Toward a fully edible sensor showing if frozen food has previously thawed

When you're standing in the frozen food aisle, it's almost impossible to know if the Salisbury steak has thaw and refrozen. A device made of table salt, red cabbage and beeswax has been designed to let you know. When it's warmed above a specific temperature, the proof-of-concept sensor can provide a color reading.

It's important to keep food cold to retain its flavor and quality, reduce the risk of food poisoning, and decrease the amount of waste. Researchers have developed devices that alert manufacturers when cold items are exposed to cold temperatures, but they only show changes above freezing. Materials with electrical properties that are altered upon melting could be used to create a sensor for frozen products. It would be great if the changes could be visible. An electronic device that uses only food and consumables would be the safest way to look at food. Ivan Ilic, Mario Caironi and colleagues set out to develop the first fully edible, self-powered temperature sensor that could be used with frozen products.

The device that generated an electrical current as it defrosted was built by the researchers and held in a plastic container. The device was tested with solutions of frozen electrolytes and naturally electrolyte-rich foods. The researchers say that the current could be adjusted based on the amount of salt and the temperature. This device was connected to a color-changing system, containing tin and gold electrodes and red cabbage juice, that produced an irreversible shift from red to blue when current was applied.

The self-powered device could be used for frozen food monitoring after the team put all of the parts together in a block of beeswax. According to the researchers, their proof-of-concept sensor paves the way for food to be used in inexpensive, safe technologies that alert customers to a frozen product's storage history.