Scientists at the Graz University of Technology are developing an innovative ink that indicates freshness in food.
When restocking the fridge, our eyes often automatically wander to supposedly "spoiled" food, quickly disposing of it to make room for fresher purchases. As it is not always possible to clearly assess whether something is still edible, people often make a hasty decision to err on the side of caution, contributing significantly to food waste. It is not uncommon for food to be thrown away that would actually still be safe to eat.
The best-before date is often intrepreted particularly strictly for perishable foods such as sausages, meat, fish or cheese. But how can you really tell whether something is still edible – especially if it's still sealed? Although such airtight packaging provides effective protection against external influences, it makes it impossible to perceive odors as a warning signal. However, researchers at the Graz University of Technology have now achieved a promising breakthrough: They have developed a special ink that changes color as soon as it comes into contact with harmful decomposition byproducts from meat, fish or cheese.
A research team led by Paolo Falcaro developed the concept, utilizing a new type of ink that features crystals interspersed with tiny pores. These microscopically small openings significantly increase the surface area of the crystals, turning them into a kind of "sponge" that can absorb harmful substances – in particular, those produced when easily spoiled foods such as meat, fish or cheese start going bad. As soon as these harmful substances are released, the pores bind them and trigger a visible warning: The color of the ink on the packaging changes from green to orange.
The physical effect behind this can be explained as follows: The crystals reflect different light waves depending on food's "degree of freshness". If the pores remain empty, green dominates – a sign that the product can be eaten with no issues. However, as soon as harmful "vapors" are absorbed, the reflected light shifts into the orange range. The crystals act as a kind of sensor that tracks a product's condition by simply changing color.
The researchers tested their ink under realistic, deliberately unfavorable, conditions in order to showcase their ink's sensitivity: Fish symbols were printed on PET film and stuck as labels on two sample containers – one contained raw salmon, the other remained empty as a control sample. After 18 hours at room temperature, the symbol in the salmon container had turned orange – a clear sign of imminent spoilage. The label in the empty container remained green and showed no reaction.
The results were published in the journal Advanced Materials. The ink is currently still in its testing phase, but it could be make it to market in the future, allowing consumers to make informed decisions on food freshness.
