STAGES OF DOWNSTREAM PROCESSING
Downstream processing is the division of harvesting the insoluble elements from the cell culture which can be done through:
Downstream processing -Floatation
The gas is introduced in the cell culture and the solid particles get absorbed in the gas bubbles and rise to form a foam layer which is collected and removed. E.g. The fatty acids chain and amines.
In flocculation the cells form large bulks to settle down. this can be catalyzed by addition of flocculating agents e.g. inorganic salt, mineral organic polyelectrolyte which builds up the ionic component so as to achieve appropriate flocculation.
This is being the most commonly used technique and its efficiency depends on many factors e.g. the size of the organisms, temperature and viscosity of the medium.In the rotary drum vacuum filters the culture containing 10%-40% particles is filtered for yeast and filamentous fungi that is picked up and deposited on the drum surface as a cake which can be easily removed.
Release of intercellular products after Downstream processing
Since there are many biotechnological products within the cell, these compounds need to be broken down and released for further processing and final isolation. These cells are disintegrated by use of enzymatic method or disrupted chemically and physically. Some of the methods used are:
Ultra sonic disintegration
Osmotic shock – used for binding proteins from gram-negative bacteria and releasing of hydrolytic enzymes
Thermolysis (heat shock) – used to break heat-stable intracellular products by subjecting them to heat
High pressure homogenization – this is where a cell is forced into the atmospheric pressure through a narrow orifice that creates a liquid shear that can break.
Chemical methods – use of alkalis, organic solvents, detergents etc.
The Downstream processing filtrate that is free from cell debris contains over 80% of water, and since the wanted constituent is very small, the water has to be removed to achieve the right product concentration. This process is achieved through:
Evaporation – the evaporators in this case have a heating device that supplies steam and a condenser in the separation unit for separatingvapor and the concentrated product. Other methods of evaporation are: Plate evaporators, falling film evaporators, Forced film evaporators, Centrifugal forced film evaporators
Reactive extraction – in this technique, the desired product is made to react with a carrier molecule e.g. phosphorous compound and is then extracted into the organic solvent.