down stream processing


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o After the fermentation has been completed, the product is

harvested and recovered. This is called (DSP).

o The fermenter is mainly determined by the DSP operations,

viz., how well the fermented product, and by-products, are

separated from the broth.

o OTA (1984) mentions the interesting case of the humulin

(human insulin) plant built by Elililly and company in which

over 85% of the company staff is employed in the DSP

phase of the plant processes.

o A representative sample of some DSP operations

may include most or all of the operations:

Separation operations

o filtration, centrifugation, flotation, disruption

Concentration operations

o Solubilisation, extraction, thermal processing

membrane filtration, precipitation.

Purification operations

o Crystallization, chromatography

Marketing operations

o Drying, packing, storage


Glucose Medium

Lactose Medium or

Whey permeate


Adjust pH

Added Nutrients





PRODUCT (Ethanol)

o The sale price of most biotechnology products is

inversely proportional to their concentration leaving the


o This circumstance has created an incentive to develop

reactor configurations, designs, and conditions that

yield a higher product broth or culture concentration.

o Considerations of this type have particularly influenced

the programmes involving mammalian cell culture.

In this culture, several different mass culturing

technologies are being tried for scale up and


These include free suspension cultures in mixed batch

flow reactors.(i.e.,)these reactors include spinner

flasks, airlift reactors in which the cells are entrapped

in spherical microcapsules.

Free cell suspension cultures require rigorous DSP

processing because they usually attain rather low cell

and product concentration.

In general, greater emphasis has been placed on

genetic engineering and fermentation technology as

compared to downstream processing aspects.

The recovery of microorganisms from fermented broth

presents a fairly difficult solid-liquid separation


Some representative solid phases that may have to be

separated from various fermenters include cells of

bacteria, fungi, algae, plants, animals, and cellular


The separation process to be applied to these various

forms depends on the concentration and size of the


Plant and animal cells usually do not withstand the

same extent of applied shearing force as do microbial


The primary stages of separation are greatly

influenced by broth conditioning, whose major

objective is to aggregate the cells to from larger

clumps or flocs and hence reduce the separation


Broth conditioning techniques are based on physical,

chemical or biological principles.

Examples of physical techniques include heating,

freezing, mechanical (e.g., homogenizers),

ultrasonic's, and electrical treatments.

Chemical techniques are exemplified by

coagulation(by multivalent metal ions), flocculation (by

organic polymers or polyelectrolyte's), pH change, and

lysis (by surfactants).

Biological techniques of broth conditioning include the

use of enzymes such as proteases, lipases, and

amylases, ageing, lysis (by antibiotics, e.g., penicillin),

antigen-antibody interaction between cells, and genetic

(e.g., incorporation of genes responsible for


o the following operations to facilitate cell separation:

1. sedimentation-used in yeast production and ethanol

production industries.

2. Flotation-Mainly used in alcoholic beverages industry.

3. Filtration and ultra filtration-Filter presses are used in

the older, brewing and distillery industries whereas

rotary vacuum drums are more often employed in the

modem bio-technological processes ,e.g.,

pharmaceutical and food industries.

Ultra filtration(UF)is a pressure-driven membrane

separation process for dissolved and suspended


o UF can be used for (a) purification of culture medium

prior to bioconversion or fermentation, (b) harvesting

of cells after fermentation, (c) removal of cell debris

after lysis, (d) concentration of product, and (e) making

pyrogen-free water for final product make-up and final

rinsing of vials.

(4) Centrifugation- this is perhaps the most popular DSP

technique, especially in cases involving large cells

fermented on a large scale.

o In general, disc nozzle machines are used for large-

scale production, e.g., of yeast, and are not very

suitable for bacteria.

(5) Cross–flow membrane filtration- This is especially

suitable for the small-scale high-value applications.

o The principle of electro-phoretically assisted cross-

flow filtration technique is illustrated.

The cross-flow technique include applied voltage,

degree of turbulence

The makes membrane processes specially suitable for

the treatment of thermally-or chemically-sensitive


In any typical microbial production system, there are

four chief areas where membranes may used to


These are(1) sterilisation of bioreactor feed

streams(e.g., nutrients, enzyme, oxygen, air, water);(2)

DSP of spent medium;(3) enzyme immobilization; and

(4) on-line monitoring of bioreactor constituents.