Kyushu University develops color-changing smart food packaging

Researchers at Kyushu University have developed a smart, self-healing hydrogel packaging film designed to indicate food spoilage through visible color changes. The material uses anthocyanins, natural pigments derived from purple sweet potatoes, which respond to changes in pH levels.

As meat spoils, bacteria break down proteins and release alkaline compounds, raising the pH level. The packaging reacts to this shift by changing from a purple-red color to a yellow-green color, allowing consumers to detect freshness issues without opening the package.

To prevent heat and light from compromising the pigment's reliability, the team integrated the anthocyanins with a metal-organic framework (MOF) known as UiO66-NH₂. This structure stabilizes the pigments against environmental factors while maintaining their sensitivity to pH. Additionally, the hydrogel is self-healing, meaning it can repair small surface cuts to prevent bacteria from entering the food through damaged packaging.