Downstream processing and its steps

The various procedure 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 product in pharmaceutical industry (Such as antibiotics, hormones, antibodies, vaccine, enzymes), Food industry etc.
In addition, the product is either present in the cell, in the medium or both.
The concentration of product is generally low, in either cases, and it is mixed with other molecules from which it has to be separated.

Steps of downstream processing

The various steps of Downstream Processing involve:

Separation of particles

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

It is generally achieved by following ways:

Different techniques of filtration are as follows:

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 salt, 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.

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:

Mechanical cell disruption: this involves the uses of shear, E.g.-, colloid mill, ball mill grinder etc., homogenizer and ultrasound.
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.
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.

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

It is generally achieved by the following:

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

Purification is achieved by the following procedures:

Crystallization: This is used for the low molecular mass compound 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:

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% – 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