Connoisseurs of Mexican and Indian cuisine expect a spicy kick from the chilies used in these ethnic dishes, but less appreciated is the science behind such mouth-numbing experiences. In reality, the burning sensation a chili leaves behind has more to do with chemistry than cooking. So much so that Professor of Chemistry Robert Thompson and senior Michael Pennino have spent the entire academic year studying the compounds that trigger this often eye-watering reaction.

The compounds, known as capsaicinoids, are present in almost every type of chili pepper. Individual peppers contain approximately 15 to 20 of these compounds, varying in both amount and potency. Scientists have traditionally focused their research on the two most abundant compounds in chilies—capsaicin and dihydrocapsaicin, as well as the synthetic compound N-vanillyl nonanamide—but Thompson and Pennino plan to isolate and study the more numerous minor capsaicinoids.

While chili peppers may seem like an odd choice for a research topic, both Thompson and Pennino are quick to point out that capsaicinoids are found in a variety of common products, including self-defense sprays and topical pain relievers. However, the individual compounds are not easy to isolate in nature or synthesize in the lab, so manufacturers routinely use a mixture of the three most common capsaicinoids, or whole extracts from peppers, in their products.

"By isolating and characterizing the minor capsaicinoids, we may discover a compound with a higher heat index or fewer side effects than ones currently in use,"says Thompson. "This will lead to a more complete picture of each compound and eventually to a better formulation of products containing capsaicinoids.”

Since September, Pennino has been working with several samples of pre-packaged capsaicinoids to find a technique that will allow him to extract and separate the multiple compounds found in chili peppers. Using a process called solid phase extraction (SPE), he is able to separate the different capsaicinoids by trapping them on a solid absorptive material. Different solvents are then added to remove and collect the individual compounds. This process, and the notes to document it, will be critical when Thompson and Pennino begin working directly with chili pepper fruits.

After they separate the capsaicinoids, Pennino will use high performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) spectroscopy to determine the characteristics of each compound. Although both processes will help him identify and eliminate the known capsaicinoids from his samples, only NMR spectroscopy will allow him to piece together a picture of the unidentified compounds through spectral analysis. This requires use of the chemistry department's nuclear magnetic resonance (NMR) spectrometer, a piece of equipment not many undergraduates can operate.

"You can learn about the history and function of certain instruments or procedures in the classroom, but that doesn't mean you'll automatically be a pro in the lab," Pennino says. "That takes a lot of time and practice. Being able to work with the NMR spectrometer and learning new techniques to separate compounds from each other has been a great experience for me." Assistant Professor of Chemistry Manish Mehta is overseeing Pennino's work with the NMR spectrometer. But in all other matters, Pennino defers to Thompson.

"Michael is very much my partner and collaborator," says Thompson. "He's done a good deal of the background research for this project and has become proficient with the NMR spectrometer.”

As an aspiring environmental chemist, Pennino hoped to find a project that would further his analytical skills and prepare him for graduate school. In his work with Thompson, Pennino has met that goal and then some. But he's also discovered a pleasant, if surprising, bonus: people understand his research.

"I like that I can talk to people about this project, even people not interested or familiar with science," he says. "I think they can relate to the idea of chili peppers and capsaicinoids, and how these compounds can be used to make food even spicier, pepper sprays more powerful, or improve the effect of arthritis creams.”