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Here is a term paper on ‘Fermentation’. Find paragraphs, long and short term papers on ‘Fermentation’ especially written for school and college students.
Term Paper # 1. Principle of Fermentation:
The growth of micro-organisms is a highly complex and co-ordinated process, ultimately expressed by increase in cell number or cell mass. The process of growth depends on availability of requisite nutrients and their transport into the cells, and the environmental factors such as aerations, oxygen supply, temperature and pH.
Doubling time refers to the time period required for doubling the weight of biomass while generation time refers to the period for doubling the cell numbers.
Doubling time normally increases with increasing cell size and complexity as given below:
Bacteria — 0.30-1 hr.
Yeasts — 1-2 hr.
Animal cells — 25-48 hr.
Plant cells — 20-70 hr.
In general, when all other factors are kept ideal, growth of the micro-organisms is dependent on the nutrient supply. The organisms can be grown in batch, fed-batch, semi continuous and continuous culture or fermentation.
Term Paper # 2. Types of Fermentation:
1. Batch Culture/Batch Fermentation:
It is regarded as a closed system. The sterile nutrient culture medium in the bioreactor is inoculated with micro-organism. The incubation is carried out under optimal physiological condition (pH, temperature, oxygen-supply, agitation, etc.). It may be necessary to add acid or alkali to maintain pH, antifoam ejects to minimize foam.
Under optimal conditions for growth, the six phases are:
(i) Lag phase.
(ii) Acceleration phase.
(iii) Log phase (exponential phase).
(iv) Deceleration phase.
(v) Stationary phase.
(vi) Death phase.
(i) Lag Phase:
During this phase the micro-organisms adapt to the environmental conditions, i.e., nutrients, pH, temperature, etc. There is no increase in the cell number but cellular mass/ weight increases to some extent. The duration of the lag phase is variable and is mostly determined by the new set of physiological conditions at which the micro-organisms were existing when inoculated.
(ii) Acceleration Phase:
It is brief transect period during which cells start growing slowly. In fact, acceleration phase connects lag and log phases.
(iii) Log Phase:
Sometimes, log phase starts immediately without lag phase. It is the most active growth phase of the micro-organisms and during this phase multiplication in the number of cells occurs. The cells undergo several doubling and the cell mass also increases. The growth of micro-organisms in this phase is independent of substrate concentration as long as excess substrate is present and there are no growth inhibitors in the medium.
(iv) Deceleration Phase:
The phase is usually of very short duration and occurs at the time of decreased growth of cells in log phase.
(v) Stationary Phase:
As the substrate in the growth medium gets depleted, and the metabolic products that are formed inhibit the growth, the cells enter the stationary phase. The microbial growth either may go slow or even stop completely. Biomass also remains constant during this phase. During this phase secondary metabolites of biotechnological importance are produced such as antibiotics.
(vi) Death Phase:
The phase is concerned with the cessation of metabolic activity and depletion of energy reserves. The cells die at an exponential rate. During this phase the cells are harvested.
2. Fed Batch Culture/Fermentation:
It is more improved form of batch fermentation. In these method substrate/nutrients is/are added in increments at different times throughout the course of fermentation while in batch fermentation substrate is added only at the beginning of the culture.
Addition of substrate prolongs the log phase and stationary phase resulting into increase of biomass. Production of metabolites, e.g., antibiotics during stationary phase is very much increased. To add the substrate, formation of organic acids, product of carbon dioxide and pH outings are measured and then substrate is added as per requirement. It results in production of recombinant proteins, (25% to 100%) as compared to batch fermentation.
Limitations:
Micro-organisms in the stationary phase produce proteolytic enzymes or proteases. These enzymes attack on the recombinant proteins which are produced during the process of fermentation.
This can be controlled by addition of substrate by which log phase is prolonged and stationary phase is delayed thus minimizing the production of proteases.
3. Semi Continuous Culture/Fermentation:
In this fermentation a portion of culture medium is removed from the bioreactor and replaced by fresh medium. The replacement of culture medium is repeated after regular intervals. In this fermentation, the non-productive phases are reduced or shortened. Semi continuous fermentation is used for commercial production of alcohol.
Disadvantages:
1. Technical difficulties in handling bioreactors.
2. Long culture periods that may lead to contamination, mutation and mechanical breakdown.
4. Continuous Culture/Fermentation:
It is an open system. It involves the removal of culture medium continuously and replacement of this with a fresh sterile medium in bioreactor.
Both addition and removal are done at the same time so that the working volume remains constant. It is used for production of antibiotics, organic solvents, beer, ethanol, waste water treatment, single cell proteins.
Advantages:
1. Size of the bioreactor and other equipments are relatively smaller for the production of same quantity of product.
2. Product yield is consistent as physiological state of cells is uniform.
3. The down time between the successive fermentation for obtaining and preparing the bioreactor for reuse is avoided in continuous fermentation.
4. It is run in a cost-effective manner.
Disadvantages:
1. It may run continuously for a period of 500-1000 hrs. This period is a barrier in maintaining sterile condition in the medium.
2. Recombinant cells with plasmid constructs cannot function continuously and therefore yield decreases.
3. Same quality of culture medium cannot be maintai01ned for all the additions.
Optimization of Fermentor:
Growth conditions of cells growing in a fermentor vary from that found in laboratory; therefore, the fermentor must be optimized by the following ways:
(i) Fermentor should be designed for the growth of desired organism and should not be contaminated by other organisms.
(ii) Leakage of medium must be prevented.
(iii) Oxygen supply must be maintained above the critical level for agitation and aeration of aerobic organisms.
(iv) pH, temperature, concentration, etc., must be maintained and properly controlled.
(v) Culture medium must be mixed thoroughly.
Term Paper # 3. Aseptic Operation of Fermentor:
For aseptic operation of fermentor following key points must be considered for successful fermentation:
(i) The culture medium and the vessel must be sterilized carefully before inoculation.
(ii) Sterilization of the fermentor is done by hot water or steam.
(iii) Surface of the vessel must be smooth and polished so that no microbial contaminants should remain attached to uneven surfaces or crevices.
(iv) The medium should also be sterilized in fermentor itself by passing heat through the cooling coils. The sterilized medium may be prepared separately and then transferred to the fermentor through a steriliser.
(v) Antifoam agents (e.g., corn oil, soybean oil, etc.) should be sterilized.
(vi) Microbe-proof air filters are used to supply sterilized air to the culture medium. Bacterial cells and fungal spores are entrapped in the millipore filter paper used for this purpose. But the bacteriophages can pass through the millipore filter paper. To prevent bacteriophages, air compressor is attached which generates sufficient heat to inactivate the bacteriophage present in air.
(vii) Use of compressor prevents coliphages also. But air discharged from the fermentor must also be sterilized if the recombinant bacteria/microbes are growing in the fermentor.
Reactor Engineering:
For the large scale production using living cells at a cheaper cost in short time, reactor engineering plays an important role. Thus the knowledge of various steps involved in production is very important.
Large scale production of bio-products includes following steps:
(i) Selection of best strain of micro-organism.
(ii) Sterilized vessels for mixing.
(iii) Growth medium.
(iv) Culture of microbial cells in small volume (5-10 ml) then transferred to 200-1000 ml flask for log phase growth then to seed fermentor of 10 L volume and ultimately to production fermentor of 1000 L containing medium rich in carbon and nitrogen, trace elements, vitamins, hormones, buffer and antifoam chemicals.
(v) Slow growth organisms pass through following steps:
Stock culture → shake flask → seed fermentor → production fermentor.
To increase spore concentration high amount of spores are blown into seed fermentor through in-going air.
(vi) Temperature, pH, aseptic conditions and sterile air are necessary requirements.
(vii) Cells and products are separated by filtration or centrifugation.
(viii) Cells are used to obtain intracellular desirable products which are purified by downstream operations.
(ix) Products are purified and tested for efficiency, packed, cost is decided and marketed.