Knowing whether a frozen food has thawed and refrozen is quite impossible, a process with possibly detrimental consequences. Therefore, scientists have built a food-grade tool from edible materials, including red cabbage, table salt, and beeswax, which lets customers know.
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The proof-of-concept sensor offers a color readout when it is warmed above a particular temperature, which is adjustable from -58 °F to 32 °F. Details of the novel sensor can be found in ACS Sensors.
Ensuring food is maintained cold while being transported and stored is crucial to preserving its quality and flavor, decreasing the risk of food poisoning, and curtailing waste. Although scientists have created devices that raise alarms when cold products are exposed to undesirable temperatures, they only specify variations above freezing.
To develop a sensor for frozen items, one answer could be to utilize materials with electrical properties that are changed upon melting. It would also be suitable if such variations could generate a signal, like a noticeable color change. Furthermore, an edible electronic device, which uses only food and consumable parts, would be the safest method to screen food. Therefore, Mario Caironi, Ivan Ilic, and their contemporaries decided to build the first-ever completely edible, self-driven temperature sensor with a visible color indicator for use with frozen items.
The researchers began by designing a device that produced an electrical current as it thawed, linking gold and magnesium electrodes through an electrolyte solution kept in a plastic container. They tried out the device with solutions of frozen consumable electrolytes, including calcium-containing salts and table salt, and naturally electrolyte-copious foods, including a melon, grape, and apple.
As the solutions thawed, they transmitted current between -58 °F and 32 °F, which the scientists say can be tweaked, based on the quantity and identity of the salt. Then, this device was linked to a color-changing system, comprising gold and tin electrodes and red cabbage juice, that created an unalterable shift from reddish purple to blue when the current was applied. Finally, the scientists place all of the components together in a block of beeswax that held the temperature-driven and indicator solutions in individual chambers and showed that the self-driven device could be used for the monitoring of frozen food.
The team stated that their proof-of-concept sensor opens the door for edible materials to be used in low-cost, safe technologies that warn customers of the storage history of a frozen item. The scientists are grateful for the funding from the European Research Council, the European Union's Horizon 2020 program, and the Sustainability Activity of Istituto Italiano di Tecnologia.
Ilic, I. K., et al. (2022) Self-Powered Edible Defrosting Sensor. ACS Sensors. doi.org/10.1021/acssensors.2c01280.