12 January - 20 June 2016

Knowing whether food has spoiled without opening the container

26 Mar 14

Commonly, the shelf-life and safety of food is controlled by the use of shelf-life information such as use by and best before dates. This information is useful only if the assumption is made that the appropriate storage and transport conditions have been maintained throughout the product lifecycle. If the material has been subjected to less than optimal conditions, it may have suffered degradation that is unacceptable to the consumer.

Time-temperature indicators have long been suggested as a way of having better control over the actual conditions a material has been subjected to and therefore minimising the risks of dangerous or unacceptable products being released to the market. Previously, however, these technologies have been shown to be hard to programme to give a good comparison to the material being tracked.

Chao Zhang et al from the University of Beijing have published a paper in the American Chemical Society Nanotechnology Journal whereby the use of a precipitation of silver over gold nanoparticles forms the basis for a colour-change reaction which can be used as a visual indicator which mimics the degradation of the food by growth of E.coli, for instance.

By adaptation of conditions such as pH or presence of reducing agents in the nanoparticles, the authors claim that the rate of reaction can be tailored to closely mimic the degradation of the specific food material under the same conditions, thus providing a real-time indication of the integrity of the food.

The technology can be easily manufactured into an indicator the size of a grain of maize, is non-toxic, and despite the use of gold and silver as the key components, the materials cost is as low as $0.002 per unit, allowing it to be utilised across a wide range of goods, even those with low cost and high consumption such as milk and dairy products. [Eurekalert], [ScienceDaily]

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