Misunderstood wood? Food packaging
Novel microbiological testing methods could promote wood’s use as a food packaging material, according to a group of French researchers.
The research is said to compound findings from other scientists, which conclude that micro-organisms do not survive easily on wood.
At present, regulations in parts of Europe and the USA limit the use of wood in food packaging. According to lead researchers, Magdalena Kutnik and Isabelle Le Bayon, this approach is due to ‘insufficient knowledge of wood's microbiological qualities relevant in food packaging’.
They add that, ‘Different sampling methods exist for analysing contaminated surfaces or packaging made of plastic or paper, but no standard exists yet for wood, as there is a real lack of a recognised method for biological analysis’.
Existing biological techniques include sampling methods based on the agar-contact plate and swabbing, stomacher, and ultrasonic sound methods. However, the researchers explain, ‘Usual microbiological methods such as agar-contact plates and swabbing analyse only the surface of the wood.’
In their research, the scientists have employed a grinding method, a vacuum pressure method, and a technique that couples ultrasonic sound and vacuum pressure. These methods have been compared with existing techniques on contaminated poplar specimens, ‘In order to improve the removal of bacteria adhering to the wood matrix, the first step, consisting of applying ultrasonic sound, is run prior to the vacuum pressure method,’ they explain. The results show that the contact agar plates and stomacher techniques yield low rates of micro-organism removal, whereas the aforementioned coupling of ultrasonic sound and vacuum pressure removes up to 72% of viable cells to quantify them, rather than for cleaning.
While the team emphasises that different methods are suitable for different aims, the coupling of the ultrasonic sound and the vacuum pressure test method is said to enable analysis of the whole wooden matrix.
The scientists add that, while wood is often considered less suitable than plastic or stainless steel for food packaging due to its porous and absorbent nature, ‘Several publications reported the fact that micro-organisms can easily survive on materials such as plastics as long as moisture is maintained on the surface’.
By contrast, they say their ‘trials have confirmed the observations of previous authors that mentioned the fact that bacterial viability on the wood surface is quite low because of the low moisture content on the wood surfaces’.
Industrial trials have already been performed on wooden crates for fruit and vegetables.