6.05.2010

msg



it was my uncle's birthday this week, and he really enjoyed this birthday because his son asked him about msg.  my uncle is super smart, he has a Ph.D. from princeton in electrical engineering and computer science, he invented some sort of computer, i think he might be a chemical engineer as well, and he makes things in his lab for fun.  so he took this opportunity to share his essay on msg with the rest of the family.  it's kind of amazing.   happy birthday uncle robin!  









MONO-SODIUM GLUTAMATE

Just came back from the tiring 2-week Silk Road trip in Shaanxi, Gansu and Xinjiang. Yes, the Uighurs and Kazakhs are interesting. I did a good job though. I successfully fended off all illicit temptations.

While flying to and from Xian, we had many hours of layovers. So I took the opportunity to write this essay on glutamate. Then as I wrote, I found that I could not stop. There is much to be said. Guess "writer's block" is not one of my many problems.

Mono-sodium glutamate, or MSG, or simply sodium glutamate, is the most common form of glutamate, or glutamic acid salt. I prefer to use the general term "glutamate" to represent all these, including glutamate sources like hydrolyzed yeast and hydrolyzed vegetable proteins.

Glutamate is one of the 20 amino acids that comprise the millions of proteins in all the living organisms on earth. All these proteins are chains of different combinations of these 20 amino acids and most proteins contain glutamate. (There are some minor complications which I am not going to discuss here.) However, we can taste it only when proteins get hydrolyzed (by our saliva, for instance) into free glutamate. ("Free" means not combined into chains.) Therefore when we talk about taste here, "glutamate" means "free glutamate".

When you first came to the United States, did you ever wonder why there was no English word for "xian" (fish+lamb)? It is different from "delicious" since sweet candy can be delicious but not "xian". All Orientals cherish this savory taste. However, the Americans had been arguing with the Japanese for a century whether "umami" ("xian" in Japanese) should be considered a taste. Then in 2001, they found umami receptors in taste buds. An electrical signal comes out if and only if glutamate is put into the receptor. This definitively indicates that it is a unique taste. In 2002, "umami" became an English word officially. It is the taste of glutamate.

Now we know that there are 5 tastes, each with a distinct chemical function:

Sweet - energy sense,
Salty - electrolyte sense,
Sour - pH sense,
Bitter - poison sense,
Umami - protein sense.

Makes sense; doesn't it?

Note that the hotness of spices and the coolness of mint are technically not considered tastes since they are sensed by skin's pain and temperature receptors and not by taste buds on the tongue.

Note even better that there are 5 tastes, not 5 kinds of tastes. There is no difference between the sweetness of the apple and the sweetness of the orange. Color, texture and smell, not taste, distinguish the apple from the orange. We can distinguish only 5 tastes but thousands of odors (tens of thousands for dogs).

The olfactory epithelium has receptors for thousands of kinds of odors. See the 2004 Nobel Prize in Medicine by Axel and Buck, who found out that DNA for those receptors are important enough to comprise as much as 3% of the whole human genome.

Glutamate receptors are found not only in taste buds, but also throughout the nervous system. In fact, it is the most prominent neurotransmitter in the body.

Out of 20 amino acids, why is glutamate singled out? Why can we taste only one out of twenty? It is because glutamate is the most common amino acid in the proteins humans consume. Not surprisingly, scientists found different amino acid receptors in other animals with non-glutamate rich diets.

How does smell affect taste? Try this simple experiment. Hold your nose, close your eyes, and taste a random jellybean from a jar. You will not be able to distinguish apple, orange, cherry and pineapple. (You might be able to distinguish orange and lemon by their different degrees of sourness.) Now open your nose. All of a sudden, different fruits taste different again.

You may also want to try to distinguish unseasoned minced pork, beef and lamb. Reason for the finely minced meats is so that you cannot distinguish them by their textures. They all taste umami because your saliva hydrolyzes the proteins into some free glutamate. However, there is no difference among the umami from these sources. Glutamate from pork is the same as the glutamate from beef. Now you understand why some vegetarian foods can taste like meat.

We have been trained to like glutamate from birth. Human breast milk has 0.02% glutamate. That is 200 mg (a pinch) in every liter of milk, not a trivial amount. Some foods like certain mushrooms, parmesan cheese, tomato and seaweed have as high as 1% glutamate naturally. In fact, glutamate was first discovered from seaweed about a century ago. Comparing this 1% to the typical Chinese restaurant food with 0.1% glutamate, say 1 teaspoon in a pot of soup, we know that nature is actually more glutamate-happy than Chinese restaurants that give you the "Chinese Restaurant Syndrome", a.k.a. glutamate allergy.

Umami is not that important to me. Then there are people like my father who would rather die than to live a life without umami food. I eat so that I can live. He lives so that he can eat. He won't eat tasteless food. Sweet is bad for his diabetes; salt is bad for blood pressure; sour hurts teeth and spice hurts hemorrhoid. So glutamate as a seasoning has its place in the kitchen. It is relatively harmless.

Now, people are going to tell me why "natural" sources are better than artificial sources. As I explained last time, naturalness is relative ("relative" again). The natural sea salt from health food stores has gone through at least several artificial processes: filtration, evaporation, crystallization and grading. Drinking seawater is certainly more natural than using health food store sea salt. I do that automatically when I swim in the ocean. I also get much calcium, magnesium, potassium, iodine and other 100% natural minerals at the same time. (That is why I prefer the ocean to the swimming pool.)

If it is relative, do I prefer more natural to less? Definitely. I prefer hunting wild game to domestic animals; but people accuse me of animal cruelty. (Wait until they see those modern farms and slaughterhouses.) I prefer wild fruits to agricultural grains and vegetables; but there are too many mouths to feed in the world. (Count the endangered species they kill when they slash and burn to make farmland.) I prefer running to driving; but my parents worry that I might get hit by cars. I prefer to live in the wilderness than in comfortable houses; but my wife promises to divorce me if we do. I prefer disciplined exercise to herbal supplements and statins. I prefer women in their natural birthday suites. I prefer sunshine to artificial vitamin pills and antiseptics; but most Orientals erroneously think that dark is ugly. ("1 white covers 3 uglinesses.") They even inject themselves with poison (Botox). Deep down, people actually give naturalness fairly low priority.

Are we free to take any amount of glutamate we want? No. Too much of anything is bad for you. Secondly, some people are allergic to peanuts, some to gluten, and some to glutamate. (By the way, celiacs are in general not allergic to glutamate.) To avoid headaches and other symptoms, people allergic to glutamate should minimize taking it, including natural foods like seaweed.

Some people still insist that "natural" glutamate tastes better than synthesized glutamate. It is psychological. Let me tell you a story to illustrate this.

A friend of mine really likes lemonade. So about two years ago, I made a gallon of lemonade from tap water, cane sugar, citric acid and fragrance chemicals. (Of course I had tested my formula against the real thing before.) I cooled it in the refrigerator for a day. Well, I even put in a small piece of plastic lemon to make it look real. Then I asked him to come to my office and let him sample my lemonade. He was amazed, "This is the best lemonade I have ever tasted in my life!" I gave him the whole bottle. He was grateful. Then as he was leaving, I told him that it was purely synthesized lemonade 100% from chemicals. He spit everything out and threw the bottle away.

So much for now. Please help me complete my thought by asking me tough questions.


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