Microwave Oven & Health

By Dr Ammar Ibne Anwar

The microwave oven is a versatile, time saving kitchen appliance that uses microwave radiation to heat food. Microwaves pass through glass and plastic, bounce off some metals, and are absorbed by any object that contains water. All foods contain varying degrees of moisture, no matter how dry they look. Heat is produced as the microwaves agitate the water molecules contained within the food.

Microwave oven, device that uses micro waves to rapidly cook food. Every microwave oven contains a magnetron, a tube in which electrons are affected by magnetic and electric fields in such a way as to produce micro wavelength radiation at about 2450 Mega Hertz (MHz) or 2.45 Giga Hertz (GHz). This microwave radiation interacts with the molecules in food. All wave energy changes polarity from positive to negative with each cycle of the wave. In microwaves, these polarity changes happen millions of times every second. Food molecules - especially the molecules of water - have a positive and negative end in the same way a magnet has a north and a south polarity.

In commercial models, the oven has a power input of about 1000 watts of alternating current. As these microwaves generated from the magnetron bombard the food, they cause the polar molecules to rotate at the same frequency millions of times a second. All this agitation creates molecular "friction", which heats up the food. This unusual type of heating also causes substantial damage to the surrounding molecules, often tearing them apart or forcefully deforming them.

The microwaves cause water molecules in the food to vibrate, producing heat, which is distributed through the food by induction. A special electron tube called a magnetron produces the microwaves. To ensure even heating, the magnetron directs its waves at a rotating metal disk with offset vanes, which scatters the waves through the oven cavity; a rotating platform for the food is sometimes used in addition. Power settings may reduce the amount of radiation by cycling a constant-output magnetron on and off for varying lengths of time, or may reduce the level of radiation constantly produced by an inverter magnetron. The magnetron may be supplemented by quartz and halogen bulbs for browning food, which microwaves do poorly. Microwaves are transmitted, reflected or absorbed by objects, depending on what the objects are made of.

HISTORY

Cooking food with microwaves was discovered by Percy Spencer while building magnetrons for radar sets at Raytheon. In 1946 Raytheon patented the microwave cooking process and in 1947, the company built the first microwave oven, the Radarange. It was almost 6 feet (1.8 m) tall and weighed 750 pounds (340 kg). It was water-cooled and produced 3000 watts, about three times the amount of radiation produced by microwave ovens today. In the 1960s, Litton bought Studebaker's Franklin Manufacturing assets, which had been manufacturing magnetrons and building and selling microwave ovens similar to the Radarange. Litton then developed a new configuration of the microwave, the short, wide shape that is now common.

ADVANTAGES OF THE MICROWAVE OVEN

Some advantages of using the microwave oven include:

It is faster than conventional methods of cooking.

Conventional methods of cooking use energy to heat oil, water or air - microwave ovens only heat the food, so you can save on your energy bills.

Nutrients are retained in the food.

Protein foods don't brown when cooked in a microwave. This reduced oxidation means that nutrients like vitamin A and E are less likely to be destroyed.

Food heated quickly in a microwave retains more nutrients than foods kept hot for a long time, such as those simmered on a stove.

Potentially dangerous micro- organisms in food tend to thrive in temperatures between 5°C and 60°C. When you use a microwave oven, food can be thawed, cooked and served quickly. So it spends less time in the dangerous temperature zone.

Lipids

Heating of food would lead to various decomposition reactions (i.e. thermolytic and oxidative reactions) of its lipid components, including triglycerides, saturated and unsaturated fatty acids, as well as cholesterol in the presence of oxygen. The subsequent increase in fat oxidation products is of particular health concern. Various studies have been conducted to investigate the stability of lipids upon microwave cooking, including studying the hydrolysis of triglycerides in soya, egg yolk and meats; fatty acid profiles in chicken and beef patties, chicken fat, beef tallow, bacon fat, rainbow trout and peanut oil; peroxidation of polyunsaturated fatty acids in meat, egg yolk and chicken. Available evidence suggested that microwave cooking did not result in significantly more chemical modifications.

Vitamins

Many studies have been conducted to compare the retention of vitamins in different types of meat and vegetables subject to conventional and microwave cooking. Generally speaking, water soluble vitamins such as vitamin B and C are more susceptible to heat treatment. The retention of vitamins varies with size and shape of the food, cooking time, internal temperature, etc. Review of available literature showed that vitamin retention in microwaved foods is equal or better than conventionally prepared foods because of the shorter heating time of microwave cooking.

Minerals

Minerals are generally not destroyed during cooking including microwave cooking. However, they might be lost in cooking water or meat drippings. Nevertheless, a study comparing microwave and conventional braised beef found that significantly more phosphorus and potassium were retained in microwave cooking.

Efficiency

Inside the conventional oven, heat is lost when the hot air inside the oven escapes to the outside, whereas for microwave cooking, heat is produced inside the food and there is less energy loss. On average most microwave oven takes only about 20% of time required by conventional oven and saves at least 20% of energy depending on the food type

HEALTH HAZARDS

Uneven heating

Food is heated for so short a time that it is often cooked unevenly. Microwave ovens are frequently used for reheating previously cooked food, and bacterial contamination may not be killed by the reheating, resulting in foodborne illness. The uneven heating is partly due to the uneven distribution of microwave energy inside the oven, and partly due to the different rates of energy absorption in different parts of the food.

Acute dangers

Liquids, when heated in a microwave oven in a container with a smooth surface, can superheat; that is, reach temperatures that are a few degrees Celsius above their normal boiling point without actually boiling. The boiling process can start explosively when the liquid is disturbed, such as when the operator grabs hold of the container to take it out of the oven, which can result in severe burns.

Utensils such as forks produce sparks when placed in the microwave. This is because while it acts as an antenna, absorbing microwave radiation just like other metal objects such as the spoon, the pointed ends of the fork will act to concentrate the electric field formed at the tips. This has the effect of exceeding the dielectric breakdown gradient of air, about 3 mega volts per meter (3×106V/m), causing sparks to form. This effect is somewhat analogous to the effect of St. Elmo's fire.

BIOLOGICAL EFFECTS OF EXPOSURE

Continually eating food processed from a microwave oven causes long term - permanent - brain damage by "shorting out" electrical impulses in the brain [de-polarizing or de-magnetizing the brain tissue]. The human body cannot metabolize [break down] the unknown by-products created in microwave food. The effects of micro waved food by-products are residual [long term, permanent] within the human body. The minerals in vegetables are altered into cancerous free radicals when cooked in microwave ovens. One of the histological studies with microwaved broccoli and carrots have revealed that the molecular structures of nutrients are deformed by high-frequency reversal of polarity, even up to the point of destroying the cell walls, whereas in conventional cooking the cell structures remained intact.

PREVENTIVE MEASURES

Make sure that frozen foods are properly thawed in the microwave before cooking, because cold spots may allow bacteria levels to rise.

Thorough cooking is more likely if you chop the food into similar sized chunks. Smaller portions cook more evenly than large portions.

The use of cooking bags and lids, or covering the container with plastic film, helps ensure even cooking and destruction of harmful bacteria.

Ensure a more even temperature by using shallow and round containers, rather than square and high-topped containers.

Stir food at least once during the cooking process.

Foods that can't be stirred (such as roasts or quiches) should be left to stand, so that the heat can penetrate more evenly throughout.

Observe recommended standing times on microwave food products, such as popcorn or pre-packaged meals.

Avoid cooking stuffed poultry, as it is hard to ensure the stuffing has reached a temperature high enough to kill harmful bacteria.

Cooking an egg within its shell would lead to steam built-up inside the shell and subsequent explosion of the egg. To avoid this problem, eggs can be cooked in microwave oven when the shell is removed or cracked and the egg yolk / white is pierced several times.

Liquids or foods can be 'super-heated', which means they may boil explosively when stirred or otherwise disturbed. Always observe recommended cooking times. If you're unsure of how long to cook a particular food or liquid, leave it to cool in the microwave oven before taking it out.

Plastic containers are commonly used for microwave cooking and re-heating food and it is getting popular nowadays for carrying take-away meals. Not all types of plastic materials are suitable for microwave cooking. Even though high density polyethylene can be used for foods with high water content, it cannot be used for foods with high fat or high sugar content as these foods may reach temperature above 100oC during microwave cooking. Among plastic materials, the most commonly used ones for microwave cooking are polypropylene and crystalline polyethylene terephthalate (CPET), which have melting points of 210-230oC.

GENERAL SAFETY SUGGESTIONS

1.Read the microwave oven's instruction manual thoroughly. Keep it handy so that you can refer to it often.

2.Only use microwave-safe containers. Glass or ceramic containers that aren't labelled 'microwave-safe' may overheat and cause burns.

3.Never use plastic grocery bags, newspaper or plastic containers for frozen foods (such as ice-cream containers) in the microwave.

4.Avoid using plastic containers or film unless the manufacturer explicitly states that these items are microwave safe. Otherwise, compounds from the heated plastic can leech into the food.

5.Don't allow plastic film to touch the food. Even plastic labeled 'microwave safe' should not touch food to avoid migration of chemicals from the plastic.

6.Use glass containers designed for microwaves to cook high-fat foods, as additives from plastic are more likely to migrate into fatty foods at high temperatures.

7.Don't use metal containers or containers with metal trims.

8.Always supervise children when they use the microwave oven. Show them how to use it safely and warn them of the possible dangers.

REFRENCES

[1] http://www.inspiredliving.com/nutrition/nutrient-loss.htm[2] http://home.howstuffworks.com/microwave1.htm[3] http://en.wikipedia.org/wiki/Microwave_oven[4] http://en.wikipedia.org/wiki/Electromagnetic_wave[5] http://www.youtube.com/watch?v=AE3dRBlQjTE[6] http://www.youtube.com/watch?v=x1jqSKHfffU

Dr. AMMAR IBNE ANWARM.D., D.N.H.E., F.R.H.S.MEMBER OF INDIAN RED CROSS SOCIETYMEMBER OF NSM SOCIETY, CALIFORNIA, U.S.A.PATRON OF VANCO. HEALTH SOCIETY, B.C., CANADA K-78, SAFINA APARTMENT ,MEDICAL ROAD,A.M.U.,ALIGARH, U.P. INDIA.

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