Investigating ion-release from nanocomposites in food simulant solutions: Case studies contrasting kaolin, CaCO3 and Cu-phthalocyanine

•A bulk-filled polypropylene with a metal-organic nanopigment and a doubly coated paperboard with a nanoscaled kaolin filler were investigated.•Up to 60 % release of Ca (from CaCO3 base coating) vs. 0.4% of Al and max. 0.7% of Si (both from kaolin top coating) were released from paperboard.•The release was mainly ionic but the presence of a few nanoparticles (NPs) consistent with Kaolin but not with CaCO3 was confirmed as well.•No Cu release was detected from the polypropylene plates and consequently no released pigment nanoparticles were found.•High ionic release rates occur for soluble NPs when the food simulant is able to penetrate into the nanocomposite and reach the NPs.