Rick Shory

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Proteins wrecked by microwave ovens?

I was out hiking with Dr. Jeff, another chemistry nerd. He has long been in touch with, and sympathetic to, the health and woo woo scene. He mentioned that people back in the 1980s were concerned that microwave ovens were racemizing the amino acids in protein.

I was astounded. Perhaps most amazing was the fact that none of the people I knew who were opposed to microwave cooking had ever mentioned this before. It seemed like it could be a very legitimate health concern. However it also seemed like it would be fairly straightforward to get a definitive answer, one way or the other. Either this is a big problem, and there’s a huge cover-up going on. Or else it’s not a problem; but if not, why not?

Amino acids (all except glycine) exist in two forms, left- and right-handed. This is analogous to how a glove can be either for your left hand or your right hand. Unlike gloves, which usually work in pairs, biological life can normally use only one of the types, say left-handed. The requisition is for shipments of only left-hand gloves.

Left- and right-hand gloves are mirror images of each other. You can toss a left-hand glove around any way you want, and it doesn’t change into a right-hand glove. Well, unless you turn it inside out.

At this point, the analogy breaks down. An inside-out glove is not “really” the other-handed glove. The stitches show, and the lining is different. But on a molecular level, if you flip an amino acid “inside out” it actually becomes the other form. Clean, with no seams.

I am not going to go into this too much, but the “handed-ness” is from the four bonds of a carbon atom being tetrahedral. You can look this up if you want, but basically, if you take a tetrahedron, and mark each of the four points a different color, you can do this in two different possible ways, and the two ways are mirror images of each other, left- and right-handed.

Atoms are not really hard little balls, as they are modeled. Everything is always swinging, jostling, twisting. The parts attached to the four tetrahedral points are getting shoved around. If things get knocked, just right, and with enough force, one point could get pushed between two of the other points, momentarily crowded in an uncomfortable way. Then the bonds would pop back into a tetrahedron — but now in the other mirror-image shape.

As soon as Dr. Jeff mentioned it, I could immediately see that microwaves might be just the right energy level to do this. They are not strong enough to break bonds, but presumably could rearrange bonds. Parts of molecules easily resonate at these low energies, with bonds stretching, swinging, scissoring. Was it dire? Or no issue?

Say you had a washer-dryer or something that had the strange power that when you ran gloves through it, it could knock them inside-out. This analogy is a bit forced, but is to explain the chemical term “racemize”. Say, you put in a batch of left-handed gloves. They would start getting turned into right-handed gloves. The process is random, so soon some of the right-handers start getting turned back into left-handers. Eventually, you end up with a fifty-fifty mix. In chemical terms, this would be a “racemic mixture”, and the molecules would be said to have been “racemized”. In biological terms, living things only want the left-handers. Are the right-handed ones inert waste? Or poisonous? Or will they have some weird effect nobody bargained on?

Armed with these search terms, I started investigating. It turns out quite a bit is known about amino acid (“AA”) racemization. In the rough-and-tumble of molecular existence, it has been going on ever since there were AAs. Some AAs are more susceptible than others. And there are factors of the molecular environment. For example, a particular AA built into a protein may be like a glove clenched around something, and therefore quite difficult to turn inside out. Or presumably, it could be otherwise, and easily flipped. Still, all else being equal, at higher temperatures it goes faster. Heat equals molecular jostling, and stronger jostling means higher probability of a strong enough knock to cause the flip.

Ok, we can start to relax. Since racemization is constantly going on, life has had to deal with it from the get-go. The wrong-handed AAs are not poisonous. Life either spits them out, or possibly has ways to pop them back into the correct form. That would be the topic for another investigation.

But, are microwaves speeding up the process, and “wasting” the food value of proteins? Interestingly, the only search hit that included “microwaves” was a process for intentionally racemizing AAs, bragging that it was as good as ordinary heat. It makes sense. Heat is just molecular motion. Microwaves jostle the molecules, and so add heat.

Since racemization is a random process, the longer time it goes on, the further it progresses. So I am probably getting more AA racemization in my slow-cooker crock pot, than in the fast zap of the microwave.

One of the most interesting links that turned up was using AA racemization to estimate the age of whales. The lens of a whale’s eye is largely protein. It gets laid down, layer by layer as the whale grows, from the outside, like rings of a tree. The inside, the “heartwood”, has been there for a long time. AA racemization has been going on, in its random way. Whales live in the sea, where the water is of relatively constant temperature, so the faster-at-higher-temperature racemization rate is not such a factor. I’ll let you look it up, if you want to know how old the whales really are.

Myself, I’ve moved on to worrying about other food problems than AA racemization.