2. INTRODUCTION
• The Term “Fermentation” Is Derived From The Latin Verb Fervere, To Boil, the boiling appearance is
due to the production of carbon dioxide bubbles caused by the anaerobic catabolism of the sugars
present in the extract. However, fermentation has come to have different meanings to biochemists
and to industrial microbiologists. Its biochemical meaning relates to the generation of energy by the
catabolism of organic compounds, whereas its meaning in industrial microbiology tends to be much
broader.
• Fermentation Technology Is The Use Of Organisms To Produce Food, Pharmaceuticals And Alcoholic
Beverages On A Large Scale Industrial Basis.
• The basic principle involved in the industrial fermentation technology is that organisms are grown
under suitable conditions, by providing raw materials meeting all the necessary requirements such
as carbon, nitrogen, salts, trace elements and vitamins.
• The end products formed as a result of their metabolism during their life span are released into the
media, which are extracted for use by human being and that have a high commercial value. The
major products of fermentation technology produced economically on a large scale industrial basis
are wine, beer, cider, vinegar, ethanol, cheese, hormones, antibiotics, complete proteins, enzymes
and other useful products.
3. FERMENTER
• Fermentation Process Is Carried Out In A Container Called The Fermenter Or Bioreactor. The
Design And Nature Of The Fermenter Varies Depending Upon The Type Of Fermentation Carried
Out. Invariably All The Fermenter Have Facilities To Measure Some Of The Fermentation
Parameters Like Temperature, Pressure, Ph, Elapsed Fermentation Time, Liquid Level, Mass Etc.
Fermenters (Or Bioreactors) Are Most Essential Part Of Any Biotechnology Based Production
Process, Whether It Is An Alcohol, Solvent, Protein, Vaccine Or Antibiotic. Today Production Plant
Have An Array Of Fermenters Ranging From 250 To 100,000 Lt Or More. The Usual Practice Is To
Start The Inoculum In A Small Fermenter And Then Transfer It To A Huge Fermenter With Pre-
sterilized Medium.
• The environment provided for the growth of the process organism must be controlled during the
fermentation such that maximum (and reliable) productivity may be achieved. Regardless of the
type of fermentation an established process may be divided into SIX basic component parts:
1. The chemical environment of the organism should be such that it supports optimum product
formation commensurate with the economics of the process. The formulation of media to be used in
culturing the process organism during the development of the inoculum and in the production
fermenter.
4. 2 .The Culture Should Be Maintained In A Pure State Throughout The Fermentation Therefore
Sterilization Of The Medium, Fermenters And Ancillary Equipment Is Required.
3 .The Production Of An Active, Pure Culture In Sufficient Quantity To Inoculate The Production
Vessel.
4 .The Growth Of The Organism In The Production Fermenter Under Optimum Conditions For Product
Formation.
5. The Extraction Of The Product And Its Purification.
6. The Disposal Of Effluents Produced By The Process.
- The fermenting microorganisms mainly involve L.A.B. like Enterococcus, Streptococcus, Leuconostoc,
Lactobacillus, and Pediococcus and yeasts and molds like Debaryomyces, Kluyveromyces,
Saccharomyces, Geotrichium, Mucor, Penicillium, and Rhizopus species.
5.
6. A TYPICAL INDUSTRIAL FERMENTER
• Fermenter Or Bioreactor Refers To A Device That Provides All The Basic Necessities Important For
Biological Product Extraction. All Bioreactors Deal With Heterogeneous Systems Dealing With Two Or
More Phases, E.G., Liquid, Gas, Solid. Therefore, Optimal Conditions For Fermentation Necessitate
Efficient Transfer Of Mass, Heat And Momentum From One Phase To The Other. Chemical Engineering
Principles Are Employed For Design And Operation Of Bioreactors.
• The Main Objective Of A Fermenter Is To Maintain A Controlled Environment That Supports The Growth
Of The Bacteria Or Any Other Organism. There Are Several Important Factors That Need To Be Accurate
To Design A Fermenter. Those Factors Are Following-
• The vessel should be well equipped to maintain aseptic conditions inside it for a number of days.
• Aeration and agitation are important for the production of biological metabolites. However, controlled
agitation is required to prevent any damage to the cells.
• It should be less expensive in terms of power consumption.
• Temperature is an important environmental factor required for microbial growth. Therefore, a temperature
control system is required.
• Optimum pH is important for the growth of the organism; therefore, the fermenter must be equipped with
a pH controller.
7. • The Fermentation Of A Huge Culture Is A Time-consuming Process. It Needs To Be Contamination-
free Until The Process Is Complete. Apart From That, It Is Also Important To Monitor The Growth
Rate Of The Organism. Therefore, An Aseptic Sampling System Is Needed To Design A Fermenter.
• The Fermenter Vessel Should Be Designed Properly To Minimize The Labor Involved In Cleaning,
Harvesting, Etc.
• It Should Be Designed In Such A Way That It Reduces Evaporation.
• The Vessel Needs To Be Equipped With A Smooth Internal Surface To Support Adequate Mixing.
CONSTRUCTION MATERIALS
As Fermentation Required Adequate Aseptic Conditions, For Better Yield Of Biomass Or Product, It Is
Important To Select A Material For The Body Of The Fermenter, Which Restricts The Chances Of
Contamination. Moreover, It Needs To Be Non-toxic And Corrosion Free. Glass Is A Material That
Provides A Smooth Surface Inside The Vessel And Also Non-toxic In Nature. Apart From That, It Is
Corrosion-proof And Due To The Transparency, It Is Easy To Examine The Inside Of The Vessel. The
main disadvantage of glass vessels is that it is difficult to top to design a pilot-scale fermenter with
glass. It is difficult to handle glass as a pilot-scale fermenter. Therefore, another non-toxic, corrosion-
proof material, stainless steel, was used for pilot scale fermenter. According to Americal Iron and Steel
Institute, steel contains more than 4% chromium is standardized as stainless steel.
8. • In Many Cases Nickel Is Also Mixed In High Concentration With The Chromium To Make The Steel
More Corrosion Resistant And It Also Provides Engineering Advantages. In This Modern-day, Stainless
Steel Fermenters Are Mostly Used For Industrial Production. However, Small Scale Production
Requires Glass Vessels.
Aeration System:
• Aeration system is one of the most critical part of a fermenter. In a fermenter with a high microbial
population density, there is a tremendous oxygen demand by the culture, but oxygen being poorly
soluble in water hardly transfers rapidly throughout the growth medium.
• It is necessary, therefore, that elaborate precautions are taken using a good aeration system to ensure
proper aeration an oxygen availability throughout the culture. However, two separate aeration devices
are used to ensure proper aeration in fermenter. These devices are sparger and impeller.
SPARGER
• A sparger is a device that introduces air into the liquid medium in a fermenter. There are three main
types of SPARGER used in industrial-scale bioreactors such as
9. • POROUS SPARGER: It Is Made Up Of Sintered Glass, Ceramics Or Metals’ And Are Mostly Used In
Laboratory-scale Bioreactors. As It Introduces Air Inside A Liquid Medium, Bubbles Are Formed.
These Bubbles Are Always 10 To 100 Times Larger Than The Pore Size Of The Aerator. The Air
Pressure Is Generally Low In These Devices And A Major Disadvantage Of Using Porous Sparger Is
That Microbial Growth May Occur On The Pores Which Hamper The Airflow.
• ORIFICE SPARGER: These Are Used In Small Stirred Fermenters Where Perforated Pipes Are Used
And Attached Below The Impeller In The Form Of A Ring. The Air Holes Are Mostly Drilled Under The
Surface Of The Tubes. Orifice Spargers Were Used To A Limited Extent In Yeast Manufacture,
Effluent Treatment And Production Of Single-cell Proteins.
• NOZZLE SPARGER: This Is Used In Industrial-scale Fermenters. The Main Characteristic Of This
Kind Of Sparger Is That It Contains A Single Open Or Partially Closed Pipe As An Air Outlet. The Pipe
Needs To Be Positioned Below The Impeller. The Design Helps To Overcome Troubles Related To
Sparger Blockage.
11. TEMPERATURE CONTROL SYSTEM
• During The Fermentation Process Heat Can Be Produced Mainly In Two Ways, Firstly Microbial
Biochemical Reactions And Secondly Mechanical Agitation. In Case Of Fermentation, A
Temperature Control Helps To Control The Temperature At The Optimum Level By Removing Or
Providing Heat. In Small Scale Production Vessel The Amount Of Produced Heat Is Negligible.
Therefore, Extra Heat Is Provided By Hot Bath Or Internal Heat Coil Or Heating Jacket With A
Water Circulation System Or Silicon Heating Jacket. The Silicon Heating Jacket Consists Of Silicon
Rubber Mats With Heating Wires And It Is Wrapped Around The Fermenter. In The Case Of Pilot-
scale Fermenters, It Is Not Possible To Use Silicon Jackets Due To Large Size. In Such Cases, An
Internal Heating Coil Is Used For Providing Extra Heat While Cold Water Circulation Helps To
Remove Excess Heat.
• Cooling jacket is necessary because sterilization of the nutrient medium and removal of the heat
generated are obligatory for successful completion of the fermentation in the fermentor. For very
large fermentors, insufficient heat transfer takes place through the jacket and therefore, internal
coils are provided through which either steam or cooling water is run.
12. a) External jacket
b) External coil for
Small bioreactors
c) Internal helical
coil
d) Internal baffles
coil for large
reactors
e) External separate
heat exchange unit
TEMPERATURE CONTROL SYSTEM OF FERMENTERS
13. IMPELLER
• The Objectives Of The Impeller Used In Fermenters Are Bulk Fluid And Gas Mixing, Air
Dispersion, Heat Transfer, Oxygen Transfer, Suspension Of Solid Particles, Maintain The Uniform
Environment Inside The Vessel, Etc. Air Bubbles Often Cause Problems Inside The Fermenter.
Impellers Involved In Breaking The Air Bubbles Produced In A Liquid Medium. There Are Mainly
Three Types Of Agitators Used In Industrial-scale Bioreactors
• Disc Turbine: It Consists Of A Disc With A Series Of Rectangular Vanes Connected In A Vertical
Plane Around The Disc.
• Vaned Disc: In This Case, The Rectangular Vanes Are Attached Vertically To The Underside Of A
Disc.
• Variable Pitch Open Turbine: This Type Of Agitator Lacks Disc And The Vanes Are Directly
Connected To A Center Shaft.
14. BAFFLES
• The Baffles Are Normally Incorporated Into Fermenters Of All Sizes To Prevent A Vortex And To Improve
Aeration Efficiency. They Are Metal Strips Roughly One-tenth Of The Fermenters Diameter And Attached
Radially To The Walls. There are four baffles that are present inside of an agitated vessel to prevent a
vortex and improve aeration efficiency. The agitation effect is slightly increased with wider baffles but drops
sharply with narrower baffles. After installation of the baffle there a gap between them and the vessel wall
which facilitates scouring action around the baffles and minimizes microbial growth on the baffles and the
fermenter wall. Baffles are often attached to cooling coils to increase the cooling capacity of the fermenter.
STIRRERS GLANDS
The most important factor of designing a fermenter is to maintain aseptic conditions inside the vessel. It is
highly challenging in the case of pilot-scale fermenters. Therefore stirrer shafts are required. These stirrer
shafts play an important role to seal the openings of a bioreactor. As a result, it restricts the entry of air from
outside. There are several types of seals used for this purpose, which are following
The Stuffing Box: The shafted is sealed by several layers of packing rings of asbestos or cotton yarn which is
pressed against the shaft by gland follower. At high stirrer speeds, the packing wears quickly and excessive
pressure may need to ensure the tightness of fit. The packing may be difficult to sterilize properly because of
unsatisfactory heat penetration and it is necessary to check and replace the packing rings regularly.
15. • The Mechanical Seal: It Is Used In Both Small Scale And Large Scale Fermenters. The
Seal Is Divided Into Two Parts, First Is The Stationary Bearing Housing And The Second
Rotates On The Shaft. These Two Parts Are Pressed Together By Springs. Steam
Condensate Is Used To Lubricate And Cool The Seals During Operation And Provides
Protection Against The Contamination.
• Magnetic Drives: This Type Of Seals Helps To Counter The Problem Originated By The
Impeller Shaft Which Is Going Through The Top Or Bottom Of The Fermenter Plate. The
Magnetic Drive Is Made Up Of Two Magnets One Is Driving And One Driven. The Driven
Magnet Held In Bearings In Housing On The Outside Of The Head Plate And Connected To
A Drive Shaft. The Internal Driven Magnet Is Placed On One End Of The Impeller Shaft And
Held In Bearings In A Suitable Housing On The Inner Surface Of The Head Plate. When
Multiple Ceramic Magnets Have Been Used It Has Been Possible To Transmit Power Across
A Gap Of 16mm. Using This Drive Water Can Be Stirred In Baffled Vessels Up To 300 Dm3
Capacity At Speeds Of 300 To 2000 Rpm.
16. PH SENSOR
• All Types Of Fermenters Are Attached With A Ph Control Sensor Which Consists Of A Ph Sensor And
A Port To Maintain The Ph Inside Of The Fermenter. Ph Alteration Can Lead To Death Of The
Organism Which Leads To Product Loss. Therefore, It Is A Crucial Instrument For A Fermenter And
Needs To Be Checked Regularly.
Controlling Devices for Environmental Factors:
• In any microbial fermentation, it is necessary not only to measure growth and product formation
but also to control the process by altering environmental parameters as the process proceeds. For
this purpose, various devices are used in a fermenter. Environmental factors that are frequently
controlled includes temperature, oxygen concentration, pH, cells mass, levels of key nutrients, and
product concentration.
18. INTRODUCTION
• In A Fermentation Process, The Choice Of The Most Optimum Micro-organisms And Fermentation
Media Is Very Important For High Yield Of Product. The Quality Of Fermentation Media Is Important
As It Provides Nutrients And Energy For Growth Of Micro-organisms. This Medium Provides
Substrate For Product Synthesis In A Fermenter.
• Detailed Investigations Are Required To Establish The Most Suitable Medium For An Individual
Fermentation. Most Fermentations Require Liquid Media, Often Referred To As Broth; Although
Some Solid Substrate Fermentations (SSF) Are Operated. Fermentation Media Must Satisfy All The
Nutritional Requirements Of The Microorganism And Fulfil The Technical Objectives Of The Process.
• Fermentation media consists of major and minor components.Major components include Carbon
and Nitrogen source. Minor components include inorganic salts, vitamins, growth factors, anti-
foaming agents, buffers, dissolved oxygen, other dissolved gases, growth inhibitors and enzymes.
Nutrients required for fermentation media also depend upon the type of fermentation organisms as
well as the type of fermentation process to be used. Poor choice of fermentation media might result
in poor yield of output. Types of nutrients present in the fermentation media always determine the
yield of the product.
19. • There Are Two Uses Of Fermentation Media
• Growth Media
• Fermentation Media
GROWTH Medium Contains Low Amounts Of Nutrients. It Is Useful In Creating Raw Material For
Further Fermentation Processes.
Fermentation Media Contains High Amounts Of Nutrients. It Is Used In Creating Final Products Using
Fermentation.
For Example, Growth Of Yeast Requires 1% Carbon. But During Fermentation Of Alcohol, Yeast
Requires 12 To 13 % Carbon In The Medium.
During the fermentation process, media contains high amounts of nutrients, micro-organism and
optimum conditions. When these micro-organisms are incubated at the desired optimum conditions,
they enjoy luxurious metabolism. Here, the fermentation organisms become hyperactive due to
presence of high quantities of nutrients, thus it results in consumption of excess nutrients and partial
degradation of fermentation media. The waste effluents excreted by the microbes could be the desired
output product of the fermentation process.
20. • The Amount Of Substrate Given To Microbes Should Not Reach Inhibitory Concentration Levels Because
Excess Substrate Inhibits Vital Enzymes And May Results In Death Of Cells. Also, Water Present In
Cytoplasm Is Important For Metabolism Process. If Excess Sugar Or Salt Is Available In The Fermentation
Media, It Would Tie Up Cytoplasm Water And May Result In Lack Of Water For Metabolism And Cause
Death Of Microbes, Thus Affecting Fermentation Output.
• Excess Substrate May Increase Osmotic Pressure And Effect Enzyme Activities In A Cell. Microbes Excrete
This Excess Substrate In The Form Of Partially Digested Fermentation Media. It Is Converted To An
Insoluble Inert Compound In The Form Of Reserve Food Material And This Reserve Food Material Is
Harmless To Cells.
• On a large scale one must use nutrient sources to create a medium which will meet as many of the
following criteria:
1 Produce the maximum yield of product or biomass per gram substrate used.
2 Produce the maximum concentration of product or biomass.
3 Permit the maximum rate of product formation.
4 Minimum yield of undesired product.
5 Consistent in quality and readily available throughout the year.
6 Cause minimal problems during media making and sterilization.
21. • 7 Cause Minimal Problems During Other Aspects Of The Production Process, Especially Aeration And
Agitation, Extraction, Purification And Waste Treatment.
• The Initial Step In Media Formulation Is The Examination Of The Overall Process Based On The Stoichiometry
For Growth And Product Formation. Thus For An Aerobic Fermentation:
CARBON & ENERGY + NITROGEN + O2 + OTHER REQUIREMENTS = BIOMASS + PRODUCTS +
CO2 + H2O + HEAT
TYPES OF MEDIA
There Are Two Types Of Fermentation Media Used In Industries.
1. Synthetic Media
2. Crude Media
22. SYNTHETIC MEDIA
• Synthetic Media Is Useful In The Field Of Research As Each And Every Component Is Chemically
Known And The Exact Composition Of Nutrients Is Predetermined. So, In Case Of Synthetic Media,
Variation In Levels And Concentration Of Nutrients Can Be Controlled. Here, By Experimentation
With Synthetic Media, The Effect Of Nutrients On Growth And Yield Of Product Can Be Analysed. We
Can Redesign The Synthetic Media As Per Our Needs. It Is Very Useful In Controlling The Growth
And Yield Of Product In A Lab Environment. We Can Also Use It To Determine The Metabolic
Pathway Used In The Synthesis Of Products.
• The Use Of Synthetic Media Allows Us To Experiment With Various Sources Of Fermentation Media
In The Lab As The Results Are Accurately Reproducible For A Given Composition. An Advantage Of A
Well Designed Synthetic Media Is That It Lacks Sources Of Protein And Peptides. Hence, There Is No
Foam Formation, And Chances Of Contamination Are Very Less. Product Recovery Is Easier Because
Synthetic Media Contains Pure Components.
• The most important aspect of fermentation is that it should be economic and profitable. Synthetic
media is never used on industrial scale because it is expensive, the major disadvantage .This process
in only suitable for experimentation in a lab on a small scale
23. CRUDE MEDIA
• Crude Media Is Generally Used On An Industrial Scale For Fermentation Process. Crude Media
Contains A Rough Composition Of Media Required For Fermentation. It Gives High Yield Of Product
And Contains Undefined Sources Of Ingredients. Crude Media Contains High Level Of Nutrients,
Vitamins, Proteins, Growth Factors, Anti-foaming Agents And Precursors. It Is Important To Ensure
That Crude Media Should Not Contain Toxic Substances That Could Effect The Growth Of Bacteria
And Yield Of Product.
• Crude substrates may provide initial cost savings, but their higher levels of impurities could
necessitate more costly and complex recovery and purification steps downstream as well as
increased waste treatment costs. The physical and chemical properties of the formulated medium
can also influence the sterilization operations employed. A medium that is easily sterilized with
minimal thermal damage is vitally important.
• Ingredients of Crude Media
1) Inorganic nutrients - Crude media contains inorganic salts containing cations and anion along
with a carbon source. Sometimes, fermentation micro-organisms have a specific requirement of ions
like magnesium ions, phosphates or sulphates. These requirements are fulfilled by addition of these
ions to balance the crude media.
24. • Carbon Sources - A Carbon Source Is Required For All Biosynthesis Leading To Reproduction,
Product Formation And Cell Maintenance. In Most Fermentations It Also Serves As The Energy
Source. Simple To Complex Carbohydrates Can Be Added To Media As A Source Of Carbon. The
Selection Of Carbon Source Depends Upon The Availability As Well As The Cost Of Raw Material. In
Most Of The Fermentation Media, Crude Source Of Carbon Is Added.
• Substrates Used As Carbon Sources: Carbohydrates Constitute The Most Predominant Source Of
Energy In Fermentation Industry. Refined And Pure Carbohydrates Such As Glucose Or Sucrose
Are Rarely Used For Economic Reasons.
• Molasses: Molasses Is A Byproduct Of Sugar Industry And Is One Of The Cheapest Sources Of
Carbohydrates. Sugar Cane Molasses (Sucrose Around 48%) Sugar Beet Molasses (Sucrose Around
33%) Are Commonly Used. Besides Being Rich In Sugar, Molasses Also Contain Nitrogenous
Substances, Vitamins And Trace Elements. There Occurs Variation In The Composition Of The
Molasses Which Mostly Depends On The Climatic Conditions And Production Process. Hydrol
Molasses, A Byproduct In Glucose Production From Corn, Is Also Used As A Fermentation
Substrate.
25. • Malt Extract: Malt Extract, An Aqueous Extract Of Malted Barley, Contains About 80% Carbohydrates
(Glucose, Fructose, Sucrose, And Maltose). Nitrogen Compounds Constitute Around 4.5% (Proteins, Peptides,
Amino Acids, Purines, Pyrimidine’s). Aqueous extracts of malted barley can be concentrated to form syrups
that are particularly useful carbon sources for the cultivation of filamentous fungi, yeast and actinomycetes.
• Starch, Dextrin And Cellulose: The Polysaccharides-starch, Dextrin And Cellulose Can Be Metabolised By
Microorganisms. They Are Frequently Used For The Industrial Production Of Alcohol. Due To Its Wide
Availability And Low Cost, The Use Of Cellulose For Alcohol Production Is Extensively Studied.
• Whey: Whey is a byproduct of dairy industry and is produced worldwide. Most of it is consumed by- humans
and animals. Whey is a reasonably good source of carbon for the production of alcohol, single-cell protein,
vitamin B12, lactic acid and gibberellic acid. Storage of whey is a limiting factor for its widespread use in
fermentation industry.
• Cellulose : Cellulose is predominantly found as lignocellulose in plant cell walls, which is composed of three
polymers: cellulose, hemicellulose and lignin. Lignocellulose is available from agricultural, forestry, industrial
and domestic wastes. Relatively few microorganisms can utilize it directly, as it is difficult to hydrolyze. The
cellulose component is in part crystalline, encrusted with lignin and provides little surface area for enzyme
attack. At present it is mainly used in solid-substrate fermentations to produce various mushrooms.
However, it is potentially a very valuable renewable source of fermentable sugars once hydrolyzed,
particularly in the bioconversion to ethanol for fuel use.
26. • Fats And Oils : Hard Animal Fats That Are Mostly Composed Of Glycerides Of Palmitic And Stearic
Acids Are Rarely Used In Fermentations. However, Plant Oils (Primarily From Cotton Seed, Linseed,
Maize, Olive, Palm, Rape Seed And Soya) And Occasionally Fish Oil, May Be Used As The Primary Or
Supplementary Carbon Source, Especially In Antibiotic Production. Plant Oils Are Mostly Composed
Of Oleic And Linoleic Acids, But Linseed And Soya Oil Also Have A Substantial Amount Of Linolenic
Acid. The Oils Contain More Energy Per Unit Weight Than Carbohydrates.
• Methanol And Ethanol: Some Of The Microorganisms Are Capable Of Utilizing Methanol And Or
Ethanol As Carbon Source. Methanol Is The Cheapest Substrate For Fermentation. However, It Can
Be Utilized By Only A Few Bacteria And Yeasts. Methanol Is Commonly Used For The Production Of
Single-cell Protein. Ethanol Is Rather Expensive. However, At Present It Is Used For The Production
Of Acetic Acid.
27. • Nitrogen Source - Salts Of Urea, Ammonia, And Nitrate Can Be Used As A Nitrogen Source. When
Fermentation Organisms Are Non-proteolytic In Nature, Pure Form Of Urea, Ammonia And Nitrate
Are Used As A Source Of Nitrogen. When Fermentation Organisms Are Proteolytic In Nature, Animal
And Plant Raw Material Is Used; Like Distillery Dried Solubles, Casein, Cereal Grains, Peptones,
Yeast Extract, Hydrolysate, And Soybean Meal Etc.
• Substrates Used As Nitrogen Sources: The Nitrogen Supply To The Fermentation Microorganisms
May Come From Inorganic Or Organic Sources.
• Inorganic Nitrogen Sources: Ammonium Salts And Free Ammonia Are Cheap Inorganic Nitrogen
Sources, Particularly In Industrialised Countries. However, Not All The Microorganisms Are Capable
Of Utilizing Them, Hence Their Use Is Limited.
• Organic Nitrogen Sources: Urea Is Fairly A Good Source Of Nitrogen. However, Other Cheaper
Organic Forms Of Nitrogen Sources Are Preferred.
28. • Yeast Extracts: They Contain About 8% Nitrogen And Are Rich In Amino Acids, Peptides And
Vitamins. Glucose Formed From Glycogen And Trehalose During Yeast Extraction Is A Good Carbon
Source. Yeast Extracts Are Produced From Baker’s Yeast Through Autolysis (At 50-55°C) Or Through
Plasmolysis (High Concentration Of Nacl). Yeast Extracts Are Very Good Sources For Many
Industrially Important Microorganisms
• Corn Steep Liquor: This Is Formed During Starch Production From Corn. Corn Steep Liquor Is Rich
In Nitrogen (About 4%) And Is Very Efficiently Utilized By Microorganisms. It Is Rich In Several
Amino Acids (Alanine, Valine, Methionine, Arginine, Threonine, Glutamate).
• Peptones: The Protein Hydro-lysates Are Collectively Referred To As Peptones, And They Are Good
Sources For Many Microorganisms. The Sources Of Peptones Include Meat, Soy Meal, Peanut Seeds,
Cotton Seeds And Sunflower Seeds. The Proteins Namely Casein, Gelatin And Keratin Can Also Be
Hydrolysed To Yield Peptones. In General, Peptones Derived From Animal Sources Have More
Nitrogen Content While Those From Plant Sources Have More Carbohydrate Content. Peptones Are
Relatively More Expensive, Hence Not Widely Used In Industries.
29. • Soya Bean Meal - Residues Remaining After Soya Beans Have Been Processed To Extract The Bulk
Of Their Oil Are Composed Of 50% Protein, 8% Non-protein Nitrogenous Compound, 30%
Carbohydrates And 1% Oil. This Residual Soya Meal Is Often Used In Antibiotic Fermentations
Because The Components Are Only Slowly Metabolized, Thereby Eliminating The Possibility Of
Repression Of Product Formation.
• Water - All Fermentation Processes, Except SSF, Require Vast Quantities Of Water. Not Only Is Water
A Major Component Of All Media, But It Is Important For Ancillary Services Like Heating, Cooling,
Cleaning And Rinsing. A Reliable Source Of Large Quantities Of Clean Water, Of Consistent
Composition, Is Therefore Essential. Important Factors To Consider When Assessing Suitability Of A
Water Supply Are: Ph, Dissolved Salts And Effluent Contamination. The Mineral Content Is Important
In Brewing (Mashing Step) And Historically Influenced The Siting Of Breweries And Types Of Beer
Produced. Before Use, Removal Of Suspended Solids, Colloids And Microorganisms Is Usually
Required. When The Water Supply Is “Hard”, It Is Treated To Remove Salts Such As Calcium
Carbonate. Iron And Chlorine May Also Require Removal. For Some Fermentations, Notably Plant
And Animal Cell Culture, The Water Must Be Highly Purified. Water Is Becoming Increasingly
Expensive, Necessitating Its Recycling/Re-usage Wherever Possible. This Minimizes Water Costs And
Reduces The Volume Requiring Waste-water Treatment.
30. • Minerals: All Microorganisms Require Certain Mineral Elements For Growth And Metabolism. In
Many Media, Magnesium, Phosphorous, Potassium, Sulphur, Calcium And Chlorine Are Essential
Components And Must Be Added. Others Such As Cobalt, Copper, Iron, Manganese, Molybdenum
And Zinc Are Present In Sufficient Quantities In The Water Supplies And As Impurities In Other
Media Ingredients. For Example, Corn Steep Liquor Contains A Wide Range Of Minerals That Will
Usually Satisfy The Minor And Trace Mineral Needs. Occasionally, Levels Of Calcium, Magnesium,
Phosphorous, Potassium, Sulphur And Chloride Ions Are Too Low To Fulfil Requirements And
These May Be Added As Specific Salts.
• Growth Factors :Crude Media Constituents Provides Enough Amount Of Growth Factors So No
Extra Addition Of Growth Factor Is Required. If There Is A Lack Of Any Kind If Vitamins Or
Nutrients, Growth Factors Can Be Added To Media. Examples Are Yeast Extract, And Beef Extract.
• Precursors: Precursors are generally present in the media as crude constituents. Precursors are
added in the fermentation media at time of fermentation as it get incorporated in the molecules of
product without bringing any kind of change to the final product. This helps in improving yield and
quality of product. Sometimes, precursors are added in pure form depending upon the need of
product. For example, Cobalt chloride is added less than 10 ppm in fermentation of vitamin B12.
31. • Buffers :The Control Of Ph May Be Extremely Important If Optimal Productivity Is To Be Achieved. A
Compound Be Added To The Medium To Serve Specifically As Buffer, Or May Also Be Used As A
Nutrient Source. Many Media Are Buffered At About Ph 7.0 By The Incorporation Of Calcium
Carbonate (As Chalk). If The Ph Decreases The Carbonate Is Decomposed. Obviously, Phosphates
Which Are Part Of Many Media Also Play An Important Role In Buffering. However, High Phosphate
Concentrations Are Critical In The Production Of Many Secondary Metabolites . The Balanced Use Of
The Metabolic Is Carbon And Nitrogen Sources will Also form A Basis For Ph Control As Buffering
Capacity Can Be Provided By The Proteins, Peptides And AMINO Acids, Such As In Corn-steep
Liquor. The Ph May ALSO Be Controlled Externally By Addition Of Ammonia Or Sodium Hydroxide
And Sulphuric Acid .
• Precursors: Precursors are defined as “substances added prior to or simultaneously with the
fermentation which are incorporated without any major change into the molecule of the fermentation
product and which generally serve to increase the yield or improve the quality of the product”. They
are required in certain industrial fermentations and are provided through crude nutritive
constituents. Some fermentations must be supplemented with specific precursors, notably for
secondary metabolite production. When required, they are often added in controlled quantities and
in a relatively pure form, examples include, D-threonine is used as a precursor in L-isoleucine
production . The use of corn steep liquor as side-chain precursors in penicillin fermentations results
in six different Penicillin as opposed to the use of phenylacetic acid which results in mainly Penicillin
G formation.
32. • Inhibitors :A Specific Product Or Metabolic Intermediate Is Formed By The Addition Of Specific
Inhibitors To The Fermentation Earliest Substrate Includes Glycerol, Which Is Produced Due To The
Microorganisms. Glycerol Production Is Possible After Modification Of Ethanol By Removing
Acetaldehyde. Acetaldehyde Is Formed As Sodium Bisulfite Is Added To Broth. As Acetaldehyde Is
Replaced By Dihydro Acetone Phosphate As It Is No Longer Available For The Reoxidation Of
NADH2, Which Is Produced In Glycolysis Process. Product Of This Reaction(glycerol-3-phosphate) Is
Transformed Into Glycerol.
• Inducers And Elicitors :If Product Formation Is Dependent Upon The Presence Of A Specific
Inducer Compound Or A Structural Analogue, It Must Be Incorporated Into The Culture Medium Or
Added At A Specific Point During The Fermentation. The Majority Of Enzymes Of Industrial Interest
Are Inducible. Inducers Are Often Substrates Such As Starches Or Dextrins For Amylase. In Plant
Cell Culture The Production Of Secondary Metabolites, Such As Flavanoids And Terpenoids Can Be
Triggered By Adding Elicitors. These May Be Isolated From Various Microorganisms, Particularly
Plant Pathogens. Inducers Are Often Necessary In Fermentations Of Genetically Modified
Microorganisms. This Is Because The Growth Of Genetically Modified Microorganisms (Gmms) Can
Be Impaired When The Cloned Genes Are “Switched On”, Due To The Very High Levels Of Their
Transcription And Translation.
33. • Antifoams : Antifoams Are Necessary To Reduce Foam Formation During Fermentation. Foaming Is Largely Due To
Media Proteins That Become Attached To The Air-broth Interface Where They Denature To Form A Stable Foam
“Skin” That Is Not Easily Disrupted. If Uncontrolled The Foam May Block Air Filters, Resulting In The Loss Of
Aseptic Conditions; The Fermenter Becomes Contaminated And Microorganisms Are Released Into The
Environment. Of Possibly The Most Importance Is The Need To Allow “Freeboard” In Fermenters To Provide Space
For The Foam Generated. If Foaming Is Minimized, Then Throughputs Can Be Increased.
• Natural Antifoams Include Plant Oils (E.G., From Soya, Sunflower And Rapeseed), Deodorized Fish Oil, Mineral Oils
And Tallow. The Synthetic Antifoams Are Mostly Silicon Oils, Poly Alcohols And Alkylated Glycols. Since Antifoams
Are Of Low Solubility, They Need A Carrier, E.G., Lard Oil, Liquid Paraffin Or Castor Oil, Which May Be Metabolised
And Therefore Affect The Fermentation Process. Many Of The Surface-active Agents, Particularly The Oils, Are
Added As Emulsions Of Suspended Oil Droplets Which Can Destabilise The Foams By Acting As Hydrophobic
Bridges Between The Two Film Surfaces Or By Displacing The Stabilising Adsorbed Material, E.G. Protein, At The
Bubble–liquid Interface. However, Those Conditions, Which Cause Collapse Of The Foam Structure, Can Also Favor
The Coalescence Of Bubbles In The Body Of The Liquid.
34. • This Results In An Increase In The Mean Bubble Diameter And A Reduction In Gas Hold-up. Both
Of These Effects Will Tend To Reduce The Specific Interfacial Area Available For Mass Transfer. The
Concentrations Of Many Antifoams Which Are Necessary To Control Foaming May Reduce The
Oxygen Transfer Rate By As Much As 50%. Thus, Antifoam Addition Should Be Kept To An Absolute
Minimum. Some Antifoams May Reduce The Oxygen Transfer Rate As Well As Adversely Affect
Downstream Processing Steps, Especially Membrane Filtration. If The Oxygen Transfer Rate Is Too
Severely Affected Mechanical Foam Breakers May Have To Be Considered.
