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A systematic evaluation of chemical migration during low temperature storage of packaged foodstuffs
Project Code: A03014
Central Science Laboratory
Castle, L ;
Kings College London
The approach used in this project was to study migration into foods packaged in plastics films and in cartonboard, that had been supplemented with model substances.
Seven substances were selected to act as model migrants and they were incorporated into inks used to print cartonboard, polyethylene and polypropylene films. The substances were toluene, xylene, limonene, acetophenone, cyclohexylbenzene, dimethylphthalate and benzophenone. Toluene and xylene were lost almost completely when the ink was dried and so these two substances could not be monitored in the subsequent migration studies. The remaining 5 substances covered the molecular weight range 120 to 194 and the boiling point range (at STP) 176 to 305 °C.
For the plastic films the model substances were incorporated through flexographic printing with a white ink applied at ca. 2 g/m2, containing each substance at 0.5% in the liquid ink. The plastic films were formed into bags and used to pack frozen peas (in polyethylene) and chocolate-coated ice cream bars (in polypropylene).
For the cartonboard the same model substances were incorporated through lithographic printing with a yellow ink applied at ca. 2 g/m2, containing each substance at 0.1% in the paste ink. The cartonboard was formed into boxes and used to pack fish fingers, sausage rolls and ice cream.
The packed bags and cartons were stored at -20°C for up to one year and packages were removed at intervals for analysis of migration. Storage at 5°C was also studied, for up to 15 days. Finally, migration studies were also conducted at -20°C and 5°C using the simulants distilled water, 95% ethanol, Tenax, olive oil (not for cartonboard) and iso-octane (not for cartonboard).
The study demonstrated that migration of low molecular weight substances into chilled and frozen foods can be quite extensive. The current standard testing protocols using short-duration contact with simulants at 5°C are appropriate both for chilled and frozen storage of foods. This is true both for plastics tested with liquid simulants and for cartonboard tested with the solid simulant Tenax. This is because:- a) the standard test conditions of 10 days at 5°C are directly comparable to the storage life and temperature of most chilled foods; b) the test temperature of 5°C is higher than the storage temperature of frozen foods (-20°C) and this compensates for the fact that the simulant is used for only 10 days whereas the food itself may be stored frozen for up to one year.
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