How hot is your chili? A new chili-shaped device could quickly indicate whether adding pepper to a meal can set the mouth on fire.
Called Chilica-pod, the device detects capsaicin, a chemical compound that helps give peppers their sometimes painful kick. In general, the more capsaicin a pepper has, the hotter it is. The Chilica-pod is sensitive, capable of detecting extremely low levels of the burning molecule, researchers reported on Oct. 23 from ACS Applied Nano Materials.
The device could be used someday to try cooked meals or fresh peppers, says analytical chemist Warakorn Limbut of Prince of Songkla University in Hat Yai, Thailand. People with capsaicin allergy could use the gadget to avoid the compound or farmers could try the harvested peppers to better indicate their spice, he says.
Adapted from ACS Applied Nano Materials 2020
The relative spiciness of a pepper is usually transmitted in Scoville heat units, an imperfect measure determined by a panel of human flavor testers. Other more accurate methods for determining how spicy are time consuming and involve expensive equipment, so the methods are not suitable for a quick response.
Introduce the portable Chilica-pod compatible with smartphones. Built by Limbut and colleagues, the instrument’s sensor is made up of stacks of graphene sheets. When a drop of a pepper and ethanol solution is added to the sensor, the pepper capsaicin triggers the movement of electrons between the graphene atoms. The more capsaicin the solution has, the stronger the electric current through the leaves.
The Chilica-pod records that electrical activity, and once its “trunk” is connected to a smartphone, it sends the information to an app for analysis. One test showed that the device can detect capsaicin levels as low as 0.37 micromoles per liter of solution, equivalent to the amount of a pepper without heat.
The Limbut team used the Chilica-pod to individually measure six dried peppers from a local market. The team found that the capsaicin concentrations of the peppers ranged from 7.5 to 90 micromoles per liter of solution. When translated to Scoville heat units, that range corresponds to the spice of peppers such as serrano or cayenne: mild varieties compared to the incipient Carolina reaper, one of the hottest peppers in the world (SN: 4/9/18).
Paul Bosland, a plant geneticist and chili breeder at New Mexico State University in Las Cruces who did not participate in the study, points out that capsaicin is just one of 24 related compounds that provide heat to peppers. “I hope (the device) can read them all,” he says.
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