Migration of nanosilver and nanoclay from food packaging materials into food

Project

Food and consumer protection

This project contributes to the research aim 'Food and consumer protection'. Which funding institutions are active for this aim? What are the sub-aims? Take a look:
Food and consumer protection

Project code: MRI-LBV-08-57
Contract period: 01.11.2009 - 01.04.2017

The use of synthetic nanomaterials in food contact materials permits e.g. the generation of functional surfaces or improved barrier properties. Data on transition of synthetic nanomaterials from food contact materials to food are hardly accessible. The two most frequently used nanomaterials in this area are nanosilver (as antibacterial-acting component) and nanoton (improved barrier properties). Therefore, it is to be investigated whether and how much nanosilver from food storage containers from model composite films is released during the duration of the project Food. The influence of the food matrices, the pH value and the temperature was analyzed by classical ICP-MS, sp-ICP-MS, AF4 and electron microscopy. One objective of this application-oriented study was focused on establishing the coupling of AF4 with single particle-ICP-MS for the characterization of AgNP containing samples derived from migrations studies with model FCMs. The combination of these two state-of-the-art nanoparticle characterization techniques enabled a highly sensitive detection and quantification of nanoparticulate silver species migrating from model films into food simulants, which offline sp-ICP-MS or classical AF4-ICP-MS coupling could not provide.

As test material two commercially available types of plastic bags were used. In addition tailor-made polymer films with different contents of nanosilver were manufactured. For this purpose a masterbatch with LDPE (ExxonMobil™ LDPE LD 100) as polymer basis, which contains AgPURE™ nanosilver (rent a scientist GmbH, D99 under 20nm), was extruded to films with a thickness of 40 µm and a nanosilver content in the range of 500 ppm to ca. 11000 ppm (film 3 - 7). A film made of LDPE without nanosilver was produced as blank test material. The exact silver content of all films was determined by inductively coupled plasma mass spectrometry (ICP-MS, Agilent 7500c) after microwave digestion of the films as described by Lin et al. (2011). The migrations experiments were carried out with self-made test pouches (10 cm x 15 cm), each filled in triplicate with 100 mL of food simulant (ultrapure water, 3% v/v acetic acid and 10% v/v ethanol), sealed and stored at 40 °C for nine days. Because with standard ICP-MS measurements no differentiation could be made between nanoparticulate and ionic silver, an ion selective electrode (ISE, Orion 9616BNWP, Thermo Scientific) was used for the detection of free silver ions in the food simulants. A clear dependency of the migrated silver from the silver content in the plastic films and the simulant used was observed. Silver release is increasing with increasing silver content in the films, whereas experiments with 3% acetic acid as a food simulant showed an overall higher silver release compared to experiments with ultrapure water and 10% ethanol. The highest silver release was determined to be 6.8 ± 0.8 µg/dm2 with film 7 and 3% acetic acid and the lowest silver release was observed in the commercially available films in trace concentrations ranging from 3 ± 1 ng/dm2 to 33 ± 3 ng/dm2. ISE measurements confirmed that the silver found in the food simulants was at least partially released in ionic form from the embedded silver nanoparticles in the plastic films. However, more refined methods for the direct measurement of nanoparticulate silver are needed for a reliable speciation analysis. Scanning electron microscopy studies and single particle ICP-MS studies are under way at present to identify any migrated silver nanoparticles. For the storage experiments fresh and frozen fillets of farmed salmon, cod, ocean perch, Nile perch from Lake Victoria and pollack from local retail markets were used. For the test series the fillets were packed in nanosilver containing bags (blank and film 1 – 4) and for reference in sterile whirl-packs and stored at 4°C in refrigerator for 7 days. 10 colonies were randomly picked for bacterial diagnostics to check, whether the bacterial flora have changed in composition due to different storage conditions. In none of the storage experiments with commercial or non-commercial plastic bags an impact of nanosilver on the bacterial growth of the spoiling flora of any fillets could be detected nor could differences in the TVBN concentration or changes in the bacterial flora be seen (data not shown). Even packaging in bags with a nanosilver content of 1000 ppm (film 4), which represents a more than 30-fold excess of nanosilver compared to a commercial food packaging product, had no significant effect. Commercially available antimicrobial food packaging materials showed silver release only in trace concentrations. Furthermore, the antimicrobial effect of these packaging materials seems to be highly questionable, because no effect on the bacterial flora of packed fish could be observed. Whether the migrating silver is released as nanoparticles, as silver ions or both is not yet completely clarified, because speciation analysis with only trace amounts is very difficult. A promising approach is to apply ICP-MS analysis in the single particle mode and scanning electron microscopy, which have the potential for analysing inorganic nanoparticles in complex matrices in trace amounts.
Furthermore, single particle ICP-MS analysis was applied in order to detect and quantify migrated AgNPs selectively. As coexistent silver ions in the migration samples had an impedient effect (decreased signal-to-noise ratio), an optimized analytical approach was developed by online-coupling of asymmetric flow field flow fractionation (AF4) to single particle-ICP-MS. The enrichment of the nanoparticle fraction and simultaneous reduction of the ionic background via AF4 resulted in a clearly improved ICP-MS detection sensitivity, which enabled a more refined identification and size characterization of the migrated silver species. Scanning transmission electron microscopy (STEM) and energy-dispersive x-ray spectroscopy (EDS) confirmed independently the presence of AgNPs and silver/polymer heteroaggregates in the migration samples.

show more show less

Section overview