Important steps have recently been taken in the development of an antibacterial packaging film based on chitin for use in products such as stand-up pouches for Heinz soup. ‘We now have a result we can work with,’ says Eddy Hilbrink, Strategic Product Developer at AFP, a film manufacturer based in Apeldoorn.
Chitin is a substance found in the exoskeletons of insects and crustaceans, as well as in some fungi. After being converted into chitosan and subsequently the monosugar glucosamine, it can be used as a dietary supplement. Chitin and chitosan have both antimicrobial properties. Wageningen UR Food & Biobased Research has developed technologies, e.g. using enzymes, to convert chitin into chitosan using less or no aggressive chemicals.
In developing an antimicrobial film containing chitosan, the researchers of the ChitoSmart project were faced with some considerable challenges from the very start. ‘Mixing the antimicrobial chitosan into the plastic film continued to cause problems,’ explains Hilbrink. ‘It was impossible to distribute this substance homogeneously. It remained lumpy in the film, possibly causing it to lose its antibacterial effect.’ The chitosan also appeared to adversely affect the film, causing a yellowish discolouration after the substance had been mixed in.
The research team – consisting of members from AFP, Wageningen UR, Heinz and TNO – decided to try a different approach: instead of mixing the chitosan into the plastic film, they developed a coating made from chitosan which was applied to the film. However, a disadvantage of this method is that it requires an additional step, making the process more expensive. Despite these drawbacks, the project recently achieved a notable success, as evident from tests of special methods developed as part of the project. Frank Schuren, microbiologist and TNO researcher, explains: ‘Our most recent series of tests shows that AFP’s latest coated film has antimicrobial properties. This is an important breakthrough in the development of a plastic packaging which can be used to keep food shelflife longer.’
Although the foundation has been laid, the coating, according to Hilbrink, is not yet ready for the supermarket. Its suitability still needs to be proven in practical trials. ‘We first need to carefully examine the adhesion of the coating on the film,’ he explains. ‘In addition, we still don’t know how the coating affects the sealing of the film.’ The tests must also demonstrate whether the antibacterial properties are just as effective in practice as during the TNO tests.
Broader range of applications
The initial success with the coated antibacterial film makes the researchers optimistic. However, Hilbrink thinks that a film into which chitosan has been mixed will turn out to be cheaper and suitable for a broader range of applications than a coated version. A coating that is applied to a flexible film can easily tear. This is less likely to happen if chitosan is mixed into the film. Tearing seems to be less of a problem if the coating is applied to less flexible products, such as plastic bottles. ‘Much still needs to be developed in terms of both coated and non-coated antibacterial films and we are eager to continue our research,’ says Hilbrink resolutely.