Modes of fermentation

growth kinetics in batch, continuous and fed batch culture

1. MODES OF FERMENTATION Submitted by : Udisha Sharma b.Sc (pc) v sem 22440 Submitted to: Dr. Neha Batra

2. Types : Batch culture fermentation Continuous culture fermentation Fed batch culture fermentation Fermenter

3. Batch fermentation Batch fermentation is a discontinuous process and the fermenter has to be cleaned after each process and a fresh batch started. It is a closed culture system which contain an initial limited amount of nutrient.The inoculated culture will pass through a no. of phases as shown:

4. Lag phase : initial phase, no apparent growth of microbes ,they adapt to the environmental conditions, but an inc. in mass. Log phase: microbial growth proceeds at the maximum possible rate. Also known as exponential phase. Stationary phase: no overall growth rate i.e death of the cells is equal to the division of cells. Most of the secondary metabolites are produced in this phase. Deceleration phase: decline in the growth rate of microbes. Death rate : no growth at all, cell starts to die and the population size decreases. Usually the fermentation stops before the death phase.

5. Continuous Fermentation It is a continuous process where nutrient is continuously added to the fermenter at a fixed rate. Exponential growth in the batch culture may be prolonged by addition of fresh medium to the vessel, provided that the medium is designed such that the growth is substrate limited and not toxin limited ,exponential growth will proceed until the additional substrate is exhausted . The organism are continuously maintained at logarithm stage. If an overflow device was fitted to the fermenter such that the added medium placed at equal volume of culture from the vessel then continuous production of cells could be achieved. The products are recovered continuously. The fermenter in this type are called “flow through fermenters”.

6. Fed Batch culture Yoshida et al in 1973 introduced the term fed batch culture to describe batch cultures which are fed continuously or sequentially with medium without the removal of culture fluid. A fed batch culture is established initially in the batch mode and is then according to one of the strategies- The same medium which is used to established batch culture is added resulting in the inc. in volume. A solution of limiting substrate at the same conc. a s that in the initial medium is added resulting in the inc. in the volume. A conc. s olution of the limiting substrate is added at the rate less than (1) & (2) resulting in inc. in volume. A very conc. s olution of limiting substrate is added at a rate less than (1),(2) &(3) resulting in insignificant inc. in volume.

7. The biomass conc. at the stationary phase in a batch culture can be described as-

8. Thus from above equation it may be concluded that input of substrate is compensated by substrate consumption. Thus ds/dt =0 Total biomass (X) concentration increases with time but cell concentration (x) remains constant, i.e. dx/dt = 0 and we can now write  μ = D This situation is quasi steady state . The difference between steady state in chemostat and quasi steady state in fed batch is that μ is constant in chemostat and it decreases in fed batch.

9. Thank you !!!