Smart oxygen sensor to let consumers know if food is safe to eat or ready for the bin

A sensor that changes colour in the presence of oxygen could be useful in the food packaging industry, according to its UK inventors. The sensor turns blue in excess oxygen, indicating to the consumer that the food should be thrown away.

Oxygen promotes food spoiling processes such as microbial growth and protein decomposition. That’s why a lot of food is packaged using modified atmosphere packaging, in which inert gases like nitrogen and carbon dioxide are flushed through the package to reduce the oxygen concentration. There are already techniques to monitor oxygen in food packages, however, they can be expensive and some require specialist analytical equipment and trained operators. The simplicity of the colour change sensor developed by Andrew Mills and co-workers at Queen’s University, Belfast, is that the package’s integrity can be seen in situ by the consumer and is cheap enough for commercial use. 


Photographs of pork, packaged along with an oxygen smart plastic film. The package was sealed in the absence of oxygen (a) and the indicator activated (b). The lid was then broken and lifted back, and photographed immediately (c), after 1 day (d), 2 days (e) and 4 days (f) in a fridge at 5 degrees Celsius

The sensor, which is made of titanium nanoparticles coated with methylene blue dye and sacrificial electron donor DL-threitol, is activated for use by photobleaching with UVA radiation. After the photobleaching stage, the sensor will only turn blue in the presence of oxygen - this process can be recycled, but only by repeating the photoactivation stage. By incorporating this technology into food packaging, huge volumes of food waste could be prevented, claims Mills. ’In the UK alone, we throw away over ?10 billion of avoidable food waste per year. Indicators in food packaging can help reduce this by informing the customer (the retailer, wholesaler or consumer) as to the state of the food,’ he says. ’Many of us throw away food simply because we are unsure of its freshness - a ’consume within’ indicator would help address this issue.’

Joe Kerry, an expert in innovative food packaging at University College Cork, Ireland, agrees that this is an interesting area of research. ’We’ve moved away from oxygen removal materials because people had all kinds of issues with the active packaging sachet, mainly because people were actually consuming them!’ he says. ’The technology presented here really is excellent and is a different kind of system to our own. The thing about this technology is that it is non-reversible - an accumulated colour change over time. There are pros and cons to using a system that is either non-reversible or reversible.’ 

Emma Eley