Design of Fermentation Media
In a fermentation process, the choice of the most optimum micro-organisms and fermentation media is very important for high yield of product. The quality of fermentation media is important as it provides nutrients and energy for growth of micro-organisms. This medium provides substrate for product synthesis in a fermentor.
Fermentation media consists of major and minor components.
- Major components include Carbon and Nitrogen source.
- Minor components include inorganic salts, vitamins, growth factors, anti-foaming agents, buffers, dissolved oxygen, other dissolved gases, growth inhibitors and enzymes.
Nutrients required for fermentation media also depend upon the type of fermentation organisms as well as the type of fermentation process to be used. Poor choice of fermentation media might result in poor yield of output. Types of nutrients present in the fermentation media always determine the yield of the product.
There are two uses of fermentation media
- Growth media
- Fermentation media
Growth medium contains low amounts of nutrients.It is useful in creating raw material for further fermentation processes.
Fermentation media contains high amounts of nutrients. It is used in creating final products using fermentation.
For example, growth of yeast requires 1% carbon. But during fermentation of alcohol, yeast requires 12 to 13 % carbon in the medium.
What is the role of Fermentation Media?
During the fermentation process, media contains high amounts of nutrients, micro-organism and optimum conditions. When these micro-organisms are incubated at the desired optimum conditions, they enjoy luxurious metabolism. Here, the fermentation organisms become hyperactive due to presence of high quantities of nutrients, thus it results in consumption of excess nutrients and partial degradation of fermentation media. The waste effluents excreted by the microbes could be the desired output product of the fermentation process.
The amount of substrate given to microbes should not reach inhibitory concentration levels because excess substrate inhibits vital enzymes and may results in death of cells. Also, water present in cytoplasm is important for metabolism process. If excess sugar or salt is available in the fermentation media, it would tie up cytoplasm water and may result in lack of water for metabolism and cause death of microbes, thus affecting fermentation output.
Excess substrate may increase osmotic pressure and effect enzyme activities in a cell. Microbes excrete this excess substrate in the form of partially digested fermentation media. It is converted to an insoluble inert compound in the form of reserve food material and this reserve food material is harmless to cells.
There are two types of fermentation media used in industries.
- Synthetic media
- Crude media
Let us discuss these types of media.
- Synthetic media
Synthetic media is useful in the field of research as each and every component is chemically known and the exact composition of nutrients is predetermined. So, in case of synthetic media, variation in levels and concentration of nutrients can be controlled. Here, by experimentation with synthetic media, the effect of nutrients on growth and yield of product can be analysed. We can redesign the synthetic media as per our needs. It is very useful in controlling the growth and yield of product in a lab environment. We can also use it to determine the metabolic pathway used in the synthesis of products.
With the help of radio-isotope labelling technique, we can determine the main ingredients that gets used up to create the final desired product. In this way, we can know the exact proportions of ingredients required for our process. We can optimise this process by using alternative sources of carbon or nitrogen, and creating a fermentation media which is the most optimum for our needs. The use of Synthetic media allows us to experiment with various sources of fermentation media in the lab as the results are accurately reproducible for a given composition.
An advantage of a well designed synthetic media is that it lacks sources of protein and peptides. Hence, there is no foam formation, and chances of contamination are very less. Product recovery is easier because synthetic media contains pure components.
Although there is a big list of advantages of synthetic media, there are some disadvantages. A major disadvantage is the cost of media. The most important aspect of fermentation is that it should be economic and profitable. Synthetic media is never used on industrial scale because it is expensive. This process in only suitable for experimentation in a lab on a small scale.
- Crude Media
Crude media is generally used on an industrial scale for fermentation process. Crude media contains a rough composition of media required for fermentation. It gives high yield of product and contains undefined sources of ingredients. Crude media contains high level of nutrients, vitamins, proteins, growth factors, anti-foaming agents and precursors. It is important to ensure that crude media should not contain toxic substances that could effect the growth of bacteria and yield of product.
Ingredients of Crude Media
1) Inorganic nutrients
Crude media contains inorganic salts containing cations and anion along with a carbon source. Sometimes, fermentation micro-organisms have a specific requirement of ions like magnesium ions, phosphates or sulphates. These requirements are fulfilled by addition of these ions to balance the crude media.
2) Carbon source
Simple to complex carbohydrates can be added to media as a source of carbon. We can add different sugars like mannitol, sorbitol, organic acids, fatty acids, proteins, peptides we can choose any of these as a source of carbon. The selection of carbon source depends upon the availability as well as the cost of raw material. In most of the fermentation media, crude source of carbon is added.
- Simple carbohydrates – simple sugars are semi purified polysaccharides and sugar alcohol are added. Sources of simple carbohydrates are Black strap molasses, Corn molasses, Beet molasses, sulphite waste liquor, Hydrol (corn sugar molasses), Cannery waste.
- Complex carbohydrates – Source of complex carbohydrates are Starch, Corn, Rice, Rye, Milo, wheat potatoes etc. Source of starch cellulose are corn cobs, straws, wood waste, saw meal etc.
3) Nitrogen source
Salts of urea, ammonia, and nitrate can be used as a nitrogen source. When fermentation organisms are non-proteolytic in nature, pure form of urea, ammonia and nitrate are used as a source of nitrogen. When fermentation organisms are proteolytic in nature, animal and plant raw material is used; like distillery dried solubles, Casein, Cereal grains, peptones, yeast extract, hydrolysate, and soybean meal etc.
4) Growth factors
Crude media constituents provides enough amount of growth factors so no extra addition of growth factor is required. If there is a lack of any kind if vitamins or nutrients, growth factors can be added to media. Examples are yeast extract, and beef extract.
Precursors are generally present in the media as crude constituents. Precursors are added in the fermentation media at time of fermentation as it get incorporated in the molecules of product without bringing any kind of change to the final product. This helps in improving yield and quality of product. Sometimes, precursors are added in pure form depending upon the need of product. For example, Cobalt chloride is added less than 10 ppm in fermentation of vitamin B12.
Buffers are used to control drastic changes of pH. Sometimes, media components may act as buffers. For example, protein, peptides, mino-acids act as good buffers at neutral pH. Sometimes inorganic buffers like K2HPO4, KH2PO4, and CaCO3 etc, can be added as required. Generally, during the fermentation process, pH changes to acidic or alkaline pH. The cheapest and easily available buffer is CaCO3.
This was a summary of fermentation media which can be used for fermentation