Saturday, June 21, 2014

microwave oven: safe to use

Alberto blurted out: Oftentimes, I am squeezed to think about whether using my microwave oven is safe for my health or not. So, I did some viral research and has found this article which may also be  useful and beneficial to all of you my friends.

A microwave oven, often colloquially shortened to microwave, is a kitchen appliance that heats food by bombarding it with electromagnetic radiation in the microwave spectrum causing polarized molecules in the food to rotate and build up thermal energy in a process known as dielectric heating.

 Microwave ovens heat foods quickly and efficiently because excitation is fairly uniform in the outer 25–38 mm of a dense (high water content) food item; food is more evenly heated throughout (except in thick, dense objects) than generally occurs in other cooking techniques.

A microwave oven heats food by passing microwave radiation through it. Microwaves are a form of non-ionizing electromagnetic radiation with a frequency higher than ordinary radio waves but lower than infrared light.

 Microwave ovens use frequencies in one of the ISM (industrial, scientific, medical) bands, which are reserved for this use, so they don't interfere with other vital radio services.

Consumer ovens usually use 2.45 gigahertz (GHz)—a wavelength of 12.2 centimetres (4.80 in)—while large industrial/commercial ovens often use 915 megahertz (MHz)—32.8 centimetres (12.9 in). Water, fat, and other substances in the food absorb energy from the microwaves in a process called dielectric heating.

Commercial microwave ovens all use a timer in their standard operating mode; when the timer runs out, the oven turns itself off.

Microwave ovens heat food without getting hot themselves. Taking a pot off a stove, unless it is an induction cooktop, leaves a potentially dangerous heating element or trivet that will stay hot for some time. Likewise, when taking a casserole out of a conventional oven, one's arms are exposed to the very hot walls of the oven. A microwave oven does not pose this problem.

Several studies have shown that microwaves negatively impact food's nutritional value. Other studies show that, if properly used, microwave cooking does not affect the nutrient content of foods to a larger extent than conventional heating, and that there is a tendency towards greater retention of many micronutrients with microwaving, probably due to the reduced preparation time. 

 Microwaving human milk at high temperatures is contraindicated, due to a marked decrease in activity of anti-infective factors.

Effects on food and nutrients: Any form of cooking will destroy some nutrients in food, but the key variables are how much water is used in the cooking, how long the food is cooked, and at what temperature.

Nutrients are primarily lost by leaching into cooking water, which tends to make microwave cooking healthier, given the shorter cooking times it requires.

 Like other heating methods, microwaving converts vitamin B12 from an active to inactive form. The amount inactivated depends on the temperature reached, as well as the cooking time. Boiled food reaches a maximum of 100 °C (212 °F) (the boiling point of water), whereas microwaved food can get locally hotter than this, leading to faster breakdown of vitamin B12.

 The higher rate of loss is partially offset by the shorter cooking times required.  A single study indicated that microwaving broccoli loses 74% or more of phenolic compounds (97% of flavonoids), while boiling loses 66% of flavonoids, and high-pressure boiling loses 47%, though the study has been contradicted by other studies. To minimize phenolic losses in potatoes, microwaving should be done at 500W.

Spinach retains nearly all its folate when cooked in a microwave; in comparison, it loses about 77% when boiled, leaching out nutrients.

Bacon cooked by microwave has significantly lower levels of carcinogenic nitrosamines than conventionally cooked bacon.

Steamed vegetables tend to maintain more nutrients when microwaved than when cooked on a stovetop.

Microwave blanching is 3-4 times more effective than boiled water blanching in the retaining of the water-soluble vitamins folic acid, thiamin and riboflavin, with the exception of ascorbic acid, of which 28.8% is lost (vs. 16% with boiled water blanching).

Direct microwave exposure is not generally possible, as microwaves emitted by the source in a microwave oven are confined in the oven by the material out of which the oven is constructed. Tests have shown confinement of the microwaves in commercially available ovens to be so nearly universal as to make routine testing unnecessary.

According to the United States Food and Drug Administration's Center for Devices and Radiological Health, a U.S. Federal Standard limits the amount of microwaves that can leak from an oven throughout its lifetime to 5 milliwatts of microwave radiation per square centimeter at approximately 5 cm (2 in) from the surface of the oven.

This is far below the exposure level currently considered to be harmful to human health.

The radiation produced by a microwave oven is non-ionizing. It therefore does not have the cancer risks associated with ionizing radiation such as X-rays and high-energy particles.

Long-term rodent studies to assess cancer risk have so far failed to identify any carcinogenicity from 2.45 GHz microwave radiation even with chronic exposure levels,i.e., large fraction of one's life span, far larger than humans are likely to encounter from any leaking ovens.

 However, with the oven door open, the radiation may cause damage by heating. Every microwave oven sold has a protective interlock so that it cannot be run when the door is open or improperly latched.

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