Downstream processing and its steps

Introduction of Downstream processing

• The various procedures involved in the actual recovery of useful products after fermentation or any other process together constitute downstream processing.
• It is a very important step in the manufacture of different products in the pharmaceutical industry (such as antibiotics, hormones, antibodies, vaccines, enzymes), the food industry, etc.
• In addition, the product is either present in the cell, in the medium, or in both.
• In either case, we generally find that the concentration of the product is low, and we mix it with other molecules from which we have to separate it.

Steps of downstream processing

The various steps of Downstream Processing involve

1. Separation
2. Cell disruption
3. Extraction
4. Isolation
5. Purification
6. Drying

Separation of particles

• It is first step of DSP and usually involves the separation of solids substances, from the liquid media.

It is generally achieved in the following ways:

• Filtration– it is used for filamentous fungi and bacteria.

Different techniques of filtration are as follows:

1. 1. Surface filtration
   2. Depth filtration
   3. Centrifugal filtration
   4. Rotating drum vacuum filtration

• Centrifugation- It may be used for bacteria, usually, protein precipitates.
• Flocculation and flotation– It is used for small bacterial cells which are difficult to separate even by centrifugation.
• Flocculation- It involves the aggregation of cells which may be induced by inorganic salts, minerals, hydrocolloids and organic polyelectrolytes.
• If flocculation isn’t effective than very minute gas bubbles is made by sparging, release of over pressure or electrolysis.
• Flotation- in any case, the gas bubble need to adsorb and surround the cell, raising the gas bubbles to the surface of media in the form of foam.

Cell disruption

• Disruption of microbial cell is usually difficult because of their small size, rigid cell walls and high osmotic pressure inside the cells.

Disruption of cell is generally achieved by mechanically, lysis or drying:

1. Mechanical cell disruption: this involves the uses of shear, E.g.-, colloid mill, ball mill grinder etc., homogenizer and ultrasound.
2. Drying: it involves the drying of cells by adding the cells into a huge amount of cold acetone and extracted using buffer or salt solution.
3. Lysis: lysis of microbial cells may be achieved by chemical means, e.g., salt or surfactants, osmotic shock, freezing, or Lytic enzymes, e.g., lysozyme, etc.

Extraction

• It involves the recovery of a compound or a group of compounds from a mixture or from cells into a solvent phase.
• It usually achieved both separation of particles as well as concentration of the product.
• The process of extraction is frequently useful for the recovery of Antibiotics and most of the lipophilic substances.

The process of extraction is achieved by:

1. 1. Liquid-liquid extraction
   2. Whole broth (medium + cells) extraction
   3. Aqueous multiphase extraction

Isolation

• Some of the product concentration may occur during the extraction step.

It is generally achieved by the following:

1. Evaporation: E.g.- continuous flow evaporator, falling film evaporator, thin film evaporator, spray dryers.
2. Membrane filtration:g.- Microfiltration, ultrafiltration, reverse osmosis and electrodialysis.
3. Ion exchange resins:g.- Dextran cellulose, polyamine, acrylate etc.
4. Adsorption resins: These may be:
   1. Polar – Sulfoxide, amide.
   2. Apolar – Styrene-divinyl benzene.
   3. Semipolar – Acrylic ester.

Purification

• It aims at recovery of the product in a highly purified state.

The following procedures achieve purification:

• Crystallization: Scientists use this for low molecular mass compounds like antibiotics.
• Chromatographic methods: it is generally, used for the purification of low molecular mass compound from mixture of similar molecules, e.g., antibiotics(homologous) and macromolecules (enzymes).

The different chromatographic procedures are:

1. 1. Adsorption
   2. Ion exchange
   3. Gel filtration
   4. Hydrophobic
   5. Affinity
   6. Partition chromatography.

Drying

• Drying is the most important step in downstream processing which makes the product suitable for handling and storage.

The most frequent approaches of drying are:

1. 1. Vacuum drying
   2. Spray drying
   3. Freeze drying.

Reference and Sources

• 1% – http://www.sjctni.edu/Department/bt/eLecture/Down%20stream%20processing.pptx
• 1% – https://www.slideshare.net/amitcasi1/downstream-processing-group-ppt
• 5% – https://www.biologydiscussion.com/industrial-microbiology-2/downstream-processing-dsp-of-products/55747 <
• 1% – https://www.sciencedirect.com/science/article/pii/S058095170870641X
• 1% – https://www.biotechnologynotes.com/industrial-biotechnology/fermentation-process/downstream-process-in-fermentation-with-methods-industries-biotechnology/13671

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