Biodegradable food packaging could alert eaters that their food is spoiling by changing colour.
Date labels put on perishable foods are often poor predictors of when food will become dangerous to eat, which can lead to both food waste and food poisoning, says at the Massachusetts Institute of Technology.
So, he and his colleagues decided to create packaging that can react to changes in the food it contains to better indicate when it has gone bad.
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They made four films similar to plastic wrap, each consisting of two layers. One layer was made from a protein extracted from silkworm silk, while the other was made of one of four so-called covalent organic frameworks (COFs). These materials contain carbon and hydrogen, but also different atoms like oxygen or nitrogen, all arranged into an even grid with enough space between them to make the material porous.
After checking that all four films were stretchy and robust enough to act as packaging, as well as non-toxic, the researchers tried to compost them. For the best performing film, 50 per cent of it degraded after being placed in soil for 30 days, which is comparable to existing biodegradable plastics.
The new material also changed colour when immersed in solutions with different pH values, due to the COF layer exchanging protons and electrons with the liquid. Because the pH of food increases as it spoils, the researchers tried to use a piece of the film as a smart, colour-changing label attached to a conventional packet of raw chicken. The label started off orange but turned yellow and got 17 per cent lighter after 20 hours at 30掳C (86掳F), indicating that the meat had begun to spoil.
Finally, the researchers exploited the COFs鈥� porous structure to load the film with an antimicrobial chemical. They then packaged soya beans in the film and left them out in high heat and high humidity. After 15 days, the beans wrapped in the new material had about a third as much mould as beans wrapped in conventional plastic.
at the University of Massachusetts Amherst says that it will be good for future packaging to change colour in response to spoiling, but for it to make a real impact it also must be affordable and easy to produce in large quantities. 鈥淭he bar for competing with plastic production is very high,鈥� says Marelli.
ACS Nano
