Researchers at Kyushu University announced on Aug. 7 the development of a soft, flexible film for food packaging that changes color to indicate spoilage. The material, described in a study published in Chemical Engineering Journal, uses a natural plant pigment to provide consumers with a visible signal about food freshness without opening the package.
The new packaging incorporates anthocyanins, pigments found in purple sweet potatoes and red cabbage, which shift from purple-red to yellow-green as pH rises—a chemical change associated with meat spoilage. To stabilize these pigments against light and heat—which can otherwise cause false readings—the team adsorbed them onto UiO66-NH₂, a metal-organic framework known for its stability.
In tests using pork, the protected pigment responded consistently as alkaline gases accumulated during spoilage. The material shifted color continuously from purple-red to yellow-green at every stage of deterioration. The researchers also incorporated this stabilized pigment into a hydrogel film that is largely plant-derived and biodegradable. This film extended the shelf life of pork by about 12 hours compared to untreated samples.
Fumihiko Tanaka, Professor at Kyushu University's Faculty of Agriculture, said, "Another interesting thing about this material is that it doesn't just protect food—it heals itself." He added, "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." When cut and pressed back together, damage became nearly invisible within minutes; tensile strength recovered to 99% within two hours.
The research team is now exploring development of a companion smartphone app intended to help manufacturers, logistics companies, and shoppers objectively assess food quality in real time.
Fumina Tanaka, Associate Professor at Kyushu University’s Faculty of Agriculture, said: "This doesn't have to stop at food packaging... Smart materials built from natural ingredients and nanotechnology may have uses we haven't imagined yet. If anyone sees a place where this could work, we'd love to hear about it."
