C2 Fermentation Technology Flashcards

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1
Q

What are the three main processes in an industrial scale fermentation?

A
  1. Upstream processing
  2. Fermentation process
  3. Downstream processing.
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2
Q

Describe the three types of fermentation medium.

A
  • Defined medium: Medium composed of pure ingredients in measured concentrations.
  • Complex medium: Composed of substrates with undefined composition. Rich in nutrients.
  • Technical medium: Cheap, complex substrates such as barley, malt, molasses etc.
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3
Q

State the four criteria for choosing an industrial fermentation medium.

A
  • Maximum yield
  • Minimum undesirable metabolites.
  • Consistent quality
  • Minimal problems during sterilization and fermentation.
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4
Q

How can a medium be sterilized?

A
  • High temperature
  • Membrane filtration
  • Microwave irradiation
  • High voltage pulses
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5
Q

What is used as the indicator for complete sterilization?

A
  • Endospores
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6
Q

Compare between batch sterilization and continuous sterilization.

A

Batch:
- Medium go through the heating, holding and cooling cycles as batches.
- Low capital, low risk of contamination, easier to control and suitable for media containing high amount of solids.

Continuous:
- Consist of heat exchangers and a holding section to maintain the medium at sterilization temperature.
- Energy efficient, low nutrient degradation.
- In efficient sterilization due to the presence of solids.

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7
Q

What type of filter is used for the sterilization of air?

A
  • PTFE (Polytetrafluoroethylene, Teflon) membrane
  • 0.2-0.01um pore size
  • Hydrophobic and water resistant.
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8
Q

What are the differences between seed fermenter and production fermenter?

A
  • Seed fermenter is for growing the starter culture (inoculum) while the production fermenter is for producing the product.
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9
Q

What are the factors to be considered for selecting a microorganism for industrial scale fermentation?

A
  • Nutritional requirement
  • Optimum temperature of microorganisms
  • Equipment and process requirement of the microorganism
  • Stability of organism
  • Productivity of the organism
  • Ease of product recovery
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10
Q

How can inoculum be added for fermentation?

A
  • Spontaneous fermentation: Fermentation by indigenous microflora of pre-treated raw materials.
  • Back-slop fermentation: Inoculation of part of a fermented product from previous batch
  • Addition of starter culture: Indigenous microflora is inactivated prior to addition.
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11
Q

Compare the two types of fermentation

A

Submerged fermentation:
- Rheological problem at high substrate conc. (Difficult to flow)
- Slow mass transfer from gas to liquid.
- Better mixing.
- Prone to contamination

Solid state fermentation:
- Solid substrates, no processing of raw materials required.
- Less contamination, lower power consumption.

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12
Q

Compare the three modes of fermentation.

A

Batch fermentation:
- Fermenter is filled with substrates and added with inoculum. After some time, products are drawn off and fermenter is sterilized for the next batch.

Fed-batch fermentation:
- Cells are grown under batch regime, the reactor is fed with substrates without removing culture fluid.
- Balanced feed keeps the desired specific growth rate.

Continuous fermentation:
- Cells are maintained in a state of balanced growth where substrate are added and products are removed constantly.
- Rate of adding fresh medium = Rate of removing culture medium.

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13
Q

Compare the two types of continuous fermenter.

A

Chemostat:
- Fresh medium is continuously added while culture liquid are removed at the same rate. Culture volume is constant

Auxostat:
- Uses feedback from a measurement taken on the growth chamber to control the media flow rate. (e.g. pH auxostat)

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14
Q

Describe the cell productivity in a continuous fermentation system.

A
  • Amount of cells increase when the amount of feed increases.
  • When Dmax (Maximum dilution) is reached, cell will not grow faster because steady-state equilibrium is reached.
  • After dilution rate exceeding Dmax, cell concentration decrease. There will be a steep increase in substrate concentration as there are fewer cells to utilize it.
  • At some point, cells will be washed out, the feed will have diluted the reactor to the point where no cells are left.
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15
Q

Describe the parts of a fermenter and their uses.

A

“MIB WISPOR”

Motor: Powers the impeller
Impeller: Mixes the contents of the fermenter
Baffles: Prevents formation of vortex

Water jacket: Controls the temperature
Inlets: Addition of nutrients and other substances
Sparger: Adds oxygen to the liquid
Probes: Measure and monitor various parameters such as pH and temperature
Outlets: Allow for the removal of samples and the final product
Rakes: Suppress foam.

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16
Q

Compare the different types of bioreactors.

A

Stirred tank bioreactor:
- Agitator mixes the medium.
- High oxygen transfer rate and low cost.

Air lift bioreactor:
- No impeller, mixing is done by air.
- Low risk of contamination, lower shear stress, increased oxygen solubility,
- High power consumption, excessive foaming, cell damage from bubbles bursting.

Fluidized bed bioreactor:
- For cells that have been immobilized onto particulate matter
- Suitable for shear sensitive cells, good mixing, high density particles can be used
- Carrier abrasion and damage, high pumping costs and leakage.

17
Q

What are the variables to be controlled during fermentation?

A

Physical variables:
Temp, impeller speed, aeration rate, pressure

Chemical variables:
pH, dissolved oxygen & CO2, redox potential

Biological variables:
Biomass, oxygen uptake rate, CO2 production rate and respiration quotient.

18
Q

What is respiration quotient?

A

The ratio between CO2 production rate and oxygen uptake rate. (CPR/OUR)

19
Q

What are the four processes of product (fermented) recovery and purification?

A

SDCC
- Cell separation
- Cell disruption
- Clarification
- Concentration

20
Q

Describe cell disruption and provide some examples of the methods for cell disruption.

A

Cell disruption is a method to break open the cell to extract the intracellular metabolites/products. Some cell disruption methods include:
- Freeze-thaw: Cycling between dry ice and 37C water bath
- High pressure homogenization: High pressure forces cells through a small gap causes shear and cavitation which disrupts cell walls & membranes.
- Sonication: Use of ultrasound
- Detergent lysis: Use of non-ionic detergent such as tween, triton etc.
- Solid shear: French press and hughes press

21
Q

What are some method of cell separation?

A
  • Settling
  • Centrifugation
  • Dead-end filtration
  • Cross-flow filtration
22
Q

Compare between dead-end filtration and crossflow filtration.

A

Dead-end filtration:
- Suitable when amount of particles to be removed is low
- Low cost
- Susceptible to clogging

Crossflow filtration:
- Suitable when amount of particles to be removed is high
- Higher cost
- Less susceptible to clogging.

23
Q

Based on size exclusion, the types of filtration process can be classified as?

A
  • Reverse Osmosis
  • Nanofiltration
  • Ultrafiltration
  • Microfiltration