Milk proteins and fat influence Ag migration from model dairy packaging containing silver nanoparticles

We investigated migration of Ag from model Ag nanoparticle (AgNP)-loaded polyethylene films into bovine milks with varying milkfat content after storage for 10 days at 20 °C. Ag migration into 2% fat milk (2.18 ± 0.03 ng/cm²) was comparable to that observed in skim milk (2.16 ± 0.14 ng/cm²), while whole milk (4% milkfat) had the lowest migration (1.80 ± 0.07 ng/cm²). Notably, Ag migration into skim, 2%, and whole milk was 1.72, 1.69, and 1.40 times higher, respectively, than that into 50% aqueous ethanol, a common simulant for whole milk. At least a portion of the migrated Ag in milk existed as nanoparticles, suggesting that milk components influence the final form of migrated Ag. We explored the behavior of Ag⁺ ions in milks and observed efficient Ag⁺ transformation to Ag⁰ NPs and Ag₂O NPs. Electron microscopy images revealed polydisperse, quasi-spherical Ag particles with sizes ranging from 5 to 70 nm. Milk proteins, particularly casein and whey, play a role in the transformation of dissolved Ag⁺ to nanoparticles, while lactose influences the nanoparticle composition. These findings highlight that Ag interactions with milk components affect Ag migration dynamics and emphasize the need for a better delineation of appropriate food simulants for migration studies with AgNP-containing polymers.