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;
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.