For about 30 years, monosodium glutamate has been repeatedly criticized. It is contained as a flavor enhancer in many dishes and is suspected of promoting nervous diseases such as Alzheimer’s and Parkinson’s.
What is monosodium glutamate?
Monosodium glutamate or sodium glutamate (MSG) is the scientific name for the sodium salt of glutamic acid, which is one of the most abundant natural non-essential amino acids. In the food industry, sodium glutamate is used as a flavor enhancer to round out the taste of dishes. In its natural form, it is an important component of proteins and is present in almost all protein-containing foods (meat, fish, seafood, milk and vegetables), with particularly large amounts in tomatoes and mushrooms. Sodium glutamate is also produced in the human body itself because it is important for normal body functions. The European Union labels sodium glutamate as flavor enhancer E 621 and determines its use in foods through regulations. It is mostly added to frozen dishes, seasoning mixes, canned foods, dry foods and dishes with fish or meat as a flavor enhancer.
Function, effect and tasks
Monosodium glutamate is one of the salts of glutamic acid, one of the 20 amino acids used to form protein. The human body depends on glutamate and can also produce it itself. It is present in foods in two different ways: in bound form, where it forms a protein with other amino acids, and in free form, where it appears as a single amino acid. Only the free glutamate is important for the taste of a food. Recent studies have demonstrated that glutamate metabolized from foods serves as a major source of energy for the intestine. However, of the total amount absorbed from food, only 4% is processed in the body; the remaining portion it needs must be produced by the body itself. Regardless of whether the body absorbs glutamate in free or bound form, it is transformed into free glutamate in the intestine and used for energy production. When the body metabolizes glutamate in bound form, it can handle it well because it is integrated into the long protein building block chains in food and is gradually released during the digestive process. However, if too much is ingested via flavor enhancers, it can be a health concern. In the brain, glutamate also serves as a neurotransmitter and, in addition, as a substrate for protein synthesis and for nitrogen transport.
Formation, occurrence, and properties
Monosodium glutamate is a natural component of many foods. It is present in bound form in meats, fish, vegetables, and cereal products, and in free form in milk, cheese, potatoes, tomatoes, and soy sauce. In addition, it is often added as a flavor enhancer to foods such as soups, sauces, savory pastries and spicy foods. Natural glutamate is found in many Asian dishes and as an artificial flavor enhancer. It is intended to enhance the natural seasoning of a dish and round it out in flavor. Sodium glutamate is produced by bakerial fermentation. In this process, certain bacteria (Corynebacterium glutamicus) are grown in a liquid medium containing sugar, starch or molasses, where they produce glutamic acid, which they excrete into the medium. In this way, glutamic acid is collected there, then filtered out, purified, crystallized and transformed into sodium glutamate via neutralization. Purification, crystallization and drying again produce a white powder that can serve as a flavor enhancer.
Diseases and disorders
Since the 1970s, sodium glutamate has come under increasing criticism, particularly due to the so-called “Chinese restaurant syndrome,” in which affected people experienced tingling in their arms, necks and backs and suffered from a feeling of weakness and palpitations after eating in a Chinese restaurant. Sodium glutamate, which had been used as a flavor enhancer in Chinese cuisine for about 100 years at the time, came under suspicion. Surprisingly, the complaints occurred mainly among Americans and Europeans, but not among the Chinese themselves, although they consume about 80% of the glutamate produced around the world. Therefore, in the last 30 years, it has been thoroughly investigated whether the complaints are related to the consumption of the sodium glutamate.Among other things, double-blind tests took place, which could not prove any connection with the complaints that occurred and the consumption of sodium glutamate. Intolerance reactions only became visible in isolated cases when a relatively high amount between 3 and 5 grams was taken on an empty stomach. However, critics see sodium glutamate as a possible cause of neurological diseases because, in their opinion, the blood–brain barrier is not completely sealed, but may be disturbed in some diseases, e.g., internal bleeding, meningitis, and Alzheimer’s disease. Strokes can cause the release of glutamate from brain cells, which destroys the cells. Researchers have also been able to identify this effect in animal studies. For this reason, sodium glutamate is also considered a neurotoxin, and a link between its ingestion and Alzheimer’s and Parkinson’s disease is considered possible. However, scientists concede that this effect only occurs at high doses and is unlikely in healthy people despite a diet rich in glutamic acid. However, if brain metabolism is disturbed, damage cannot be ruled out. In addition, it is suspected of artificially creating a feeling of hunger and preventing a natural feeling of satiety, which can lead to weight gain.
