Researchers at Kyushu University have reportedly developed a flexible film embedded with a natural plant pigment that shifts colour as food spoils, giving consumers a visible signal without opening the package. The material can also repair its own cuts, keeping bacteria out during shipping and handling.
Announced via a study published in Chemical Engineering Journal, the film utilizes anthocyanins - the pigments behind the colour of purple sweet potatoes and red cabbage – to track chemical signature shifts in food such as meat. As the food’s pH rises, the anthocyanins turn from purple-red to yellow-green, and their natural origin is said to make them safe for food contact.
However, the researchers say light and heat can disrupt their colour response, causing false readings and making them unreliable as a long-term indicator. To stabilize the anthocyanins, the team used UiO66-NH₂, a metal-organic framework (MOF) known for its ‘thermal and chemical stability’.
“MOFs have attracted enormous attention because of their unique porous structures and versatile functions, and I became curious whether they could be used for something closer to everyday life, like food preservation,” recalls Xirui Yan, corresponding author of the study and a JSPS researcher at Kyushu University’s Faculty of Agriculture.
Apparently, anthocyanin molecules absorb onto the MOF’s surface through multiple chemical interactions, anchoring it in place. The molecules are shielded from the oxygen, light and heat that drive degradation while remaining sensitive to pH. In food tests using pork, the protected pigment proved consistently responsive: as the meat spoiled and alkaline gases accumulated, the material shifted continuously from purple-red to yellow-green, giving a readable signal at every stage.
The team then incorporated the anthocyanin-loaded MOF into a hydrogel, producing a soft, shapeable film that is ‘largely plant-derived’ and biodegradable. The researchers state that the material also extended the shelf life of pork by about 12 hours compared to untreated samples.
The film is also capable of repairing itself; when cut and pressed back together, the damage becomes ‘nearly invisible’ within minutes and tensile strength recovers to 99% within two hours. Fumihiko Tanaka, professor at Kyushu University’s Faculty of Agriculture, says: “In conventional packaging, any crack is permanent and becomes an entry point for bacteria. This material bonds back together on its own. The wound heals, and so does its ability to protect what’s inside, which makes it more durable and reliable in practical use.”
The team is now exploring a companion smartphone app, hoping to give manufacturers, logistics companies and shoppers a reliable, objective way to assess food quality in real time.
In similar news, Vitsab International unveiled its Freshtag Flight Label in May, designed to change colour based on temperature exposure and tackle food waste in perishable airline meals. The label uses ‘stoplight’ colour-change technology to signal a product’s integrity: green for safe conditions, yellow for moderate, and red after exposure to unsuitable temperatures.
This month Altopack introduced a new resealable zip pack for spaghetti allowing consumers to reseal the pack after each use, preserving product freshness and protecting it from external contamination over time. Altopack states the new pack has been specifically developed for spaghetti and is also available in a bundled version, featuring individual 100 gram portions wrapped with food-grade paper bands.
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