Scary-scary glutamate
The great career of glutamic acid: all the pros and consR.Akasov, "Chemistry and Life" No. 11-2010
Published on the website "Izvestia Nauki"If you ask a biochemist which of the amino acids is the most necessary for a person, he is unlikely to answer this question.
And for an economist, the answer is obvious: of course, glutamic. Three million tons per year is exactly how much of this substance is produced on the planet now. At the same time, production is constantly growing, but has not yet managed to catch up with consumption – glutamic acid deficiency is estimated at 800-900 thousand tons per year. The closest pursuer is the amino acid lysine with an annual production of about 1,100,000 tons. The rest lagged behind the leader even more. How to become a champion among amino acids? About this in today's article.
Salt from algae
The discovery of glutamic acid happened quite quietly. The German chemist Heinrich Ritthausen in 1866 isolated it from vegetable protein, in particular from wheat gluten. By tradition, the name of the new substance was given by its source: das Gluten in German – gluten. By the way, two years later Ritthausen isolated another amino acid from asparagus seedlings, which bears the Latin generic name Asparagus. It is not difficult to guess that this substance was aspartic acid.
Recall that amino acids are organic compounds, which, as the name implies, contain both carboxyl and amine groups. About 300 amino acids are found in living organisms, 20 of them are part of human proteins, and 10 of these twenty are "irreplaceable", that is, our body is not able to synthesize them and must receive them with food.
Glutamic acid is one of the most common in the composition of proteins, moreover, among the remaining 19 protein amino acids there is also its derivative glutamine, which differs from it only by an additional amino group. But for the body, these are two different substances, each with its own biochemical functions, and they should not be confused. But glutamate is almost the same glutamic acid, only in the form of salt. Actually, the salt of glutamic acid should be called glutamate, but because of the English spelling of the substances glutamic acid - glutamate and not very attentive translators, "glutamate" has become fixed in the language. However, Russian science, even the most official, has not recently encountered such "translation difficulties", so let's not be too strict.
Glutamic acid is sometimes also called glutamic acid, less often alpha-aminoglutaric acid. Very rarely, although chemically correct – 2-aminopentanedioic. All these names hide the same formula and the same substance, which in its pure form is unremarkable colorless crystals, poorly soluble in water.
HOOC–CH 2–CH 2–CH(NH 2)–UNSW
The real history of glutamic acid began in the XX century, when Ikeda Kikunae, a professor at the University of Tokyo, asked the question: why does food become tastier and more appetizing if it is flavored with some types of dried algae, long known to Southeast Asian cooks? In 1907, Ikeda isolated glutamic acid from kelp and konbu algae and found out that it was responsible for their characteristic taste, and two years later patented the technology of producing its sodium salt from algae. The taste that this seasoning gave to the food could not be called either salty, sour, bitter, or even more sweet. Therefore, it received its own name "umami", which is usually translated into Russian by the epithet "meat taste".
The seasoning, produced under the trade name "Ajinomoto", that is, the "soul of taste" (the manufacturer was also called the same way), quickly became popular, but in the West it was learned about only after the Second World War. The idea of using monosodium glutamate as a flavor enhancer was spied by the Americans. Before that, the rich meat taste of food was given mainly with the help of fats. In 1947, the additive began to be officially used in the United States. Its new name is MSG, Mono Sodium Glutamate, the monosodium salt of glutamic acid.
At the same time, glutamic acid was also used in psychiatry as a stimulating and stimulating agent. There is much more in common between these two different uses of the same substance than it might seem. Glutamic acid is a neurotransmitter, that is, an intermediary, the "baton" of the nervous system. It binds to specific receptors of neurons and causes their excitation. In this case, a special enzyme can convert glutamic acid into gamma-aminobutyric acid (GABA), which plays the role of an inhibitory neurotransmitter, that is, suppresses the nerve impulse. When we add glutamate to food, something similar happens: an amino acid molecule interacts with the taste buds of the tongue and excites them, increasing sensitivity.
Is it dangerous or useful?
Since the beginning of the industrial production of glutamic acid and until now, the use of this substance has only grown. However, as it turned out, not everyone liked it – in the truest sense. In the mid-70s, American neurophysiologist John Olney, working with rats, stated that sodium glutamate can cause brain damage in them. And Japanese scientist Oguro Hiroshi suggested that this supplement changes the retina of the eye in rats. Soon there were complaints from people who often eat food with sodium glutamate. Headache, increased heartbeat, heavy breathing, general weakness and fever – these symptoms began to be called "Chinese restaurant syndrome".
Fortunately, further research turned out to be much more encouraging. The effects noted in rats were not manifested in the human body. And the "Chinese restaurant syndrome" turned out to be overblown: there was no reliable connection between the use of glutamate and unpleasant effects, including in experiments with "blind" control. Which, however, does not negate the possibility of an individual allergic reaction to one or another component of an unfamiliar cuisine – at least to monosodium glutamate.
However, everything happened as in the old joke: the spoons were found, but the sediment remained. Many people are sure of the negative effects of sodium glutamate, and some television programs like to scare viewers with "chemistry". But all this is mostly horror stories from scratch. In Russia, sodium glutamate (E621), as well as potassium glutamates (E622), calcium (E623), ammonium (E624), magnesium (E625), as well as glutamic acid itself (E620) are allowed for use – up to 10 grams of the substance per kilogram of the product, and in seasonings and spices the permissible concentration is still higher. However, magnesium and ammonium glutamates are not allowed for retail sale. All this is regulated by Sanitary norms and rules (SanPiN 2.3.2.1293-03). Moreover, both the acid itself and its salts are recognized as safe all over the world, including by the World Health Organization.
Today, glutamates are used to enhance the taste and aroma of soups, broths, including instant cooking, in chips, sauces, various meat products, and canned food. The dosage is approximately 0.1–0.5%, that is, from 1 to 5 grams of glutamic acid per kilogram of the product. Considering that in a bound form (that is, as part of proteins) we consume about 20 grams of this amino acid daily, the increase from the seasoning is not so significant. Besides, eating too much of it is almost as difficult as eating over-salted or over-peppered food. Glutamates are usually added to the product together with salt, while the dosage of salt is reduced by 10%. In addition, glutamate is often used in a mixture with inosinate and sodium guanylate (salts of nucleotides, the very ones that make up DNA). A mixture of these substances in a certain ratio, called glurinate, gives a more balanced taste and allows you to reduce the concentration of each individual component.
There is a lot of glutamic acid in the most common foods – meat, milk, vegetables. In proteins, about a third of the total number of amino acids is accounted for by glutamine and glutamic acid. And our body regularly synthesizes these substances for its needs. Moreover, increased doses of glutamate are prescribed for developmental delays, epilepsy, psychosis, depression and many other diseases of the nervous system. Glutamic acid stimulates the immune system and the intensity of metabolism in general, since transamination reactions involving this substance accompany the synthesis of all interchangeable amino acids. In addition, glutamic acid binds toxic ammonia released during certain biochemical reactions, forming a harmless and necessary glutamine cell.
However, fighters with glutamate can be understood to some extent. On the one hand, amino acids in foods are destroyed during storage, especially glutamine is unstable. The addition of glutamic acid salts in this case only compensates for the lost taste. On the other hand, with the help of seasoning, you can turn an initially inedible product into something appetizing. And some manufacturers actively use it. Only here the possible harm will come from the product as a whole, and not from glutamate in any way. Perhaps the only category of people who are not recommended this supplement is children under three years old. However, the requirements for baby food are generally very strict, and literally a few additives are allowed to be used.
The most important thing is to remember that the properties of a substance do not depend on the method of its preparation. Therefore, synthetic, "chemical" glutamic acid will not differ in any way from natural, unless, of course, we are talking about a pure substance. Glutamate in a bag with seasoning is the same glutamate that the Japanese have been using as part of seaweed for many years. And their life expectancy, by the way, is one of the highest in the world.
Three million tons
That's how much glutamic acid and its salts are produced today every year. The technology invented by Professor Ikeda – extraction from seaweed – naturally could not provide such an amount of product, even though the amount of glutamic acid in kelp can reach up to 1% of the mass of algae.
The second possible way to obtain glutamic acid, which has been used for a long time in Europe and the USA, is the hydrolysis of proteins, for example, the same gluten from which this substance was first obtained. Wheat or corn gluten was usually used, in the USSR – beet molasses. The technology is quite simple: raw materials are purified from carbohydrates, hydrolyzed with 20% hydrochloric acid, neutralized, humic substances are separated, other amino acids are concentrated and precipitated. The glutamic acid remaining in the solution is again concentrated and crystallized. Depending on the purpose, food or medical, additional cleaning and recrystallization are carried out. The yield of glutamic acid in this case is about 5% of the weight of gluten, or 6% of the weight of protein itself.
Chemical synthesis of glutamic acid is also possible. The raw material in this case is acrylonitrile, which is also used in the production of synthetic rubber and artificial fiber. Aconitrile itself is obtained from propylene. The reaction of aconitrile with hydrogen and carbon monoxide is carried out at high temperature and pressure, using a cobalt-based catalyst. As a result, beta-cyanopropionic aldehyde is formed. By further transformations, it is converted into DL-glutamic acid, which is then divided into optical antipodes by continuous crystallization: the L-isomer is selected as a product of production, and the D-isomer is heated with water to a temperature of 200-220 ° and converted again into racemic glutamic acid.
All of these methods have serious drawbacks: expensive or inconvenient raw materials, the difficulty of separating optical isomers. Therefore, a real breakthrough in glutamic acid provided a biotechnological method of obtaining. For the first time this method was used in the same Japan in 1957. A suitable bacterium was found using a beautiful, albeit time-consuming, method. A large number of soil bacteria were planted on a nutrient medium and left to grow for a while. Then these cups were filled with agarized medium with other bacteria that needed glutamic acid for growth. In those areas where these indicator bacteria grew, and it was necessary to look for producers of glutamic acid.
Acid is made by bacteria
Many microorganisms can produce glutamic acid in large quantities, but technologists mainly use bacteria – they have a higher yield of the product relative to the substrate, up to 40-50%. As a rule, Corynebacterium glutamicum and Brevibacterium flavum are attracted to production activities, sometimes - Microbacterium and Micrococcus. On average, 2.4 tons of starch or 7 tons of molasses are required to produce a ton of the substance.
In general, the process of industrial production of glutamic acid seems to be created in order to talk about it – it is so beautiful and logical. Imagine a cell growing in an environment with glucose. The cell consumes delicious glucose and by glycolysis breaks it down into two molecules of pyruvic acid, from each of which then departs a molecule of CO2. As a result, two acetyl molecules are formed, which combine with the carrier, coenzyme A, and go into the tricarboxylic acid cycle. That's where the fun begins.
Glutamic acid, which is produced by microorganisms in quite industrial quantities, is born in their cells in the tricarboxylic acid cycle, or the Krebs cycle. This cyclic biochemical process is designed to extract energy from substances that are formed during the breakdown of carbohydrates, fats and proteins. And as a result, the cell receives not only energy in the form of ATP, but also other useful substances, including glutamic acid.
In the cycle, acetyl undergoes a number of transformations and as a result, at one stage it appears as alpha-ketoglutaric acid, which at the next stage should be oxidized to succinic acid. If you weaken the enzyme responsible for this reaction, then almost all of the acetyl trapped in the tricarboxylic acid cycle will remain in the form of alpha-ketoglutarate. It is enough to attach an amino group to it – and you will get glutamic acid. This reaction is called transamination, and it is characteristic of the entire metabolism of amino acids. However, accumulating intermediates will slow down the cycle, and the cell uses excess acetyl to produce other substances. To avoid this, limit the amount of biotin in the medium. This vitamin is responsible for many reactions associated with the transport of CO2. If there is a lot of it, by–products are formed - alanine, fatty acids, aspartic and lactic acids. The yield of glutamic acid decreases at the same time. But if there is no biotin at all, the cells will not be able to grow and divide.
That is why the synthesis of glutamic acid is carried out in two stages. At the first stage, the bacteria grow on a rich nutrient medium in which biotin is present. Cells divide rapidly and actively consume biotin, but almost do not produce the necessary product. Over time, there are a lot of cells, and biotin is not enough. Division slows down, but cells do not die: they have a certain amount of stored energy, enzymes and other necessary substances have been developed. At this stage, almost the entire substrate is converted to glutamate. Moreover, the absence of biotin makes the bacterial membrane less dense, and glutamic acid actively enters the solution without suppressing its biosynthesis and making it easier for the technologist to isolate. Also, some surfactants and antibiotics are added to the nutrient medium - this also increases the permeability of the membrane.
It is also important to choose the amount of oxygen: if there is a lot of it, the bacteria will grow more intensively, spend more energy on biomass production and less on product synthesis. Too low oxygen concentration will cause the bacteria to produce more alanine and lactic acid.
Methods of selection of microorganisms and genetic engineering can facilitate the task of technologists. For example, the original strain of Corynebacterium glutamicum synthesized quite a lot of glutamic acid, up to 50 grams per liter of culture fluid, only provided that the concentration of biotin is very small – 2-3 mcg/ l. This limited the use of beet molasses, a cheap and affordable raw material, but usually containing a lot of biotin. The researchers gradually increased the amount of biotin in the nutrient medium, selecting those forms that were most resistant to a large amount of it. As a result, after sorting through about 8000 clones, they got a strain producing 50 g / l of glutamic acid on molasses.
It is also not so difficult to isolate glutamic acid. At the first stage, lime milk or quicklime is added to the culture liquid, and then the excess of calcium ions is precipitated with phosphoric acid. The resulting slightly soluble salt settles together with the cells of microorganisms. It is separated by centrifugation or filtration, and then the remaining liquid is cleaned of pigment impurities. The clarified glutamic acid solution is evaporated and acidified to pH 3.2. In this case, the amino acid begins to precipitate from the solution, since it is at this pH value that its molecules cease to electrostatically repel each other. The precipitate is separated, recrystallized and dried.
In 1982, the global production of glutamic acid was 270 thousand tons per year, today it is ten times more. Most likely, it will continue to grow in the future. The largest manufacturing company is still the same "Ajinomoto", with which the great career of glutamate began. Several large factories have been built in China. But Russia does not seem to need glutamic acid – we not only do not produce it, but also import it very reluctantly, about 10-12 thousand tons per year. More precisely, they are already imported as part of food products. Although there are resources for the production of this amino acid in the country. And it's not just molasses or starch. You can even find projects for the use of beer pellets as raw materials – large-tonnage waste from beer factories, of which there are at least 400 pieces in Russia. But, alas, practically no one produces amino acids in Russia.
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02.12.2010