Introduction

Monosodium glutamate, also known as MSG, Ve-tsin or E621 is used as a flavour enhancing agent, in many kinds of food products to enhance their original flavour. Glutamic acid as well as different salts of glutamic acid other than MSG, like monopotassium glutamate, show the same effect. Glutamate also imparts an unique taste called ‘umami' in food, and it was scientifically recognized as the fifth basic taste along with sweet, sour, salty and bitter. As glutamate is a major component of protein, it is found naturally in virtually all protein-containing foods such as meat, poultry, seafood, vegetables and milk. Naturally occurring glutamate has been traditionally used to impart the umami taste.

In the past, there were some anecdotal reports indicating glutamate caused subjective symptoms like numbness, weakness and palpitation. It was called 'Chinese-restaurant-syndrome.' However, it has never been scientifically confirmed using double-blind, cross-over placebo-controlled studies, that these reactions are really caused by glutamate.

The amount of glutamate used in foods is usually within the range of 0.1% to 0.8% of the food as it is served. This is similar to levels of naturally occurring glutamate found in traditional dishes. The taste of glutamate is self-limiting. This means that once the appropriate amount has been included in a recipe, adding more contribute little to flavour or may even be detrimental to the flavour balance of the dish.

To bring a bit more clearness and a better understanding of what glutamate is, the texts below provide answer some frequently asked questions about glutamate. Information on the labelling of monosodium glutamate and other flavour enhancing agents is also supplied.

Origin and function in the body

Monosodium glutamate, is a salt of glutamic acid. Glutamic acid is one of the 20 amino acids making up proteins. From a nutritional standpoint it is called a non-essential amino acid which means that it can be synthesized in our body.

In food as well as in tissue glutamic acid can be present in two forms: in a ‘bound' form when it is linked to other amino acids to make up proteins or in a ‘free' form when present as a single amino acid. Only free glutamate plays an important role in food flavour.

Recent studies have demonstrated that food-derived glutamate is the main energy source of the intestine. The intestine has such a voracious appetite for glutamate, and it has been shown that of all the glutamate eaten as food only about 4% passes into the body. This implies that the rest of the body has to synthesize nearly all of the glutamate that it needs.

Any glutamate in the food, whether bound in protein or free, or added, is converted in the intestine into free glutamate, and used for energy production by the intestine. Glutamate is also used in the brain as a neurotransmitter. However, the blood brain barrier which controls what type of molecules can enter the brain, does not allow its passage. Therefore, the brain has to synthesize its own glutamate from glucose and other amino acids.

Due to the central position of glutamate in metabolism, it has important functions such as substrate for protein synthesis, precursor of glutamine, nitrogen transport, and so on.

Occurrence and production

Glutamate occurs naturally in many foods. It is present in meat, fish, vegetables or grain products in the protein-bound form and in tomato, milk, potato, soy sauce, as well as many kinds of cheese in the free form.
Besides its natural occurrence, it can be added to many foods. It is often used in soups, sauces, crisps and any kinds of savory processed foods.

Many Asian dishes are characterized by the taste of glutamate which comes both from natural origin like soy or fish sauce and added glutamate as a flavour enhancer. In the case of Italian cuisine, glutamate from cheese and tomato makes it tasty. It increases the original taste of the food and makes the food taste more savoury.

The commercial production of monosodium glutamate was started in 1909. In the past, it was produced by hydrolysis of natural proteins, such as wheat gluten and soybean flakes. Nowadays, the production of monosodium glutamate is carried out through bacterial fermentation. The bacteria (Corynebacterium glutamicus) are grown in a liquid medium containing sugars, molasses or starch as a fermentation substrate. The bacteria are able to produce and to excrete glutamic acid into the medium. Glutamic acid thus accumulates in the medium and is later separated by filtration, purified and converted by neutralization into monosodium glutamate. After additional purification, crystallization, and drying, a white powder of monosodium glutamate is ready to use as flavour enhancer.

Related products

Flavour enhancers other than monosodium glutamate are also used. Some of them are based on glutamate, which are such as: monopotassium glutamate, calcium diglutamate, monoammonium glutamate, and magnesium diglutamate.

Flavour enhancers not based on glutamate and having the same taste properties are guanylic acid, disodium guanylate, dipotassium guanylate, calcium guanylate, inosinic acid, disodium inosinate, dipotassium inosinate, calcium inosinate, calcium 5'-ribonucleotides, and disodium 5'-ribonucleotides.

Flavour enhancers are mentioned in the ingredients list of a foodstuff in the following way: name of the food additive category they belong to, i.e.: ‘flavour enhancer', followed by either their specific name or their corresponding E code number. The E-numbers of flavour enhancers (E620 to E 640) are shown in the following table.

E-number	Name
E620	Glutamic acid
E621	Monosodium glutamate
E622	Monopotassium glutamate
E623	Calcium diglutamate
E624	Monoammonium glutamate
E625	Magnesium diglutamate
E626	Guanylic acid
E627	Disodium guanylate
E628	Dipotassium guanylate
E629	Calcium guanylate
E630	Inosinic acid
E631	Disodium inosinate
E632	Dipotassium inosinate
E633	Calcium inosinate
E634	Calcium 5'-ribonucleotides
E635	Disodium 5'-ribonucleotides
636	Maltol
637	Ethyl maltol
E640	Glycine and its sodium salt

Note: E636 – E637 and E 640 are flavour enhancers without ‘umami' taste

For more information on these products, see the E-number section of this site.

Side effects of MSG

Many years ago reports were published indicating that asthmatic subjects could suffer from asthma attacks after the consumption of food containing monosodium glutamate. For that reason research was carried out to show whether there was a relationship between asthma and monosodium glutamate and to determine whether there were health risks due to the consumption of monosodium glutamate. No relation between monosodium glutamate and the occurrence of asthma attacks could be established. In different trials people who perceived themselves to suffer from an increase of asthmatic symptoms after consumption of monosodium glutamate in comparison to asthmatic people that did not complain about that effect were fed with monosodium glutamate as well as with placebos. No correlation could be found between the consumption of monosodium glutamate and the occurrence of asthma attack. People reacted on monosodium glutamate in the same way as on the given placebos.

People who perceive themselves as monosodium glutamate-intolerant may react to another compound in the food, but not to monosodium glutamate.

Similar trials were performed with people said to be suffering from headaches, dizziness and other (neurological) problems. Often these problems were due to the increase of sodium and the lack of enough moisture in the body (‘hangover effect'). No clear scientific relation with the intake of MSG and symptoms could be established.

A summary of different experiments assessing the effects on health of monosodium glutamate was published by Raif et al., 2000. Their final conclusion was that the results of numerous researches performed on monosodium glutamate allow to consider it as a generally safe food ingredient. Neither epidemiological nor challenge studies could provide any evidence that intake of monosodium glutamate leads to adverse reactions in the population at large. Some experiments showed that large doses of monosodium glutamate taken without food may lead to subjective symptoms in people who believe that they react to monosodium glutamate. However these symptoms are rare and neither serious nor persistent and these reactions did not take place when monosodium glutamate was given with food.

It can thus be concluded that the intake of glutamate is safe for the general population. However, proper labelling offers persons who prefer not to consume foods with added MSG the possibility to avoid those products.