Pique the Geek 20091115. The Things we Eat. Monosodium Glutamate (MSG)

(noon. – promoted by ek hornbeck)

Monosodium glutamate (MSG) is often used as a flavor enhancer in many savory dishes.  What most people know is that it often added to foods.  What most people do not know is that is present in many foods naturally, either in free form or as glutamic acid in proteins, since glutamic acid is a very common naturally occurring amino acid.

There is considerable controversy surrounding MSG, mostly due to the so-called Chinese Restaurant Syndrome (CRS).  Symptoms commonly reported include numbness and tingling of the extremities, facial flushing, and several others.  Tonight we shall take a fairly in-depth view of MSG.

Monosodium glutamate is the sodium salt of glutamic acid, a non-essential amino acid.  The term non-essential is a bit misleading for folks who are not biochemists, because that very old term means that this particular amino is not necessary in the diet of laboratory rats for growth.  However, it IS essential for mammalian nervous system function.  Both rats and humans can synthesize glutamic acid from other materials, so even though we have to have it, we do not have to eat it.  Here is the structural formula.  Note that it is also possible to have disodium glutamate if the hydrogen on the left hand side of the molecule is replaced by a second sodium ion.

MSG

All foods with a significant amount of protein contain significant amounts of glutamic acid.  It is particularly abundant in wheat glutin, hence the name, and was once manufactured from it.  There are cheaper ways to make it now, and in the United States most is made from the molasses residue from beet sugar production.  Here is a structural diagram of glutamic acid:

Glutamic acid

At the pH of the body, the right hand hydrogen is ionized away, so glutamate is the form in which free glutamic acid exists in the body.  Everybody has it.

MSG was first discovered around the turn of the previous century by a Japanese chemist named Kikunae Ikeda while studying the brown alga known as kombu (Saccharina japonica).  It turns out that actual crystals of MSG form on the surface of kombu when it is dried, and those crystals have the characteristic flavor of many algae and also of soy sauce.  Kombu has been used for centuries as a base for soups, and interestingly it is only just brought to the boil and removed, which extracts mainly the MSG and leaves other flavor compounds behind.

Kombu

Note the whitish deposits of MSG on the kombu.

Dr. Ikeda named this flavor umami, and it has been proven that it in indeed a fundamental taste in humans, and the receptor in taste buds for it have been identified.  Umami sort of translates to “delicious”, but most people do not like this flavor unless it accompanied by the salty flavor as well.

Well, where else is MSG found?  It is abundant in meats and cheeses, and is an essential part of their flavor profile.  Soy sauce contains lots of it, due to the fermentation of wheat gluten (the type of soy sauce that we are accustomed to is brewed from a mixture of wheat and soy beans, with more wheat than soy), and in hydrolyzed yeast, a very common food additive.  Just today I saw the Swanson broth advert where the turkey runs away when the person reached for a can of “ordinary” chicken broth because of the MSG in most commercial brands.  It came back when she chose Swanson.  The dirty secret is that Swanson used hydrolyzed yeast, which is, as I just said, a prime source of MSG.  I find this advert to be downright deceptive, but is legal because of the very brief, fine print disclaimer that indicates that the hydrolyzed yeast contributes a “trivial” amount of MSG.  I suspect that over 99% of folks who see this advert do not catch that part.

It is actually difficult to avoid foods that contain added MSG because of the various sources of it.  The hydrolyzed yeast extract does not have to be called MSG, and there are other sources as well, such as hydrolyzed soy protein, hydrolyzed vegetable proteins, and others.  Sometimes “natural flavor” is used for MSG that is added as a part of another product.  In other words, unless a food processor adds the pure stuff, it does not have to be declared as MSG.

Most all salty snack foods contain MSG in one form or another, with the exception of plain potato, corn, and tortilla chips.  Guy’s potato chips used to have it, under the trade name “Flavorite”.  When the Chinese Restaurant Syndrome (CRS) controversy started up in the late 1960’s, they removed it, so my mum would grind up some Accent and add it to the bag and give it a shake.

In the body, glutamate is one of the major neurotransmitters, being one of the excitatory neurotransmitters.  Interestingly, one of glutamate’s metabolites, gamma amino butyric acid (GABA) is the principal inhibitory neurotransmitter, sort of a molecular-level yin and yang.  Glutamate is essential in the memory-forming process, but eating MSG will not make you any smarter since it does not cross the blood-brain barrier, but rather is generated in situ in neurons.

Now, glutamate needs to be in the proper place in neurons, either in storage vesicles or bound to a receptor, but not in the synaptic space itself.  Therefore, there are a number of enzymes that see to it that glutamate is properly placed.  However, this mechanism can break down after brain injury, causing glutamate to accumulate outside of the neurons.  This is very bad, because that allows excess calcium ions to enter the neuron, and they damage the energy producing part of the cell (the mitochondria), and cause cell death.  Much of the brain damage from stroke is due to this, as is some of the damage of Alzheimer’s disease.  There are several other pathological conditions caused in this manner as well.

Now to the matter of CRS, Chinese Restaurant Syndrome.  As I said earlier, in the late 1960’s a number of people reported tingling, dizziness, numbness, and even chest pains after eating Chinese food containing relatively large amounts of MSG.  Of course the media got hold of it and sensationalized it.  Subsequent research, horribly flawed research at that, seemed to indicate that there was a correlation between MSG intake and these symptoms in some people.  One fundamental flaw in the research was that it was not double-blind, not single-blind, and in fact not blind at all.

It is probably appropriate to explain these terms.  In a double-blind study, a group of subjects is selected and randomly assigned either a placebo or an active ingredient.  The test subjects do not know which they are receiving.  In addition, the people conducting the test do not know which one the subjects are receiving, either.  This is a very powerful method to reduce bias, both in the test subjects and in the test conductors.  In a single-blind study, the subjects do not know which they are receiving, but the test conductors do.  This reduces bias on the part of the subjects, but not on the part of the conductors.  When both the subjects and the conductors know who is getting what, bias is always a serious concern.  In the research cited above, both groups knew who was getting what.  In addition, the test subjects had previously self-identified as being sensitive to MSG, thus assuring a bias.

More recent studies have been conducted, again using self-identified “sensitive” subjects, but these cases in a double-blind fashion.  The results indicated that there might be a weak correlation between MSG and the CRS symptoms, but only when the MSG was administered without food.  There was no correlation when food was ingested at the same time.  The paper is here, and it references several other, earlier papers.  The evidence is pretty strong that CRS is extremely uncommon, and this is consistent with the fact that most of the population is not constantly suffering from it, considering the ubiquity of MSG in food, whether added or not.  My personal feeling about CRS is as follows, and it is consistent with the data.

Because of the popular media, the general public has a phobia about “chemicals”.  Just today I saw an advert about a steam cleaner for hard floors, and it was touted as “using absolutely no chemicals”.  Welllllll, steam is vaporized water, and water, the last time I looked, is a chemical.  It is also true that water can kill you, either by drowning or by water intoxication.  The only thing with no chemicals is an absolute vacuum.  In any event, people are afraid of chemicals.  Add to this the unfortunate but very real widespread ignorance of science in the general public, and it is easy to scare folks into thinking that they have some sensitivity when in fact they do not.  Another factor is that, for some perverse reason, there are a group of people who like being victims.  Thus, being “sensitive” to MSG fulfills all of the criteria I just enumerated.

Now, here is the real kicker.  Common vegetables contain lots of free glutamate, whilst meats contains lots of protein bound glutamic acid.  Check this out:

Parmesan cheese has 1200 mg/100g of free glutamate, but I have never heard of any Italian Restaurant Syndrome.  This is a third greater that of Japanese-style soy sauce, at 782.  That tablespoon of soy sauce, at 15 grams, has only 117 mg, whilst that ounce of Parmesan cheese has 336.  Yeah, Doc, but Italian cooking uses a lot of tomatoes, so there is not much overall.  Well, fresh tomatoes have 140 mg per 100g, and they get cooked down by a factor or two or three when made into sauce.  Let us say that you have a cup of sauce on that pasta, along with an ounce of Parmesan, and three cups of tomatoes were cooked down to make the cup of sauce.  A cup of tomatoes weighs about 250 g, so that is 350 mg in the sauce plus the the 336 from the cheese for a total of 686 mg.  Potatoes are also high in glutamate, at 180 mg per 100 g.  Thus, a restaurant sized baked potato, around half a pound, has 450 mg.  The source for these figures was a document released by Food Standards Australia New Zealand, and can be found here.  (Caution:  PDF format).

The bottom line is that, for the vast majority of people, MSG is safe and a wholesome addition to a diet.  If you happen to be sensitive, and remember that the controlled studies did not find any sensitivity when MSG was given with food, only when given alone in a single, large dose, then the symptoms are not life-threatening.  Even the reports about it making asthma worse have been debunked.  Thus, it will not kill you.  Actually, MSG may be a good thing for lots of people, because often less salt than otherwise would be used is ingested because of the flavor enhancement.

There are a couple of other umami triggers, most notable amongst them disodium inosinate, disodium guanylate, inosine monophosphate, and guanosine monophosphate.  These interact syngeristically with MSG, in that a little of any of these along with some MSG has a greater flavor response than an equal weight of any single component.  You can sort of use this as an indicator as to whether or not MSG has been added to food in a disguised form (remember, when things like hydrolyzed yeast extract are added, they are added for the MSG but it does not have to be declared).  If any of the four compounds just mentioned are on the label, it is almost certainly because of synergism with MSG, because they are all much more expensive to produce and it would not make sense to add them with no cheap MSG with which to interact.

Personally, I use MSG is several home-cooked dishes.  I like a little in tuna salad and in bean salad (bean salad is really not very good without it), and in most other savory hot dishes.  Just be careful adding it, because of the large number of ingredients that already have it in them.  Too much MSG tends to overwhelm, but a little really does perk up soups and sauces.  It is not so good for solid pieces, like on a steak, but a little can be blended into ground beef for hamburgers.  Note that in one form or another, it is present in most “veggie burgers” to boost the flavor of what is a fairly bland product.

The legal status of MSG in the United States, and most of the world, is that it is not really considered a food additive, but rather a flavoring, sort of like salt is regulated.  In the US it is on the GRAS (Generally Recognized as Safe) list, meaning that there is not really a limit to how much can be added to foods.  Of course, too much makes the food inedible, just like too much salt does.  The report from the Select Committee on GRAS Substances (SCOGS) Reviews is here and explains the reasoning used by FDA to come to this determination.

Well, you have done it again.  You just wasted a perfectly good batch of photons reading this poor excuse for an essay.  And even though Carrie Prejean gives up spouting out about family values when she reads me say it, I always learn much more than I could possibly hope to teach by writing this series.  Please keep comments, questions, corrections, and other thoughts coming.  Remember, no science or technology issue is off topic in this series.

Warmest regards,

Doc

Crossposted at Dailykos