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Industrial microbiology came primarily based on a naturally occurring microbiological process called fermentation. There are many evidences which clearly shows that ancient man knew fermentation process and practiced it more as an art rather than as a science. Early fermentation process practiced by man included the leavening of bread, retting of flax, preparation of vinegar from wine, production of various alcoholic beverages like beer, wine, mead and the production of various fermented foods and milk. Due to invention of microscope, discovery of microorganisms and understanding of their metabolic processes, lead to clear understanding of the fermentation, this paved the way for the development of Industrial Microbiology. The use of microorganisms in food also has a long history.

The microscope was available during the mid‐1600s, and an English scientist named Robert Hooke made key observations. He is reputed to have observed strands of fungi among the specimens of cells he viewed. In the 1670s and the decades thereafter, a Dutch merchant named Anton van Leeuwenhoek made careful observations of microscopic organisms, which he called animalcules. Until his death in 1723, van Leeuwenhoek revealed the microscopic world to scientists of the day and is regarded as one of the first to provide accurate descriptions of protozoa, fungi, and bacteria. Louis Pasteur worked in the middle and late 1800s. He performed numerous experiments to discover why wine and dairy products became sour, and he found that bacteria were to blame. Pasteur called attention to the importance of microorganisms in everyday life and stirred scientists to think that if bacteria could make the wine “sick,” then perhaps they could cause human illness. The development of microbiology. In the late 1800s and for the first decade of the 1900s, scientists seized the opportunity to further develop the germ theory of disease as enunciated by Pasteur and proved by Koch. There emerged a Golden Age of Microbiology during which many agents of different infectious diseases were identified. Many of the etiologic agents of microbial disease were discovered during that period, leading to the ability to halt epidemics by interrupting the spread of microorganisms. Despite the advances in microbiology, it was rarely possible to render life‐saving therapy to an infected patient. Then, after World War II, the antibiotics were introduced to medicine. The incidence of pneumonia, tuberculosis, meningitis, syphilis, and many other diseases declined with the use of antibiotics and more important products as shown in the Table 2.

Due to invention of microscope, discovery of microorganisms and understanding of their metabolic processes, industrial microbiology is divided into five phases.

Phase I (up to 1900): Alcohol fermentation period

A fermentation process is a biological process and, therefore, has requirements of sterility and use of cellular enzymic reactions instead of chemical reactions aided by inanimate catalysts, sometimes operating at elevated temperature and pressure. Industrial microbiology came primarily based on a naturally occurring microbiological process called fermentation. There are many evidences which clearly shows that ancient man knew fermentation process and practiced it more as an art rather than as a science. Early fermentation process practiced by man included the leavening of bread, retting of flax, preparation of vinegar from wine, production of various alcoholic beverages like beer, wine, mead and the production of various fermented foods and milk. Industrial fermentation processes may be divided into two main types. These are batch fermentations and continuous fermentations

Batch fermentations

A tank of fermenter is filled with the prepared mash of raw mate¬rials to be fermented. The temperature and pH for microbial fermen¬tation is properly adjusted, and occassionally nutritive supplements are added to the prepared mash. The mash is steam-sterilized in a pure culture process. The inoculum of a pure culture is added to the fermenter, from a separate pure culture vessel. Fermentation proceeds, and after the proper time the contents of the fermenter, are taken out for further processing. The fermenter is cleaned and the process is repeated. Thus each fermentation is a discontinuous process divided into batches.

Continuous fermentation

Growth of microorganisms during batch fermentation confirms to the characteristic growth curve, with a lag phase followed by a loga¬rithmic phase. This, in turn, is terminated by progressive decrements in the rate of growth until the stationary phase is reached. This is because of limitation of one or more of the essential nutrients. In continuous fermentation, the substrate is added to the fermneter continously at a fixed rate. This maintains the organisms in the logari-thmic growth phase. The fermentation products are taken out conti¬nuously. The design and arrangements for continuous fermentation are somewhat complex. He believed fermentation as a disintegration process in which molecules present in the starter substance like starch or sugar underwent certain changes resulting in the production of alcohol.

In the middle of 18th century, the chemist Liebig considered fermentation purely as a chemical process. Louis Pasteur conveniently proved that yeast is required for conversion of sugars into alcohol. In 1857, he discovered the association of different organisms other than yeasts in the conversion of sugars into lactic acid. These observations led Pasteur to conclude that different kinds of organisms are required for different fermentations. While working on butyric acid fermentation in 1861, Pasteur made another important discovery that the fermentation process can proceed in the absence of oxygen. The rod shaped organisms responsible for butyric acid fermentation, remains active in the absence of oxygen. This organism was later on identified as butyric acid bacterium. These observations subsequently lead to the emergence of a new concept of anaerobic microorganisms and a classification of three organisms broadly into two categories, viz., aerobic and anaerobic microorganisms.

Aerobic fermentations

A number of industrial processes, although called \'fermentations\', are carried on by microorganisms under aerobic conditions. In older aerobic processes it was necessary to furnish a large surface area by exposing fermentation media to air. In modern fermentation processes aerobic conditions are maintained in a closed fermenter with submerged cultures. The contents of the fermenter are agitated with au impeller and aerated by forcing sterilized air.

Anaerobic fermentations

Basically a fermenter designed to operate under micro-aerophilic or anaerobic conditions will be the same as that designed to operate under aerobic conditions, except that arrangements for intense agitation and aeration are unnecessary. Many anaerobic fermentations do, how¬ever, require mild aeration for the initial growth phase, and sufficient N agitation for mixing and maintenance of temperature.                        

Phase II (1900-1940) : Antibiotic period

The development of acetonebutanol fermentation by Weisman, which was considered to be truly aseptic and anaerobic fermentation. The techniques developed for the production of these organic solvents were major advances in fermentation technology, which led to the successful introduction of aseptic aerobic processes, which facilitated in the production of glycerol, citric acid and lactic acid. Another remarkable milestone in the industrial microbiology was the large-scale production of an antibiotic called penicillin, which was in great demand to save lives of thousands of wounded soldiers of Second World War. The technology established for penicillin fermentation paved the way for the development of a wide range of new processes such as production of other antibiotics, vitamins, amino acids, gibberellins, enzymes and steroid transformations. At about the same time Dubos at Rockfeller Institute, discovered a series of microbial products which showed antimicrobial properties and hence useful in treating certain human diseases. Waksman, a soil microbiologist, and his associates have discovered many antibiotics produced by species of Streptomyces, soil inhabiting, which is now widely used.

Phase III (1940-1964) : Single cell protein period

This period is marked by the production of proteinaceous food from the microbial biomass. As the cost of the resultant product was very low there was a need for large-scale production of microbial biomass. This led to the development of largest mechanically stirred fermenters ranging from 80,000 to 1,50,000 liters or even more in diameter, which were to be operated continuously for several days, if they were to be economical. Thus, a new fermentation process called continuous culture fermentation came into existence. The most long-lived continuous culture fermentation was the ICI Pruteen animal feed process employing the culture of Methylophillus methylotrophus.

Phase IV (1964-1979) Metabolite production period

During this period, new microbial processes for the production of amino acids and 51 - nuclosides as flavour augmenters were developed in Japan. Numerous processes for enzyme production, which were required for industrial, analytical and medical purposes, were perfected. Techniques of immobilization of enzymes and cells were also developed. Commercial production of microbial biopolymers such as Xanthan and dextran, which are used as food additives, had been also started during this period. Other processes that were developed during this period includes the use of microorganisms for tertiary oil recovery.

Phase V (1979 onward): Biotechnology period

Rapid strides in industrial microbiology have taken place since 1980, primarily because of development of new technique like genetic engineering and hybridoma technique. By genetic engineering it was made possible to in vitro genetic manipulations which enabled the expression of human and mammalian genes in microorganisms so thereby facilitating large scale production of human proteins which could be used therapeutically. The first such product is the human insulin used for treating the ever growing disease, diabetes. This was followed by the production of human growth hormone, erythropoietin and myeloid colony stimulating factor (CSFs), which control the production of blood cells by stimulating the proliferation, Erythro-poietin used in the treatment of renal failures, anemia and platelet deficiency associated with cancer, gametocyte colony stimulating factor (GCSF) used in cancer treatment and several growth factors used in wound healing processes. The hybridoma technique, which is employed for the production of monoclonal antibodies which aid in medical diagnosis and therapeutics, is also developed during this period.

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