Monosodium glutamate (MSG)

Monosodium glutamate (MSG) is the sodium salt of glutamic acid, an amino acid that plays a significant role in many functions in the body, including the disposal of excess nitrogen, cellular metabolism, and neurotransmission. Glutamic acid is a nonessential amino acid, meaning that it can be synthesized by the body. MSG is widely used in the food industry as a flavor enhancer in much the way salt and sugar are, and is also used in home kitchens for additional seasoning. Many of the misconceptions about it associate it with Asian food, but it is no less commonly used in western cuisine, is classified as Generally Recognized As Safe (GRAS) by the US Food and Drug Administration (FDA), is a permitted food additive in the European Union, and can be found in most supermarkets under popular brand names like Accent. Furthermore, MSG occurs naturally in numerous foods, and is a common source of the "fifth taste," umami.

Background

Glutamic acid was "discovered" twice. In 1866, German chemist Karl Heinrich Ritthausen derived it from wheat gluten, and named it accordingly. Its importance was not understood, however, until the work of Tokyo Imperial University's Kikunae Ikeda. Professor Ikeda sought to understand the science of taste, and specifically what the source was of the taste in his cucumber soup that was neither sweet, salty, sour, or bitter, the four tastes that had been scientifically identified. Much of what we think of as "taste" is actually aroma, delivered by the olfactory system; taste itself is limited to these more basic categories. His cucumber soup had been prepared with kelp, a seaweed widely used in Japanese soups like dashi. His extended study of kombu kelp led to identifying the presence of a sodium salt of glutamic acid, which he named monosodium glutamate. Anions and salts of glutamic acid are called glutamates; thus monosodium glutamate is "glutamate with one sodium."

Ikeda called the fifth taste "umami," from the Japanese for "delicious taste." English translations like "savoriness," "meatiness," or even "more-ishness" have been proposed, but the taste is more widely known by its Japanese name, even in the West. Subsequent science has confirmed Ikeda's work, though it took until 1985 before an international scientific standard was adopted. MSG is difficult to taste on its own, which accounts for the long delay before the taste of umami was identified. It is very obvious in side by side comparisons of dishes, however. The presence of umami seems to enhance the experience of certain aromas, especially those associated with broths and meats. This may account for the way naturally umami-rich foods have been used for centuries before the presence of MSG or glutamic acid in them was known: tomato ketchup on hamburgers, parmesan cheese on pasta, soy sauce on stir-fries. Traditional steak sauces and Worcestershire sauce are very high in glutamates. Once identified, MSG was not only manufactured for use in the packaged foods industry but sold for home use under various brand names, or as part of condiments or seasoning blends.

Overview

Even apart from its natural occurrence in foods that have been consumed for the whole of human history, MSG has been used for over a century. Despite this, there is a widespread belief, especially among Americans, that it is unsafe or implicated in various health problems. This misconception can be traced to the coining of the term "Chinese restaurant syndrome," allegedly characterized by weakness, palpitations, and numbness after eating Chinese restaurant food, in a 1968 letter to the New England Journal of Medicine. That this was a letter is important to remember; too often MSG opponents refer to it as an article, which would imply some degree of rigorous study, experimentation, and peer review. But in fact double-blind studies have never been able to find a link between MSG or glutamic acid and migraines, headaches, or other short-term health effects, when used in typical doses.

Its links to long-term health problems like obesity are less clear, and it is true that MSG is one of a group of amino acids called excitotoxins, which might be able to damage parts of the brain if consumed in large doses. Excitotoxins are so named because they are absorbed so quickly by the GI tract, they can cause a spike in glutamate levels in the bloodstream, resulting in neurotoxicity. It is generally agreed that this is possible in lab rats, and that isolated MSG used as an additive passes through the tract more quickly than do the more complex molecules of proteins containing naturally occurring MSG in foods. It is not yet agreed, though, whether humans are as vulnerable as rats to these excitotoxins, nor what level of consumption in what period of time would constitute toxicity. MSG opponents claim the level is very low, at least lower than the levels at which MSG is used in cooking and packaged food preparation; the science does not currently support these claims. Furthermore, like the other basic tastes apart from sweet, umami is not a pleasant taste beyond a certain concentration; it is very possible that an excitotoxic level of MSG would be too unpalatable to be a marketable food product.

In addition to MSG itself, several other food additives have been developed from glutamic acid: hydrolyzed vegetable protein, autolyzed yeast, yeast extract, monopotassium glutamate, calcium glutamate, monoammonium glutamate, magnesium glutamate, and sodium glutamate. Glutamates like MSG are naturally present in kelp and nori seaweeds (the foods with the highest concentrations), Marmite and Vegemite spreads, fish sauce, certain cheeses (notably Roquefort and parmesan, which are otherwise very different), soy sauce, oyster sauce, cured meats like ham, shellfish and certain fish like sardines and anchovies, peas, tomatoes, corn, potatoes, and grapes. They are even naturally present in meats, eggs, and milk (including human breast milk). The appeal of umami helps to explain many very old food traditions, from the pairing of blue cheese or steak sauce with steak to Japanese dashi, which combines kombu (kelp) and dried bonito (fish), each of which is rich in a different but complementary source of glutamates.

Bibliography

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