Monosodium glutamate, otherwise known as MSG, is a commonly discussed food additive used throughout the world today. While some countries use it minimally, and place high restrictions on its use, other countries use it on a consistent basis, in many foods. This paper will examine MSG, and its uses. Additionally, this paper will examine each step of how MSG is made, using fermentation. The discussion will include technical details of the process, the equipment commonly used, the use of enzymes and bacteria, as well as an examination of the product packaging and quality control procedures. Finally, this paper will include a brief description of the market of MSG, and the socio-economic aspects of the product.
Monosodium glutamate, or MSG, is the sodium salt of glutamic acid. Glutamate is an amino acid that occurs naturally in many foods known for their flavor, such as tomatoes and mushrooms. Additionally, glutamate is found as a naturally occurring amino acid in foods such as meat, fish, and many vegetables. It can also be found in foods such as ice cream, yogurt, soda, canned soups, flavored crackers, and chips. Glutamate is also produced in the human body naturally, helping to regulate the body's metabolic rate (WHO, 1988).
Monosodium glutamate is primarily used as a food additive. In 1907, Professor Kikunae Ikeda noted that the flavor of foods such as tomatoes, cheese, and meat were common, but did not seem to fit into the four main categories of flavor. He began work on experiments with seaweed, and succeeded in extracting crystals of what is now known as Glutamic Acid. He named the flavor of the substance "umami" (Blue Diamond, 2000).
Once Ikeda was able to extract the source of the flavoring, he quickly created a seasoning from the materials. For the materials to work as seasoning, he needed the substance to be similar to other forms of seasonings, such as soluble in water, yet able to withstand humidity. MSG was found to have these characteristics, and since it has no texture to speak of, it was found to be useful in almost any combination of dishes, without disturbing the natural flavor of the foods (Blue Diamond, 2000).
Until the 1950's, MSG was produced in small quantities through extraction from acid hydrolysate of plant proteins, such as the gluten or proteins present in sugar beet waste. In hydrolysis, the proteins are hydrolyzed with strong mineral acids used to free amino acids. Then, the glutamic acid is separated from the mixture, purified, and converted to MSG (Leung & Foster, 1996). However, this method led to small-scale results, unable to keep up with the consumer demands.
In the 1950's, bioprocessing of materials began to develop. This led to the current method of large-scale MSG production, that of biological fermentation. In general terms, this method involves the use of bacteria grown aerobically in a liquid nutrient medium with a carbon source. In addition, the liquid contains a nitrogen source, and mineral ions. The bacteria use the nitrogen and minerals to produce L-Gln, which is then excreted into the mixture. The mixture is then separated by filtration, purified, and crystallized (Leung & Foster, 1996).
Specifically, the process begins with the selection of the most productive bacteria. In the case of MSG production, both the corynebacterium glutanicum and the brevibacterium flavum have been found to have the highest output of L-Gln under optimal fermentation conditions (Aida, et al., 1986). Thus, these are the bacterium generally used in the fermentation process.
First, a fermentation tank is used. The tank is cleaned and sterilized to ensure a non-contaminated product. Since the bacterium used in L-Gln production are generally weaker and susceptible to contamination than wild strains of the bacterium, sanitation is even more important (Kusumoto, 2001). In addition, it is also important to maintain the tank with positive pressure by aeration during the fermentation process to prevent other microorganisms from compromising the mixture (Ajinomoto, 1996).
Next, the mixture to use with the fermentation process is created. This mixture consists of glucose or other carbohydrate base as the carbon source, ammonia as a nitrogen source, and small amounts of various minerals and vitamins as growth factors. Additionally, the microorganisms used require dissolved oxygen, so dissolved oxygen is generally maintained at 60% using a valve at the side of the tank, and an oxygen-measuring device within the fermentation tank. The mixture is combined to form the fermentation broth (Kusumoto, 2001).
The mixture is then added to the fermentation tank. Next, the fermentative organism is added to the mixture (Ajinomoto, 1996). In the beginning of the process, small amounts of L-Gln are created. Glutamate begins to accumulate when the bacterium in the mixture reach a certain level (Kusumoto, 2001)
As the sugars or other carbohydrate source are taken in by the bacterium, the microorganisms used in the fermentation process begin to produce glutamate. This glutamate is then excreted into the fermented broth (Ajinomoto, 1996). In the first stage of the process, the concentration of sugar mixture is very high, while the numbers of brevibacterium microorganisms are typically low. As the sugar or carbohydrate mixture is taken in by the bacterium, and as the bacterium levels rise, more glucose is added to the mixture to increase the production of the organisms (Kusumoto, 2001).
Optimal fermentation levels of pH, temperature, and agitation speeds are controlled. The optimal levels are pH 5.65, 30 degrees Celsius, and 180 rpm agitation speeds (Nampoothiri, et al., 1999). Standard liquid thermometers are used to measure temperatures, while standard pH meters are used to monitor pH levels. As pH levels rise or fall in the mixture, the L-Gln is easily hydrolyzed to L-Glutamic acid, as the pH levels shift from the isoelectric point. Thus, maintaining proper levels of pH are very important to the fermentation process (Kusumoto, 2001).
Once the fermentation process is finished, the L-Gln must then be separated from the fermentation broth. This is generally done using a centrifuge or a membrane filter, used to separate the cells from the debris. While it is desirable that the crude L-Gln crystals are harvested through direct filtration, this is sometimes not possible to do while still maintaining adequate purity of the cells (Kusumoto, 2001).
In these cases, it may be necessary to use repeated ion exchange resin treatments and crystallization to purify the L-Gln cells. Using ion exchange, ions in the resin used are exchanged with the impure organics present in the crude L-Gln (DeSilva, 1997). After passing through the resin treatment, the remaining mixture may still be impure, however.
Often, chromatographic treatments are used in these cases (Kusumoto, 2001). This treatment is used to further separate the L-Gln from the fermentation mixture. The most common methods used are gas chromatography and high performance liquid chromatography, since these two methods deal with the removal of organic ions. In the chromatographic process, the fermentation mixture is injected into the system. A sample mixture of known quality L-Gln is then injected at the injection port, and gas or liquid carries the compounds into the column. As the sample components interact with the mixture, the compounds begin to separate as they move through the column (Aida, et al., 1986).
Once the crude L-Gln is extracted and purified in the above manner, it then needs to be crystallized. All amino acids can be crystallized, but L-Gln crystallization can only be done in a single form. So, while other amino acids can be purified by duel crystallization, L-Gln cannot. With duel crystallization, L-Glutamic acid, for example, can be crystallized to the ^-form, where the crystals are then dissolved. The crystals are then reformed into B-form. This process allows impurities to be removed, based on their differences between the two forms (Kusumoto, 2001).
L-Gln, however, can only be crystallized to the ^-form. Thus, in order to use the crystallization process for purification, there is no alternative other than to crystallize the material, dissolve it, and recrystallize it into the same form. This is inefficient and rather repetitive, so the other methods of ion exchange and chromatographic treatments should be used (Kusumoto, 2001).
Another step in the creation of L-Gln is to ensure that purification is done rapidly. In cruse form, L-Gln is highly susceptible to biodegradation. As mentioned, pH levels of 5.65 are optimal for fermentation. However, with the introduction of contaminating bacteria in the fermentation solution, or in the crude L-Gln crystals, L-Gln can be almost half decomposed in a matter of 24 hours. On the other hand, when sterilized, L-Gln is almost completely non-degradable. Thus, it is extremely important to quickly and efficiently purify the crystals (Kusumoto, 2001).
The crystallization of the mono sodium glutamate and their purification leads then to a drying process. This drying process further crystallizes the MSG. The product is then sent to quality assurance. The QA area double-checks the purity of the product, and the product is only distributed after each step in the fermentation process has been verified. The product is then packaged, and shipped to various outlets, including health food stores, Asian…