Exploring the role of real food matrices on the behavior and toxicity of polystyrene nanoplastics during digestion simulation

Nanoplastics are emerging contaminants that can enter the human body through food consumption, raising concerns about their potential health impacts. Among these, polystyrene nanoplastics (PS-NPs) are frequently used in toxicological studies due to their widespread use in food-contact materials and their well-defined physicochemical properties. In this study, we investigated the behavior and cytotoxicity of PS-NPs in the presence of a nutritionally relevant, real food matrix (milk) under simulated three-phase gastrointestinal digestion. PS-NPs of three different sizes (30 nm, 100 nm, and 450 nm) were characterized before and after digestion using SEM, TEM, DLS, and XPS to monitor changes in aggregation and corona structure. Our findings demonstrated that milk proteins and digestive enzymes adsorbed onto the PS-NP surfaces, forming a complex protein corona. The aggregation behavior and composition of the protein corona were markedly influenced by particle size during the digestion process. Corona structures were detected on all particle sizes following digestion; however, extensive web-like agglomerates were uniquely observed in the 30 nm particles. While the presence of milk during digestion did not significantly alter the cytotoxicity of the 30 nm and 450 nm particles, it resulted in a marked reduction in cell viability for the 100 nm particles. These results suggest that the food matrix significantly modulates nanoplastic behavior and toxicity in the gastrointestinal environment.