Automatic flow-through oral bioaccessibility method for real-time monitoring of zinc leachability from bio-based food packaging edible films

Recent trends in food packaging for reducing the use of petroleum-based plastics and waste focus on the development of sustainable protecting films based on metal nanostructure embedded biopolymers. However, the safety of such bionanocomposites if human ingested has been poorly explored so far. In this work, crosslinked alginate films embedding ZnO nanostructures (Alg/ZnO) were prepared and analyzed as a case study. A dynamic flow-through approach mimicking human digestion by simulated gastric fluid (SGF) extraction was assembled. It consisted of an automatic sequential injection analysis (SIA) setup that enabled evaluating the zinc oral bioaccessibility from the as-prepared composites. The temporal release of Zn2+ from 50 mg of Alg/ZnO films was monitored on-line by pumping SGF across film fragments in a flow-through container. Under fluidized-bed conditions, a quantitative retrieval of overall bioaccessible Zn2+ was achieved using only 12 mL of extractant (6 cycles of 2 mL SGF each), resulting in a cumulative extraction time of 30 min. For every extraction cycle, 50 μL aliquot of the gastric extract was automatically aspirated and mixed on-line with buffered Zincon colorimetric reagent for the on-line spectrophotometric detection of bioaccessible Zn2+. The gastric bioaccessible zinc fraction from Alg/ZnO films was about 70%. In the event of ingestion of 0.4 g of high-content Alg/ZnO films, a human daily intake of 0.52 mg Zn was estimated. This value is significantly lower than the maximum tolerable daily intake of 40 mg/day for adults. The proposed approach represents an interesting solution for the assessment of metal ion human bioaccessibility in antimicrobial-containing packaging without using cell tests.