Researchers at the São Carlos Institute of Chemistry at the University of São Paulo (IQSC-USP) in Brazil have developed a starch-based sensor that changes color when moisture enters food packaging.

The sensor uses cobalt chloride, a material that changes from blue to pink as it absorbs water vapor. When moisture levels decrease, the sensor changes back to blue. The color shift occurs because hydration alters the chemical structure of cobalt chloride, producing a visible change that can indicate humidity conditions inside a package.

Source: Bianca Maniglia

To incorporate cobalt chloride into the sensor, the researchers developed a cryogel, a highly porous structure produced by freezing polymers and removing the frozen water through sublimation. The process preserves the porous structure created during freezing, giving the material a large surface area that allows it to interact rapidly with moisture in the surrounding environment.

The resulting sensor takes the form of a small, starch-based cylinder that can respond to a range of humidity conditions, from very dry to highly humid environments. The researchers suggest that the color-changing sensor could eventually allow food quality to be monitored using a cellphone camera rather than complex equipment.

In laboratory tests, the team placed the sensor near cream crackers, which are highly sensitive to moisture. The sensor rapidly shifted between shades of blue and pink as moisture levels changed. The color changes tracked increasing moisture levels and strongly correlated with losses in cracker texture, indicating that the sensor could reflect changes in storage conditions.

Further development is needed before the technology can be used commercially. Because cobalt chloride is toxic, the sensor in its current form cannot come into direct contact with food. Conventional packaging would therefore need to be redesigned to keep the sensor separated from the food while still allowing exposure to moisture inside the package.

An article describing the sensor, “Starch-based cryogels incorporating cobalt chloride as colorimetric moisture sensors for food packaging,” appears in the journal Food Chemistry.