Thursday, October 30, 2014

How does a microwave oven work?

Posted on Oct. 20, 2013 at 1:00 a.m.

Mary Ann Lienhart-Cross

Food & Nutrition

Apples and pumpkins are plentiful this year, and we should be planning to enjoy them in a variety of ways in our healthy eating plans. I have had calls and emails with questions on microwave cooking, asking how a microwave works and what happens to the food value when cooked in a microwave.

Almost every American home has at least one microwave and many have two. The convenience offered by a microwave oven is undeniable. There is a lingering feeling that using a microwave to cook food may somehow make food less healthy. Knowing how microwaves work can help you understand.

Microwave ovens cook food with waves of oscillating electromagnetic energy that are similar to radio waves but move back and forth at a much faster rate. These quicker waves are remarkably selective, primarily affecting molecules that are electrically asymmetrical: one end positively charged and the other negatively so. Chemists refer to that as a polarity.

So the next part that helps in understanding is to know that water is a polar molecule, so when a microwave oven cooks or heats up food, it does so mainly by energizing it, which is to say heating up water molecules, and the water energizes its molecular neighbors.

In addition to being more selective, microwave-oven energy is also more penetrating than heat that emanates from an oven or stovetop. It immediately reaches molecules about an inch or so below the surface. In contrast, regular cooking goes through food rather slowly, moving inward from outside by process of conduction.

What you need to know is that some nutrients do break down when they’re exposed to heat, whether it is from microwave or a regular oven. Vitamin C is perhaps the clearest example. So, as a general proposition, cooking with a microwave does a better job of preserving the nutrient content of foods because the cooking times are shorter.

As far as vegetables go, it’s cooking them in water that robs them of some of the nutritional value because the nutrients leach into the cooking water. So when you are cooking broccoli it loses glucosinolate, the sulfur-containing compound that may give the vegetables its cancer fighting properties as well as the taste that many find distinctive and some not enjoyable. So that is why I steam vegetables in the microwave, the broccoli holds on to more glucosinolate.

Vegetables, pretty much any way you prepare them, are good for you. Most of us don’t eat enough of them. The microwave oven is a marvel of engineering, a miracle of convenience and a real bonus is that it is nutritionally advantageous.

Mary Ann Lienhart-Cross is county extension director and extension educator in health and human sciences at Purdue Extension Elkhart County. Reach her at 574-533-0554 or lienhart@purdue.edu.