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Successful microwave cooking depends on understanding the limitations as well as the benefits of this type of cooking.
majority of reports published on the nutritive value of foods cooked in
microwave ovens indicate that food prepared in this manner is at least
as nutritious as comparable food cooked by conventional methods.
of these studies have concentrated on vitamin retention and indicate
that cooking in minimal water for a reduced time, as occurs with
microwaving, promotes the retention of the water-soluble vitamins
particularly of vitamin C and thiamin.
Microwave cooking is
preferable to boiling to minimise the leaching of vitamins into the
cooking water; in this regard it is similar to steaming. For the same
reasons given for vitamin C, microwave cooking enhances mineral
retention in vegetables.
Studies have not revealed any non-heat
related effects on the macronutrients of foods, proteins, fats and
carbohydrates, when cooked in microwave ovens. There may be slight
differences in denaturation rates of proteins when food is heated in a
microwave oven compared with conventional heating but this is due to
differences in the time and temperature to which the food is subjected.
Recent reports reveal that cooking vegetables in a microwave oven
leads to a greater loss of soluble phenolic antioxidant compounds than
does conventional cooking.
However, this appears to have been at
least partly due to the use of more cooking water than is necessary with
microwaves. The role of these phenolic compounds in human nutrition
remains an open question.
Far less information is currently
available on the effect of microwave cooking on other food components
such as carbohydrates, lipids and fat-soluble vitamins. The quality of
protein is higher in microwaved than in conventionally cooked food as
far less oxidation occurs in meat cooked in a microwave.
browning is visible evidence that heating is gentler, and makes it
likely that vitamins A and E are better retained than in conventional
cooking. However, these differences are likely to be slight and of
little nutritional significance.
Reheating food quickly in a
microwave retains more nutrients than holding food hot for long periods;
this is significant in institutions and hospitals where food may be
held hot for several hours in traditional catering systems.
nutritional value of food does not depend only on the way in which it is
cooked. Just as important are shopping wisely for quality products,
correct temperature control during storage and preparation and serving
food promptly after it is prepared.
Leaching effects aside, there
seems to be little difference to the retention of nutrients between
food cooked by microwaves or by conventional means, provided
that cooking time and temperature guidelines are carefully followed.
food undergoes changes when heated. There is no firm evidence that
microwaves cause any effect on food other than those due to rapid
heating. Care should be taken to avoid overcooking.
in a microwave oven does not present a radiation risk. Microwaves cease
to exist as soon as the power to the magnetron of a microwave oven is
switched off. They do not remain in the food and are incapable of making
either it or the oven radioactive.
Consumer concern has been
caused by media coverage of isolated reports which suggest that
microwave heating produces chemical changes in foods with the formation
of potentially toxic compounds.
The most widely reported of these was a letter which appeared in the reputable journal The Lancet
in 1989. This work was reviewed by an expert committee of the National
Health and Medical Research Council (NHMRC) which concluded that the
results obtained in the experiment were not relevant to the way food is
prepared and consumed.
A second more recent report in a little known Swiss journal also appears to be irrelevant to domestic use of microwave ovens.
cooked in a microwave oven does not heat uniformly and unwanted
microorganisms may survive in portions of poorly heated food.
use stirrer fans and turntables and recommend standing times to help
alleviate the problem of uneven heating. Many microwaveable meal packs
carry the instruction to stir the food part way through the cooking
process. Items such as lasagne that can't be stirred should be allowed
standing time to allow the whole product to reach a uniform temperature.
far microwaves are able to penetrate into the food will also depend on
the thickness of portions and on the composition and moisture content of
the food. When heating large quantities of food it is more effective to
divide it into smaller portions for reheating than it is to heat a
large amount for longer.
Care should be taken that frozen food
has been completely thawed. Water absorbs microwaves far more easily
than ice does; incomplete thawing will result in uneven cooking and the
potential survival of undesirable microorganisms in those parts of the
food which have been insufficiently heated.
A positive feature of
microwave ovens with regard to food safety is that food can be taken
from the freezer, thawed quickly, cooked and served without it spending
long periods of time in the danger temperature zone between 4 °C and 60
°C, which provides favourable conditions for the growth of dangerous
ovens are less likely to cause burns than conventional ovens. However,
the potential hazard of burns associated with microwave cooking is not
often considered, and many people allow young children to operate these
Burns have occurred from the
steam emitted from microwaveable popcorn bags and similar closed
packages and from the boiling portions of foods which heat unevenly.
An example of this is a jam-filled donut—the jam centre may exceed
the boiling point of water while the donut itself is only warm.
macaroni cheese is another example as the cheese reaches a high
temperature more quickly and retains more heat than the macaroni.
Moreover, severe scalding has also occurred when babies have been given
milk heated in a microwave oven.
When using new crockery for the
first time in a microwave oven, use oven gloves to remove the item after
heating until you are aware of its heating characteristics. There have
been instances when some types of crockery mugs have absorbed more heat
than the liquid they contained causing unexpected burns.
designed for the purpose should be used in a microwave oven. However,
as there are no standards currently available for claims such as
'microwave-safe', any concerns about the safety of such products should
be referred to the manufacturer.
Some additives used in the
manufacture of plastics, particularly those which make it pliable, may
migrate into food, especially at high temperatures. Only those plastic
containers which have been specifically designed for microwave cooking
should be used, and they should be discarded when the surface shows any
signs of breaking down.
When plastic films are used in microwave
ovens it is preferable that they are not in direct contact with the food
they cover. Meals to be reheated on a plate may be covered with clean
white absorbent kitchen paper to prevent spatter.
It is very
important that food containers which have been designed to package
frozen or chilled foods such as ice cream or margarine, are not exposed
to high temperatures in a microwave oven. The low melt temperatures of
these plastics may result in migration of undesirable contaminants into
the food or in physical disintegration of the containers themselves.
As migration is more likely to occur in hot fatty foods, glass
containers are preferred to plastic for heating them. Container shape
may also influence the way a food reacts to reheating.
or oval containers help prevent edges of the food burning because energy
absorption occurs evenly around the edges. Square containers tend to
encourage burning on the edges of a product.
are a good choice for heating foods because they provide a large surface
area. Packaging for microwavable meals has been especially designed for
use at high temperatures. This sophisticated packaging may incorporate
susceptors (surface layers) to compensate for some of the limitations of
Susceptors consist of a plastic film
metallised usually with aluminium and laminated to paper or paperboard
to hold the required shape. They are designed to enhance browning and
crisping of a product and to improve its texture. For example without
the use of susceptors, pizzas heated in a microwave oven would be soggy.
absorb microwave energy and heat food mainly by direct contact.
Susceptor materials have been tested both for migration levels of
undesirable chemicals and the release of any volatiles, but tests have
not revealed that they pose any threat to consumer safety.
packaging industry recognises the problems of potential migration from
packaging into food and constantly monitors and improves manufacturing
Microwave oven doors are designed with at least two features that ensure that power is cut off immediately the door is opened.
it is possible for microwaves to leak out around the edges of a poorly
fitting or damaged door. If a door does not fit squarely and operate
smoothly or if it shows signs of corrosion or damage, the oven should be
inspected by a qualified technician.
Samples of all models of
microwaves are tested for leakage before sale as prescribed in
Australian Standard 3801-1980, and the National Health and Medical
Research Council (NHMRC) has determined a standard of safety for the
power flux density of radiation for microwave ovens which it believes
safeguards public safety.
Microwave oven leakage levels which
exceed the recommended levels are extremely rare. An oven in good
condition and used correctly is safe. Most microwave oven repair shops
will test ovens for leakage at a reasonable cost.
Leakage detectors for domestic use are available but only those which comply with Australian Standard AS2889-1987, Microwave oven leakage detectors for household use, should be purchased and their instructions followed carefully for an accurate result.
Australian Radiation Protection and Nuclear Safety Agency
(ARPANSA) closely monitors potential radiation hazards in consumer
products. Read ARPANSA's general precautions and possible hazards
associated with radiation emissions from microwave ovens.
microwave cooking depends on understanding the limitations as well as
the benefits of this type of cooking. If correctly used, microwave ovens
offer a convenient and safe method of food preparation without any
detrimental effects on consumer safety or nutrition.
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Last updated: Last updated: 26 February 2015
Printed from: Microwave oven safety (http://csiroaucd2-cdc.it.csiro.au/en/Research/Health/Food-safety/Microwave-oven-safety)