Researchers have developed an artificial tongue that uses milk powder to quickly detect the spiciness of food. Inspired by the way casein proteins in milk bind to capsaicin and relieve the burning sensation of spicy foods, the team incorporated milk powder into a gel sensor. The prototype, reported in ACS Sensors, successfully detected capsaicin and other pungent-flavoured compounds, such as those in garlic.
“Our flexible artificial tongue holds tremendous potential in spicy sensation estimation for portable taste-monitoring devices, movable humanoid robots, or patients with sensory impairments like ageusia, for example,” says Weijun Deng, the study’s lead author.
Currently, measuring flavour compounds requires either human taste testers or complex laboratory methods. While scientists have developed artificial tongues for tastes like sweet and umami, the stinging and burning sensations from compounds like capsaicin in chillis or allicin in garlic are hard to replicate with synthetic materials.
The team created the sensor by adding casein to an electrochemical gel material to measure spiciness through a change in electrical current that occurs when casein binds to capsaicin.
Capsaicin cuts current
The tongue-shaped film was created by combining acrylic acid, choline chloride, and skim milk powder, which was then exposed to UV light. This resulted in a flexible, opaque gel that conducts an electrical current. When the researchers added capsaicin to the film, the current decreased after ten seconds.
Initial tests showed the material responded to capsaicin concentrations ranging from below human detection to beyond the oral pain threshold. It also detected pungent compounds found in ginger, black pepper, horseradish, garlic, and onion.
As a proof-of-concept, the team tested eight pepper types and eight spicy foods on the artificial tongue. The results from the device and a panel of human taste testers matched well. The researchers say the sensor could be used to quickly test a food’s spiciness level without risk to human taste buds.
