New sensor could help tell if meat or fish has gone bad

According to a report on the website of German weekly Der Spiegel on June 5, nearly one-third of the world's food is thrown into the garbage dump. The average German throws away 55 kilograms of fruit, vegetables, bread and meat every year. This is not only a waste of food, but also has an adverse impact on the environment.

About half of the food that is thrown away is still edible. It is just thrown away as garbage because it is past its expiration date.

Researchers have now developed a sensor that can help identify whether meat and fish have gone bad.

The device consists of a sheet of paper with tiny carbon electrodes printed on it. Firat Guder of Imperial College London and his colleagues built a prototype by exploiting the hygroscopicity of paper. "Although the paper feels and looks dry, it is always wet," they wrote in the professional journal Sensors of the American Chemical Society. At 50% relative humidity, the water accounts for about 5% of the total weight of the paper.

The scientists go on to write that by measuring the conductivity of the thin film of water in the paper, it is possible to tell which substances are dissolved in it. If there are water-soluble gases in the surrounding environment, the conductivity of the paper will increase. Ammonia and trimethylamine, which are produced when meat or fish spoil, are also water-soluble gases. The measurement results can be read out using an app.

The researchers also integrated their sensor with a near-field communication chip. This technology can read information through electromagnetic induction. When no decaying gases are detected in the paper and the meat and fish are still edible, the researchers' app will automatically pop up, while if the food is spoiled, the app will not respond.

The researchers said that in laboratory tests on packaged fish and chicken, the sensor's detection results were more accurate than existing technologies. At the same time, the new system costs only 2 cents per unit, which is very cheap. And the sensor is biodegradable and non-toxic. Therefore, it meets several key points that have caused problems in previous attempts to develop similar sensors.

Researchers are also developing packaging materials that change color according to the state of food. However, so far, they have not been used commercially because the cost is too high or the results are difficult to interpret.

Judel and his colleagues point out that the sensor currently developed is the first commercially available variant of its kind. It is technically feasible to mass-produce the sensor. The scientists hope that food manufacturers and supermarkets will introduce the instrument within the next three years.

Before then, they plan to further improve the system and expand the detection of other foods. Most of the food that is thrown away is fruits and vegetables. To detect the status of fruits and vegetables, the researchers are developing a system that can identify single types of gases and humidity changes in packaging.