The Recovery and Purification ofFermentation Products

Product intracellular or extracellular

Concentration of the product in the fermentation broth.

Physical and chemical properties of the desired product

Intended use of the product.

Minimal acceptable standard of purity.

Magnitude of bio-hazard of the product or broth.

Impurities in the fermenter broth.

Market price for the product.

The choice of recovery process is based on the following criteria:

Selection of a micro-organism which does not produce pigments orundesirable metatlolites

Modification of the fermentation to reduce the production of metabolites

Precise timing of harvesting

pH control after harvesting

Temperature treatment after harvesting

Addition of flocculating agents

Use of enzymes to attack cell walls

How to reduce purification cost

Capital and Processing costs

Throughput requirements

Yield potential and Product quality

Technical expertise available

Conformance to regulatory requirements

Waste treatment needs

Continuous or batch processing

Automation

Personnel health and safety

The recovery and purification of many compounds may be achieved by a numberof alternative routes. The decision to follow a particular route involves comparingthe following factors to determine the most appropriate under a given set ofcircumstances:

REMOVAL OF MICROBIAL CELLS AND OTHER SOLID MATTER

Use of electrophoresis and dielectrophoresis to exploit the charged properties ofmicrobial cells, ultrasonic treatment to improve flocculation characteristics and magneticseparations.

FOAM SEPARATION

Foam separation depends on using methods which exploit differences in surface activity of materials.

The material may be whole cells or molecules such as a protein or colloidal, and is selectivelyadsorbed or attached to the surface of gas bubbles rising through a liquid, to be concentrated or separatedand finally removed by skimming.

It may be possible to make some materials surface active by the application of surfactants such aslong-chain fatty acids, amines and quaternary ammonium compounds.

Materials made surface active and collected are termed colligends whereas the surfactants are termedcollectors.

PRECIPITATION

Precipitation may be conducted at various stages of the product recovery process.

It is a particularly useful process in that it allows enrichment and concentration inone step, thereby reducing the volume of material for further processing.

It is possible to obtain some products (or to remove certain impurities) directlyfrom the broth by precipitation, or to use the technique after a crude cell lysate hasbeen obtained.

Agents used in precipitation

Acids and bases to change the pH of a solution until the isoelectric point of the compound isreached and pH equals pI, when there is then no overall charge on the molecule and its solubility isdecreased.

Salts such as ammonium and sodium sulphate are used for the recovery and fractionation ofproteins. The salt removes water from the surface of the protein revealing hydrophobic patcheswhich come together causing the protein to precipitate. The most hydrophobic proteins willprecipitate first, thus allowing fractionation to take place.

Organic solvents. Dextrans can be precipitated out of a broth by the addition of methanol.Chilled ethanol and acetone can be used in the precipitation of proteins mainly due to changes inthe dielectric properties of the solution.

Non-ionic polymers such as polyethylene gylcol (PEG) can be used in the precipitation ofproteins and are similar in behaviour to organic solvents.

Polyelectrolytes can be used in the precipitation of a range of compounds, in addition to theiruse in cell aggregation. Protein binding dyes (triazine dyes) bind to and precipitate certain classesof protein.

Affinity precipitants are an area of much current interest in that they are able to bind to, andprecipitate, compounds selectively

Polyelectrolytes are polymers whose repeating units bearan electrolyte group. Polycations and polyanions are polyelectrolytes. Thesegroups dissociate in aqueous solutions (water), making the polymers charged.Polyelectrolyte properties are thus similar to both electrolytes (salts) and polymers(high molecular weight compounds) and are sometimes called polysalts. Like salts, theirsolutions are electrically conductive. Like polymers, their solutions are often viscous.

Like ordinary electrolytes (acids, bases and salts), they dissociate in aqueous solutions(water) and bear one or more charges depending on the pH value. Thus, the properties ofpolyelectrolytes are similar to both electrolytes and polymers. The salts, i.e. the productsof a polyacids (polyanions) with a monomeric base and vice versa are called polysalts.Like regular salts, their solutions are electrically conductive and like polymers, theirviscosity strongly depends on the molecular weight and polymer concentration.

The three most common anionic groups are carboxylate (–COO-), phosphonate (–PO3H-, –

PO32-), and sulfonate (–SO3

-) and the most common cationic groups are primary,secondary and quaternary ammonium (–NH3

+, =NH2+ & ≡N+). The type of ionic group, its

counter ion and the structure of the repeat unit determine the properties of apolyelectrolyte such as solubility in water and other polar and hydrogen-bonding liquids(alcohols etc.), electrical conductivity, and solution viscosity. Unlike nonionic polymers,these properties strongly depend on the pH and salt content.

Filtration is one of the most common processes used at all scales of operation to separate suspendedparticles from a liquid or gas, using a porous medium which retains the particles but allows theliquid or gas to pass through.

Filtration

The most suitable type of equipment to meet the specified requirements at minimum overall cost, including

The properties of the filtrate, particularly its viscosity and density.

The nature of the solid particles, particularly their size and shape, the size distribution and packing characteristics.

The solids: liquid ratio.

The need for recovery of the solid or liquid fraction or both.

The scale of operation.

The need for batch or continuous operation.

The need for aseptic conditions.

The need for pressure or vacuum suction to ensure an adequate flow rate of the liquid.

Batch filters

PLATE AND FRAME FILTERS

The plates and frames are assembled on a horizontal framework and held together by means ofa hand screw or hydraulic ram so that there is no leakage between the plates and frames whichform a series of liquid-tight compartments.

The slurry is fed to the filter frame through the continuous channel formed by the holes in thecorners of the plates and frames.

The filtrate passes through the filter cloth or pad, runs down grooves in the filter plates and isthen discharged through outlet taps to a channel.

On an industrial scale the plate and frame filter is oneof the cheapest filters per unit of filtering space andrequires the least floor space, but it is intermittent inoperation (a batch process) and there may beconsiderable wear of filter cloths as a result of frequentdismantling.

This type of filter is most suitable for fermentationbroths with a low solids content and low resistance tofiltration

PRESSURE LEAF FILTERS

(i) Vertical metal-leaf filter: This filter consists of a number of vertical porous metalleaves mounted on a hollow shaft in a cylindrical pressure vessel. The solids from theslurry gradually build up on the surface of the leaves and the filtrate is removed from theplates via the horizontal hollow shaft. In some designs the hollow shaft can be slowlyrotated during filtration. Solids are normally removed at the end of a cycle by blowing airthrough the shaftand into the filter leaves.

(ii) Horizontal metal-leaf filter:- In this filter the metal leaves are mounted on a verticalhollow shaft within a pressure vessel. Often, only the upper surfaces of the leaves areporous. Filtration is continued until the cake fills the space between the disc-shaped leaves orwhen the operational pressure has become excessive. At the end of a process cycle, the solidcake can be discharged by releasing the pressure and spinning the shaft with a drive motor.

(iii) Stacked-disc filter:- One kind of filter of this type is the Metafilter. This is a very robustdevice and because there is no filter cloth and the bed is easily replaced, labour costs are low.It consists of a number of precision-made rings which are stacked on a fluted rod (Fig. 10.9).The rings 22 mm external diameter, 16 mm internal diameter and 0.8 mm thick) are normallymade from stainless steel and precision stamped so that there are a number of shoulders onone side.

ROTARY VACUUM FILTERS

Continuous Filters

Large rotary vacuum filters are commonly used by industries which produce large volumes of liquidwhich need continuous processing.

The filter consists of a rotating, hollow, segmented drum covered with a fabric or metal filter which ispartially immersed in a trough containing the broth to be filtered.

The slurry is fed on to the outside of the revolving drum and vacuum pressure is applied internally sothat the filtrate is drawn through the filter, into the drum and finally to a collecting vessel.

The interior of the drum is divided into a series of compartments, to which the vacuum pressure isnormally applied for most of each revolution as the drum slowly revolves (~ 1 rpm).

However, just before discharge of the filter cake, air pressure may be applied internally to help ease thefilter cake off the drum.

A number of spray jets may be carefully positioned so that water can be applied to rinse the cake. Thiswashing is carefully controlled so that dilution of the filtrate is minimal.

(i) String discharge.(ii) Scraper discharge.(iii) Scraper discharge with precoating of the drum.

The mechanism of cake discharge from the drum:

Different type of cake discharge mechanism

Cross-flow filtration (Tangential filtration)

In the filtration processes previously described, the flow of broth was perpendicular tothe filtration membrane. Consequently, blockage of the membrane led to lower rates ofproductivity and/or the need for filter aids to be added, and these were seriousdisadvantages.

In contrast, an alternative which is rapidly gaining prominence both in the processing ofwhole fermentation broths and cell lysates is cross-flow filtration. Here, the flow ofmedium to be filtered is tangential to the membrane, and no filter cake builds up on themembrane.

(a) Efficient separation, > 99.9% cell retention.

(b) Closed system; for the containment of organisms with no aerosol formation.

(c) Separation is independent of cell and media densities, in contrast to centrifugation.

(d) No addition of filter aid .

The benefits of cross-flow filtration are:

Many factors influence filtration rate

Pressure: if the pressure drop is too great the membrane become blocked.

Temperature and Viscosity: Higher temperatures will increase filtration rate by lowering the viscosity of the media, though this is clearly of limited application in biological systems.

Filtration rate is inversely proportional to concentration, and media constituents can influence filtration rate in three ways.

Low molecular weight compounds increase media viscosity and high molecular weight compounds decrease shear at the membrane surface,both leading to a reduction in filtration rate.

Broth constituents can 'foul' the membrane, primarily by adsorption onto the membrane‘s surface, causing a rapid loss in efficiency.

This can be controlled by modification of the membrane or media formulation in particular by reducing the use of antifoaming agents.

CENTRIFUGATION

Micro-organisms and other similar sized particles can be removed from a broth by using a centrifuge when filtration is not a satisfactory separation method.

1. Filtration is slow and difficult.

2. The cells or other suspended matter must be obtained free of filter aids.

3. Continuous separation to a high standard of hygiene is required.

Non-continuous centrifuges are of extremely limited capacity and therefore not suitable for large-scale separation.

The centrifuges used in harvesting fermentation broths are all operated on a continuous or semi-continuous basis.

Some centrifuges can be used for separating two immiscible liquids yielding a heavy phase and light phase liquid, as well as a solids fraction. They may also be used for the breaking of emulsions.

The rate of sedimentation of spherical particles suspended in a fluid of Newtonianviscosity characteristics is proportional to the square of the diameter of the particles,thus the rate of sedimentation of a particle under gravitational force is:

Stoke's law,

This is a measure of the separating powerof a centrifuge compared with gravitysettling. It is often referred to as therelative centrifugal force and given thesymbol ‘Z'.

A field of centrifugal force is generated if avessel is filled with liquid and spun. Thiscreates a centrifugal acceleration, a. Thecentrifugal acceleration is not constant likethe gravity g in a stationary vessel. Thecentrifugal acceleration increases withdistance from the axis of rotation (radius, r)and with the speed of rotation, expressedas angular velocity ω,So: a = w2r

The diameter of the cells (could be increased by coagulation/flocculation) andthe viscosity of the liquid.

Ideally, the cells should have a large diameter, there should be a large densitydifference between cell and liquid and the liquid should have a low viscosity.

However, In practice, the cells are usually very small, of low density and areoften suspended in viscous media.

Thus it can be seen that the angular velocity and diameter of the centrifuge arethe major factors to be considered when attempting to maximize the rate ofsedimentation (and therefore throughput) of fermentation broths.

NEWTONIAN FLUIDSA Newtonian fluid's viscosity remains constant, no matter the amount of shear applied for a constant temperature.. Thesefluids have a linear relationship between viscosity and shear stress. exmples: Water, Mineral oil, Gasoline, Alcohol

NON-NEWTONIAN FLUIDSYou can probably guess that non-Newtonian fluids are the opposite of Newtonian fluids. When shear is applied to non-Newtonian fluids, the viscosity of the fluid changes. The behavior of the fluid can be described one of four ways:Dilatant - Viscosity of the fluid increases when shear is applied. For example:

QuicksandCornflour and waterSilly putty

Pseudoplastic - Pseudoplastic is the opposite of dilatant; the more shear applied, the less viscous it becomes. Forexample: KetchupThis chart shows how viscosity changes in respect to the amount of shear or stress applied to the fluid.

Rheopectic - Rheopectic is very similar to dilatant in that when shear is applied, viscosityincreases. The difference here, is that viscosity increase is time-dependent. For example:

Gypsum pasteCream

Thixotropic - Fluids with thixotropic properties decrease in viscosity when shear isapplied. This is a time dependent property as well. For example:

PaintCosmeticsAsphaltGlue

This chart shows how viscosity changes in respect to shear applied over time to the fluid.

Cell aggregation and flocculation

In industrial fermentation it is quite common to add flocculating agents to the broth to aidde-watering.

Widely practised in the effluent-treatment industries for the removal of microbial cells andsuspended colloidal matter.

It is well known that aggregates of microbial cells, although they have the same density asthe individual cells, will sediment faster because of the increased diameter of the particles(Stokes law).

This sedimentation process may be achieved naturally with selected strains of brewingyeasts, particularly if the wort is chilled at the end of fermentation, and leads to a naturalclearing of the beer.

Micro-organisms in solution are usually held as discrete units in three ways.

1. Firstly, their surfaces are negatively charged and therefore repulse each other.

2. Secondly, because of their generally hydrophilic cell walls a shell of bound water is associated withthe cell which acts as a thermodynamic barrier to aggregation.

3. Finally, due to the irregular shapes of cell walls (at the macromolecular level) steric hindrance willalso play a part.

During flocculation one or more mechanisms besides temperature can induce cell flocculation:

(a) Neutralization of anionic charges, primarily carboxyl and phosphate groups, on the surfaces of themicrobial cells, thus allowing the cells to aggregate. These include changes in the pH and the presenceof a range of compounds which alter the ionic environment.

(b) Reduction in surface hydrophilicity.

(c) The use of high molecular weight polymer bridges. Anionic, non-ionic and cationic polymers canbe used, though the former two also require the addition of a multivalent cation.

Flocculation usually involves the mixing of a process fluid with the flocculating agent under conditions ofhigh shear in a stirred tank. This stage is known as coagulation, and is usually followed by a period of gentleagitation when flocs developed initially are allowed to grow in size.

Various compounds for flocculating bacteria, yeasts and algae, including alum (potassium aluminiumsulfate; KAl(SO4)2·12H2O ), calcium salts and ferric salts.

Other agents which are now used include tannic acid, titanium tetrachloride and cationic agents such asquaternary ammonium compounds, alkyl amines and alkyl pyridinium salts. Nucleic acids, polysaccharides and proteins released from partly lysed cells may also bring aboutagglomeration. In SCP processes, phosphoric acid has been used as a flocculating agent since it can be usedas a nutrient in medium recycle with considerable savings in water usage.

The majority of flocculating agents currently in use are polyelectrolytes, which act by charge neutralizationand hydrophobic interactions to link cells to each other.

The range of centrifuges

THE BASKET CENTRIFUGE (PERFORATED-BOWL BASKET CENTRIFUGE)

Basket centrifuges are useful for separating mould mycelia or crystalline compounds. The centrifuge is most commonly used with a perforated bowl lined with a filter bag of nylon, cotton, etc.

A continuous feed is used, and when the basket is filled withthe filter cake it is possible to wash the cake before removing it.

The bowl may suffer from blinding with soft biologicalmaterials so that high centrifugal forces cannot be used.

These centrifuges are normally operated at speeds of up to 4000rpm for feed rates of 50 to 300 dm3 min -1 and have a solidsholding capacity of 30 to 500 dm3

The basket centrifuge may be considered to be a centrifugalfilter.

THE TUBULAR-BOWL CENTRIFUGE

This is a centrifuge to consider using forparticle size ranges of 0.1 to 200 p.m and up to10% solids in the in-going slurry (SharplesSuper-Centrifuge).

The main component of the centrifuge is a cylindricalbowl (or rotor) (which may be of a variable designdepending on application, suspended by a flexibleshaft (B), driven by an overhead motor or air turbine(C). The inlet to the bowl is via a nozzle attached tothe bottom bearing (D). The feed which may consistof solids and light and heavy liquid phases isintroduced by the nozzle (E). During operation solidssediment on the bowl wall while the liquids separateinto the heavy phase in zone (0) and the light phasein the central zone (H). The two liquid phases arekept separate in their exit from the bowl by anadjustable ring, with the heavy phase flowing overthe lip of the ring. Rings of various sizes may befitted for the separation of liquids of various relativedensities.

(a) Light-phase/heavy-phase liquid separation.

(b) Solids/light-liquid phase/heavy-liquid phase separation.

(c) Solids/liquid separation (using a different rotor, Fig. 1O.16b).

Thus the centrifuge may be altered to use for

The advantages of this design of centrifuge are the highcentrifugal force, good dewatering and ease of cleaning.

The disadvantages are limited solids capacity, difficulties in therecovery of collected solids, gradual loss in efficiency as the bowlfills, solids being dislodged from the walls as the bowl is slowingdown and foaming.

Plastic liners can be used in the bowls to help improve batchcycle time. Alternatively a spare bowl can be changed over inabout 5 minutes.

SOLID-BOWL SCROLL CENTRIFUGE (DECANTER CENTRIFUGE)

This type of centrifuge is used for continuous handling of fermentation broths, cell lysatesand coarse materials such as sewage sludge

The slurry is fed through the spindle of an archimedean screw within the horizontalrotating solids bowl. Typically the speed differential between the bowl and the screw is inthe range 0.5 to 100 rpm The solids settling on the walls of the bowl are scraped to theconical end of the bowl. The slope of the cone helps to remove excess liquid from thesolids before discharge. The liquid phase is discharged from the opposite end of the bowl.The speed of this type of centrifuge is limited to around 5000 rpm in larger models becauseof the lack of balance within the bowl, with smaller models having bowl speeds of up to10000 rpm. Bowl diameters are normally between 0.2 and 1.5 metres, with the length beingup to five times the diameter. Feed rates range from around 200 dm3 h-1 to 200 m3 h-1

depending on scale of operation and material being processed.

A number of variants on the basic design are available:

(a) Cake washing facilities (screen bowl decanters).(b) Vertical bowl decanters.(c) Facility for in-place cleaning.(d) Bio-hazard containment features; steam sterilization in-situ, two or three stage mechanical seals, control ofaerosols, containment casings and the use of high pressure sterile gas in seals to prevent the release of micro-organisms.

THE MULTICHAMBER CENTRIFUGE

In the multi-chamber centrifuge (Fig. 10.18), a series of concentric chambers are mountedwithin the rotor chamber (ideal for 5% solids of particle).

The broth enters via the central spindle and then takes a circuitous route through thechambers. Solids collect on the outer faces of each chamber.

The smaller particles collect in the outer chambers where they are subjected to greatercentrifugal forces (the greater the radial position of a particle, the greater the rate ofsedimentation).

Greater solids capacity than tubular bowls withoutloss of efficiency

The mechanical strength and design limits theirspeed to a maximum of 6500 rpm for a rotor 46-cmdiameter.

Because of the time needed to dismantle andrecover the solids fraction, the size and number ofvessels must be of the correct volume for the solidsof a batch run.

This centrifuge relies for its efficiency on the presence of discs in the rotor or bowl (Fig. 10.19).

A central inlet pipe is surrounded by a stack of stainless-steel conical discs.

Each disc has spacers so that a stack can be built up.

The broth to be separated flows outwards from the central feed pipe, then upwards and inwards between the discs atan angle of 45° to the axis of rotation.

The close packing of the discs assists rapid sedimentation and the solids then slide to the edge of the bowl, providedthat there are no gums or fats in the slurry, and eventually accumulate on the inner wall of the bowl.

Ideally, the sediment should form a sludge which flows, rather than a hard particulate or lumpy sediment.

The main advantages of these centrifuges are their small size compared with a bowl without discs for a giventhroughput. Some designs also have the facility for continuous solids removal through a series of nozzles in thecircumference of the bowl or intermittent solids removal by automatic opening of the solids collection bowl.

The arrangement of the discs makes this type of centrifuge laborious to clean. However, recent models such as theAlfa Laval BTUX 510 (Alfa Laval Sharples Ltd, Camberley, Surrey, U.K.) systemare designed to allow for cleaningin-situ.

In addition this and similar plant have the facility for in-situ steam sterilization and total containment,incorporating double seals to comply with containment regulations. Feed rates range from 45 to 1800 dm3 min-1, withrotational speeds typically between 5000 and 10,000 rpm. The Westfalia CSA 19-47-476 is also steam sterilizable andhas been used for the sterile collection of organisms. Similarly, the Westfalia CSA 8 can be modified for containedoperation and steam sterilization

THE DISC-BOWL CENTRIFUGE

CELL DISRUPTION

Micro-organisms are protected by extremely tough cell walls. In order to release their cellular contents a number of methods for cell disintegration have been developed

Containment of cells can be difficult or costly to achieve in many of the methods describedbelow and thus containment requirements will strongly influence process choice. Methods available fall into two major categories:

Physico-mechanical methods

(a) Liquid shear.(b) Solid shear.(c) Agitation with abrasives.(d) Freeze-thawing.(e) Ultrasonication.

Chemical methods(a) Detergents.(b) Osmotic shock.(c) Alkali treatment.(d) Enzyme treatment.

LIQUID SHEAR

Liquid shear is the method which has been widely used in large scale enzyme purification.

High-pressure homogenizer used in the processing of milk and other products the foodindustry have proved to be very effective microbial cell disruption.

The microbial slurry passes through a nonreturn valve and impinges against the operative valveset at the selected operating pressure. The cells then pass through a narrow channel between thevalve and an impact ring followed by a sudden pressure drop at the exit to the narrow orifice. Thelarge pressure drop across the valve is believed to cause cavitation in the slurry and the shockwaves so produced disrupt the cells. the size of the pressure drop to be very important inachieving effective disruption, and as with all mechanical methods, cell size and shape influenceease of disruption.

The need for cooling the slurry to between 0 and 4°C to minimize loss in enzyme activitybecause of heat generation during the process. The increase in slurry temperature isapproximately proportional to the pressure drop across the valve. Because of problems caused byheat generation and because cell suspensions can be surprisingly abrasive, it is common practiceto operate such homogenizers in a multi-pass mode but at a lower pressure. The degree ofdisruption and consequently the amount of protein released will influence the ease of subsequentseparation of the product from the cell debris in high-pressure homogenizers and bead mills

Solid Shear

Pressure extrusion of frozen micro-organisms at around – 25 oC through a small orifice is a well established technique at a laboratory scale using a Hughes press or an X-press to obtain small samples of enzymes or microbial cell walls.

Disruption is due to a combination of liquid shear through a narrow orifice and the presence of ice crystals.

Semi-continuous X-press operating with a sample temperature of - 35°C and an X-press temperature of - 20°C.

It was possible to obtain 90% disruption with a single passage of S. cerevisiae using a throughput of 10 kg yeast cell paste h-1.

This technique might be ideal for microbial products which are very temperature labile.

Agitation with Abrasives

The mechanical cell disruption can also be achieved in a disintegrator containing a seriesof rotating discs and a charge of small beads. The beads are made of mechanicallyresistant materials such as glass, alumina ceramics and some titanium compounds

In a small disintegrator, the Dyno-Muhle using a flow rate of 180 dm3 h-1, 85%disintegration of an 11% w/v suspension of S. cerevisiae was achieved with a single pass.

Temperatures of up to 35°e were recorded in the disintegrator, the specific enzymeactivities were not considered to be very different from values obtained by other techniques.

Dissipation of heat generated in the mill is one of the major problems in scale up, thoughthis can generally be overcome with the provision of a cooling jacket.

In another disintegrator, the Netsch LM20 mill, the agitator blades were alternatelymounted vertically and obliquely on the horizontal shaft.

A flow rate of up to 400 dm3 h–1 was claimed for a vessel with a nominal capacity of 20dm3

FREEZING-THAWING

Freezing and thawing of a microbial cell paste will inevitably cause ice crystals toform and their expansion followed by thawing will lead to some subsequent disruptionof cells.

It is slow, with limited release of cellular materials, and has not often been used as atechnique on its own, although it is often used in combination with other techniques.

ULTRASONICATION

High frequency vibration (- 20 kHz) at the tip of an ultrasonication probe leads tocavitation, and shock waves thus produced cause cell disruption.

The method can be very effective on a small scale.

But a number of serious drawbacks make it unsuitable for large-scale operations.

Power requirements are high, there is a large heating effect so cooling is needed, theprobes have a short working life and are only effective over a short range.

Continuous laboratory sonicators with hold-up volumes of around 10 cm3 have beenshown to be effective

A number of detergents will damage the lipoproteins of the microbial cell membraneand lead to release of intracellular components.

The compounds which can be used for this purpose include quaternary ammoniumcompounds, sodium lauryl sulphate, sodium dodecyl sulphate (SDS) and Triton X-100.

Unfortunately, the detergents may cause some protein denaturation and may need tobe removed before further purification stages can be undertaken.

Outer membrane can be extracted using DETERGENTS strategy

The cells were suspended in pH 7.8 buffer and 1% sodium cholate was added. Themixture was stirred for 1 hour to solubilize most of the enzyme

The use of Triton X-100 in combination with guanidine-HCl is widely and effectivelyused for the release of cellular protein.

DETERGENTS

OSMOTIC SHOCK

Osmotic shock caused by a sudden change in salt concentration will causedisruption of a number of cell types. However, the effect on microbial cells isnormally minimal.

Enzyme extraction was achieved by osmotic lysis using a ratio of 1 g of cell pasteto 4 cm3 of cold distilled water with stirring for 15 to 30 minutes.

Only low levels of soluble protein were released using this technique.

ALKALI TREATMENT

Alkali treatment might be used for hydrolysis of microbial cell wall material provided that the desired enzyme will tolerate a pH of 11.5 to 12.5 for 20 to 30 minutes.

L-asparaginase was extracted using this technique.

ENZYME TREATMENT

There are a number of enzymes which hydrolyse specific bonds in cell walls of a limited numberof micro-organisms.

Enzymes shown to have this activity include lysozyme and enzyme extracts from leucocytes,Streptomyces spp., Micromonospora spp. Penicillium spp., Trichoderma spp., and snails.

Although this is probably one of the most gentle methods available,unfortunately it is relativelyexpensive and the presence of the enzyme(s) may complicate further downstream purificationprocesses.

The use of immobilized lysozyme has been investigated by a number of workers and may providethe solution to such problems

Chemical and enzymic methods for the release of intracellular products have not been usedwidely on a large scale, with the exception of lysozyme.

However, their potential for the selective release of product and that they often yield a cleanerlysate mean that they are potentially invaluable tools in the recovery of fermentation Products

Enzymes may also be used as a pretreatment to partially hydrolyse cell walls prior to celldisruption by mechanical methods.

LIQUID-LIQUID EXTRACTION

The separation of a component from a liquid mixture by treatment with a solvent inwhich the desired component is preferentially soluble is known as liquid-liquid extraction.

The specific requirement is that a high percentage extraction of product must beobtained but concentrated in a smaller volume of solvent.

Prior to starting a large-scale extraction, it is important to find out on a small scale thesolubility characteristics of the product using a wide range of solvents.

A simple rule to remember is that 'like dissolves like‘.

The important 'likeness' as far as solubility relations are concerned is in the polarities ofmolecules.

Polar liquids mix with each other and dissolve salts and other polar solids. The solventsfor non-polar compounds are liquids of low or nil polarity.

The dielectric constant is a measure of the degree of molar polarization of a compound. Ifthis value is known it is then possible to predict whether a compound will be polar ornon-polar, with a high value indicating a highly polar compound. The dielectric constantD of a substance can be measured by determining the electrostatic capacity C of acondenser containing the substance between the plates. If Co is the value for the samecondenser when completely evacuated then

There are n mixer/separator vessels in line and the raffinate goes from vessel 1 to vessel n.

Fresh solvent is added to each stage, the feed and extracting solvent pass through the cascade in the same direction.

Extract is recovered from each stage.

Although a relatively large amount of solvent is used, a high degree of extraction is achieved.

The co-current system is illustrated as following.

A counter-current system is illustrated in Fig. 10.26. There. are a number ofmixer/separators connected in series.

The extracted raffinate passes from vessel 1 to vessel n while the product-enriched solventis flowing from vessel n to vessel 1.

The feed and extracting solvent pass through the cascade in opposite directions.

The most efficient system for solvent utilization is counter-current operation, showing aconsiderable advantage over batch and co-current systems. Unless there are special reasonsthe counter-current system should be used.

The two liquid streams are forced to flow counter-current to each other through a longspiral of channels within the rotor.

The Podbielniak centrifugal extractor (Fig. 10.27) consists of a horizontal cylindrical drum revolving at up to5000 rpm about a shaft passing through its axis.

The liquids to be run counter-current are introduced into the shaft, with the heavy liquid entering the drum at theshaft while the light liquid is led by an internal route to the periphery of the drum.

As the drum rotates, the heavy liquid is forced to the periphery of the drum by centrifugal action where it contactsthe light liquid.

The solute is transferred between the liquids and the light liquid is displaced back towards the axis of the drum.The heavy liquid is returned to the drum's axis via internal channels.

The two liquid streams are then discharged via the shaft. Flow rates in excess of 100,000 dm3 h - 1 are possible inthe largest models. Probably the most useful property of this type of extractor is the low hold-up volume of liquidin the machine compared with the throughput.

Penicillin G is an antibiotic which is recovered from fermentation broths by centrifugal counter-current solvent extraction. At neutral pHs in water penicillin is ionized:

In acid conditions this ionization is suppressed and the penicillin is more soluble in organic solvents. At pH 2 to 3 the distribution ratio of total acid will be

For penicillin this value may be as high as 40 in a suitable solvent (Podbielniak et al., 1970). The penicillin extraction process may involve the four following stages:

1. Extraction of the penicillin G from the filtered broth into an organic solvent (amyl or butyl acetate or methyl iso-butyl ketone).

2. Extraction from the organic solvent into aqueous buffer.3. Extraction from aqueous buffer into organic solvent.4. Extraction of the solvent to obtain the penicillin salt.

At each extraction stage progressively smaller volumes of extractant are used to achieveconcentration of the penicillin (see also Fig. 10.2). Unfortunately, penicillin G has a half-life of 15minutes at pH 2.0 at 20°. The harvested broth is therefore initially cooled to 0° to 3°.

The cooled broth is then acidified to pH 2 to 3 with sulphuric or phosphoric acid immediatelybefore extraction. This acidified broth is quickly passed through podbielniak centrifugal counter-current extractor using about 20% by volume of the solvent in the counter flow. Ideally, the hold-uptime should be about 60 to 90 seconds.

The penicillin-rich solvent then passes through second Podbielniak extractor counter-current to anaqueous NaOH or KOH solution (again about 20% by volume) so that the penicillin is removed to theaqueous phase (pH 7.0 to 8.0) as the salt.

These two stages may be sufficient to concentrate the penicillin adequately from a broth with a high titre.

Penicillin will crystallize out of aqueous solution at a concentration of approximately 1.5 X 106 units cm-3.

If the broth harvested initially contains 60,000 units cm- 3, and two five-fold concentrations are achieved in the two extraction stages, then the penicillin liquor should crystallize.

A major item of equipment in an extraction process is the solvent-recovery plantwhich is usually a distillation unit.

It is not normally essential to remove all the raffinate from the solvent as this will berecycled through the system.

In some processes the more difficult problem will be to remove all the solvent fromthe raffinate because of the value of the solvent and problems which might arise fromcontamination of the product.

SOLVENT RECOVERY

1. Evaporation, the removal of solvent as a vapour from a solution.

2. Vapour-liquid separation in a column, to separate the lower boiling more volatile component from other less volatile components.

3. Condensation of the vapour, to recover the more volatile solvent fraction.

Distillation may be achieved in three stages:

Evaporation is the removal of solvent from a solution by the application of heat to thesolution.

A wide range of evaporators is available. Some are operated on a batch basis andothers continuously.

Most industrial evaporators employ tubular heating surfaces. Circulation of the liquidpast the heating surfaces may be induced by boiling or by mechanical agitation.

In batch distillation (Fig. 10.28) the vapour from the boiler passes up the column andis condensed. Part of the condensate will be returned as the reflux for counter-currentcontact with the rising vapour in the column.

The distillation is continued until a satisfactory recovery of the lower-boiling (morevolatile) component(s) has been accomplished.

The ratio of condensate returned to the column as reflux to that withdrawn asproduct is, along with the number of plates or stages in the column, the major methodof controlling the product purity.

A continuous distillation (Fig. 10.29) is initially begun in a similar way as with abatch distillation, but no condensate is withdrawn initially.

There is total reflux of the condensate until ideal operating conditions have beenestablished throughout the column. At this stage the liquid feed is fed into the column atan intermediate level.

The more volatile components move upwards as vapour and are condensed, followedby partial reflux of the condensate. Meanwhile, the less volatile fractions move downthe column to the evaporator (reboiler).

At this stage part of the bottoms fraction is continuously withdrawn and part isreboiled and returned to the Column. Counter-current contacting of the vapour andliquid streams is achieved by causing:

(a) vapour to be dispersed in the liquid phase (plate or tray column)

(b) liquid to be dispersed in a continuous vapour phase (packed column).

Continuous distillation

The plate or tray column consists of a number of distinct chambers separated byperforated plates or trays.

The rising vapour bubbles through the liquid which is flowing across each plate, and isdispersed into the liquid from perforations (sieve plates) or bubble caps. The liquid flowsacross the plates and reaches the reboiler by a series of overflow wiers and down pipes.

A packed tower is filled with a randomly packed material such as rings, saddles,helices, spheres or beads. Their dimensions are approximately one-tenth to one-fiftieth ofthe diameter of the column and designed to provide a large surface area liquid-vapourcontacting and high voidage to high throughput of liquid and vapour.

The heat input to a distillation column can be considerable.

The simplest ways of conserving heat are preheat the initial feed by a heat exchangerusing from:

(a) the hot vapours at the top of the column,

(b) heat from the bottoms fraction when it is removed in a continuous process,

(c) a combination of both.

TWO-PHASE AQUEOUS EXTRACTION

Liquid-liquid extraction is a well established technology in chemical processing and incertain sectors of biochemical processing.

However, the use of organic solvents has limited application in the processing ofsensitive biologicals.

Aqueous two-phase systems, on the other hand, have a high water content and lowinterfacial surface tension and are regarded as being biocompatible

Natural and synthetic hydrophilic polymers are used today to create two (or more)aqueous phases.

Phase separation occurs when hydrophilic polymers are added to an aqueous solution,and when the concentrations exceed a certain value two immiscible aqueous phases areformed.

Settling time for the two phases can be prolonged, depending on the components usedand vessel geometry.

Phase separation can be improved by using centrifugal separators or novel techniquessuch as magnetic separators

Many systems are available:

i) Non-ionic polymer/non-ionic polymer/water, e.g. polyethylene glycol-dextran.

ii) Polyelectrolyte/non-ionic polymer/water, e.g. sodium carboxymethyl cellulose/polyethylene glycol.

(iii) Polyelectrolyte/ polyelectrolyte/ water, e.g. sodium dextran sulphate/ sodiumcarboxymethyl Cellulose

Two phase aqueous systems have found application in the purification of many solutes;proteins, enzymes, cells and sublcellular particles, and in extractive bioconversions.

Several aqueous two-phase systems for handling large scale protein separation haveemerged, the majority of which use PEG as the upper phase forming polymereither dextran, concentrated salt solution or hydroxypropyl starch as the lower phaseforming material

SUPERCRITICAL FLUID EXTRACTION

The technique of supercritical fluid extraction utilizes the dissolution power ofsupercritical fluids, i.e. fluids above their critical temperature and pressure.

Its advantages include the use of moderate temperatures, and that several cheap and non-toxic fluids are avail.

Supercritical fluids are used in the extraction of hop oils, caffeine, vanilla, vegetable oilsand b-carotene. It has also been shown experimentally that the extraction certain steroids andchemotherapeutic drugs can be achieved using supercritical fluids.

Other current and potential uses include the removal of undesirable substances such aspesticide residues, removal of bacterio-static agents from fermentation broths, the recoveryof organic solvents from aqueous solutions, cell disintegration, destruction and treatment ofindustrial wastes and liposome preparation.

Thus, the number of commercial processes utilizing supercritical fluid extraction isrelatively small, mainly due to the existence of more economical processes.

However, its use is likely to increase in some sectors, for example the recovery of highvalue biologicals, when conventional extractions are inappropriate, and in the treatment oftoxic wastes

(i) Phase equilibria of the solvent/solute system is complex, making design ofextraction conditions difficult.

(ii) The most popular solvent (carbon dioxide) is non-polar and is therefore most usefulin the extraction of non-polar solutes. Though co-solvents can be added for theextraction of polar compounds, they will complicate further downstream processing.

(iii) The use of high pressures leads to capital costs for plant, and operating costs mayalso be high.

Disadvantages in the utilization of this technology:

In many fermentation processes, chromatographic techniques are used to isolate and purifyrelatively low concentrations of metabolic products.

Depending on the mechanism by which the solutes may be differentially held in a column,the techniques can be grouped as follows:

(a) Adsorption chromatography(b) Ion-exchange chromatography(c) Gel permeation chromatography(d) Affinity chromatography(e) Reverse phase chromatography(f) High performance liquid chromatography

Chromatographic techniques are also used in the final stages of purification of a number ofproducts.

The scale-up of chromatographic processes can prove difficult, and there is much currentinterest in the use of mathematical models and computer programmes to translate dataobtained from small-scale processes into operating conditions for larger scale applications

CHROMATOGRAPHY

Separates molecules by their chemical and physical differences

Most common types:

Size exclusion (Gel filtration): Separates by molecular weight

Ion exchange: Separates by charge

Affinity chromatography: Specific binding

Hydrophobic Interaction: Separates by hydrophobic/hydrophilic characteristics of the molecules

Adsorption chromatography

Reverse phase chromatography.

High performance liquid chromatography.

Column Chromatography

Types of Liquid Chromatography:Techniques in LC are classified according to the method of solute separation

1. Adsorption chromatography 2. Affinity chromatography

3. Partition chromatography 4. Size-exclusion chromatography

5. Ion-exchange chromatography

Adsorption chromatography involves binding of the solute to the solid phase primarilyby weak Van de Waals forces.

The materials used for this purpose to pack columns include inorganic adsorbants (activecarbon, aluminium oxide, aluminium hydroxide, magnesium oxide, silica gel) and organicmacro-porous resins.

Adsorption and affinity chromatography are mechanistically identical, but arestrategically different. In affinity systems selectivity is designed rationally whilst inadsorption selectivity must be determined empirically.

Di-hydro-streptomycin can be extracted from filtrates using activated charcoal columns.It is then eluted with methanolic hydrochloric acid and purified in further Stages

Active carbon may be used to remove pigments to clarify broths.

Adsorption chromatography

Adsorption ChromatographySeparates solutes based on their adsorption to underivatized solid particles.Similar to gas-solid chromatography in that the same material is used as both the stationary phase and

support material

Advantages:

Retain and separate some compounds that can not be separated by other methods such as Separationof geometrical isomers

Disadvantages:– very strong retention of some solutes

– may cause catalytic changes in solutes

– solid support may have a range of chemical and physical environments non-

symmetrical peaks and variable retention times

Mobile phase

Adsorption chromatography stationary phase (or solid support) may be either polar or non-polar

Adsorbent Surface Type Application

Silica Slightly acidic General Purpose – Basic compounds

Alumina Slightly basic General Purpose – Acidic Compounds

Charcoal Non-polar Non-polar Compounds

Florisil Strongly acidic General purpose – Basic Compounds

Polyamides Basic Phenols and Aromatic Nitro Compounds

Others (clay, Kieselguhr, diatomaceous earth, celite, etc.)

Relatively Non-polar Polar Compounds

For polar supports (silica/alumina), the weak mobile phase is a non-polar solvent (hexane, benzene, etc.) and the strong mobile phase is a polar solvent (water, methanol, etc.)

For non-polar supports (charcoal), the weak mobile phase is a polar solvent and the strong mobile phase is a non-polar solvent.

Common applications of Adsorption LC:- purification of synthetic organic compounds from reaction mixtures- separation of geometrical isomers (ortho/meta/para, cis/trans, etc)

Gel Filtration/Size exclusion Chromatography

Gel permeation separates molecules on the basis of their size.

The smaller molecules diffuse into the gel more rapidly than the larger ones, and penetrate thepores of the gel to a greater degree.

Larger molecules present in the voids in the gel will be eluted first.

A wide range of gels are available, including cross-linked dextrans (Sephadex and SephacryOand cross-linked agarose (Sepharose) with various pore sizes

Size Exclusion Chromatography (SEC)Separates molecules according to differences in their size

SEC is based on the use of a support material that has a certain range of pore sizes

As solute travels through the support, small molecules can enter the pores while large molecules can not Since the larger molecules sample a smaller volume of the column, they elute before the smaller molecules.

Separation based on size or molecular weight

SEC is based on the different interactions of solutes with the flowing mobile phase and the stagnant mobile phase.

- no true stationary phase is present in this system

- stagnant mobile phase acts as the “stationary phase”

SEC does not have a “weak” or “strong” mobile phase since retention is based only on size/shape of the analyte and the pore distribution of the support.

- gel filtration chromatography: if an aqueous mobile phase is used

- gel permeation chromatography: if an organic mobile phase is used (usually tetrahydrofuran)

Common applications of SEC:

- Separation of Biological Molecules (e.g., proteins from peptides)

- Separation/analysis of organic polymers

- molecular-weight determination

LC Detectors:

Common types of LC Detectors

1. Refractive Index Detector 2. Conductivity Detector

3. UV/Vis Absorbance Detector 4. Electrochemical Detector

5. Fluorescence Detector

As in GC, the choice of detector will depend on the analyte and how the LC method is being used (i.e., analytical or preparative scale)

Detector Selectivity Sensitivity Notes

Refractive Index Poor Poor Any component that differs in refractive index from the eluate can be detected, despite its low sensitivity. Cannot be used to perform gradient analysis.

UV/Vis Moderate Good A wide variety of substances can be detected that absorb light from 190 to 900 nm. Sensitivity depends strongly on the component.

Fluorescence Good Excellent Components emitting fluorescence can be detected selectively with high sensitivity. This is often used for pre-column and post-column derivatization.

Conductivity Moderate Good Ionized components are detected. This detector is used mainly for ion chromatography.

Electrochemical Good Excellent Electric currents are detected that are generated by electric oxidation-reduction reactions. Electrically active components are detected with high sensitivity.

Ion Exchange Chromatography Ion Exchange Chromatography relies on charge-charge interactions between the protein of interestand charges on a resin (bead).

Ion exchange can be defined as the reversible exchange of ions between a liquid phase and a solidphase (ion-exchange resin) which is not accompanied by any radical change in the solid structure.

Ion exchange chromatography can be subdivided into cation exchange chromatography, in which apositively charged protein of interest binds to a negatively charged resin; and anion exchangechromatography, in which a negatively charged protein of interest binds to a positively charged resin.

One can manipulate the charges on the protein by knowing the pI of the protein and using buffers ofdifferent pHs to alter the charge on the protein.

Once the protein of interest is bound, the column is washed with equilibration buffer to removeunattached entities.

Then the bound protein of interest is eluted off using an elution buffer of increasing ionic strength orof a different pH. Either weakens the attachment of the protein of interest to the bead and the proteinof interest is bumped off and eluted from the resin.

Ion exchange resins are the cheapest of the chromatography media available and are thereforealmost always used as a step in biopharmaceutical protein production purification.

Cationic ion-exchange resins normally contain a sulphonic acid, carboxylic acid or phosphonicacid active group. Carboxy- methyl cellulose is a common cation exchange Resin.

A common anion exchange resin, DEAE (diethylaminoethyl) cellulose is used for the separation of negatively charged solutes.

In the recovery of streptomycin, the harvested filtrate is fed on to a column of a weak-acid cationic resin such as Amberlite IRC 50 which is in the sodium form. The streptomycin is adsorbed on to the column and the sodium ions are displaced.

Isoelectric Focusing or IEF

pH < pI < pH+ 0 -

Once you know the pI of your protein (or the pH at which your protein is neutral), youcan place it in a buffer at a lower or higher pH to alter its charge.

If the pH of the buffer is less than the pI, the protein of interest will become positivelycharged.

If the pH of the buffer is greater than the pI, the protein of interest will becomenegatively charged.

Ion-exchange Chromatography (IEC)Separates solutes by their adsorption onto a support containing fixed charges on its surface. A highconcentration of a competing ion is often added to the mobile phase to elute the analytes from thecolumn

xRSO3-H+ + Mx+ « (RSO3

-)xMx+ +xH+

xRN(CH3)3OH- + Ax- « [RH(CH3)3+]xAx- + xOH-

Two General Types of Stationary Phases Can be Used in IEC:

Cation-exchangers: have fixed negatively charged groups, used to separate positively-charged ions

Anion-exchangers: have fixed positively-charged groups, used to separate negatively-charged ions

Chemical Structure Functional Group Chemical Nature Type of Exchange

-SO-H+ Sulfonic acid Strong acid Cation

-COO-H+ Carboxylic acid Weak acid Cation

-CH2COO-H+ Carboxymethyl Weak acid Cation

-CH2N+(CH3)3Cl- Quaternary ammonium

Strong base Anion

Quaternary ammonium

Strong base Anion

Tertiary ammonium Weak base Anion

Diethylaminoethyl (DEAE)

Weak base Anion

CH2N+

CH3

CH3

CH2CH2CH(Cl-)

CH2NH+

CH3

CH3

OH-

CH2CH2NH+

CH2CH3

CH2CH3

OH-

The charged groups that make up the stationary

phase can be placed on several different types of

support materials:

Cross-linked polystyrene resins: for use with the

separation of inorganic ions and small organic ions

Carbohydrate-based resins: for low-performance

separations of biological molecules (dextran,

agarose, cellulose)

Silica-based supports: for high-performance

separations of biological molecules

A strong mobile phase in IEC:

- contains a high concentration of a competing ion for displacement of the

sample ion from the stationary phase

cation exchange resin (Kex):

Tl+ > Ag+ > Cs+ > Rb+ >K+ >NH4+ > Na+ > H+ > Li+

Ba2+ > Pb2+ > Sr2+ > Ca2+ > Ni2+ > Cd2+ > Cu2+ > Co2+ > Zn2+ > Mg2+ > UO22+

anion exchange resin (Kex):

SO42- > C2O4

2- > I- > NO3- > Br- >Cl- > HCO2

- > CH3CO2- > OH- > F-

or

- a solvent that has a pH which decreases ionization of the analyte or stationary phase

rigid polystyrene/divinyl benzene beads

Factors That Affect Mobile Phase Strength Are:

- Mobile phase pH

especially for weak acid or base analytes and weak acid or base

stationary phases

- Mobile phase concentration of competing ion

- Type of competing ion

Ne

t C

har

ge O

n P

rote

in

Attached to cationexchangers

Iso

elec

tric

po

int

Range of Stability

Attached to anionexchangers

Common applications of IEC:

Removal or replacement of ionic compounds in samples (sample pretreatment)

Separation of inorganic ions and organic ions

Analysis/purification of charged biological compounds amino acids, proteins, peptides, nucleic acids

Affinity ChromatographyAffinity chromatography separates the protein of interest on the basisof a reversible interaction between it and its antibody coupled to achromatography bead (here labeled antigen) .

With high selectivity, high resolution, and high capacity for the proteinof interest, purification levels in the order of several thousand-fold areachievable.

The protein of interest is collected in a purified, concentrated form.Biological interactions between the antigen and the protein of interest canresult from electrostatic interactions, van der Waals' forces and/orhydrogen bonding.

To elute the protein of interest from the affinity beads, the interactioncan be reversed by changing the pH or ionic strength.

The concentrating effect enables large volumes to be processed. Theprotein of interest can be purified from high levels of contaminatingsubstances.

Making antibodies to the protein of interest is expensive, so affinitychromatography is the least economical choice for productionchromatography.

This technique depends on the highly specific interactions between pairs of biological materialssuch as enzyme-substrate, enzyme-inhibitor, antigen-antibody, etc.

The ligand is attached to the matrix by physical absorption or chemically by a covalent bond.

The pore size and ligand location must be carefully matched to the size of the product for effectiveseparation.

Coupling procedures have been developed using cyanogen bromide, bisoxiranes, disaziridines andperiodates, for matrixes of gels and beads. Four polymers which are often used for matrix materialsare agarose, cellulose, dextrose and polyacrylamide.

Agarose activated with cyanogen bromide is one of the most commonly used supports for thecoupling of amino ligands.

Silica based solid phases have been shown to be an effective alternative to gel supports in affinitychromatography

Affinity chromatography was used initially in protein isolation and purification, particularlyenzymes, enzyme inhibitors, antibodies, interferon and recombinant proteins.

In the scale-up of affinity chromatographic processes (Katoh, 1987) bed height limits thesuperficial velocity of the liquid, thus scale-up requires an increase in bed diameter or adsorptioncapacity.

Time (min)

Abs 280nm

Affinity Chromatography

Affinity Chromatography (AC)

Separates based on the use of immobilized biological molecules (and related compounds) as thestationary phase

Based on the selective, reversible interactions that characterize most biological systems

- binding of an enzyme with its substrate or a hormone with its receptor

- immobilize one of a pair of interacting molecules onto a solid support

- immobilized molecule on column is referred to as the affinity ligand

Two Main Types of Affinity Ligands Used in Affinity Chromatography:

High-specificity ligands – compounds which bind to only one or a few very closely relatedmolecules

General or group specific ligands – molecules which bind to a family or class ofrelated molecules

Affinity Ligand Retained Compounds

Antibodies Antigens

Antigens Antibodies

Inhibitors/Substrates Enzymes

Nucleic Acids Complimentary Nucleic acids

Affinity Ligand Retained Compounds

Lectins Glycoproteins, carbohydrates, membrane proteins

Triazine dyes NADH- or NADPH Dependent Enzymes

Phenylboronic acid Cis-Diol Containing Compounds

Protein A/Protein G Antibodies

Metal Chelates Metal-Binding Proteins & Peptides

Note: the affinity ligand does not necessarily have to be of biological origin

Due to the very selective nature of most biological interactions, the solute of interest is often retained with little interference from other components of the sample.

A weak mobile phase is usually a solvent that mimics the pH, ionic strength and polarity of the solute and ligand in their natural binding environment.

A strong mobile phase is a solvent that produces low retention for the solute-ligand interaction:

- by decreasing its binding constant

or

- displaces solute by the addition of an agent with competes for solute sites on the column

pHbuffer

compound

Two Approaches to Elution Used in Affinity Chromatography:

- Biospecific Elution: solutes are eluted by a mobile phase that contains a compound which competes with sample solutes for the ligand’s active sites.

- very gentle

- useful in purification of active biological molecules

- produces slow elution with broad solute peaks

- Non-specific elution: change conditions in the column to disrupt the interactions between the sample solutes and immobilized ligand

- done by changing pH or ionic strength

- harsher than biospecific elution

- gives narrow peaks and faster run times

- commonly used in analytical applications of AC

Common applications of AC:

- Purification of enzymes, proteins and peptides- Isolation of cells and viruses

- Purification of nucleic acids

- Specific analysis of components in clinical and biological samples- Study of biomolecular interactions

Purification of His-Tag Protein Using a pH Change

Hydrophobic Interaction Chromatography (HIC) HIC is finding dramatically increased use inproduction chromatography.

Antibodies are quite hydrophobic andtherapeutic antibodies are the most importantproteins in the biopharmaceutical pipeline.

Since the molecular mechanism of HIC relies onunique structural features, it serves as a non-redundant option to ion exchange, affinity, and gelfiltration chromatography.

It is very generic, yet capable of powerfulresolution.

Usually HIC media have high capacity and areeconomical and stable.

Adsorption takes place in high salt and elutionin low salt concentrations.

Separates solutes based on their partitioning between a liquid mobile phase and a liquidstationary phase coated on a solid support.

Mobile phase

Support Material – is usually silica, originally involved coating this support with some liquidstationary phase that was not readily soluble in the mobile phase

Two main types of partition chromatography based on the type of stationary phase:

1. Normal-phase liquid chromatography2. Reversed-phase liquid chromatography

Partition Chromatography

Normal Phase liquid Chromatography (NPLC).

- partition chromatography where the stationary phase is polar

NPLC column strongly retains polar compounds

- weak mobile phase is a non-polar liquid: organic solvent

- strong mobile phase is a polar liquid: water or methanol

- stationary phase must have a low miscibility with the mobile phase so the stationary

phase is not dissolved from the column

examples of liquid NPLC stationary phases:

<Dimethylsulfoxide <Water

<Ethylene glycol <Ethylene diamine

CN Cyanopropyl

NH2 Aminopropyl

PSA N-propylethylenediamine

Si CH2CH2CH2CN

Si CH2CH2CH2NH2

Si CH2CH2CH2NHCH2CH2NH2

These liquid stationary phases slowly bleed from the column, changing the properties and solute retention time .

Use stationary phases chemically attached to the support

Common applications of NPLC:

- purification of synthetic organic and inorganic compounds from reaction mixtures

- general purpose separation of polar/non-polar compounds when the sample is in a non-polar solvent

PrepLCMS Analysis (50 mg injection)

4.36

5

2e7

4e7

6e7

8e7

Inte

nsity

, cps

DesiredProduct

Automated chromatography purification of designed drug combinatorial libraries

This chromatographic method utilizes a solid phase (e.g. silica) which is modified soas to replace hydrophilic groups with hydrophobic alkyl chains.

This allows the separation of proteins according to their hydrophobicity.

More-hydrophobic proteins bind most strongly to the stationary phase and aretherefore eluted later than less-hydrophobic proteins.

The alkyl groupings are normally eight or eighteen carbons in length (C8 and C18).

RPC can also be combined with affinity techniques in the separation of, for example,proteins and peptides

Reverse phase chromatography (RPC)

Reverse Phase liquid Chromatography (RPLC).

- partition chromatography where the stationary phase is non-polar

reverse polarity of normal phase LC

retains non-polar compounds most strongly

- weak mobile phase is a polar liquid: water

- strong mobile phase is more non-polar liquid: methanol or acetonitrile

- stationary phase must have a low miscibility with the mobile phase so the stationary phase is not dissolved from the column

examples of liquid RPLC stationary phases:

<heptane < squalene

<hydrocarbon polymers <dimethylpolysiloxane

Comparison of RPLC & NPLC

Type Stationary phase Weak mobile phase Strong Mobile phase

RPLC Non-polar Polar liquid More non-polar

NPLC polar Non-polar liquid Polar liquid

C18 Octadecyl

C8 Octyl

C2 Ethyl

CH Cyclohexyl

PH Phenyl

Si C18H37

Si C8H17

Si C2H5

Si

Si

Use stationary phases chemically attached to the support, C8 and C18 are most common

Like NPLC, these liquid stationary phases slowly bleed from the column, changing the properties and solute retention time.

Common applications of RPLC:

- most popular type of liquid chromatography

separation of a wide variety of non-polar and polar solutes

- popularity weak mobile phase is a polar solvent (e.g., water)

ideal for the separation of solutes in aqueous-based samples, such as biological compounds

Common applications of RPLC (continued):

- purification of biological and organic compounds present in aqueous solutions

- pharmaceutical analysis (drug quantitation and quality control)

- protein & peptide mapping

- analysis of soil and water samples

- clinical analysis of blood and urine samples

RPLC Analysis of Patient blood serum for presence of drug during clinical trial

HPLC is a high resolution column chromatographic technique.

Improvements in the nature of column packing materials for a range of chromatographic techniques(e.g. gel permeation and ion-exchange) yield smaller, more rigid and more uniform beads. (Minimizespeak broadening of eluted species.

It was originally known as high pressure liquid chromatography because of the high pressuresrequired to drive solvents through silica based packed beds.

The stationary phase must have high surface area/unit volume, even size and shape and be resistant tomechanical and chemical damage. (lead to high pressure requirements and cost)

This may be acceptable for analytical work, but not for preparative separations.

Thus, in preparative HPLC some resolution is often sacrificed (by the use of larger stationary-phaseparticles) to reduce operating and capital costs.

For very high value products large-scale HPLC columns containing analytical media have been used.

Affinity techniques can be merged with HPLC to combine the selectivity of the former with the speedand resolving power of the latter

High Performance Liquid Chromatography

Ultrafiltration can be described as a process in which solutes of high molecular weight areretained when the solvent and low molecular weight solutes are forced under hydraulicpressure (around 7 atmospheres) through a membrane of a very fine pore size. It is

Ultra-filtration

There may be concentration polarization caused by accumulation of solute at themembrane surface which can be reduced by increasing the shear forces at the membranesurface either by conventional agitation or by the use of a cross-flow system (seeprevious section).

Secondly a slurry of protein may accumulate on the membrane surface forming a gellayer which is not easily removed by agitation.

Formation of the gel layer may be partially controlled by careful choice of conditionssuch as pH.

Finally, equipment and energy costs may be considerable because of the highpressures necessary; this also limits the life of ultrafiltration membranes

Reverse osmosis is a separation process where the solvent molecules are forced by an appliedpressure to flow through a semi-permeable membrane in the opposite direction to that dictated byosmotic forces, and hence is termed reverse osmosis.

It is used for the concentration of smaller molecules than is possible by ultrafiltration.

Concentration polarization is again a problem and must be controlled by increased turbulence atthe membrane surface.

Reverse osmosis

DRYING

The drying of any product (including biological products) is often the last stage of amanufacturing process .

It involves the final removal of water from a heat-sensitive material ensuring that there isminimum loss in viability, activity or nutritional value. Drying is undertaken because:

(a) The cost of transport can be reduced.

(b) The material is easier to handle and package.

(c) The material can be stored more conveniently in the dry state.

It is important that as much water as possible is removed initially by centrifugation or in a filter press to minimize heating costs in the drying process.

Driers can be classified by the method of heat transfer to the product and the degree of agitation of the product.

In contact driers the product is contacted with a heated surface. This may beused for more temperature stable bio-products.

A slurry is run onto a slowly rotating steam heated drum, evaporation takes place and the dry product is removed by a scraper blade in a similar manner as for rotary vacuum Filtration.

The solid is in contact with the heating surface for 6-15 seconds and heat transfer coefficients are generally between 1 and 2 kW m-2 K- 1. Vacuum drum driers can be used to lower the temperature of drying.

A spray drier is most widely used for drying of biological materials when the starting material is in theform of a liquid or paste.

The material to be dried does not come into contact with the heating surfaces, instead, it is atomizedinto small droplets through for example a nozzle or by contact with a rotating disc.

The wide range of atomizers available are available. The droplets then fall into a spiral stream of hotgas at 150° to 250°. The high surface area:volume ratio of the droplets results in a rapid rate ofevaporation and complete drying in a few seconds, with drying rate and product size being directlyrelated to droplet size produced by the atomizer.

The evaporative cooling effect prevents the material from becoming overheated and damaged. Thegas-flow rate must be carefully regulated

Spray drying

Why Spray drying

The spray drying is the technology widest used in the liquid technology shaping and in the drying industry. The dryingtechnology is most suitable for producing the powder , particle or block solid products from the materials, such as:solution, emulsion , soliquoid and pumpable paste states . For this reason, when the particle size and distribution of thefinal products, their residual water contents, the stacking density and the particle shape must meet the precision standard,the spray drying is one of the most desired technologies.

Principles

After filtering and heating, the air enters into the air distributor at the top of the drier. The hot air enters into the dryingchamber in the spiral from and uniformly. By passing through the high-speed centrifugal spray at the top of the tower ,thematerial liquid will rotate and be sprayed into the extremely fine mistliquid beads. Through the very short time ofcontacting the heatair, the materials can be dried into the finished products . The waste gas will be discharged fromblower.

FeaturesAt a high speed of drying, after the spraying of the liquid material, the surface area of the material will be increasedgreatly. In the hot-air flow, 95%-98% of water can be evaporated at a moment. The time of completing the drying needsonly several seconds.

This id especially suitable for drying the heat sensitive materials. Its final products own the good uniformity, mobility,dissolving capacity. And the final products are high in their purity and good in their quality.

The production procedures are simple and the operation and control are easy. The liquid with the moisture contents 40-60% (for special materials, The contents may reach 90%). can be dried into the powder or particle products.

After the drying, there is no need for smashing and sorting, so as to reduce the operation procedures in the productionand to enhance the product purity. The product particle diameters, looseness and water contents can be adjusted throughchanging the operation condition in a certain scope. It is very convenient to carry out the control and management.