Why do we eat what we eat?

Sensory Evaluation Center looks at the factors behind food choice.

When it comes to food choice, Nadia Byrnes is something of a natural. “My friends always joke that when they need a new place to eat they don’t Google it, they just ask me,” says the Penn State doctoral student. “My bucket list is restaurants.”

Not exactly a surprise, then, that Byrnes eventually landed in the laboratory of John Hayes, assistant professor of food science. Hayes, who directs the University’s Sensory Evaluation Center, is interested in why people eat the foods they do. He approaches this complicated question from the relatively fresh angle of sensory  science. “Technically,” Byrnes explains, “it’s a subset of food science. But it has roots in neurobiology and psychology as well.”

Could measurable personality characteristics like sensation seeking, or sensitivity to punishment or reward, be linked to a love of spicy food?

“I’m interested in why people eat the food they do,” Hayes says, “and I study that using sensory science methods within a broader biobehavioral framework. We use scientific methodology to take out a lot of the biases people have when reporting what they experience in terms of flavor.”

Applied sensory testing at Penn State dates back to the early 1970s, but the University invested anew in sensory science in 2006 with the construction of the Sensory Evaluation Center as part of a new Food Science Building. The Center is a state-of-the-art testing facility used for both industry trials of new food products and cutting-edge research. When Hayes was hired in 2009, he became the first tenure-track faculty member in sensory science.

Accounting for Taste

Hayes’ work explores variations in individual taste perception, with recent studies showing biological differences in people’s abilities to taste salt and judge the qualities of wine. In 2011, he embarked on a large multiyear project aimed at sorting out the welter of genetics, biology, and personality factors involved in chemesthesis, or what he calls “all the non-taste stuff that goes on in the mouth.”

The tingle of carbon dioxide, the cooling of menthol, the astringency of red wine, the burn of chili pepper—all are chemesthetic sensations. As a part of Hayes’ larger study, Byrnes has focused on the last of these, exploring the possible relationship between the love of capsaicin, chili’s active ingredient, and aspects of personality.

Earlier researchers have looked at the psychology of spicy food, Byrnes notes. In the 1970s, Paul Rozin at the University of Pennsylvania, coined the term “benign masochism” to explain why a person would develop an affinity for the “biologically aversive stimulus” of a mouth that feels like it’s on fire. To him it seemed akin to the thrill of gambling or riding a roller coaster, slaking a desire for new and slightly dangerous sensations.

The tingle of carbon dioxide, the cooling of menthol, the astringency of red wine, the burn of chili pepper—all are chemesthetic sensations.

Hayes and Byrnes wanted to push that insight even further. Could measurable personality characteristics like sensation seeking, or sensitivity to punishment or reward, be linked to a love of spicy food?

Break for Chocolate

Burn intensity is another important variable. Are the people who most dislike chili’s  heat simply the ones who feel it most? To gauge individual variability, Hayes’ team gave out sample cups of water spiked with mounting concentrations of capsaicin.

Another of Hayes’ graduate students, Meriel Harwood, is looking at chocolate, and specifically, at how much bitterness chocolate lovers will tolerate in their favorite treat.

Female student hold cutting board with chopped chocolate.

Meriel Harwood

Food science graduate student Meriel Harwood tested chocolate lovers to see how much bitterness they would tolerate in their favorite treat. Her findings may lead to cost savings for the food industry.

Image: Patrick Mansell

Working with Hayes and Greg Ziegler, professor of food science, Harwood divided study participants into two groups based on whether they preferred milk chocolate or dark chocolate. Participants tried a series of dime-sized chocolate samples, some of them containing increasing amounts of a bitter-tasting substance called sucroseoctaacetate, or SOA.

While the milk chocolate group quickly rejected the SOA-laced samples, she reports, the dark chocolate group continued to like the candy. In the end, the dark chocolate group had a “rejection threshold” more than 2.5 times that of milk chocolate lovers.

Harwood suggests that tests of rejection thresholds in food may be a simpler and more direct way to test food preferences than the more commonly used detection threshold.

“There may be a disconnect between preferences and the ability to detect tastes, like bitterness,” she says. “In other words, using detection threshold tests may not predict consumer acceptability.” Using rejection threshold tests instead, she suggests, may lead to cost savings for the food industry.

Feel the Burn

Of her own preliminary results, Byrnes says, “We expected that subjects who reported liking the burn would eat more spicy food, and that’s what we found. We also expected those who reported eating more would have lower burn intensity, but we didn’t find any evidence of that.” The discrepancy may be due to variation in subjects’ own definitions of what constitutes spicy, she concedes, “but even without taking into account the possible differences in the actual grams of capsaicin ingested, we found some interesting relationships between personality traits and liking of spicy food.

“We expected the sensation-seekers to rate spicy meals higher, for example, and they did. But there was variation in their responses depending on the type of spicy meal. Some people like Asian cooking—which may include capsaicin but has other chemesthetic ingredients, too, like ginger and Wasabi—yet they don’t like chili barbecue. Why do they like one type of spicy and not another?”

Perhaps predictably, Byrnes reports, sensation seekers don’t seem as sensitive to the heat. “They don’t rate it as intense. And again we’re not sure if that means that biologically they’re not getting as much of a response, or if they’re desensitized, or if they are the type of person who went skydiving the day before, so the burn of capsaicin in relation to the rush of adrenalin doesn’t rate that high.”

A female graduate student in blue lab coat holds a swab up to the tongue of a male volunteer.

Nadia Byrnes

Food science graduate student Nadia Byrnes demonstrates taste-test technique in Penn State's Sensory Evaluation Center, a state-of-the-art facility used for both industry trials of new food products and cutting-edge research.

Image: Patrick Mansell

There’s still a lot to sort out, in short. “Food choice,” Byrnes stresses, “is a really complex system that takes into account cultural expectations, the physical environment, cost, cravings—and as we’re learning, there may be genetic components, too. It isn’t easy to separate.”

As Harwood puts it, “We bring a bunch of cultural and emotional baggage with us when we eat. What you grow up with, what you are used to, what you know, for example, can all influence your preferences.”

Hayes is even more succinct. “We don’t all live in the same taste world,” he says.