第四章 发酵过程控制 发酵工艺

Measurement of Cell Mass
➢ Dry weight- time consuming and not very sensitive ➢ Turbidimetric measures- quick, easy and sensitive
➢optical density the number of microbes ➢E. coli, 1 OD600 = ~ 8 x 108 cells/ml
All the nutrients needed for cell growth will only be added once at the beginning of fermentation.
Batch Fermentor
Advantages ➢ Optimum levels of product recovery ➢ Simple operation
It can be controlled in two ways
1.Turbidostatic control (internally controlled) 2.Chemostatic control (externally controlled)
The Turbidostat
➢Regulates the flow rate of media through vessel to maintain a predetermined turbidity ➢Maintain the highest growth rate ➢No limiting nutrient
The Chemostat
➢ Rate of incoming medium = rate of removal of medium from vessel
➢ Maintain the exponential growth phase ➢ An essential nutrient is in limiting quantities
Measurement of the changes in number of cells or mass of population.
Measurement of Cell Numbers
➢Direct cell counts - counting chambers ➢Viable cell counts - plating methods
➢Cells are most susceptible to adverse environmental factors (e.g. radiation, antibiotics)
Stationary Phase
➢ Population size begins to stabilize
Number of cells produced = Number of cells dying
Chapter 4 Fermentation Monitoring
Common Features of a Fermentor
➢A large vessel ➢Made of stainless steel ➢Equipped with 来自百度文库emperature,
pH and dissolved oxygen measurement and control systems
➢Population size begins to decrease
Number of cells dying > Number of cells produced
➢Most of the nutrients in the medium have been consumed
Methods for measuring microbial growth
Lag Phase
➢Period of adjustment to new conditions ➢Cell growth is minimal
Log Phase
➢ Cell growth rate and metabolic activity are the highest
Number of cells produced ﹥Number of cells dying
Types of Fermentation Process
Batch, continuous and fed batch processes
batch
chemostat
fed batch
12
Batch culture
The sterile growth medium is inoculated with the microorganisms and no additional growth medium is added.
Disadvantages
➢ The wastage of unused nutrients ➢ Labour and time lost between batches
Continuous culture
Maintains cells in log phase at a constant biomass concentration for extended periods.
➢Factors that slow down microbial growth
•Accumulation of toxic waste materials •Acidic pH of media • Limited nutrients • Insufficient oxygen supply
Death or Decline Phase
Types of Fermentor
mechanical agitation fermentor
self priming fermentor
Tower fermentor Airlift fermentor
Unit 1 Fermentation Basics
Four Phases of Bacterial Growth Curve ➢Lag phase ➢Log phase ➢Stationary phase ➢Death phase