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How to study 'product recovery' as a part of downstream bioprocess in microbial technology.
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Unit 5 MBT notes5.1 stages of upstream and downstream processing.
industrial fermentations comprise both upstream processing (USP) and
downstream processing (DSP) stages.
USP involves all factors and processes leading to the fermentation and
consists of three main areas.
The first area relates to aspects associated with the producer
microorganism. They include the strategy for initially obtaining a
suitable microorganism, industrial train improvement to enhance
productivity and yield, preparation of a suitable inoculum and the
continuing development of selected strains to increase the economic
efficiency of the process.
The second expect of USP involves fermentation media especially the
selection of suitable cost effective carbon and energy sources along
with other essential nutrients.
This media optimisation is a vital aspect of process development to
ensure maximization of yield and profit
The third component of USP relates to the fermentation which is
usually performed under rigorously controlled conditions developed to
optimise the growth of the organism or the production of a target
microbial product.
DSP has a primary aim of efficiently, reproducively and safely
recovering the target products to the required specifications while
maximizing recovery yield and minimising cost.
Purity of an enzyme is expressed as units of enzyme activity per unit of
total protein.
Fermentation factors affecting DSP includes the properties of
microorganisms, particularly morphology, flocculation characteristics,
size and cell wall rigidity. These factors have major influences on the
filtrability, sedimentation and homogenization efficiency.
The physical and chemical properties of the product along with its
concentration and location are obviously key factors as the determine
the initial separation steps and overall purification strategy.
DSP can be divided into a series of distant unit processes linked
together to achieve product purification
In many cases, integration of fermentation and DSP is now preferred.
Integration can often increase productivity, decrease the number of
unit operations and reduced both the overall process time and cost.
, In situ to remove all of products involves extraction, adsorption or
stripping which often increase yield and productivity.
In Ex situ removal of products, product is removed outside the
fermenter and the process to medium is return to the fermentation
Figure 7.1
Figure 7.3
5.2 CELL HARVESTING
The first step in the downstream processing of suspended cultures is a
solid-liquid separation to remove the cells from the spent medium.
Choice of solid liquid separation method is influenced by the size and
morphology of the microorganism (single cell aggregates or mycelia)
and the specific gravity, viscosity and rheology of the spent
fermentation medium. These factors can also have major influences on
the transfer of the liquid through pumps and pipes.
5.2 Broth Conditioning
In certain cases cross conditioning may be used to promote rotation.
This uses the ability of some cells to absorb to the gas-liquid interfaces
of gas bubbles and float to the surface for collection.
Certain flock precipitation methods are also used at the end of many
traditional beer and wine fermentation processes where the addition of
finings (egg albumin,isinglass) may be employed to precipitate yeast
cells.
Major advantages of this techniques are the low cost and ability to
separate microbial cells from large volume of medium.
Some organism naturally flocculate, which can be enhanced by
chemical, physical and biological treatments.
Coagulation the formation of small flocs from dispersed colloids, cells
or other suspended material, can be promoted using coagulating
agents (simple electrolytes, acids, bases, salts,multivalent ionsand
polyelectrolytes)
Subsequent flocculation, the agglomeration of these smalldr flocs into
larger settleable particles is often aided by inorganic salts(Calcium
Chloride) or polyelectrolytes.
These are high molecular weight, water soluble, anionic, cationic or
non-ionic organic compounds such as polyacrylamide and polystyrene
sulphate.
5.3 sedimentation
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