the overview of fermentation processes
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1. Describe the fermentation process
2. Distinguish major groups of commercially
important fermentation.
3. Discuss the basic components infermentation
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The term fermentation is derived from latinverb, fervere, to boil, describing theappearance of the action of yeast on extractsof fruit or malted grain. The boilingapperance is due to the production of CO2
bubbles caused by anaerobic catabolism ofsugars presents in the extract
the term used to describe any process for the
production of a product by means of themass culture of a microorganism.
Product?
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The product can either be:
1. The cell itself: referred to as biomass production.2. A microorganisms own metabolite: referred to as a
product from a natural or genetically improved
strain.
3. A microorganisms foreign product: referred to as a
product from recombinant DNA technology or
genetically engineered strain
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Acetic acid manufacture by fermentation is based upon the
oxidation of fermented liquors (10-15% alcohol) by air in the
presence ofmycoderma aceti.
A 3-7% solution of acetic acid is got and it is called vinegar.
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The biochemical metabolism classes:a. the anabolic pathways (anabolism) synthesize the
complex molecules and their intermediate
precursors
b. the catabolic pathways (catabolism) supply the
energy needed for the anabolic processes.
Aerobic microorganisms:carry out their metabolism using oxygen
Anaerobic microorganisms:
can substitute nitrate, others sulfate or ferric ion for
oxygen
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BATCH FERMENTATION
A batch fermentation can be considered to be a closedsystem.
At time t=0 the sterilized nutrient solution in the
fermentor is inoculated with microorganisms andincubation is allowed to proceed.
In the course of the entire fermentation, nothing is added,except oxygen (in case of aerobic microorganisms), anantifoam agent, and acid or base to control the pH.
The composition of the culture medium, the biomass
concentration, and the metabolite concentration generallychange constantly as a result of the metabolism of thecells.
After the inoculation of a sterile nutrient solution withmicroorganisms and cultivation under physiologicalconditions, four typical phases of growth are observed
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Lag phase
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Lag phase
Physicochemical equilibration between microorganism and the environment following
inoculation with very little growth.
Log phase
cells have adapted to the new conditions of growth. a doubling of cell number per unit time for bacteria and yeasts, or a doubling of biomass per
unit time for filamentous organisms as fungi.
the cells alter the medium through uptake of substrates and excretion of metabolic products,
the growth rate remains constant during the log phase.
Growth rate is independent of substrate concentration as long as excess substrate is present.
Stationary phase
As soon as the substrate is metabolized or toxic substances have been formed, growth slows
down or is completely stopped.
The biomass increases only gradually or remains constant during this stationary phase,
although the composition of the cells may change.
new substrates are released which then may serve as energy sources for the slow growth ofsurvivors.
The various metabolites formed in the stationary phase are often of great
biotechnological interest.
Death phase
The cells are dying at an exponential rate. The length of time between the stationary phaseand the death phase is dependent on the microorganism and the process used.
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FED BATCH FERMENTATION
substrate is added in increments as the fermentation progresses.
the nutrient solution are added in small concentrations at the
beginning of the fermentation and these substances continue to beadded in small doses during the production phase.
CONTINUOUS FERMENTATION
an open system
Sterile nutrient solution is added to the bioreactor continuouslyand an equivalent amount of converted nutrient solution withmicroorganisms is simultaneously taken out of the system.
In the case of a homogeneously mixed bioreactor we refer to achemostat or a turbidistat.
In the chemostat in the steady state, cell growth is controlled byadjusting the concentration of one substrate.
In the turbidistat, cell growth is kept constant by using turbidity tomonitor the biomass concentration and the rate of feed of nutrientsolution is appropriately adjusted.
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1. Formulation of mediums to be used in culturing
2. Sterilization of the medium, fermenters and ancillary
equipments
3. The production of an active, pure culture in sufficientquantity to inoculate the production vessel
4. The growth of the organism in the production fermenter
under optimum condition for product formation
5. The extraction of the product and its purification
6. The disposal of effluents produced by the process
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Carbohydrates
Glucose is the most readily metabolized sugar. Most fungi can usedisaccharides.
Lipides
Long-chain fatty acids like linoleic acid and oleic acid are required forbacteria and fungi. Generally, steroids, other than cholesterol, are
not required or utilized by microorganisms. In all fungi, and includingyeast, ergosterol is a nutritional requirement.
Purines and pyrimidines
It is generally only in bacteria that cases of purine and pyrimidinemetabolism have been reported. Algae do not utilize these
compounds at all.
Vitamins and growth factors
There is considerable species variation in the requirements ofvitamins and related factors by other microorganisms. Generally,vitamins A, C, D, and K are not necessary for growth.
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Amino acids
Amino acids are not generally required by algae, although several algae species are
capable of utilizing them.
Species of other microorganisms are capable of utilizing all amino acids, except for
yeasts, where there is no evidence ofcritrulline being used. It is usually the L-form of
the acids that are biologically active but, unlike higher animals, some bacteria can also
utilize the D-amino acids.
Nitrogen sources
It should be stressed that not all species require or utilize these compounds but rather
that some species have been identified that are able to utilize these compounds. Fungirequire ammonia, nitrate and nitrite.
Sulfur sources
Some species of yeasts can utilize elemental sulfur and sulfate. Generally yeasts do not
require or utilize sulfur containing organic compounds.
Bacteria require glutathione and thio-acetic acid while yeasts require sulphonic acid
amides, thioacetate, thiocarbonate,thioglycolate and glutathione.
Chemical elements and inorganic ions
Mineral nutrients required by microorganisms are species dependent but consists
generally of Fe, K, Mg, Mn. Sometimes S, N, Ca, Co, Cu, P, Zn is required.
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A microbial fermentation can be viewed as a three-
phase system
The liquid phase contains dissolved nutrients,dissolved substrates and dissolved metabolites.
The solid phase consists of individual cells,
pellets, insoluble substrates, or precipitatedmetabolic products.
The gaseous phase provides a reservoir for oxygen
supply and for CO2 removal.
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The stirring of a bioreactor brings about the following:
Dispersion of air in the nutrient solution
Homogenization to equalize the temperature and the concentration of nutrients
throughout the fermentor
Suspension of microorganisms and solid nutrients
Dispersion of immiscible liquids
Nutrient solutions can be subdivided into two groups according to the way they
behave when stirred:
a. viscous solutions with Newtonian and non-Newtonian properties
e.g. Uninoculated solutions and bacterial cultures
b. viscoelastic solutions, in which normal liquid-state properties are not observed in
stirred vessels.
e.g. polysaccharides and certain antibiotic fermentations
The viscosity, the ability of a material to resist deformation, is the most significant
property affecting the flow behavior of a fluid. Such behavior has a market effect
on pumping, mixing, heat transfer, mass transfer and aeration.
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