Colour-chain metals could support supply chain safety

Dr Cathleen Crudden and her colleagues at Queen’s University in Ontario have discovered modified metals that change colour in the presence of gases, including nitrogen, oxygen and carbon monoxide.

The discovery could potentially form the basis of an early warning system to alert manufacturers, distributors or retailers if modified atmosphere packaging (MAP) is compromised, for example.

However, such a system is unlikely to be useful for alerting consumers, cautions Kaarin Goodburn, secretary general of the Chilled Food Association in the UK:

“This sort of development could potentially have a use further up the food supply chain where people might understand how to use it, but it couldn’t be used in consumer packaging where it might create a conflict between the use by date and the gas indicator.” ​

Goodburn told FoodProductionDaily that MAP is generally used in foods subject to use-by-dates that relate to food safety, so manufacturers cannot risk introducing a potentially conflicting warning system that might cause confusion among consumers.

This is different from the situation with pop-up warning buttons on jars and bottles, for example, because those foods are typically subject to best before dates that relate to product quality rather than safety.

Crudden is a professor in the Department of Chemistry. She and her colleagues first discovered the novel colour changes when working with rhodium – the main metal used in the production of catalytic converters. "We initially found out by accident that modified rhodium reacts in a colourful way to different gases,"​ she says.

Rhodium that is modified using carbon, nitrogen or hydrogen-based complexes changes to yellow in the presence of nitrogen, deep blue in the presence of oxygen and brown in the presence of carbon monoxide.

The colour change occurs because of the way that the gases bind to the compound’s central metal, say the researchers. The changes take place without disrupting the exact placement of individual atoms in the compound’s crystalline lattice.

The team is now investigating whether cobalt, a significantly cheaper metal than rhodium, reacts similarly.