Description
L-(+)sodium glutamate (monosodium L-glutamate, MSG) has a unique taste, known as “umami”, which is different from the four basic tastes of sweet, salty, sour, and bitter.
MSG is used in large quantities as a flavor enhancer throughout the world. MSG is not a direct taste enhancer but a complex flavor enhancer for gravies, meats, poultry, sauces, and in other combinations. MSG is also used to enhance the taste of tobacco and to treat hepatic coma. As a salt of amino acid, MSG is also safe in practices of use and concentration in cosmetics, such as skin care products.
References
[1] Tetsuya Kawakita, L-Monosodium Glutamate (MSG), Kirk-Othmer Encyclopedia of Chemical Technology, 2000
[2] Leslie T. Webster and Charles S. Davidson, The effect of sodium glutamate on hepatic coma, The Journal of Clinical Investigation, 1956, vol. 35, 191-199
[3] DV Belsito, Safety Assessment of α-Amino Acids as Used in Cosmetics
Description
History of development. The best known and most widely used flavor enhancer is monosodium glutamate (MSG). In 1866, a German chemist, Ritthausen, isolated glutamic acid. Later, another chemist converted the acid to a sodium salt, monosodium glutamate. In doing their work, neither had any interest in flavor.
More than 40 years later, in 1908, a Japanese chemist at the University of Tokyo, Dr. Kikunae Ikeda, discovered the flavor enhancing properties of MSG. Dr. Ikeda had set out to find out why and how a certain seaweed, Laminaria japonica, affected flavor. Japanese cooks had used this seaweed for centuries to improve the flavor of soups and certain other foods. Dr. Ikeda discovered that the ingredient in the seaweed that made the difference was MSG, and that it had an unusual ability to enhance or intensify the flavor of many high protein foods.
After isolating MSG, Dr. Ikeda developed a process for extracting it from wheat flour and other flours. Working with the Japanese chemical company, Suzuki and Co., he supervised the construction of a plant and, as a partner with the company, began commercial production of MSG in 1909.
There were several attempts to produce MSG in the United States in the years following, but it was not until the 1940s that large- scale MSG production began in this country. By 1968, U.S. production had grown to 46 million pounds per year. The latest production figures (1987) reported 18.6 million pounds per year.
Flavor and enhancing properties. At one time, it was felt that MSG had a somewhat meaty flavor and that this flavor was a factor in its ability to intensify the flavors of other foods, particularly protein-rich foods. It was discovered, however, that the meaty taste came rather from contaminants in the crude glutamate, and when these contaminants were sharply reduced, the flavor characteristic also was reduced considerably.
MSG is not flavorless. In large enough concentrations, or by itself, it has been found to have a taste of its own, sometimes described as sweet-saline. There are some, in fact, who feel that MSG is nothing more than a seasoner which gains its effect by combining with and intensifying the flavors of the foods to which it is added. However, to say that MSG only intensifies the flavor of foods is too simplistic. When monosodium glutamate is added to food, several specific flavor characteristics are enhanced - such as impact, body or fullness, continuity, mouth fullness, mildness, and complexity. Glutamate also harmonizes the wide range of flavors present in sauces, soups and casseroles, promoting a highly blended and full-bodied perception of flavor.
The savory taste of glutamate is to tomatoes, cheese, and meat what sweetness is to sugar, sourness is to lemons, saltiness is to anchovies and bitterness is to coffee. Just as each of these foods has a distinctive taste, food high in glutamate has a basic and independent taste. In China and Japan, there is a concept for this independent taste, which they call Xian-Wei (China) and Umami (Japan). Current research has found more than 40 umami substances of which glutamate is most common. In fact, umami is an integral part of cuisines throughout the world and has been described by Westerners as “savory,” “broth-like” and “meaty.”.
Production. MSG is commonly produced using a fermentation process using a glucose (often sugar molasses) as a starting substance. Once the glucose is converted to glutamic acid, the glutamic acid is filtered, dissolved and converted to monosodium glutamate by neutralization with sodium hydroxide. The monosodium glutamate solution is decolorized. Monosodium glutamate is then crystallized, dried, sieved, packed and shipped.
Chemical Properties
Monosodium glutamate, the best-known and most widely used flavor enhancer, is practically odorless and may have
either a slightly sweet or slightly salty taste. Addition of monosodium glutamate to food enhances several specific flavor characteristics, such as impact, body of fullness, continuity, mouth fullness, mildness and complexity. For a detailed description of this
compound refer to Burdock (1997)
Chemical Properties
Monosodium glutamate occurs as white free-flowing crystals or a
crystalline powder. It is practically odorless and has a meat-like
taste.
Chemical Properties
Colorless powder
Occurrence
Reported found in certain seaweeds including Laminaria japonica
Uses
MSG is used as a food additive, mainly in oriental cuisine, to
enhance and impart a meaty flavor.
Uses
sodium glutamate is an amino acid with skin-conditioning, odormasking, and hair-conditioning action.
Uses
Flavor enhancer for foods in concentration of
about 0.3%.
Definition
ChEBI: An optically active form of monosodium glutamate having L-configuration.
Production Methods
Monosodium glutamate is the monosodium salt of the naturally
occurring L-form of glutamic acid. It is commonly manufactured by
fermentation of carbohydrate sources such as sugar beet molasses.
In general, sugar beet products are used in Europe and the USA.
M
452 Monosodium Glutamate Other carbohydrate sources such as sugar cane and tapioca are used
in Asia.
Preparation
Monosodium glutamate is commonly produced by a fermentation process using glucose (often sugar molasses) as a
starting substance. Once the glucose is converted to glutamic acid, it is filtered, dissolved and converted to monosodium glutamate
by neutralization with sodium hydroxide. The monosodium glutamate solution is decolorized and then crystallized, dried, sieved,
packed and shipped
General Description
White or off-white crystalline powder with a slight peptone-like odor. pH (0.2% solution)7.0.
Air & Water Reactions
Water soluble.
Reactivity Profile
L-(+)Sodium glutamate is an amide. Amides/imides react with azo and diazo compounds to generate toxic gases. Flammable gases are formed by the reaction of organic amides/imides with strong reducing agents. Amides are very weak bases (weaker than water). Imides are less basic yet and in fact react with strong bases to form salts. That is, they can react as acids. Mixing amides with dehydrating agents such as P2O5 or SOCl2 generates the corresponding nitrile. The combustion of these compounds generates mixed oxides of nitrogen (NOx).
Fire Hazard
Flash point data are not available for L-(+)Sodium glutamate, but L-(+)Sodium glutamate is probably combustible.
Pharmaceutical Applications
Monosodium glutamate is used in oral pharmaceutical formulations
as a buffer and a flavor enhancer. For example, it is used with
sugar to improve the palatability of bitter-tasting drugs and can
reduce the metallic taste of iron-containing liquids. It has also been
used in subcutaneous live vaccine injections such as measles,
mumps, rubella and varicella-zoster live vaccine (ProQuad).
However, the most widespread use of monosodium glutamate is
as a flavor enhancer in food products. Typically, 0.2–0.9% is used in
normally salted foods, although products such as soy protein can
contain 10–30%. The use of monosodium glutamate in food
products has been controversial owing to the apparently high
number of adverse reactions attributed to the substance, which gives
rise to the so-called ‘Chinese Restaurant Syndrome’.
The current consensus is that there is no clinically compelling
evidence to suggest that monosodium glutamate may be harmful at
the current levels used in foods.
Biochem/physiol Actions
Monosodium glutamate(MSG) is a food additive and an environmental agent, that can affect inflammation.
Safety Profile
Moderately toxic by
intravenous route. Mildly toxic by ingestion
and other routes. An experimental
teratogen. Other experimental reproductive effects. Human systemic effects by ingestion
and intravenous routes: somnolence,
hallucinations and distorted perceptions,
headache, dyspnea, nausea or vomiting,
dermatitis. The cause of "Chnese restaurant
syndrome." When heated to decomposition
it emits toxic fumes of NOx and Na2O.
Safety
Monosodium glutamate is widely used in foods and oral
pharmaceutical formulations. It is generally regarded as moderately
toxic on ingestion or intravenous administration. Adverse effects
include somnolence, hallucinations and distorted perceptions,
headache, dyspnea, nausea or vomiting, and dermatitis. The lowest
lethal oral dose in humans is reported to be 43 mg/kg.The use of
monosodium glutamate in foods has been controversial due to the
so-called ‘Chinese Restaurant Syndrome’, although
it is generally regarded as safe at intake levels of up to 6 mg/kg bodyweight.In Europe, total glutamate intake from food ranges from
5–12 g/day.
There has been a report of a foreign body granuloma caused by
monosodium glutamate after a BCG vaccination.
Synthesis
The industrial production of glutamic acid is primarily carried out in the form of monosodium glutamate (MSG), mainly through microbial fermentation. This process has replaced earlier methods such as protein hydrolysis and chemical synthesis. In this modern and efficient production method, specific bacterial strains, such as Corynebacterium glutamicum, are cultivated in large fermenters using carbohydrates such as sugarcane, sugar beets, or molasses as raw materials. These bacteria secrete glutamic acid into the culture medium. After fermentation, the glutamic acid is separated, purified, and then neutralized with sodium hydroxide, ultimately yielding the product—monosodium glutamate (MSG).
Environmental Fate
MSG is a white, odorless powder with high water solubility. If
released into the air, it remains in the particulate phase until
removed by deposition.
storage
Aqueous solutions of monosodium glutamate may be sterilized by
autoclaving. Monosodium glutamate should be stored in a tight
container in a cool, dry place.
Toxicity evaluation
Although several mechanisms have been proposed to be
responsible for causing CRS, none has been extensively studied.
One hypothesis has been that the effects are due to an immediate
hypersensitivity reaction. Since no immunoglobulin E
(IgE)-mediated reaction has been documented, there is no
direct evidence that this is the case. Another hypothesis is that vitamin B6 deficiency plays a role in the response because the
symptoms were prevented by supplementing individuals with
the vitamin. Since glutamate can be converted to acetylcholine
by the tricarboxylic acid cycle, it has also been proposed that
the effects are due to an increase in acetylcholine levels. It has
been noted that after MSG ingestion, there is a decrease in the
levels of cholinesterase (the enzyme that breaks down acetylcholine).
Due to inadequate investigations, it is not currently
known if any or all of these mechanisms are responsible for
CRS. The neurotoxicity of MSG has only been demonstrated in
rodent species and rabbits after exposure to very large doses.
The neurotoxic effect has been attributed to excitotoxicity.
Regulatory Status
GRAS listed. Accepted in Europe for use as a food additive in
certain applications. Included in the FDA Inactive Ingredients
Database (oral syrup). Included in nonparenteral medicines licensed
in the UK. Included in subcutaneous vaccine injections.
