Migration solvents for free isocyanates in food contact materials using experimental design

Abstract

Agglomerated cork stoppers are currently used for still wines, semi-sparkle and gaseous wines, beer and cider. Methylene diphenyl diisocyanate (MDI) is presently the adhesive in use due to its lowest toxicity comparing with toluene diisocyanate (TDI) previously employed. However, free monomeric MDI can migrate from agglomerated cork stoppers to food stuff and this is worrying subject according to food contact materials. The objective of this study is to determine which solvent is better to extract isocyanates from agglomerated cork stoppers, essentially MDI to quantify its free monomer. A long term migration study was performed in order to compare with soxhlet extraction. Firstly a global migration test was performed in order to select the best solvents for soxhlet extraction. A Design of Experiments (DOE) with two factors, solvent and wax (to spike adhesive film), at six and two levels, respectively, was done. Six different solvents were put in contact with adhesive film during ten days at a temperature of forty degrees. Experiments were replicated and repeated three times. Through a TWO-WAY ANOVA the significance of solvents was evaluated and the three better solvents selected. Afterwards, soxhlet extraction was performed with the three better solvents, ethanol, acetonitrile and n-heptane, regarding ANOVA results. The other control factors were cycles’ number (20, 55 and 90) and sample type (natural, agglomerated cork stopper and adhesive film). In a fractional factorial DOE, with three factors at three levels, nine experiments with three replicates were performed. The significance of the factors/interactions was evaluated and the best level’s factors were selected. The Design of Experiments reveals to be a suitable statistical tool to determine the best conditions to measure the migration of free isocyanates from agglomerated cork stoppers to real foodstuff. The best solvent to monitor the migration from cork to wine by soxhlet extraction was ethanol although in long term migration the best solvent was acetonitrile.Financial support from ADI under the frame of project 5012-LIRACor