Are packaging and cooking utensils "microwaveable"?

A microwave oven produces a magnetic field that causes a strong agitation of the water molecules present inside the food, and this process induces a very rapid rise in temperature. The emission of heat is increased by the presence of other molecules that act as brakes and hinder the moving water molecules. In the oven, energy in the form of microwaves is irregularly distributed, and food prepared in this way sometimes shows alternating hot and cold zones. What's more, the heat produced in food subjected to the same electromagnetic field varies according to its composition. Heat is dissipated from the surface to the core of the food. Compared to a conventional oven, food cooking times are shorter in a microwave oven.

As for containers (packaging and cooking utensils), they are heated by the dissipation of heat from the food to the materials and not by the action of microwaves.

There are questions about the safety of food reheated in microwave ovens. According to the Canadian Ministry of Health (Health Canada), microwaves do not alter the chemical components of food and should therefore not lead to the formation of new components such as carcinogens. Studies have been carried out to analyze the possible adverse health effects of microwave ovens. These studies, which have been evaluated by the competent Canadian authorities, reveal no signs of toxicity or carcinogenicity.

So, the health and safety issues associated with microwave cooking are generally similar to those associated with other cooking methods. These include the risk of excessive temperature rise, which can have several consequences:

burns if the consumer is exposed to very hot parts of the container or food;

• increased transfer of constituents from container materials to food through the chemical phenomenon of migration;
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• deterioration of food nutrients;
• physical alteration of materials in contact (e.g. melting of a plastic material or geometric deformation of packaging or cooking utensils).

To meet the needs of manufacturers of packaging or cooking utensils, a test bench specialized in studying the behavior of packaging or cooking utensils in microwave ovens has been developed. The temperature of the container in contact with the food is measured at the interface using fiber-optic thermometers during reheating in a microwave oven. This equipment makes it possible to map temperature variations and assess the resistance of materials and items.

Using this equipment, it is possible to measure:

• the temperature of plastics and objects at the plastic/food interface during heating in conventional or microwave ovens in order to select the appropriate temperature for migration testing (standard EN 14233 - February 2003).
• the resistance of plastic materials or objects to microwave heating (Standard EN 15284 - July 2007).

To increase its experience on this subject, LNE has conducted, in association with the Agence nationale de sécurité sanitaire (ANSES), a study of the impact on substance migration of reheating or microwave cooking of previously frozen or unfrozen food in plastic containers (packaging or containers intended for food preparation or consumption). The study provided data on:

• temperatures at the Material/Food pair interface during reheating in a microwave oven with a view to establishing mappings;
• analysis results for the migration of substances derived from plastics and subject to regulatory use restrictions (LMS) in food simulants and under conditions of temperature, duration and repetition of contact corresponding to the reheating of food in a microwave oven;
• temperatures at the Material/Food interface in relation to plastic types, food types for given microwave oven operating parameters.

Update date: April 2012

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