Last year, the Danish government ordered a recall of three Buldak spicy ramyeon products from Samyang Foods Co., saying they were too spicy. It determined that the high capsaicin content that produces spiciness posed a risk of acute poisoning. But after consumers clamored for the recall to be halted, sales later resumed for two products after their safety was recognized.
Amid a K-wave sweeping the world, food companies are competing to make spicier products. Developers are having a hard time tasting spicy prototypes every day. Scientists have found an alternative to protect food researchers' tongues: an electronic tongue that judges spiciness just like a person.
◇Matches spiciness ratings by people in their 20s
A team led by Professor Jing Hu of the Department of Chemical Engineering at East China University of Science and Technology said it succeeded in judging the spiciness of peppers and sauces like a person using an artificial tongue made of skim milk gel, according to a paper published in the international journal ACS Sensors last month.
It is hard to judge from appearance alone whether a pepper is as mild as a bell pepper or will set your mouth on fire. Sweetness, bitterness, saltiness, and umami are easier to test with an electronic tongue because there are receptor proteins that bind to the substances producing those tastes, but spiciness is different. Capsaicin itself does not produce taste; instead, it gives a heat sensation on the tongue that we perceive as spiciness.
The team mixed acrylic acid and choline chloride into skim milk to create a soft gel electronic tongue like a real tongue. Normally, the electronic tongue allows negatively charged chloride ions and positively charged hydrogen ions to move freely, letting current flow. But when it touches capsaicin, ion movement decreases, and the current drops accordingly. Using the degree of current decrease, the team assessed capsaicin content and spiciness for eight kinds each of peppers and spicy foods.
At the same time, the team had seven men and women with an average age of 22 taste the same peppers and foods evaluated by the electronic tongue. They were selected for being better than others at detecting spiciness. The team said the spiciness judged by people at 25 C indoors was almost the same as the electronic tongue's results. "The artificial tongue can quickly test the spiciness of foods without putting the taste cells of food developers' tongues at risk," the team said.
The team said it will reduce the device's size and compare its ratings with those of a wider range of people to improve accuracy. Then it could be developed into a portable taste sensor to help people who cannot properly perceive taste. Combined with other taste sensors, a humanoid robot could taste and cook like a person.
◇Inspired by how milk tamps down spiciness
When you eat spicy food, capsaicin opens an ion channel called TRPV1 in the membrane of sensory nerve cells. When positively charged ions such as calcium, hydrogen, or sodium enter the cell, they generate an electrical signal, which the brain recognizes as a sensation of heat or pain.
TRPV1 is originally a heat-pain sensor designed to respond to high temperatures above 43 C or acidic conditions, but capsaicin produces a hot sensation even at lower temperatures. The team took advantage of the fact that milk, rather than water, is good at easing pain on the tongue in this situation.
Capsaicin is a hydrophobic substance that does not combine well with water, so drinking water does not wash it off the tongue. In contrast, the fat in milk dissolves capsaicin and washes it away. Above all, a protein in milk called casein wraps around capsaicin and blocks ion flow, which relieves pain on the tongue.
In this electronic tongue as well, casein protein formed aggregates with capsaicin and blocked current. The team said the current began to decrease 10 seconds after the electronic tongue was exposed to capsaicin. The more the current decreased, the more capsaicin there was, indicating stronger spiciness.
References
ACS Sensors (2025), DOI: https://doi.org/10.1021/acssensors.5c01329