Optimization of extraction protocols for microplastics analysis in lipid-rich food matrices by experimental design

The presence of microplastics (MPs) in food raises concerns about human exposure through ingestion. Reliable identification of MPs in lipid-rich matrices remains challenging due to inefficient digestion and spectral interference during Fourier-Transform Infrared (FTIR) spectroscopic analysis. A Design of Experiments (DoE) approach was applied to optimize MP extraction protocols in fish at different lipid content, such as salmon, tuna, and cod. Recovery percentage and carbonyl index (CI) were used as proxies for extraction efficiency and residual lipid interference in absorbance spectra. Screening Design and Response Surface Methodology allowed evaluation of digestion time, temperature, and solvent type effects. Specific optimal conditions were identified as: Lipase at 60 °C for 30 h for salmon, 10% KOH at 45 °C for 40 h for tuna, and 10% KOH at 55 °C for 36 h for cod, achieving high recoveries and low CI values together with reliable chemical characterization. Analysis of real fish samples confirmed MPs contamination, with 42–57% of the total items confidently characterized, with abundances ranging 0.7–2.9 items/g of dry weight and fibers as the dominant morphology. The effectiveness of DoE for optimizing MPs extraction in complex food matrices was demonstrated, and highlighting the need for matrix-specific analytical protocols to support harmonized food safety assessments.