Brazilian scientists develop sensor for moisture in snack packaging

Researchers have developed a sensor that uses cobalt chloride to detect when moisture enters food packaging to preserve the crispness of food products such as cookies and crackers. 

The research team, led by scientists at the São Carlos Institute of Chemistry at the University of São Paulo (IQSC-USP), Brazil, placed a starch-based cylinder with cobalt chloride next to a cream cracker. The team revealed that the salt in the cylinder changed its color in the presence of moisture. 

“What set this study apart was having a larger surface area for the sensor, making it highly sensitive and allowing us to observe different humidity conditions inside the packaging,” says Bianca Maniglia, advisor for the study and professor at IQSC-USP. 

“If I place it in a very dry environment, it responds. Conversely, if I place it in a very humid environment, it also responds,” she adds. According to the study, the salt looks blue when dry and pink when hydrated. 

The sensor can be connected to a mobile phone to allow consumers and manufacturers to monitor the quality and crispiness of packaged foods, IQSC-USP outlines.

The research project received support from the São Paulo Research Foundation and was published in Food Chemistry.

Further studies are needed as the presence of cobalt chloride makes the sensor toxic and not suitable for use with food products, Maniglia notes. 

Nostalgic concept requires a revamp

The research team explains that the idea to create a moisture sensor based on cobalt chloride was sparked by the memory of a type of weather roosters that were commonly found in Brazilian and Portuguese homes during the 1990s. 

The weather roosters were shaped like the Rooster of Barcelos, the national symbol of Portugal, and used cobalt chloride to indicate if the weather will be sunny or rainy. 

After several tests, the researchers decided to coat the sensor with the same material used to coat the roosters. However, they ended up using a starch-based cryogel — a highly porous material manufactured by freezing polymers.

“The starch gel is frozen and subjected to freeze-drying (dehydration),” Maniglia continues. 

“During the process, the frozen water is removed by sublimation, passing directly from the solid state to vapor. The removal of the aqueous phase preserves the porous structure formed during freezing, resulting in a material with a high capacity for interacting with the environment.”

Maniglia elaborates: “For commercial use, conventional packaging would need to be redesigned because, for now, the presence of cobalt chloride makes the sensor toxic, and therefore it can’t come into direct contact with food.” 

The research group indicates that it is currently evaluating different types of techniques and materials to address the salt’s toxicity problems, including the use of bioactive compounds from fruits such as jabuticaba peel. 

“These natural pigments are sensitive to pH variations, exhibiting color changes that can be used as visual indicators, in addition to possessing antioxidant activity,” Maniglia continues. 

“In this case, the goal is to develop a system that can monitor the spoilage process of meat, for example. Incorporating these natural compounds is also important because it helps add value to them.”

Recently, Packaging Insights spoke to Nathalie Lavoine, an associate professor at North Carolina State University in the US, about her efforts to develop a plasma-based surface treatment that improves the moisture resistance of bio-based films for food packaging.

Last year, researchers at the Georgia Institute of Technology, also in the US, told us that they developed a bio-based film capable of blocking moisture and oxygen as effectively as conventional plastic packaging materials.

Commercially, ProAmpac expanded its Moisture Protect series to offer a range of moisture-adsorbing films for diverse packaging applications, and collaborated with Ozzi to launch a moisture-absorbent film for powder products.