Think you can judge a chili’s heat by sight? An artificial tongue can and it senses spiciness faster than humans, helping food testing, robots, and health monitoring.
Determining how spicy a food is cannot be done by looking at it. The visual appearance of a hot sauce or pepper does not reflect its heat, and current methods to assess spiciness rely on taste testers or complex laboratory procedures. These approaches are slow, subjective, and not practical for many uses.
To address this, researchers at Shanghai Institute of Technology have developed an artificial tongue capable of quickly detecting spice levels. The device could benefit food manufacturers, chefs, portable taste-monitoring devices, mobile humanoid robots, and patients with sensory impairments such as ageusia, providing a fast and objective measure of spiciness.
The team was inspired by casein proteins in milk, which bind to capsaicin and reduce the heat of spicy foods. Using this principle, they incorporated milk powder into a gel sensor. The spiciness is measured through changes in electrical current caused when casein binds to capsaicin.
To build the sensor, the researchers combined acrylic acid, choline chloride, and skim milk powder, then exposed the mixture to UV light, producing a flexible, opaque, and electrically conductive tongue-shaped film. When capsaicin was applied to the surface, the current decreased within 10 seconds, showing the material’s ability to detect spicy compounds.
Initial tests demonstrated that the milk-based material responded to capsaicin concentrations ranging from below the human detection threshold to levels exceeding oral pain limits. It also detected other pungent compounds commonly found in hot sauces, including ginger, black pepper, horseradish, garlic, and onion.
In a proof-of-concept study, the team tested eight pepper varieties and eight spicy foods, including several hot sauces. The artificial tongue measured spiciness through electrical current changes, and its readings closely matched evaluations from a panel of human taste testers.
The researchers suggest that this casein-based artificial tongue could provide a rapid, reliable method to determine food spiciness, helping protect taste buds from potential discomfort while enabling broader applications in food quality testing and sensory monitoring.
