Glutamate fermentation

Buckel W, HA Barker (1974) Two pathways of glutamate fermentation by anaerobic bacteria. J Bacterial 117 1248-1260. 

T. (1972) L-Glutamate fermentation with acetic acid by an oleic acid requiring mutant. II. Inhibitory factors against the extracellular accumulation of L-glutamate. J. Ferment Technol, 50, 182-191. 

Fig. 1. Path of glutamate fermentation by Cl. tetanomorphum. The two reactions involved in the interconversion of glutamate to mesaconate are readily isolated from the subsequent reactions by the addition of oipyridyl which inhibits the Fe +-dependent conversion of mesaconate to citramalate. The latter reaction is also strongly inhibited by Og.

Wachsman, J. T. and Barker, H. A. (1955) Tracer experiments on glutamate fermentation by Clostridium tetanomorphum. J. Biol. Chem. 217, 695-702. 

In the 1950s, a group of coryneform bacteria which accumulate a large amount of L-glutamic acid in the culture medium were isolated (21). The use of mutant derivatives of these bacteria offered a new fermentation process for the production of many other kinds of amino acids (22). The amino acids which are produced by this method are mostiy of the T.-form, and the desired amino acid is singly accumulated. Therefore, it is very easy to isolate it from the culture broth. Rapid development of fermentative production and en2ymatic production have contributed to the lower costs of many protein amino acids and to their availabiUty in many fields as economical raw materials. 

Microorganisms requite several minerals such as ferrous and potassium ions which play important roles in glutamic acid fermentation. Other important culture conditions include regulating aeration stirring. The biosynthesis of L-glutamic acid is performed under regulated aerobic conditions. 

Progress in fermentation technology has made it possible to raise the accumulation and the yield of L-glutamic acid above 100 g/L and 60% based on the total amount of sugar. AppHcation of genetic engineering techniques for further improvement is also in progress. 

An industrial fermentor of capacity up to several hundred kiloliters equipped with aeration and stirring devices, as well as other automatic control systems, is used. The cultures must be sterilized and aseptic air must be used owing to the high sensitivity to bacterial contamination of L-glutamic acid fermentation. 

Fermentation Feedstock. Sucrose, in the form of beet or cane molasses, is a fermentation feedstock for production of a variety of organic compounds, including lactic, glutamic, and citric acids, glycerol, and some antibiotics. Lesser amounts of itaconic, aconitic, and kojic acids, as well as acetone and butanol, are also produced (41,51—53). Rum is made by fermentation of cane molasses. Beet and cane molasses are used for production of baker s and brewer s yeast (qv). 

Molasses is also used as an inexpensive source of carbohydrate in various fermentations for the production lactic acid, citric acid, monosodium glutamate, lysine, and yeast (60). Blackstrap molasses is used for the production of mm and other distilled spirits. 

Despite the advantages of continuous cultures, the technique has found little application in the fermentation industry. A multi-stage system is the most common continuous fermentation and has been used in the fermentation of glutamic add. The start-up of a multi-stage continuous system proceeds as follows. Initially, batch fermentation is commenced in each vessel. Fresh medium is introduced in the first vessel, and the outflow from this proceeds into the next vessel. The overall flow rate is then adjusted so that the substrate is completely consumed in the last vessel, and the intended product accumulated. The concentration of cells, products and substrate will then reach a steady state. The optimum number of vessels and rate of medium input can be calculated from simple batch experiments. 

MSG is the sodium salt of the amino acid glutamic acid. It is made commercially by the fermentation of molasses, but exists in many products made from fermented proteins, such as soy sauce and hydrolyzed vegetable protein. 

Glutamates can be produced by fermentation of starches or sugars, but also by breaking the bonds between amino acids in proteins, leaving free amino acids. This process is done by heat or by enzymes it is called hydrolyzing, because the bonds are broken by adding water. 

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