Cooking food in microwavable plastic containers: in situ formation of a new chemical substance and increased migration of polypropylene polymers

•Microwavable food plastic containers can be the source of exogenous substances.•Cooking food within plastic materials increases migration of IAS and NIAS.•Compounds from these materials or leftovers from synthesis can react with foodstuff.•For the first time, in situ formation of NIAS has been detected in foodstuff.•Lifestyle changes can reduce the intake of migrants from plastic materials. Microwavable plastic food containers can be a source of toxic substances. Plastic materials such as polypropylene polymers are typically employed as safe materials in food packaging, but recent research demonstrates the migration of plastic substances or their by-products to food simulants, to foodstuff, and, more recently, to the human body through food consumption. However, a thorough evaluation of foodstuff in food contact materials under cooking conditions has not yet been undertaken. Here we show for the first time that plastic migrants present in food contact materials can react with natural food components resulting in a compound that combines a UV-photoinitiator (2-hydroxy-2-methyl-1-phenylpropan-1-one) with maltose from potato starch; this has been identified after cooking potatoes in microwavable plastic food containers. Additionally, polypropylene glycol substances have been found to transfer into food through microwave cooking. Identifying these substances formed in situ requires state-of-the-art high-resolution mass spectrometry instrumentation and metabolomics-based strategies.