Chemists discover ‘anti-spice’ that could make chili peppers less hot

Accidentally made your food too spicy? One day, you might be able to reach for an “anti-spice” condiment to tame the heat of a dish, thanks to the discovery of chemicals found in chilli peppers that counteract their spicy sensation.

A chilli’s heat comes from compounds called capsaicinoids, which bind to receptors on nerve fibres within your mouth, sending impulses to the brain that create a burning sensation similar to those caused by a fire’s heat or a sting.

Chilli aficionados compare the heat of different strains using the Scoville scale, which is based on the concentration of capsaicinoids, yet some varieties aren’t quite as hot as their Scoville rating suggests they should be. To investigate, Devin Peterson at the Ohio State University and his colleagues used an analytical method known as liquid chromatography-mass spectrometry to determine how much of two capsaicinoids – capsaicin and dihydrocapsaicin – were in powdered samples of 10 types of peppers, including chile de árbol, African bird’s eye and Scotch bonnet.

Then they gave samples of tomato juice containing powder from the different chillis to a panel of tasters. Each contained the same amount of capsaicin and dihydrocapsaicin – which should have been enough to give all the samples a relatively mild kick of 800 Scoville units.

But the tasters perceived the heat from the 10 peppers as different, so Peterson and his colleagues performed additional chemical analyses. This identified three compounds in the chilli powder – capsianoside I, roseoside and gingerglycolipid A – that were present in high quantities in the chillies that weren’t as intense as they should have been according to the Scoville scale. All three compounds are glucosides, molecules that contain the sugar glucose.

A group of 37 tasters then tested two samples at once, one containing these suspected spice-killing compounds and one without, placed on either side of their tongue to stop an enflamed tongue affecting a second taste test. Their feedback revealed that the compounds decreased the chilli intensity by between 0.7 and 1.2 points on a 15-point scale, on average.

“They are effectively anti-spice compounds,” says Peterson. He isn’t yet sure how they work, but says they could be altering receptors on nerve fibres in the mouth in a way that results in a reduction in their burning signals.

Knowing about these anti-spice chemicals could allow growers to breed or genetically modify plants so they lack them to create valuable, even hotter chillis, or breed very mild fruit with higher amounts of anti-spice, says Peterson.

Using the compounds could also enable the creation of a household ingredient to tone down excessive heat in dishes, he says, or they could work as relievers for severe pain by blocking pain signals.

“Sometimes when I’ve ordered food with my kids and it’s too spicy, that’s a no-go,” says Peterson. “So, the idea of having some kind of a natural compound to dial it back may be appealing.”

“The way the study was done using the half tongue was very clever,” says Barry Smith at the University of London’s School of Advanced Study, adding that it shows the Scoville scale isn’t a very precise instrument for describing how hot a chilli is.

Smith also wonders if the perceived intensity of menthol or mint, which cause a cooling sensation in a similar way to how capsaicinoids cause a burning one, could also be muted by these kinds of compounds.