Brazilian researchers have developed a biodegradable, starch-based sensor that changes color when moisture enters food packaging. Thanks to the addition of cobalt chloride, the smart device changes color from blue to pink as moisture levels rise or fall. This technology enables consumers and manufacturers to easily monitor the quality and crispness of foods, such as cookies, with the naked eye or via a cell phone screen, eliminating the need for complex equipment.
The research was led by scientists at the São Carlos Institute of Chemistry at the University of São Paulo (IQSC-USP) and received support from FAPESP through three projects ( 23/10141-2 , 20/08727-0 , and 25/26623-1 ). The results were published in June in the journal Food Chemistry.
The authors began the tests using cream crackers, which are highly sensitive to moisture and quickly lose their crispness when stored under inappropriate conditions.
The results showed that the color change corresponded to an increase in moisture, which was strongly correlated with a loss of texture in the crackers. This indicates that the sensor successfully reflects actual changes in storage conditions.
In just a few seconds, the small, starch-based cylinder placed near the crackers changes color, shifting between various shades of blue and pink. When the salt is dry, it turns blue. When it becomes hydrated, it turns pink, indicating the presence of water vapor. This occurs because cobalt chloride undergoes hydration in the presence of water, causing a change in its chemical structure and, consequently, a change in color.
"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. If I place it in a very dry environment, it responds. Conversely, if I place it in a very humid environment, it also responds," explains Bianca Maniglia , a professor at IQSC-USP and the research advisor.
According to recent data released by the Brazilian Packaging Association (ABRE), the packaging sector currently generates approximately BRL 165.7 billion per year in Brazil.
It is expected that, in the future, the industry and consumers will be able to use this new technology to determine the crispness and moisture content of various products.
Inspiration from childhood memories
The idea to use cobalt chloride to create the sensor came from a childhood memory. While developing the project, Maniglia recalled the "weather rooster," a kitchen ornament inspired by the "Rooster of Barcelos," one of Portugal's national symbols. Common in Brazilian and Portuguese homes in the 1980s, the object changed color to indicate whether it would rain or be sunny.
After conducting several tests, the researchers decided to coat the sensor with the same material used to coat the roosters. However, they adapted it for another technology the research group is developing: cryogel, a highly porous material manufactured by freezing polymers (hence the name "cryo").
"The starch gel is frozen and subjected to freeze-drying [dehydration]. During that 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," the scientist explains.
Further studies still need to be conducted. "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," Maniglia notes.
According to the scientist, the research group is evaluating various types of techniques and materials, including the use of bioactive compounds derived 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. 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," says the researcher.
About São Paulo Research Foundation (FAPESP)
The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at www.fapesp.br/en and visit FAPESP news agency at www.agencia.fapesp.br/en to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at http://agencia.fapesp.br/subscribe.
