Downstream processing in fermentation

                                   Downstream process 

  • The various stages of downstream  processing that occur after the completion of the fermentation,          including separation, purification, and packaging of the product.

Stages;

 Removal of Insoluble

 Product Isolation 

 Product Purification 

 Product Polishing 

 A few product recovery methods may be considered to combine two or more stages. For example,      expanded bed adsorption accomplishes removal of insoluble and product isolation in a single             step.  Affinity chromatography often isolates and purifies in a single step.

•   Removal of insoluble 

• Separation of cells, cell debris or other particulate matter 

• Typical operations to achieve this:

 1) Filtration

 2) Centrifugation 

3) Sedimentation 

4) Flocculation a process where a solute comes out of solution in the form of floc or flakes.

5) Gravity settling

1. Filtration -

• It is a type of mechanical operation used for the separation of solids from fluids (liquids or gases)         by a porous membrane through which the fluid can pass, but the solids in the fluid are hold in the       porous membrane.  

• The solid particles deposited on the filter form a layer, which is known as filter cake. 

• All the solid particles from the feed are stopped by the cake ,and the cake grows at the rate at which     particles are bought to its surface. 

• All of the fluid goes through the cake and filter medium.

2.Centrifugation-

• Centrifugation is a technique used to separate the solid  particles (100 – 0.1 micrometer) from         liquid by using  centrifugal forces. 

• It depends on particles size,density difference between the cells and the broth and broth viscosity.

• Use of the centrifugal force for the separation of particles from the  mixtures of component. 

• More-dense components migrate away from the axis of the centrifuge(ruter).

• Less-dense components  migrate towards the axis. 

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3.Chromatography-

• Separation of mixtures on the basis of their colour.

• Passing a mixture dissolved in a "mobile phase" through a stationary phase, which separates the            analyte to be measured from other molecules in the mixture and allows it to be isolated.

Types of chromatography 

1. Ion-exchange chromatography 
2. Affinity chromatography 
3. HPLC chromatography 
4. Paper chromatography 
5. TLC chromatography 
6. Size exclusion chromatography 

4.Ultrafiltration-

• UF is governed by a screening principle and dependent on particle size.

• UF membranes have a pore size between 1 nm and 100 nm (10 and 2000 Å), thus allowing                   retention of compounds with a molecular weight of 300 to 500 000 Dalton. 

• Typically, the process is suitable for retaining biomolecules, bacteria, viruses, polymers, colloidal particles and sugar molecules

5.Flocculation-

• Process where a solute comes out of solution in the form of flocs or flakes. 

• Particles finer than 0.1 µm in water remain continuously in motion due to electrostatic charge              which  causes them to repel each other.

• Once their electrostatic charge is neutralized (use of coagulant) the finer particles start to collide         and combine together . 

• These larger and heavier particles are called flocs.

Product isolation-

• Removal of those components whose properties vary markedly from that of the desired product. 

• Water is the chief impurity 

a) Isolation steps are designed to remove it (i.e.dialysis) 

b) Reducing the volume 

c) Concentrating the product. 

d) Liquid –liquid extraction, adsorption, ultrafiltration, and precipitation are some of the unit operations involved.