The controlled action of selected microorganisms

   Treat waste
–   Production of new products
–   Helps preserve foods
–   Alter texture of foods

Main advantages

• Lower energy consumption 
• Generally simple technology
• High efficiency
• Environmental friendly

Microorganisms used in fermentation








Factors that control the growth of MO in food fermentation

Intrinsic factors

•Parameters that are an inherent part of the medium and can alter MO growth

Extrinsic factors

•Properties of the storage environment that affect the growth of MO

Intrinsic factors

•Nutrient content 
•Substrate pH 
•Redox Potential 
•Water activity

Extrinsic factors

•Storage temperature 
RH of environment 
•Presence of other MO


• A bioreactor is a reactor system used for the culture of microorganisms.
•They vary in size and complexity from a 10 ml volume in a test tube to computer controlled fermenters with liquid volumes greater than 100 m3.

Types of Bioreactors

•Continuous fermentations•Batch fermentations

Some examples for bioreactors 

•Standing cultures
Shake flasks
•Stirred tank reactors 
•Bubble column and airlift reactors
•Fluidized bed reactors 

Standing cultures

•Large Pyrex flasks are used for the small  scale production of fermented products. 

Standing cultures - Surface cultures

•The Aspergillus niger mycelia are grown on the surface of liquid media in large shallow trays.
•The solids may be continuously or periodically turned over to improve aeration and to regulate the culture temperature. One example of a commercial scale, solid substrate fermentation is the production of koji by Aspergillus oryzae on soya beans which is part of the soya sauce process.

Shake flasks

•Shake flasks are commonly used for small scale cell cultivation. Through continuous shaking of the culture fluid, higher oxygen transfer rates can be achieved as compared to standing cultures. Shaking continually breaks the liquid surface and thus provides a greater surface area for oxygen transfer. Increased rates of oxygen transfer are also achieved by entrainment of oxygen bubbles at the surface of the liquid.

•Although higher oxygen transfer rates can be achieved with shake flasks than with standing cultures, oxygen transfer limitations will still be unavoidable particularly when trying to achieve high cell densities.

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