Microplastic residue in recycled food co-products from mechanical depacking systems: a simulation study for animal food

This study is the first to determine the potential generation and transfer of microplastic (MP) into depacked food co-products from various food packaging using a commercial depacking system. Barium sulfate (BaSO₄, 564 ± 108 nm) was dispersed into four polymer types, including low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS). Polymers containing BaSO₄ were converted into food packaging matching their traditional packaging. A depacker separated packaging from food co-products. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) was applied to quantify BaSO₄ as a MP indicator. Depacked foods were digested using an enzymatic approach to maintain the morphology of MPs then characterized using a 3D surface profiler. BaSO₄ concentration in recovered food from HDPE, LDPE, and PP was below method limit of detection (≤290.65 ng BaSO₄/g depacked food or ≤ 22.13 µg microplastic/g depacked food). The concentration in depacked food from PS was measured at 1278.65 ± 17.7 µg/g corresponding to low recovery of PS from the depacker. MPs were detected using 3D surface profiling in depacked food from PS after enzymatic digestion. Packaging waste mass recovery from depacking was significantly greater (p < 0.05) for film packaging materials than more rigid/brittle materials suggesting mechanical properties of packaging materials, such as rigid versus flexible containers, can influence MP generation and packaging recovery during depacking. This study also developed a novel method using barium-doped plastic to analyze the release of MPs from food co-products using ICP-OES.