Initially, cellulose filters (20–25 μm, Whatman grade 4) were used for all digestion protocols. This size was chosen to be the largest acceptable filter size to assess human exposure risks. Filtration through 25 μm was unsuccessful for enzymatic digestions. Due to the cost of Proteinase-K, this technique was abandoned. Filtration of trypsin, on the other hand, due to its lower cost and hazardousness as well as time needed (see supplementary information ‘Costs, time needed and hazardousness of reagents’) was attempted with 63 μm carbon fibre mesh. Optimisation of filtration to achieve filtering over smaller pore sizes was attempted for the remaining digestion protocols. For this, cellulose nitrate (5 μm, Whatman) and glass fibre (1.2 μm, Whatman GF/C) filters were used.