Researchers have found that silver embedded in antimicrobial plastic - often used for food and beverage packaging - could lead the packaging and form into its contents, especially for sweet and sugary foods.

Antimicrobial packaging prevents microbes' growth in its contents, being used for longer shelf life and safety of foods. It involves specially engineered materials such as polymers containing agents with biological properties - with silver nanoparticles. With these materials, the packaging slow spoilage and risks of foodborne illnesses making its way to consumers. While these specialized polymers are still not approved for use in the United States, researchers have investigated different polymers carrying nanoparticles for food storage.

A new report published in ACS Applied Materials & Interfaces examines the response of antimicrobial packaging across different contents.

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Antimicrobial Packaging Leaches Nanoparticles

Previous studies have illustrated how some of these nanoparticle-embedded polymers leach their agents, dissolved compounds, and charged particles into water-based food simulants. However, not much has been discovered with regards to how antimicrobial packaging affects real foods and beverages. Sugar compounds, a common food and beverage ingredient have converted silver ions to potentially harmful substances, especially when consumed by humans.

It prompted Timothy V. Duncan from the US Food and Drug Administration's Center for Food Safety and Applied Nutrition, together with his colleagues, to examine complex compounds in foods and beverage and see how it affects the formation of these potentially harmful silver nanoparticles - both for direct exposure to silver and when stored inside antimicrobial packaging that contains silver particles.

Researchers added silver into liquid food and beverage to examine whether dissolve silver forms aggregates in food materials. The tested foods include naturally and artificially sweetened solutions such as soft drinks, milk, fruit juices, yogurt, and slurry. The food samples were then stored at an incubator at 104 degrees Fahrenheit (40 degrees Celsius) to simulate long-term storage in commercial packaging.

Sugary Compounds Encourage Silver Nanoparticle Aggregation

Researchers found nanostructures forming at two silver concentrations, with one of them being at an expected range from polymer-contact leaching. Simultaneously, the other was detected at an unusually high concentration, with the nanoparticle formation being monitored visually.

Researchers discovered that sugary liquids containing starch, citrate, and fats grew the most silver nanoparticles among the tested food and beverage materials. On the other hand, acidic liquids also formed silver aggregates at first but were later dissolved by the liquid.

Researchers conducted another experiment where they stored water and a pair of sugary liquids in small packets of polyethylene polymer with silver particles for the same temperature settings for 15 days. While silver was leached from the polymer layers, only the sugary solutions showed more leaching and the aggregation of silver nanoparticles. Researchers then concluded that silver nanoparticle exposure is at increased risks with sugary food and beverage in antimicrobial packaging materials under typical long-term storage conditions.


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