The inadequacy of date labels on perishable foods, which often fail to accurately predict when they become unsafe to consume, can have adverse consequences such as increased food waste and a higher likelihood of foodborne diseases. To address this concern, Benedetto Marelli from the Massachusetts Institute of Technology suggests the adoption of biodegradable food packaging that alters its color, which will provide a visual cue for eaters to identify spoiled food.
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Benedetto and his colleagues took the initiative to create packaging that responds to changes in contents so as to provide a more effective indication of food spoilage.
They developed four films that were similar to plastic wrap, each comprising two layers. One layer incorporated a protein sourced from silkworm silk, whereas the second layer featured one of four covalent organic frameworks (COFs). These COFs encompass carbon and hydrogen, alongside diverse atoms like oxygen or nitrogen, meticulously arranged in a grid-like fashion to allow for material porosity.
Once the researchers had ensured the elasticity, durability, and non-toxicity of all four films for packaging, they proceeded to test their compostability. The film that performed the best showed a 50 percent degradation within 30 days when placed in soil, a level comparable to currently available biodegradable plastics.
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When exposed to solutions of varying pH values, the new material underwent a color transformation as a result of proton and electron exchange between the COF layer and the liquid. Taking advantage of the fact that the pH of food rises during spoilage, the team of scientists conducted an experiment using a segment of the film as a clever, color-changing label on a traditional packet of raw chicken. Initially orange, the label transformed into yellow and became 17 percent lighter after 20 hours at 30°C (86°F), signaling the beginning of spoilage.
Ultimately, the researchers harnessed the porous composition of the COFs to infuse the film with an antimicrobial compound. They then wrapped soya beans in this film and expose them to extreme heat and humidity. After a span of 15 days, the beans encased in the innovative material displayed approximately one-third the amount of mold growth as beans wrapped in conventional plastic.
Julian McClements, a professor at the University of Massachusetts Amherst, believes that future packaging should change color when spoiled, but in order for this to have a real impact, it must be both affordable and easy to manufacture. Marelli emphasizes that meeting the high standards set by plastic production is a formidable hurdle.
The findings of the team's study were published in the journal ACS Nano.
