Micro-granulate cork stoppers: study on overall and specific migration

A new type of agglomerated cork stopper, generically called "micro-granulated cork stopper" or "micro-agglomerated cork stopper", is increasingly widespread on the wine market. It is identified by each cork factory with different names and is defined by the ISO 633:2007 as "agglomerated cork stopper-treated cork". It is a "stopper obtained by agglutination of cork granulates grain size between 0.25 and 8 mm, with addition of an adhesive and having at least 51% of cork granulate by mass”. Despite the alarming news that sometimes occur on food contamination by substances released to wine from these type of closure, no scientific reports have been done till now to detect the extent of the problem. This work aims to evaluate both the sum of all substances (Overall Migration - OM) and the individual molecules (Specific Migration - SM) that are able to be transferred from micro-granulated cork stoppers under specific time-temperature conditions and different simulant solutions as stated by the EC Regulation 10/2011, DM 21/03/1973, and ISO 10106:2003. Replicate migration trials involved samples of micro-granulated cork stoppers and natural cork stoppers (as controls) that were both fully immersed (worst conditions) in simulant solutions and put in contact only with one stopper face (real conditions). Molecule identification was carried out by means of target and non-target MS analysis coupled with UHPLC system and MS-Q-TOF detector (UHPLC/Q-TOF). Results highlighted variable values for OM and SM according to the test conditions including contact time, temperature and test medium (type of simulant solution). OM and SM limits (OML and SML) were exceeded by few samples of micro-granulated cork stopper under worse conditions than those of foreseeable use for closing and storing bottled wines.