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  Fermentation, Chemistry tutorial

History of fermentation:

Fermentation is a natural procedure. People applied fermentation to make products like cheese, wine and beer long before the scientific nature of the procedure was understood. This nature was primary discovered by Louis Pasteur, a French chemist who considered fermentation as a life procedure. According to him, all the fermentative changes are related with and produced via living organisms. Justus von Liebig, a German chemist, on the other hand, considered it to be a simple chemical procedure brought about via complex nitrogenous substances, already present in the cells of microorganisms. The controversy between Pasteur and Liebig over the nature of alcoholic fermentation was uncovered via Eduard Buchner, a German chemist and zymologist. His findings exposed that fermentation could take place in the presence of oxygen and was caused due to an enzyme that he named zymase.

Classification of fermentation:

Fermentation is a method through which a raw material is transformed into a product by the action of micro-organisms or by means of enzymes. The two main classes of industrial fermentation are as follows:

Microbial fermentation:

These are promoted via micro-organisms like viruses, bacteria, fungi and protozoa. Throughout the microbial fermentation, the rate of transformation of raw materials to products is at first low as the micro-organisms (that serve as the catalytic agent) are few. As more micro-organisms are made, the rate begins to rise. The rate then reaches a maximum when there is optimum ratio of unconverted material and the micro-organisms. The rate then drops as the raw material becomes depleted. Ultimately the rate stops if the raw material is finished. Micro-organisms are capable to catalyze numerous kinds of reactions. As a result, microbial fermentation yields in more than one product that makes purification necessary.

Enzymatic fermentation:

These are catalyzed via enzymes. Enzymes are natural proteins that act as biocatalysts which bring about particular biochemical reactions devoid of their structure or quantity being changed. Their activity based on temperature, pH, storage time and storage conditions. As enzymes are specific in action, juts one product is produced from a chosen enzyme and thus, its purification is less costly compared to the microbial fermentation. Though, enzymes are more costly as compare to the micro-organisms.

Fermentation Process:

The fermentation procedure comprises the following:

Culture Preservation:

For any fermentation procedure to be successful, a preserved high yielding micro-organism strain is a fundamental requirement. The preserved culture is a valuable benefit and as little as possible must be employed to initiate the process. Usually this preserved stock is in the form of inert spores.

Scale Up:

Scale up is a significant part of numerous cell driven methods. For some fermentation, it is necessary to amplify the beginning inoculum via a sequence of ever increasing volumes until adequate material exists to inoculate the production system. In bacterial and yeast systems where vigorous growth is anticipated, scale up to an initial: final inoculum ratio of 1:20 to 1:100 is general.

The seed tanks are steel tanks designed to give an ideal atmosphere for growing microorganisms. They are filled by all the things the particular microorganism would require to survive and thrive, comprising warm water and carbohydrate foods such as lactose or glucose sugars. Moreover, they have other essential carbon sources, like acetic acid, alcohols or hydrocarbons and nitrogen sources such as ammonium salts. Growth factors such as vitamins, amino acids and minor nutrients complete the composition of the seed tank contents. The seed tanks are equipped by mixers that keep the growth medium moving and a pump to deliver sterilized, filtered air. After around 24 to 28 hours, the material in the seed tanks is transferred to the main fermentation tanks.

Fermentation:

Fundamentally, the fermentation tank is a bigger version of the seed tank. It is filled by the similar growth media found in the seed tank and as well gives an atmosphere conducive for the growth and multiplication of the microorganisms.

Throughout this method, they excrete big quantities of the desired product. The tanks are cooled to keep up the right temperature. The fermentation tank is continuously agitated, and a continuous stream of sterilized air is pumped into it. Anti-foaming agents are periodically added to inhibit foaming. Acids or bases are added to control pH to the level that is optimal for the growth of the micro-organism. 

The fermenter is the heart of any fermentation procedure. The design of fermentation equipment and the operation of the fermentation procedure must make sure the method is contamination free, and in the case of pathogens, they should be contained by high degree of safety. Most production fermenters are made up of stainless steel construction having impellers for good bulk liquid mixing features to make sure homogeneity in the vessel. Air is sparged to the vessel beneath the bottom impeller. Fermenters generate heat via dispersion of kinetic energy and metabolism, thus the vessel should encompass a cooling system.

Product recovery and purification:

Recovery and purification are very necessary steps for the fermentation product to be economically attractive. Certain products are contained within the cells and are not discharged or are only partially liberated to the medium. It might be essential to wash the cells to eliminate impurities before breaking them to get the product. 

Some cells encompass high resistance to shear and need specialized equipment to rupture them. Ultrasonic vibrations, grinding in mills and high pressure can be employed to rupture cells. Centrifuges and rotary-drum filtering are generally employed in the separation of the cells from the broth. Products in the broth might be recovered via a variety of unit operations like distillation, extraction by salts and solvents, membrane ultra filtration, precipitation and chromatography.

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