Microplastics in simulated digestion: Surface modifications, enzyme interference, and chemical migration

The transformation of microplastics (MPs) under gastrointestinal digestion conditions and their associated risks to human health remain unclear. This study investigated the behavior of four food-grade polymers, polystyrene (PS), polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) under simulated in vitro human digestion with dietary components (starch, protein, and lipids). MPs of ≈200 μm and ≈50 μm size were analyzed for chemical modifications, enzyme interactions, and additive migration. Zeta potential significantly decreased after digestion, with PET showing the largest shift from -10.22 mV to -48.17 mV in protein-rich conditions, indicating strong protein adsorption. Enzyme inhibition was size and concentration dependent, with 50 μm PS strongly inhibiting α-amylase, α-glucosidase, and lipase, while pepsin showed minimal inhibition. LC-MS revealed higher di-n-butyl phthalate release, particularly during gastric digestion. These findings demonstrate that MPs interact with digestive components, impair enzyme function, and release harmful additives, highlighting need for further in vivo research.