On glutamate

A translation of this article by Sergey Belkov, Chemist, Flavorist, blogger:

What is Sodium glutamate?

Sodium glutamate is a salt of glutamic acid - one of the amino acids, from which proteins are built. It exists in every protein without exception, without it protein fundamentally cannot exist. In addition, it is the most common of all the 20 amino acids. In some vegetable proteins, the proportion of glutamic acid can reach 20-40%. In organisms it fills a vast quantity of functions, so one can say that an organism simply cannot live without it. But, happily, it is an “non-essential” amino acid: even if there isn’t enough of it in food, the human body can easily synthesize it, and if there is an excess in food, the body can easily use it for other purposes. It is impossible to abstain from glutamic acid – if you were to try, you’d have to abstain completely from protein.

The fuss about glutamate arises because glutamic acid, in addition to carrying important biological functions, also has a taste – the taste of umami. This is one of five fundamental tastes, for which the tongue has specialized receptors. Molecules of glutamate carry this taste in just the same way that table salt, sodium chloride (or more specifically, the sodium ions in salt), is the carrier of the salty taste, acids in the form of hydrogen ions are carriers of the sour taste, sugar carries the sweet taste, and many alkaloids are carriers of the bitter taste.

This happened through the process of evolution: glutamic acid can be thought of as a marker for protein. High protein foods have, as a rule, a certain amount of this amino acid, and so we recognize umami. This is the mechanism by which organisms find high protein foods. This is the reason why this taste is pleasant, and why it is useful for food processing.

But not just industrial food processing – most of the methods for cooking food actually create glutamate from protein: for example, stewing, frying, and boiling. Protein in the presence of acid under high temperatures or during fermentation reacts with water. This reaction essentially is analogous to what happens to protein in the digestive tract, and always leads to the long protein molecules falling apart into small fragments or even individual amino acids. These amino acids – chief among them being glutamic acid – are what gives foods a pleasant savory taste.

Fermentation itself is the production of glutamate: soy sauce, fish sauce, cheeses, especially hard cheeses. Sometimes people use a natural glutamate source, for example ketchup. Ketchup is practically glutamate made from tomatoes – that’s why it’s so tasty. Chefs figured out the umami taste by trial and error, by taste, but chemistry made these intuitive findings real in the form of a substance that we can add to food.

Why is glutamic acid important, but we use glutamate?

Man is essentially water with things dissolved in it, and all reactions inside us happen in solution. This is the reason why, in actual fact, it doesn’t really matter, whether we eat sodium glutamate, potassium glutamate, ammonium glutamate, or straight glutamic acid. In industrial food processing they use the sodium salt, because it is easier to purify it by crystallization.

Glutamic acid is a dicarboxylic acid, and in solution it exists as a mixture of four forms. Depending on the pH of the solution, one or two of these forms predominate. But it doesn’t matter which form we eat, or whether we eat it as a salt or the amino acid. Close to neutral pH, the negatively charged anion of glutamate will predominate in solution, and this is the one that has the umami taste and participates in biochemical processes in our bodies.

We talk about glutamic acid whenever we list the fundamental building blocks of protein. But when we talk of a solution of the substance, in food, in the synapses of the brain, or in the blood – then it is more logical and correct to use the word “glutamate”. This is because, as I said, glutamic acid doesn’t really exist in solution.

Why do people use sodium glutamate instead of potassium glutamate or glutamates of other elements?

Again, this happens because it’s easier. Sodium glutamate was the first to be isolated, the first to have a process developed for extracting and purifying it. Cost plays a role as well: the sodium salt is the cheapest form. Additionally, the umami taste is most clearly expressed in sodium glutamate, in comparison with potassium glutamate, for example.

How was sodium glutamate discovered, and how was it connected with the umami taste?

In the beginning of the 20^th century a Japanese chemistry processor named Kikunae Ikeda set a goal: figure out what substance in the seaweed called kombu makes food to which it has been added so tasty. Glutamic acid at that time was already known and characterized. But Ikeda, having isolated in 1908 glutamic acid from kombu, established a direct link: sodium glutamate is responsible for the umami taste. He got a patent and figured out production: Ikeda obtained glutamate from hydrolysis of soy and wheat protein.

How is sodium glutamate produced in industrial settings?

Earlier, people used artificial synthesis to produce sodium glutamate, but these methods were rather complicated, so they never really caught on. It’s important to understand that glutamic acid can exist in two isomers, but only one of them has taste. When we do a direct synthesis, we get both isomers, and so we have to figure out how to separate them, which is difficult. Additionally, the synthesis itself was rather dirty. Somewhere in the 1960s-1970s people came up with the ideal solution: they found a bacteria that had the ability to synthesize glutamate. They did some work to select the right strains, and started modern production. Now we feed these bacteria with molasses, which is a syrup left over from sugar production, as well as ammonia as a nitrogen source, and the bacteria produce glutamate, which we then receive as the sodium salt. So formally, from the point of view of technical regulations that classify substances as natural and artificial, glutamate is a natural substance, because it is produced by fermentation.

Does glutamate, naturally present in all those foods differ in taste from glutamate produced by an artificial means?

Of course not. The properties of a substance do not depend on its origin. The first person who can prove differently will invalidate all chemical science for the past 200 years. And in general, the distinction between natural and artificial is invented by humans. Everything in the world is natural. The choice of atoms and their ordering in a molecule is important, but you can’t differentiate between glutamate that was synthesized by chemical means from that produced by biotechnology or isolated from meat. It is one and the same glutamate.

Which foods have the highest amount of glutamate?

Glutamate is in all foods that have protein. Glutamate exists in two forms. The first is when it is chemically bound: this is glutamic acid that forms part of a protein. Proteins are made of sequences of amino acids. Proteins unlink into their constituent parts in the stomach or intestines, and so the amino acid enters the bloodstream. In this form, glutamate has no taste.

In the second case, glutamate exists in a free form, and then has a clearly expressed umami taste. Free glutamate can be formed through fermentation, such as in many Asian sauces, including soy sauce and fish sauce, and also in certain cheeses, such as Parmesan. Natural foods that are rich in glutamate include mushrooms, meat and tomatoes. Tomatoes are actually a big exception: other berries and vegetables generally don’t have much free glutamate. So you understand why ketchup found such an important place in world food.

How is glutamate used in the body?

In different ways. The cells of the intestines use it as an energy source, they burn it for their own purposes, and that’s the end. Ninety to ninety-five percent of glutamate ends up in the cells of the intestines, and so it never enters the blood.

But a key use of glutamate for humans is as a neuromediator. Through glutamate about 60% of nerve impulses are transmitted. This is the reason why we’ve heard so many stories about how glutamate from food can cause nervous system illnesses. It’s important to point out that if this were true, it would be true from any glutamate, not just food with soy sauce, or food with crystallized glutamate added, but also from ordinary meat. Or from cottage cheese: most people consider nonfat cottage cheese to be a high-protein food, but cottage cheese contains about eight times more glutamate than chips, for example. In cottage cheese the glutamate exists in a bound form, so it doesn’t have much taste, but that doesn’t matter – as soon as it enters an organism, it participates in metabolism.

Glutamate cannot cause nervous system illnesses for two reasons. Firstly, the body can synthesize its own glutamate, if a deficiency exists, and metabolize it, if there is too much. Secondly, between the bloodstream and the central nervous system, the blood-brain barrier allows only certain substances through, and protects against others. Glutamate cannot penetrate this barrier, and so it does not enter the brain. This is also an invention of evolution: the human diet is chock full of glutamate. And it’s been like that since the beginning, ever since we were little one-celled bacteria, all the way until we grew up to be so big but not always very smart.

Even more importantly, glutamate is hundreds of times more concentrated in the brain than in the blood, so the idea that glutamate from food can reach problematic concentrations in the brain seems far from the truth. All the glutamate that’s used by the nervous system is synthesized and used in place.

When sodium glutamate is added to different foods, does it enter into some chemical bonds?

No, it just dissolves into the mass.

Why do people add artificially synthesized sodium glutamate to food?

To make it taste better – for the same reason people add salt and sugar. It’s ironic that even though we know excess salt and sugar can cause harm, while excess glutamate has no effect on health, people still point fingers at glutamate.

Let’s take sausage as an example. If you want to make sausage from good quality meat, especially from selected meat that’s been properly fermented, the sausage will taste good without any additional glutamate. There are some old Soviet legends that sausage is supposed to be healthy – but they’re not true, sausage never was and never will be healthy, it is a cheap product for the masses. From the beginning no one expected that sausage would be made from high quality meat. You can make sausage with emulsions and extracts from pig hides, from blood plasma protein, from soy isolate, from other ingredients. To the ear, this sounds terrible and unpleasant. But from the point of view of biology, there’s nothing scary here. The problem is that all these things don’t have much taste, because they don’t have enough free glutamate (even though they contain a lot of bound glutamate), which is why people add glutamate: to give sausage the taste of meat.

Is sodium glutamate safe? What if you eat too much?

Thanks to a great deal of research, we know more about the fate of glutamates in the human body than we know about the health effects of eating carrots. Table salt, for example, has a lethal dose of 3 grams per kilogram of weight, meaning that a person who weighs 70 kilograms has a good chance of dying if they eat 210 grams of salt in one sitting. For glutamate, the index is 16 grams per kilogram. (Both of these figures were obtained by experiments on rodents that were force fed the corresponding substances. Unfortunately, science is not always kind.)

In other words, in order to die, a human needs to eat more than one kilogram of glutamate in one sitting. This is not physically possible. The concentration of glutamate in foods where it has been artificially added reaches a maximum of 0.5%, so overdose is not possible for technical reasons. This is the reason why the international compendium of food standards called the Codex Alimentarius does not contain acceptable norms for daily glutamate consumption, unlike many other substances that have clear limits. It’s impossible to eat enough glutamate to harm oneself.

It’s often said that industrial food has too much glutamate added to it. But it’s important to know that glutamate has a specific optimal concentration for best taste: this is somewhere between 0.1% and 0.3% by mass for liquids and bouillons, in dry products it’s a little bigger: from 0.5%-1%. If there is less glutamate, the food won’t taste as good. If there’s more, nothing good happens. It’s like with salt – there’s an optimal amount where things taste good, but if you add twice as much, it is by far worse than adding none at all. Adding too much glutamate to food would also be a financial waste. And, I remind you – this specific optimum, of around 0.3%, is several times lower than the concentration of glutamate in cottage cheese.

Why do they call sodium glutamate a flavor strengthener?

This is simply a poor translation. In English it is called a flavor enhancer. The only taste that glutamate can strengthen is the umami taste. This is just the same as salt, which strengthens the salty taste, and sugar strengthens the sweet taste.