Migration testing of plastics and microwave‐active materials for high‐temperature food‐use applications

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Abstract
Temperatures have been measured using a fluoro‐optic probe at the food/container or food/packaging interfaces as appropriate, for a range of foods heated in either a microwave or a conventional oven. Reheating ready‐prepared foods packaged in plastics pouches, trays or dishes in the microwave oven, according to the manufacturers’ instructions, resulted in temperatures in the range 61–121° C. Microwave‐active materials (susceptors) in contact with ready‐prepared foods frequently reached local spot temperatures above 200°C. For foods cooked in a microwave oven according to published recipes, temperatures from 91°C to 200°C were recorded, whilst similar temperatures (92–194°C) were attained in a conventional oven, but over longer periods of time. These measurements form the basis for proposing high‐temperature test conditions to be used in statutory methods for examining compliance with specific and overall migration limits for plastics materials. The testing conditions proposed depend on the intended use of the plastic—for microwave oven use for aqueous foods, for all lidding materials, and for reheating of foods, testing would only be required with aqueous simulants for 1 h at 100°C; for unspecified microwave oven use, testing with olive oil would be required for 30 min at 150 C; and for unspecified use in a conventional oven testing with olive oil would be required for 2 h at 175 °C. For microwave‐active materials, it is proposed that testing is carried out in the microwave oven using a novel semi‐solid simulant comprising olive oil and water absorbed onto an inert support of diatomaceous earth. The testing in this instance is carried out with the simulant instead of food in a package and heating in the microwave oven at 600 W for 4 min for every 100 g of simulant employed. There is an option in every case to test for migration using real foods rather than simulants if it can be demonstrated that results using simulants are unrepresentative of those for foods. The proposed testing conditions were validated as being realistic by measurement of the specific migration of various components from different plastics into foods under actual conditions of use and comparing with migration into simulants. Migration of plasticizers from PVC and VC/VDC copolymer films was monitored for both microwave reheating and cooking of foods. Total oligomer concentrations were measured from poly(ethylene terephthalate) (PET) trays, and volatile aromatics from thermoset polyester trays, using both types of container in microwave and conventional ovens. For microwave‐active materials, total PET oligomer concentrations as well as those of an individual oligomer (cyclic trimer) were used as migration indicators into foods and simulants.

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