BioTechniques News
Beatrice Bowlby
Figuring out when your food has started to spoil can be a tricky task, but what if the packaging it’s contained in could give you a heads-up? A new color-changing hydrogel that indicates food freshness could be on the horizon.
A newly designed hydrogel from researchers at Kyushu University (Fukuoka, Japan) could innovate food preservation and freshness monitoring by offering consumers the opportunity to identify whether their food has gone off without so much as opening its packaging. The biomaterial, which incorporates plant-derived anthocyanin and a metal–organic framework, can also repair itself and exhibits antibacterial activity, allowing it to extend food shelf life.
As the global food industry develops rapidly and concerns about food safety increase, the packaging our produce comes in is evolving. Scientists are now looking to hydrogels, which offer the flexibility, biocompatibility and structural stability necessary for robust and dynamic food storage. By integrating anthocyanins – flavonoid pigments responsible for the red-purple coloration of plants including red cabbage and purple sweet potato – the hydrogels are also able to indicate food freshness.
Anthocyanins change color in a pH-dependent manner, shifting from purple–red to yellow–green when pH rises, as it does when food is on the turn, making them ideal natural pH sensors for monitoring food quality and spoilage. Unfortunately, free anthocyanins are prone to photodegradation, thermal decomposition and leaching in aqueous environments, diminishing their color response; hence the researchers behind the latest study introduced 3D metal–organic frameworks into their hydrogel to bolster its stability.
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They started by extracting anthocyanins from freeze dried and powdered purple sweet potato roots. These were then immobilized onto a UiO66-NH2 metal–organic framework and further incorporated it into a cellulose nanofiber scaffold that used borax as a crosslinking agent with poly vinyl alcohol.
The resulting hydrogel was molded into various shapes, such as flowers, hearts and birds, indicating its impressive plasticity and cohesive integrity. To test the gel’s self-healing properties, the researchers cut it into two pieces and brought them into close contact, finding that the surfaces rejoined rapidly and the cut became nearly invisible within several minutes.
Meanwhile, they tested the antimicrobial effects of the hydrogel against Staphylococcus aureus and Escherichia coli using the agar diffusion method, demonstrating that the material enhanced antibacterial performance.
Finally, the team tested out the hydrogel on samples of fresh pork. They placed the gel alongside the meat in a sealed Petri dish and stored it at 20°C for up to 96 hours. Color changes were recorded every 24 hours using a digital camera and color difference meter. At the same time, pork samples were homogenized and pH was measured using a portable pH meter. The hydrogel produced pH-responsive color changes, allowing for pork quality monitoring. Total viable count of bacteria in the meat was used as an indicator of freshness and revealed that the hydrogel extended shelf life by approximately 12 hours relative to the control.
In conclusion, the novel material not only successfully identified pork spoilage, but it was also able to delay spoilage owing to its antibacterial properties, enabling simultaneous meat preservation and real-time freshness monitoring. Moreover, should this multifunctional hydrogel be used for food packaging in future, its self-healing abilities would make it less likely for bacteria to enter via cuts created during shipping and handling, further protecting the food inside.
It’s good news for food safety, and possibly beyond, explained study author Fumina Tanaka: “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.”
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