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When biting into a chili pepper, you expect a fiery sensation on your tongue. This spiciness is detected because of capsaicinoid compounds. But for some peppers, despite high levels of capsaicinoids, the heat is mysteriously dull.

Now, researchers reporting in the have identified three compounds that lessen peppers' pungency. These results challenge the reliability of the century-old Scoville scale, which traditionally bases its rating on two capsaicinoids.

"The discovery of natural dietary compounds that reduce pungency presents promising opportunities for both the food and pharmaceutical industries," says Devin Peterson, the corresponding author of the study.

Capsaicinoids are a group of compounds that produce the strong spicy sensation or pungency that comes with consuming chili peppers. The combined amount of capsaicin and dihydrocapsaicin in a pepper is used to calculate its heat intensity rating on the Scoville scale, ranging from zero Scoville Heat Units (SHU) for bell peppers to millions of SHU for the hottest peppers.

However, some of these fruits have less heat than would be expected from their Scoville rating, which suggests that something else in the pepper influences that spicy sensation. So, Peterson, Joel Borcherding and Edisson Tello wanted to investigate multiple chili pepper varieties for potential spiciness suppressors.

Initially, they collected dry, powdered samples from 10 types of peppers, including Chile de árbol, serrano, African bird's eye, Fatalii and Scotch bonnet. The amount of capsaicin and dihydrocapsaicin in each was determined by liquid chromatography mass spectrometry. Then a trained panel of taste testers evaluated the intensity of the powders in tomato juice.

Each mixture had 800 SHU (a level meant to be spicy but tolerable). Despite the same amount of capsaicin and dihydrocapsaicin in each tasting sample, the 10 peppers' perceived heat intensities ranged significantly, suggesting other chemical constituents in the peppers impacted the sensation.

After additional chemical composition analyses on the pepper powders and performing complex statistical analysis, the researchers identified five compounds that could be modulating pepper spiciness.

Another set of panelists assessed whether these compounds, alone or in combination, changed the pungency of capsaicin and dihydrocapsaicin. Three of the five compounds (capsianoside I, roseoside and gingerglycolipid A) reduced the heat intensity, though they didn't have an additive effect when combined. In addition, none of the spiciness suppressors had a noticeable flavor in water.

"These advancements could enable the customization of desirable spicy flavor profiles or lead to the creation of a household ingredient designed to tone down excessive heat in dishes—the anti-spice," says Peterson. "Additionally, they hold significant medical potential in the design of (non-opioid) analgesic agents for pain management."