Systematic evaluation of food design, treatments, packaging and storage conditions on microplastic concentrations in complex matrices

• Systematic evaluation of microplastics in multiple food samples pre-consumption. • Matrix-specific digestion protocols developed for milk, plant milk and juice. • Acidic food and plastic packaging contributed more to microplastic levels. • Thermal treatment or storage time showed no significant effects. • FTIR imaging with chemometrics overcame matrix interferences. Worldwide, 44 % of plastic products are used as packaging materials, exposing humans to micro(nano)plastics potentially through food ingestion. Here, we evaluated the microplastic concentrations throughout the pre-consumption phase, considering the effects of food design (milk, plant milk and orange juice), treatment (thermal), packaging (glass and polypropylene) and storage duration (0, 90 and 180 days). Due to the rich organic matter in food samples, >12 digestion protocols were tested and optimized to establish matrix-specific digestion protocols. Microplastics (> 10 μm) from milk, tiger nut milk and orange juice samples were quantified using micro-Fourier-transform infrared (µ-FTIR) imaging. The microplastic concentrations were 37 ± 34 n/100 mL milk, 18 ± 19 n/100 mL tiger nut milk, and 62 ± 68 n/100 mL orange juice samples, suggesting that acidic food environments released more microplastics. PP was the most frequently detected polymer, followed by polyethylene terephthalate fibers and polystyrene, indicating the contribution from plastic packaging and the ambient environment. No significant difference was observed among thermally treated and non-treated, or various storage duration groups for the three food types. A majority (69 %) of detected microplastics were below 50 µm. Chemometric analyses revealed spectral interference from the matrix with the IR spectra of plastic polymers. This study provides the first systematic evaluation of the MP concentrations across multiple food types during commercial food processing, packaging and storage steps pre-consumption, that determined human exposure to microplastics via food intake to guide future mitigation strategies.