Concentration as a stage in downstream processing and what it entails

In concentration as a stage in downstream processing, the filtrate which is free from suspended

particles normally contains 80-98 of water. The product that is desired is a very minor constituent. In

order to achieve the product’s concentration, the water has to be removed. The following techniques

are commonly used in concentrating biological products for downstream processing;

 Evaporation

 Liquid-liquid extraction

 Membrane filtration

 Precipitation

 Adsorption

In evaporation, the evaporators in general, have a unit for the separation of concentrated product and

vapour, a heating device to supply steam, a condenser to condense the vapour, control equipment and

accessories. Capacity of the equipment may range from a small laboratory to industrial scale.

In liquid-liquid extraction, concentration of biological products can be achieved by transferring

desired product from one liquid phase to another liquid phase. This technique in downstream

processing is also useful for partial product purification. The efficiency of this process is dependent

on the partition coefficient. This process may be broadly categorized as the extraction of low

molecular weight products and extraction of high molecular weight products.

Membrane filtration involves the use of semi permeable membrane that retains the particles

selectively. The membranes used are made up of polymeric materials such as polyvinyl di fluoride

and polyethersulfone. It is normally difficult to sterilize membrane filters.

In precipitation involves the use of high molecular weight polymers, organic solvents and neutral

salts. Both temperature alteration and PH are used in this process.

Adsorption involves concentrating biological products of fermentation using adsorbent particles.

Activated charcoal was used in the early days as the adsorbent material. Cellulose based adsorbents

are used in the recent days. Polystyrene, acrylate based matrices and methacrylate are used for

concentration of low molecular weight compounds. This process can be carried out by passing culture

broth through a bed of adsorbent column.

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