| Monosodium glutamate | |
|---|---|
|
Sodium 2-Aminopentanedioate |
|
| Identifiers | |
| CAS number | 142-47-2 |
| PubChem | 85314 |
| ChemSpider | 76943 |
| UNII | C3C196L9FG |
| EC-number | 205-538-1 |
| Jmol-3D images | Image 1 |
|
|
|
|
| Properties | |
| Molecular formula | C5H8NNaO4 |
| Molar mass | 169.111 g/mol |
| Appearance | white crystalline powder |
| Melting point |
232 °C, 505 K, 450 °F |
| Solubility in water | 74g/100mL |
| Hazards | |
| LD50 | 16600 mg/kg (oral, rat) |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
|
| Infobox references | |
Monosodium glutamate, also known as sodium glutamate or MSG, is the sodium salt of glutamic acid, one of the most abundant naturally occurring non-essential amino acids.[1] It has been classified by the U.S. Food and Drug Administration as generally recognized as safe (GRAS) and by the European Union as a food additive. MSG has the HS code 29224220 and the E number E621.[2] The glutamate of MSG confers the same umami taste of glutamate from other foods, being chemically identical.[3] Industrial food manufacturers market and use MSG as a flavor enhancer because it balances, blends and rounds the total perception of other tastes.[4][5] Trade names of monosodium glutamate include AJI-NO-MOTO®, Vetsin, and Ac'cent.
Contents |
Pure MSG does not have a pleasant taste by itself if it is not combined with a consonant savory smell.[6] As a flavor and in the right amount, MSG has the ability to enhance other taste-active compounds balancing and rounding the overall taste of certain dishes. MSG mixes well with meat, fish, poultry, many vegetables, sauces, soups and marinades, and increases the overall preference of certain foods like beef consomme.[4]But like other basic tastes except sucrose, MSG improves the pleasantness only in the right concentration. An excess of MSG quickly ruins the taste of a dish. Although this concentration varies with the type of food, in clear soup the pleasantness score rapidly falls with more than 1 g of MSG per 100 ml.[7] Moreover, there is an interaction between MSG and salt (sodium chloride) and other umami substances such as nucleotides. All need to be in an optimum concentration for maximum palatability. With these properties, MSG can be used to reduce salt intake (sodium), which predisposes to hypertension, heart diseases and stroke. The taste of low-salt foods improves with MSG even with a 30% salt reduction. The sodium content (in mass percent) of MSG is roughly 3 times lower (12%) than in sodium chloride (39%).[8]Other salts of glutamate have been used in low-salt soups, but with a lower palatability than MSG.[9]
MSG has been used safely for more than 100 years to season food. During this period, extensive studies were conducted to elucidate the role, benefits and safety of MSG. At this point, International and national bodies for the safety of food additives consider MSG safe for human consumption as a flavor enhancer.[10] The "MSG symptom complex" was originally termed as the "Chinese Restaurant Syndrome" when anecdotally Robert Ho Man Kwok reported the symptoms he felt after an American-Chinese meal. Kwok suggested multiple reasons behind the symptoms, including alcohol from cooking with wine, the sodium content, or the MSG seasoning. But MSG became the focus and the symptoms have been associated with MSG ever since. The effect of wine or salt content was never studied.[11] With the years, the list of non specific symptoms has grown on anecdotal grounds. In normal conditions, we have the ability to metabolize glutamate that has a very low acute toxicity. The Oral lethal dose to 50% of subjects (LD50) is between 15 to 18 g/kg body weight in rat and mice respectively, 5 times greater than the LD50 of Salt (3 g/kg in rats). Therefore, the intake of MSG as a food additive and the natural level of glutamic acid in foods do not represent a toxicological concern in humans.[10] A report from the Federation of American Societies for Experimental Biology (FASEB) compiled in 1995 on behalf of the United States Food and Drug Administration (FDA) concluded that MSG is safe when "eaten at customary levels" and although there seems to be a subgroup of apparently healthy individuals that respond with the MSG symptom complex when exposed to 3 g of MSG in the absence of food, causality by MSG has not been established because the list of MSG Symptom complex was based on testimonial reports.[12] This report also indicates that there is no data to support the role of glutamate in chronic and debilitating illnesses. A controlled double-blind multicenter clinical trial failed to demonstrate the relationship between MSG Symptom complex and the consumption of MSG in individuals that believed to react adversely against MSG. No statistical association has been demonstrated, there were few responses and they were inconsistent. Symptoms were not observed when MSG was given with food.[13][14][15][16]
Adequately controlling for experimental bias includes a double-blind placebo-controlled experimental design (DBPC) and the application in capsules because of the strong and unique after-taste of glutamates.[14] In a study performed by Tarasoff and Kelly (1993) 71 fasting participants were given 5 g of MSG and then administered a standard breakfast. There was only one reaction, and it was to the placebo in a self-identified MSG sensitive individual.[11] In a different study done by Geha et al. (2000), they tested the reaction of 130 subjects that reported sensitivity to MSG. Multiple DBPC trials were performed and only subjects with at least two symptoms proceeded. Only 2 people out of the whole study responded in all four challenges. Because of this low prevalence, the researchers concluded that the response to MSG was not reproducible.[17]
Additional studies that have looked into whether MSG causes obesity have given mixed results.[18][19] There have been several studies investigating an anecdotal link between MSG and asthma; current evidence does not support any causal association.[20]
Since glutamates are important neurotransmitters in the human brain, playing a key element in learning and memory, there is ongoing study by neurologists about possible side-effects of MSG in food but no conclusive studies drawing any connections.[21]
Food Standards Australia New Zealand[22] (FSANZ) cites "overwhelming evidence from a large number of scientific studies" to explicitly deny any link between MSG and "serious adverse reactions" or "long-lasting effects", declaring MSG "safe for the general population". It does, however, describe that in less than 1% of the population, sensitive individuals may experience "transient" side effects such as "headache, numbness/tingling, flushing, muscle tightness, and generalised weakness" to a large amount of MSG taken in a single meal. People who consider themselves sensitive to MSG are encouraged to confirm this through an appropriate clinical assessment.
Standard 1.2.4 of the Australia and New Zealand Food Standards Code requires the presence of MSG as a food additive to be labeled in packaged foods. The label must bear the food additive class name (e.g., flavor enhancer), followed by either the name of the food additive, MSG, or its International Numbering System (INS) number, 621.[23]
Monosodium glutamate (MSG) is one of several forms of glutamic acid found in foods, in large part because glutamic acid, being an amino acid, is pervasive in nature. Glutamic acid and its salts can also be present in a wide variety of other additives, including hydrolyzed vegetable proteins, autolyzed yeast, hydrolyzed yeast, yeast extract, soy extracts, and protein isolate, which must be labeled with these common and usual names. Since 1998, MSG cannot be included in the term "spices and flavorings". The food additives disodium inosinate and disodium guanylate, which are ribonucleotides, are usually used in synergy with monosodium glutamate-containing ingredients. However, the term "natural flavor" is now used by the food industry when using glutamic acid (MSG without the sodium salt attached). Due to lack of FDA regulation, it is impossible to determine what percentage of "natural flavor" is actually glutamic acid.
The FDA considers labels such as "No MSG" or "No Added MSG" to be misleading if the food contains ingredients that are sources of free glutamate, such as hydrolyzed protein. In 1993, the FDA proposed adding the phrase "(contains glutamate)" to the common or usual names of certain protein hydrolysates that contain substantial amounts of glutamate.
In the 2004 version of his book On Food and Cooking, food enthusiast and author Harold McGee states that "[after many studies], toxicologists have concluded that MSG is a harmless ingredient for most people, even in large amounts."[24]
Since the first time that MSG was released into the market, it has been produced by three methods: (1) hydrolysis of vegetable proteins with hydrochloric acid to disrupt peptide bonds (1909 -1962), (2) direct chemical synthesis with acrylonitrile (1962 - 1973), and (3) bacterial fermentation; the current method. [25]
Initially, wheat gluten was used for hydrolysis because it contains more than 30 g of glutamate and glutamine in 100 g of protein. But as the production to achieve the ever-increasing demand for MSG augmented, new production processes were studied: chemical synthesis and fermentation. The polyacrylic fiber industry began in Japan in the mid 1950s and acrylonitrile was adopted then as starting material to synthesize MSG.[26]
Currently, most of the world production of MSG is by bacterial fermentation in a process similar to wine, vinegar, yogurt and even chocolate. Sodium is added later through the step of neutralization. During fermentation, selected bacteria (coryneform bacteria) cultured with ammonia and carbohydrates from sugar beets, sugar cane, tapioca or molasses, excrete amino acids into the culture broth from where L-glutamate is isolated. Kyowa Hakko Kogyo Co Ltd developed the first industrial fermentation to produce L-glutamate.[27] Nowadays, the conversion yield and production rate from sugars to glutamate continues to improve in the industrial production of MSG, which allows for keeping up with demand.[25] The final product after filtration, concentration, acidification and crystallization is pure glutamate, sodium and water. It appears as a white and odorless crystalline powder that in solution dissociates into glutamate and sodium. It is freely soluble in water, but not hygroscopic and practically insoluble in common organic solvents such as ether.[28]In general, MSG is stable under the conditions of regular food processing. During cooking, MSG does not decompose, but like other amino acids, browning or Maillard reactions will occur in the presence of sugars at very high temperatures.[29]
Professor Kikunae Ikeda isolated glutamic acid as a new taste substance in 1908 from the seaweed Laminaria japonica, kombu, by aqueous extraction and crystallization, and named its taste "umami".[30] He noticed that the Japanese broth of katsuobushi and kombu had a peculiar taste that had not been scientifically described at that time and was differed from sweet, salty, sour and bitter. [31]To verify that ionized glutamate was responsible for umami taste, Professor Ikeda studied the taste properties of many glutamate salts such as calcium, potassium, ammonium, and magnesium glutamate. All salts elicited umami in addition to a certain metallic taste due to the other minerals. Among those salts, sodium glutamate was the most soluble and palatable, and crystallized easily. Professor Ikeda named this product monosodium glutamate and submitted a patent to produce MSG.[32] Suzuki brothers started the commercial production of MSG in 1909 as AJI-NO-MOTO®, meaning the essence of taste in Japanese, the first time that monosodium glutamate was produced in the world.[29][33][25]