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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The Overview of Fermentation Processes