'Sniff test' technology for meat and fish products

Use-by dates and even the good old ‘sniff test’ are currently used by consumers to see if their food is safe to eat. Now researchers based at Imperial College London have developed laboratory prototype sensors costing just two US cents each, which could make these food test methods a thing of the past.

Known as 'paper-based electrical gas sensors' or PEGS, the technology detects spoilage gases such as ammonia and trimethylamine in meat and fish products.

Existing food spoilage sensors are not commonly used because they're either too expensive (often comprising a quarter of overall packaging costs) or too difficult to interpret. Colour-changing sensors could in fact increase food waste as consumers might interpret even the slightest colour change as 'bad food'.

The researchers who developed PEGS made the sensors by printing carbon electrodes onto readily available cellulose paper. The biodegradable materials are eco-friendly and nontoxic, so they don't harm the environment and are safe to use in food packaging. The sensors are combined with near field communication (NFC) tags — a series of microchips that can be read by nearby mobile devices.

During laboratory testing on packaged fish and chicken, PEGS picked up trace amounts of spoilage gases quickly and more accurately than existing sensors, at a fraction of their price.

The researchers say the sensors could also eventually replace the 'use-by' date — a less reliable indicator of freshness and edibility.

Lead author Dr Firat Güder, of Imperial's Department of Bioengineering, said: "Although they're designed to keep us safe, use-by dates can lead to edible food being thrown away. In fact, use-by dates are not completely reliable in terms of safety as people often get sick from foodborne diseases due to poor storage, even when an item is within its use-by.

"Our vision is to use PEGS in food packaging to reduce unnecessary food waste and the resulting plastic pollution."

Features of the PEGS technology include:

• Function effectively at nearly 100% humidity, where most sensors struggle above 90%.
• Work at room temperature and do not need to be heated, so they consume very low amounts of energy.
• Are sensitive only to the gases involved in food spoilage, whereas other sensors can be triggered by non-spoilage gases.

What's next?

The researchers used ballpoint pens and robotic cutters to create the sensors. Dr Güder said: "We believe our very simple technique could easily be scaled up to produce PEGS on a mass scale by using existing high-volume printing methods such as screen printing and roll-to-roll printing."

The authors hope that PEGS could have applications beyond food processing, like sensing chemicals in agriculture and sensing air quality, and detecting disease markers in breath like those involved in kidney disease. However, before they can be applied beyond their current use, the researchers hope to address how sensitive PEGS are to lower humidity.

Next, the authors hope to expand the usefulness of PEGS by applying them to other types of food and industries. They are currently developing an array of PEGS in which each sensor detects a different chemical. Using this technique, the array will give unique signals for different gases and/or changing humidity, which would make the technology applicable to a wider variety of food types and applications.

The research was published in ACS Sensors and the work was funded by the Engineering and Physical Sciences Research Council (EPSRC).

Image credit: ©stock.adobe.com/au/Sergey Ryzhov