This is a significant step forward. There has been great interest in the food packaging sector about coated packaging films that actively fight against bacteria could help stop food going mouldy without the use of food preservatives.
Bacteria settle themselves at the exact spot where the foodstuff touches the packaging, and multiply rapidly from there. To put paid to the unwanted settlers, film-packaged foodstuffs often contain added food preservatives such as benzoic or sorbic acid.
However, discerning consumers prefer to have as few additives as possible in their food. The concept of bacteria-fighting packaging is therefore of great interest to food manufacturers eager to appeal to consumer demand for less additives, while at the same time making food products safer.
This is why scientists at the Fraunhofer Institute for Process Engineering and Packaging IVV, working in the Alliance for Polymer Surfaces POLO, have initiated a project to find out how this concept can be developed.
The researchers found that instead of adding preservatives to the food, they could coat the packaging film with them.
"This places the substances directly at the surface of the foodstuff, which is where they need to act," said group leader Dieter Sandmeier. "In that way we can cut food preservatives to a minimum."
The coating layer is applied using special techniques and materials based on substances such as Ormocers. These plastics contain elements of inorganic glass and organic polymers.
"We have managed to develop films that can protect solid products from attack by all kinds of bacteria," said Sandmeier.Films such as these are not good enough when it comes to protecting liquid foods like milk, however. This is because the food preservatives introduced do not remain on the surface as they would on cheese or sausage. They spread through the entire product and are heavily diluted.
Packaging materials for liquids therefore need to be sterilised with hydrogen peroxide, for example, before being brought into contact with foodstuffs. But this complex procedure is performed at temperatures in excess of 70 °C, which is too high for certain plastics such as PET.
The IVV researchers therefore looked to the medical profession for inspiration, and saw that doctors sterilise medical instruments with plasma, an ionised gas.
There is just one drawback in applying this to industrial packaging however; the treatment takes at least half an hour, or even up to one and a half hours - far too long for an industrial bottling process.
The scientists however have now optimised the process so that it only takes one to five seconds. In this way they have no problem complying with environmental protection regulations, and energy consumption can be reduced by a factor of up to 1,000.
Antibacterial packaging is a growing field of research. A recently published report in the Journal of Agricultural and Food Chemistry found that herb basil, when incorporated into plastic wrapping, can enhance food safety. The basil, which has long been known to contain bacteria-fighting properties, can be incorporated into the plastic wrapping to preserve foods.
The extracts methyl chavicol and linalool ooze out of the wrapping and slow the growth of eight types of lethal bacteria including E. coli and listeria. Experiments showed the wrapping extends the shelf life of cheese and most likely of meats, fish, baked goods, fruits and vegetables.
The research scientists from the Fraunhofer Institute are presenting this and related topics at the "K" fair in Düsseldorf, which finishes tomorrow.