The visual characteristics of a hot sauce or pepper do not indicate its spice levels. Therefore, researchers have developed an artificial tongue that quickly detects spiciness.
Inspired by the casein proteins in milk that bind to capsaicin and relieve the effects of spicy foods, researchers incorporated milk powder into a gel sensor. This prototype, recorded in ACS Sensors, detected capsaicin and pungent-flavored compounds in various foods.
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.
Weijun Deng, Study Lead Author, Shanghai Institute of Technology
Assessing flavor compounds in food currently involves taste testers and intricate laboratory techniques. As an alternative, researchers are developing artificial tongues capable of detecting various tastes, including sweet and umami.
However, compounds such as capsaicin in chili peppers, piperine in black pepper, and allicin in garlic elicit stinging, tingling, or burning sensations that are challenging to replicate and quantify using synthetic materials.
Jing Hu and team observed that the heat from peppers, for instance, can be mitigated when capsaicin interacts with casein proteins present in milk. Consequently, the research team aimed to develop an artificial tongue that incorporated casein into an electrochemical gel and measured the spiciness through variations in electrical current that occur when casein binds with capsaicin.
The researchers developed a film shaped like a tongue by merging acrylic acid, choline chloride, and skim milk powder, before exposing the mixture to UV light. The resulting gel was flexible, opaque, and capable of conducting an electrical current. After 10 seconds of applying capsaicin to the film's surface, a decrease in current was observed, indicating its potential use as an artificial tongue for detecting spices.
Preliminary tests revealed that the milk-based material was responsive to capsaicin concentrations that ranged from levels below human detection to those exceeding the threshold of pain experienced orally. The material identified other pungent compounds commonly found in hot sauce ingredients, including ginger, black pepper, horseradish, garlic, and onion.
In a proof-of-concept study, the researchers evaluated eight varieties of peppers and eight spicy foods, which included several hot sauces, using an artificial tongue to assess their spiciness based on variations in electrical current.
A group of taste testers also rated the spiciness of the same items. The findings from the artificial tongue correlated closely with the assessments made by the tasting panel. Consequently, the researchers propose that the casein-based artificial tongue could serve as a rapid method for determining the spiciness level of foods, protecting one’s taste buds from potential discomfort.
The authors received financial support from the National Natural Science Foundation of China and the Fund of Fujian Provincial Key Laboratory of Leather Green Design and Manufacture.
Journal Reference:
Deng, W., et al. (2025) A Soft and Flexible Artificial Tongue for Pungency Perception. ACS Sensors. doi.org/10.1021/acssensors.5c01329.