Hidden Losses: Do Isolation Protocols Degrade Microplastics in Food Analysis?

Introduction: Microplastics (MPs) are defined as plastic particles ranging in size from 0.1 µm to 5 mm. MPs have been found as contaminants in food, including infant and enteral nutrition products. Potassium hydroxide and hydrogen peroxide are frequently used for the isolation of MPs from high-protein matrices. However, methods for the determination of MPs in food have not yet been standardized. Furthermore, it remains unclear whether the isolation conditions may cause degradation of MPs. The aim of this study was to evaluate the effect of reagents and conditions commonly used for the digestion of high-protein food matrices on the stability of polyethylene (PE) and polypropylene (PP) MPs in the absence of the food matrix.

Methods: PE MPs (34–50 µm) and PP MPs (50–80 µm) were exposed to 10% H₂O₂ and 10% KOH at 60 °C for 45 minutes. After filtration, drying, and weighing, the particles were examined for morphological changes and chemical composition. The analyses were performed using scanning electron microscopy (SEM) and Fourier-transform infrared microspectroscopy (µ-FTIR).

Results: SEM images revealed initial signs of PE MPs degradation, manifested as surface cracking, after heating at 60 °C for 45 min. Exposure to 10% H₂O₂ and 10% KOH further intensified PE degradation. In the case of PP MPs, degradation into smaller particles was observed only in the presence of 10% KOH. No changes in the chemical composition of PE and PP MPs were observed under any of the tested conditions.

Conclusions: The applied isolation conditions may induce physical degradation of PE and PP MPs into smaller particles. This may lead to an underestimation of MPs content, as particle size is a major limitation of microspectroscopic techniques used for their determination.

Research was financially supported by Medical University of Gdańsk program (“Młody Badacz”, project 01-66025).