State all the advantages of fermentation (>6).
- Preservation: Organic acids, bacteriocins, alcohols, etc make environment unfavorable for MO growth
- Increase nutritional value: MO may produce essential vitamins, amino acids and fatty acids which improve the overall nutritional value of the food.
- Improve flavors, aromas and textures: Production of organic acids, alcohols, flavor compounds like diacetyl and acetaldehyde can provide unique flavors to the food.
- Improve digestibility: Fermenting MOs may contain enzymes that are absent in human such as cellulase, pectinase, lactase and breakdown starchy foods to allow absorption in the gut. Lactic acid fermentation also helps in lactose digestion.
- General health benefits: Anti-inflammatory properties, improve gut health, anti-cancer, cholesterol lowering, inhibition of pathogenic bacteria adhesion.
- Removal of naturally occurring toxin and anti-nutritional substances
What are the differences between industrial and traditional fermentation?
Industrial:
- Starter cultures that have been standardized and cultured are used
- Fermentation mode can be batch, fed-batch or continuous
- Low variation in between different production batches
- Strict control on fermentation parameters such as pH, temperature, oxygen supply etc.
- Uses complex, industrial scale equipment & bioreactors
- High production yield
Traditional fermentation:
- Fermentation occurs via spontaneous fermentation or back-slopping.
- Batch fermentation mode
- Variation in between different batches are common
- Less control on fermentation parameters
- Uses simple equipment such as jars, flip-top bottles etc.
- Low production yield
What are the different types of fermentation available? State their applications.
- Lactic acid fermentation: Yoghurt, a product of lactic acid fermentation of milk.
- Alcoholic fermentation: Beer, a product of alcoholic fermentation of malted barley.
- Acetic acid fermentation: Acetic acid bacteria converts ethanol from alcoholic liquids into acetic acid.
- Fermentation yielding meat-like texture: Tempeh, fermented soybeans that has a firm texture and often used as a meat substitute.
Compare between stirred tank, airlift and fluidized bed bioreactors.
Stirred tank
- Uses an agitator for mixing and distributing nutrients
- Excessive foam formation
- Not suitable for shear-sensitive cells
- Higher risk of contamination because more valves are required
Air-lift
- Gas distributor pumps air from the bottom of the tank through the liquid to mix the nutrients
- Simple, low risk of contamination
- Increased oxygen solubility
- High power consumption
- High capital investment
Fluidized bed
- For cells that have been immobilized onto particulate matter
- Suitable for shear sensitive cells.
- Good mixing and medium distribution
- High pumping cost and leakage
- Carrier abrasion and damage.
Compare between submerged and solid state fermentation.
Submerged:
- Medium contains high water activity
- Better mixing and medium distribution
- Rheological problems at high substrate concentrations
- Slow mass transfer from gas to liquid phase
- Complex control: pH, temperature, substrate concentration, aeration, growth rate.
Solid state fermentation:
- Solid, low moisture content medium
- Less contamination
- No processing of raw material required
- Low power consumption
- Simpler control
- Cannot be done continuously
State the problems and solutions associated with fermenting pickles.
Bloating: N2 purging
Softening in defective pickle: Use chlorinated, acidified brine added with sodium acetate; add P. cerevisiae and L. plantarum
Growth of oxidative yeast: Use aerobic tank
Liquefaction: Use young cucumbers
State the problems and solutions associated with fermenting kimchi.
Unacceptable flavor and color: Decrease salt conc (<5%)
Acidic and soft: Increase salt conc (2-3%)
State the problems and solutions associated with fermenting olives.
Bitterness: Soak in lye to remove oleuropein
State the problems and solutions associated with frying carrots.
High reducing sugar content: Reduce with LAB fermentation
