Microbial Fermentation

Question 1

What is fermentation?

Answer 1

Fermentation is a metabolic process that produces chemical changes in organic substrates through action of enzymes.

Question 2

What is zymology

Answer 2

The science of fermentation

Question 3

What are the five major bio-ingredient categories the fermentation industry is composed of?

Answer 3

• Proteins & amino acids
• Organic acids
• Antibiotics
• Enzymes
• Vitamins/ hormones

Question 4

What is the fermentation industry driven by?

Answer 4

• The cost and availability of feedstocks
  -The efficiency of industrial microorganism
  -Fermentation condition and optimization
  -Down stream process and end-product recovery efficiency
• Fermentation by-product utilization
  -Utility consumption and labor cost.

Question 5

Fermentation media compositions

Answer 5

• Carbon source
• Nitrogen source
• Minerals
• Growth factors
• Precursors (mutants)

Optimum balance of the media is mandatory for cells propagation and for the maximum production of target metabolite (end-product).

Question 6

What are the two main types of fermentation

Answer 6

• Solid state fermentation
• Liquid state fermentation (Surface culture & submerged culture)

Question 7

What are the other types of fermentation

Answer 7

• Alcoholic fermentation using yeast to make alcoholic beverages
  -Lactic acid fermentation using lactic acid bacteria to produce lactic acid
• Acetic Acid fermentation using acetic acid bacteria to produce acetic acid
• Alkaline fermentation using mainly Bacillus species to produce amino acids.

Question 8

What is solid state fermentation

Answer 8

• It is defined as microbial growth on particles without presence of free water.
• These particles are solid culture substrate such as rice or wheat bran saturated with water and inoculated with (mold, yeast, bacteria) in controlled room temperature.

Question 9

Advantages of Solid state fermentation

Answer 9

• Employs simple natural solids as the media.
• Ideal for growing filamentous fungi
• More cost effective (smaller vessels low water consumption, reduced waste water treatment costs, lower energy consumption and less contamination problems).
• Low technology, low energy expenditure requires less capital investment.
• No need for sterilization, less microbial contamination and easy downstream processing.
• The yield of the products is reasonably high.

Question 10

Solid state fermentation process

Answer 10

1. Pre-treatment of substrate raw materials either by mechanical, heat chemical or biochemical processing to enhance the availability of the bound nutrients and reduce size of components.
2. Hydrolysis of primarily polymeric substrates
3. Solid Fermentation of hydrolysis products (Stirring, aeration)
4. Separation and purification of end products.

Question 11

Applications of solid state fermentation

Answer 11

• Potentially many high value products such as extra-cellular enzymes, primary metabolites, and antibiotics could be produced in SSF
• It is estimated that nearly a third of industrial enzyme produced is made by SSF process.
• Production of organic and ethanol from starchy substrates
• Digestibility of fibers and lignocelluloses materials for both human and animal consumption.

Question 12

Liquid State fermentation/ Submerged culture

Answer 12

• Cultivation approach that is primarily based upon the culture media comprising high water content by using the bioreactors.
• Submerged culture is performed in tanks which can reach in size 100,000 gallons.
• Ideal for growing unicellular organisms such as bacteria and yeast.

Question 13

What are the LSF methods

Answer 13

• Batch fermentation
• Fed-batch fermentation
• Continuous fermentation
• Semi-continuous fermentation

Question 14

Difference between solid state and submerged

Answer 14

Essay question

Question 15

Batch fermentation

Answer 15

• Closed system
• The sterilized media in the fermenter is inoculated with the microorganism.
• Incubation is allowed under the optimum conditions (aeration, agitation, temperature).
  -During entire fermentation nothing is added except air, antifoam and acid/base.

Question 16

Briefly explain the production of penicillin via batch fermentation

Answer 16

1) Penicillium mold produces the antibiotic penicillin
2) Scientists grow mold in deep batch fermenters by adding sugar and other key ingredients.
3) Scientists separate the penicillin from the mold
4) Penicillin is purified for use as an antibiotic medicine

Question 17

What is fed-batch fermentation

Answer 17

• It is a enhancement of batch fermentation.
• Nutrients are continuously added in a small doses during the fermentation.
• The method in controlling nutrients feeding process is by measuring methods.
• The main advantage: Elimination of catabolite repression (feed-back inhibition).

Question 18

Typical growth curve consists of following stages

Answer 18

• Lag phase
• Acceleration phase
• Log/exponential phase
• Deceleration phase
• Stationary phase
• Death phase

Question 19

What is continuous fermentation

Answer 19

• It is an open system
• Continuously sterile nutrient is added and the converted nutrient is taken out from the fermenter.
• In continuous process cell loss as a result of outflow must be balanced by growth of the microorganism.

Question 20

Important factors for continuous fermentation

Answer 20

• The system must be stable for at least 500 hours.
• Maintaining sterile conditions for all period of fermentation time
• The composition of nutrients must be constant all the time
• Maintaining the strain stability for constant high production yield (concerning about reverse mutation)

Question 21

What is semi-continuous fermentation

Answer 21

In which a fraction of fermentation is replaced with fresh media at regular intervals.

Question 22

What are the three main basic different types of fermentation

Answer 22

1) Lactic acid fermentation: When yeasts and bacteria convert starches or sugars into lactic acid in foods like pickles and yogurt.
2) Ethyl alcohol fermentation: Pyruvate molecules in starches or sugar are broken down by yeasts into alcohol and carbon dioxide molecules to produce wine and beer.
3) Acetic acid fermentation: Starches or sugars from grains or fruit into sour tasting vinegar and condiments.

Question 23

Difference between microbial fermentation and mammalian culture

Answer 23

Essay question