running has a theory that the more a person consumes bitter foods, the more proteins their saliva will develop that bind to polyphenols, compounds that make the food taste bitter or become astringent.
“Astringency—that’s a sort of dry, rough feel in your mouth,” Running clarified.
In other words, the SPIT Lab wants to find out if eating more bitter foods can produce proteins that help increase tolerance to bitter flavors.
One of the difficulties Running and her team faced was noticeable gustatory difference between cow milk and almond milk. She said there may have been bias in the responses due to people’s like or dislike of the different types of milk.
“They can tell the difference,” she said. “We didn’t intentionally try to make them perfectly match, which would have been impossible, anyway.”
So far, the experiments are inconclusive, though Running hopes to see more concrete results in future studies.
“Maybe (the study participants) were just too used to what we were feeding them and so we didn’t really see changes in the ratings by the end of the test,” she said. “Or maybe we didn’t change them enough as part of this experiment, or maybe it doesn’t change. Maybe I’m wrong.
"But I would think that over time this could add up to some small but real changes in how strong the bitterness of these sorts of molecules are.”
Richard Mattes, another professor in the department of nutrition science, considers Running’s research to be important concerning the way we consume nutrients.
He says that though there are people in the United States who experience hunger, on the whole, we experience more nutritional problems due to abundance of junk food than to scarcity of healthy food.
“We spend less than 10% of our discretionary income on food—some nations, it’s up to 50%," he said. "For us food is ridiculously cheap.
"We don’t have to eat anything we don’t like—we have such an array of other things but many of those other things are not as nutrient-dense and so (Running) is concerned about finding ways to help people find more healthful foods.”
Mattes explained that the main reason people may avoid bitter foods in the first place is due to evolutionary instinct.
“Bitterness seems to be a sensate that is a warning signal,” he said. “If we come across it, it means caution, that this might be a toxin. So many toxins are bitter that the association there is quite strong.
"Now, that’s our inherent reaction, but we certainly learn through culture and through our own dietary experience that everything that is bitter is not necessarily dangerous.”
According to Running, the research was funded by Purdue’s AgSEED program due to interest in how bitter flavors could impact the sales and production of commodities such as milk or grains.
“It has implications for the food supply and for people who raise cattle, soybeans, almonds and things like that,” Running said.
In the future, however, Running hopes to replicate the test using a simpler compound than milk.
“We’d like to try it in water and make a really simple tea-like solution,” she said. “Can we see a better distinction of what’s happening? Can we hone in on what we’re causing to happen?
"And we’d like to expand it. It’s like, we looked at this type of bitter molecule, let’s see if we find something similar occurring for other types of bitter molecules, maybe for spicy molecules… see if we can find some other things that we’d like to be able to help people eat more of.”
The SPIT Lab doesn’t spend all its time researching taste perception, however.
For the past six months, Running has collaborated with Georgia Malandraki, professor in the department of speech, language, and hearing sciences and the head of the Imaging, Evaluation and Treatment of Swallowing Research Laboratory (I-EaT Lab), located in Lyles-Porter Hall.
According to Malandraki, it is common practice for hospitals and other institutions to administer thickened liquids to people who struggle with swallowing, particularly elderly patients.
“That’s because a lot of times those patients have difficulty swallowing liquids safely,” she said. “The reason for that is because as we swallow, the swallow response is a very fast and very complex. If we are not careful we may choke.”
According to Malandraki, when patients experience dysphagia, things that would be merely discomforting for a healthy person can become potentially fatal.
Over time, food and liquid can become stuck in the lungs, increasing chances of infection and other complications. Thickened water can help reduce these risks, but with a cost.
“It’s a nectar-type or a smoothie-type consistency,” said Malandraki. “It’s extremely unpleasant and all our patients say that. They all complain about it. It doesn’t quench your thirst, really. You’re still drinking the water but because it’s thick it’s not satisfying at all.”
According to Malandraki, patients who are instructed to drink thickened water often end up dehydrated, as they avoid drinking the liquid. Running and Malandraki decided to work together to come up with more pleasant solutions to keep patients hydrated and healthy.
Running is in charge of flavoring liquids and adding carbonation to see if people respond differently to the change. Malandraki said that research has shown spicy or sour flavors can make a person swallow more quickly, thereby decreasing the risk of choking.
Apart from seeing how different flavors affect people’s perceptions of the drinks, Malandraki and her team test the safety of different mixtures by conducting videofluroscopic swallow studies in the I-EaT Lab. This means that they take X-rays of liquids as participants swallow them and ensure that they are going down the correct pipe and that there are no complications.
Malandraki explained that such experiments are carefully monitored. Specialized pathologists, who can help if a participant starts to choke, stand by during each test. Small amounts of liquid are tested at a time, so risk is minimal.
“It’s not unsafe at all,” Malandraki said. “It’s done multiple times per day in most hospitals in the country and in a lot of labs, including our lab.”
The I-EaT lab stands out, however, as one of the only labs in the country that has its own X-Ray machine outside a medical setting.
“Most people that do swallowing research with an X-Ray machine do so in a hospital,” Malandraki explained. “We are the only speech pathology department in the country as far as I know, or maybe one of the two top departments, that have a fully-equipped swallowing research lab and clinic. We also see patients here as well.”
Malandraki, Running and Mattes hope that these research efforts will lead to improved tastes and experiences of food for all.
"A lot of foods that are nutrient-rich don't have the best flavor," Mattes said.
"If we could figure out ways to minimize the off-flavors in them—the bitterness, the astringency, and so on—perhaps they would find them more appealing and would consume them in higher quantities."