Fiber-based food packaging materials in view of bacterial growth and survival capacities.

Understanding interactions of bacteria with fiber-based packaging materials is fundamental for appropriate food packaging. We propose a laboratory model to evaluate microbial growth and survival in liquid media solely consisting of packaging materials with different fiber types. We evaluated food contaminating species (Escherichia coli, Staphylococcus aureus, Bacillus cereus), two packaging material isolates and bacterial endospores for their growth abilities. Growth capacities differed substantially between the samples as well as between bacterial strains. Growth and survival were strongest for the packaging material entirely made of recycled fibers (secondary food packaging) with up to 10.8 log10 CFU/ml for the packaging isolates. Among the food contaminating species, B. cereus and E. coli could grow in the sample of entirely recycled fibers with maxima of 6.1 log10 and 8.6 log10 CFU/mL, respectively. Escherichia coli was the only species that was able to grow in bleached fresh fibers up to 7.0 log10 CFU/mL. Staphylococcus aureus perished in all samples and was undetectable after 1-6 days after inoculation, depending on the sample. The packaging material strains were isolated from recycled fibers and could grow only in samples containing recycled fibers, indicating an adaption to this environment. Spores germinated only in the completely recycled sample. Additionally, microbial digestion of cellulose and xylan might not be a crucial factor for growth. This is the first study describing bacterial growth in food packaging materials itself and proposing functionalization strategies toward active food packaging through pH-lowering.

Single- and Multilayer Build-Up of an Antibacterial Temperature- and UV-Curing Sol-Gel System with Atmospheric Pressure Plasma.

The versatility of sol-gel systems makes them ideal for functional coatings in industry. However, existing coatings are either too thin or take too long to cure. To address these issues, this paper proposes using an atmospheric pressure plasma source to fully cure and functionalize thicker sol-gel coatings in a single step. The study explores coating various substrates with sol-gel layers to make them scratch-resistant, antibacterial, and antiadhesive. Microparticles like copper, zinc, or copper flakes are added to achieve antibacterial effects. The sol-gel system can be sprayed on and quickly functionalized on the substrate. The study focuses on introducing and anchoring particles in the sol-gel layer to achieve an excellent antibacterial effect by changing the penetration depth. Overall, this method offers a more efficient and effective approach to sol-gel coatings for industrial applications. In order to achieve a layer thickness of more than 100 µm, the second part of the study proposes a multilayer system comprising 15 to 30 µm thick monolayers that can be modified by introducing fillers (such as TiO2) or scratch-resistant chemicals like titanium isopropoxide. This system also allows for individual plasma functionalization of each sol-gel layer. For instance, the top layer can be introduced with antibacterial particles, while another layer can be enhanced with fillers to increase wear resistance. The study reveals the varying antibacterial effects of spherical particles versus flat flakes and the different scratch hardnesses induced by changes in pH, number of layers, and particle introduction.