An Apple A Day Won't Keep Me Away
A recent post here on the Verge alerted me of an article from NYT telling the story of genetically engineered apples that won't turn brown. Apparently, the idea of GMOs is still considered controversial by some, so I though I should give you my 2 cents on why these apples are completely harmless to us and to our environment.
Apples and other fruits turn brown when cut because some of their cells are ruptured and intracellular enzymes come in contact with the atmospheric oxygen. The enzyme responsible for the brown color is called polyphenol oxidase, and the color substance is the oxidation product of polyphenols that are naturally contained in the fruit.
In order to prevent this quite natural chemical reaction from hapenning, one can either increase the acidity on the surface of the cut apple (by adding lemon juice for example), or prevent the access of oxygen (by placing the cut fruit under water). Importantly, there's another way to prevent oxidation -- by using antioxidants. This has actually been in use in fastfood chains providing healthier alternatives to deep-fried snacks -- I have been able to buy pre-sliced packaged apples at my local McDonalds for years, and they magically hadn't turned dark. Needless to say, the antioxidant used is a completely harmless (and even healthy) chemical, none other than Vitamin C.
My guess was, and the NYT article confirmed it, that those genetically engineered apples either lack the enzyme responsible, or have very little amount of it, thus slowing down the oxidation process. A smart way to achieve this could be to actually supress the production of the enzyme only in the fruits, so that it would not lead to decreased viability of the plant organism as a whole due to lack of the enzyme in the vegetative parts of the plant.
Most likely, the only effect that consuming these GM fruits can have on a human is that we miss ingesting the enzyme otherwise present in non-modified apples. Enzymes are protein molecules that are present in miniscule quantities and have practically zero nutritional value, therefore we would not miss anything substantial from our diet (fruits aren't a good source of protein anyway).
There is zero possibility that the genetic modification may affect our own genes: the genes present in the food are destroyed in our digestive tract, and even if they weren't they have no way of reaching our own genetic material. Now even if we would artificially produce those genes and inject them directly in our cells, they wouldn't do much because they are incompatible with ours -- think of this as of running a Mac program on Windows, only a zillion times more impossible.
The possibilities that the modified genes may escape by cross-polinating some plants other than apples are in practice extremely unlikely, and even if this hapenned it would only result, in the worst case, in some wild bush the fruits of which don't turn brown when cut. It is important to note that most genetic modifications engineered by humans actually reduce the adaptability of the recipient organisms to the wild environment, so they will be killed off by natural selection within only a couple of generations (still talking about the non-brown wild bush).
So there you have it, TL/DR: have no fear, GMOs are good for you and for the planet.
Thus spoke the good doctor.