Monosodium glutamate (MSG) also known as “Ajinomoto” or “Chinese seasoning” is a salt of glutamic acid with molecular formula C5H8NO4Na. It is a white crystalline odorless powder which is soluble in water, but it is not hygroscopic. Glutamic acid is a non essential amino acid, i.e. it is synthesized by the body and there is no need of external intake. Glutamic acid belongs to the category of compounds called glutamates which are the sources of very specific taste. MSG is one of the glutamates and is used as a food additive for the enhancement of the flavor. Glutamic acid is found in many food items such as cheese, fermented bean paste, soy sauce and mainly in seaweeds.
In 1907 Japanese researcher Kikunae Ikeda from Tokyo Imperial University identified the new taste and chemical responsible for this specific taste. He named that taste as ‘Umami’ and then patented the method for mass production of crystalline salt monosodium glutamate.
MSG is strictly a food additive. It is a flavor enhancing food additive used in meat, fast food items, and packaged food items like crackers, chips, soups, pre-made gravies, instant noodles, salad dressing and many others. It gives umaminess to the food. Umami is recognized as the fifth taste in addition to sweet, salty, sour and bitter. It also intensifies other tastes particularly, sour and salty taste.
MSG is also useful as a cosmetic additive and dietary supplement. It is also applied in fertilizers and pesticide production.
MSG proves pleasant only in the right concentration. Excess of MSG may lead to headache and nausea. International and national bodies for the safety of food additives consider MSG safe for human consumption.
MSG is an optically active compound and only (S) isomer is useful as a food additive because (R) isomer is tasteless. MSG is produced by neutralization of (S) glutamic acid by sodium hydroxide. The solution is decolorized by activating carbon, concentrated under vacuum at 60°C and then crystallized by cooling. There are three ways of producing (S) glutamic acid
1. Glutamic acid by fermentation process
It is the best method for the production of glutamic acid. In this method, optically pure (S) glutamic acid is produced using bacteria named Corynebacterium Glutamicum. Sugar cane molasses and beet are used as the carbohydrate source. When biotin (vitamin essential for cell growth) is present in sufficient quantity cell membrane is impermeable to glutamic acid so biotin inhibitors are added to the culture medium. Ammonia gas or urea is added as a source of nitrogen and the fermenter is aerated for oxygen source as fermentation is aerobic. Ammonia also helps in maintaining the pH in between 7 to 8. After a 35 to 45 hour batch time, synthesized (S) glutamic acid solution is separated and concentrated under reduced pressure.
The biological reaction takes place as follows:
C12H22O11 + 3O2 + 2NH3 + 2C5H9O4N + 2CO2 + 5H2O
The yield of this process is about 60% and product is obtained as high as 100 g/L.
2. Glutamic acid from protein hydrolyzates
First glutamic acid was isolated from protein hydrolysis. The main raw material was wheat gluten, which contain 25% glutamic acid by weight. Gluten is hydrolyzed by aqueous HCL, hydrolyzate was then concentrated under reduced pressure. The product was acidified by concentrating HCL to get (S) glutamic hydrochloride, which was very less soluble in concentrated HCL than other amino acids. The product is filtered and again dissolved in the warm water, all humic material is removed, pH is adjusted to 3.2 by the addition of sodium hydroxide in which glutamic acid has its lowest solubility. Crystallized glutamic acid is further converted to MSG.
3. Glutamic acid from Steffen waste
Glutamic acid can also be produced by hydrolysis of Steffen waste and finesse which is the worst after ethanol distillation. This waste contains pyroglutamic acid (a cyclic form of glutamic acid) which is converted to (S) glutamic acid at about 11 pH and 85°C temperatures. No racemic mixture is formed because of mild conditions.
4. Chemical synthesis of glutamic acid
In chemical synthesis acrylonitrile is subjected to Oxo reaction to produce beta cynopropionaldehyde. It is then converted to glutamic acid by a Strecker process in which aldehyde is converted to amino analog of cyanohydrins which is then hydrolyzed to glutamic acid. It is a continuous process and yield is more, but it gives the racemic mixture and separation of isomers is difficult.
MSG is a famous food additive. It is used for taste enhancement. MSG is added to food to add ‘Umami flavor’ and to increase palatability and satisfaction. It is extensively found in processed foods, including meat, candy, non-alcoholic beverages, baked goods, breakfast cereals, milk products, cheeses, soups, snack foods, fish products and among others. It mixes well with meat, many vegetables, sauces and soups and enhances other taste active compounds, improving the overall taste of that food product.
2. Cosmetic additive
MSG is compatible with a wide variety of chemicals. It is water soluble and palatable, and can thicken the fluid. It is used as a cosmetic additive in skin care products, hair conditioners and shampoos. MSG is safe for human consumption and it has no side effects on the skin or hair when it’s consumed in low quantity. Moreover glutamic acid is found in many natural compounds and living cells.
3. Dietary supplement
MSG is found to be useful in dietary supplements. Taste thresholds for MSG is very low (0.3 g/L) as compared to salt (2 g/L) and sugar (5 g/L). It can be used in low quantity with little amount of salt. As it enhances salty taste, it can be used to reduce sodium intake which is supposed to be low for hypertension, heart diseases and stroke patients.
4. Other applications
Recently in USA, MSG is also approved as safe to be used as a fertilizer. It is employed as a plant growth enhancer. It is also useful as fungicides and spraying wine grapes with MSG is an approved process by the California Department of Pesticide Regulation (CDPR).
|Synonym||Sodium Hydrogen Glutamate|
|Appearnace||–||White small crystals|
|Specific Rotation||–||+24.9 to 25.3|
|Loss or Drying||%||0.3(max)|