The ink can be used by processors as another way of assuring wary consumersthat their products are protected against faulty packaging and tampering. Once oxygen enters a foodpackage, either accidentally or by tampering, the ink changes colour, warning the consumer that the food is no longer safe to eat.
The ink was developed by Andrew Mills and a team of scientists at the University of Strathclyde in Glasgow.The "intelligent ink" was created using light-sensitive nanoparticles, which only detect oxygen when they are 'switched on' withultraviolet light.
Leaking food packages are not uncommon, said Mills. Once oxygen get in the freshness of the foodis drastically reduced so it may no longer be safe to eat.
"Our technology has the potential to eliminate food poisoning due to poor packaging ortampering," he said. "The labels will also reassure customers that the food theyare feeding their families is as fresh and safe as it left the factory."
The patented ink could be used on labels on any kind of food, from milk to meat, bread andcoffee, he suggests. It is also inexpensive, making it suitable for use in large numbers of labels,he claimed.
According to a brief of the research by the American Chemical Society, the ink is blue in air and ambient room light. When it is irradiatedwith a pulse of UV light, the colour changes to white but reverts to blue under normal room light. In an oxygen-freeatmosphere the ink remains colorless after the UV pulse.
"Our paper reports the first example of a generic approach to chemical gas sensing in which the indicator is switched on by UV light,"said Mills.
The formulation consists of four common and inexpensive ingredients: an aqueous dispersion of a semiconductor (TiO2), a sacrificialelectron donor (triethanolamine), and aqueous solutions of a redox-indicator dye (methylene blue) and an encapsulating polymer(hydroxyethylcellulose).
The TiO2 particles create electron-hole pairs when exposed to UV light. The electrons reduce the dye, causing it to be bleached, andthe holes oxidize the triethanolamine. Polymer encapsulation allows the dye to be spin-coated onto plastic, metal, paper, or othersurfaces.
"The ink can be reused by repeated application of UV light. A variety of differentcolour changes and sensitivities are possible using the technology.
The ink could also be used to indicate if the original modified atmosphere insidea package has changed. Modified-atmosphere packaging (MAP) is used extensively in the food industryas a means of extending shelf life. Typically, air is removed from the space above the food as it is being packed by flushing the package with an inert gas such ascarbon dioxide or nitrogen.
Current oxygen sensors tend to be unreliable in checking if the mix of air iscorrect. New research at the University of Strathclyde has discovered a novel sensor for measuring oxygen levels within MAP. Critically, the sensor changes colour on the detection of oxygen.
Nanotechnology is becoming increasingly important and has a value to the food industry of £220 million in 2006. It is expected to grow to more than £3 billion by 2012.