The microwave oven is an invention that in the last years has saved a lot of time in the kitchen: we use it often, even if it is not so necessary. But not everyone knows that some foods should never be cooked or heated in a microwave oven: there could be various consequences, from the loss of the beneficial properties of food to food poisoning. So, here are the foods you should never put in the microwave oven.
Microwave oven and nutritional properties of foods
After debunking many myths about the microwave oven – such as the fear that the radiations emitted could hurt us – the scientific community, in recent years, has focused on investigating whether and how many nutritional properties of food are lost during microwave oven cooking. Unfortunately there are no unanimous results on this question: some researches show that broccoli cooked in the microwave oven, immersed in water, lose between 74% and 97% of antioxidants, which is not the case with other methods; others show the opposite: there are no differences in the mineral salts content of spinach cooked in three different ways, boiled, in a pressure cooker or in the microwave oven. Finally, a research published in the Journal of Food Biochemistry, has analyzed the effects of microwave oven, boiling and pressure cooking on 7 vegetables and their content of phenolic compounds concluding that that all the cooking methods involve a certain loss of phenolic compounds, but boiling and microwave oven reduce this loss.
So how do you find your way in choosing cooking methods? According to Harvard University scholars, “the cooking method that retains the best nutrients is the one that cooks quickly, heats the food in the shortest possible time and uses few liquids. Microwave oven cooking meets all these criteria: using the microwave oven with small quantities of water essentially cooks food from the inside out, which allows you to retain many more mineral salts and vitamins than other cooking methods". Productive or not, one thing is certain: microwave oven cooking is only suitable for certain foods. Some types of food should never be cooked or heated with this method: let’s see which ones they are.
Celery is one of those foods that should never be cooked, but not even heated, in the microwave oven. If you love dishes with celery, cooking with more traditional methods is mandatory: in fact, if heated in the microwave, this food not only loses all of its beneficial properties, but it also produces toxic nitrates and carcinogenic nitrosamines, substances that are very dangerous for humans.
There are several reasons for never cooking an egg in the microwave oven. First reason, due to the temperature that rises very quickly inside the egg, a lot of steam is created and this thing could even cause the explosion of the egg (if cooked with the whole shell). Second reason, scrambled eggs or omelettes in the microwave oven take on a bitter taste. Third and far more important reason, eggs cooked in the microwave oven become toxic.
Spinach and other green leafy vegetables often contain nitrate ions, which they absorb from the soil in which they are grown: elements that are harmless until cooked in the microwave oven. In fact, in this case the nitrate ions become nitrosamines that are carcinogenic and harmful to human health.
Mushrooms contain good amounts of protein, vitamins and amino acids: if heated in the microwave oven after being cooked, due to the high temperatures the protein composition changes, and this could cause bloating and stomach pain to those who eat them. The best thing to heat the mushrooms already cooked would be to heat them with a method that does not exceed 70 degrees.
Again, just like mushrooms, the problem lies in how potatoes are preserved after cooking. If they are allowed to cool at room temperature, the conditions can stimulate the growth of Clostridium botulinum (the botulism bacterium): heating them in the microwave oven does not protect you from intoxication.
The bacteria contained in chicken meat are generally neutralized by traditional cooking: this is not the case, if you cook the chicken in the microwave oven. The reason is simple: the microwave oven waves reach a maximum of 2 cm deep, while the rest cooks by induction. The bacteria could therefore survive and even multiply in the meat: therefore opt for a more classic method, both for cooking chicken meat and for heating it.
Beets have many nutritional properties and keep them quite intact even with prolonged cooking, such as those of a soup or a stew. On the other hand, cooking or heating the beets in the microwave oven is absolutely not recommended: they could release nitrite, a substance highly harmful to human health.
Rice is rich in nutrients and it is part of the basic diet for many people, but it can also contain spores of bacteria that can survive cooking. If the rice is left at room temperature after preparation, the bacteria multiply and this could cause food poisoning. Heating the rice in the microwave oven will not kill the bacteria, so it is best to eat the rice as soon as it has been cooked or freeze it within an hour after cooking and eat it the next day.