Downstream Processing

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Downstream Processing

- Separation and Purification of a specified product.

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Bioproducts

Pharmaceutical applications - Proteins, Antibiotics (metabolites)Food and Beverages - Baker’s yeast, EthanolSolvents – Butanol, acetone

- Cost of separation and purification - between 20-80% based on the nature of the product and its application.

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Stages involved

• Removal of solids- Cell debris, unused media components

• Isolation of the product - Extraction of the product from the supernatant

• Purification of the product - Remove impurities from the product

• Product polishing - preparing product for consumption

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Unit Operations/Techniques involved

• Removal of solids - Filtration, Centrifugation

• Isolation of the product - Solvent extraction, Precipitation

• Purification of the product - Chromatography

• Product polishing - Lyophilization, Drying, Crystallization.

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Basis of separations• Size and shape

• Density

• Solubility

• Diffusivity

• Volatility

• Electrostatic charge

• Polarity

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Physical forms separatedParticle – liquid separation :

1. Separation of cells from cell culture medium2. Separation of blood cells from plasma in the

manufacture of plasma proteins3. Removal of bacteria and viruses from protein

solutions

Solute – solvent separation1. Removal of a solvent from a solute product (e.g.

protein concentration enrichment)2. Removal of dissolved impurities from a liquid

product

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Solute – solute separation1. Separation of serum albumin from other

serum proteins

Liquid – liquid separation:1. Separation of ethanol and acetone from an

aqueous medium (in the manufacture of solvent)

Solid-Liquid separation: 1. Removal of solvent from the product during drying

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Bioproducts can be broadly classified into three categories: small molecules, large molecules, and particulate products.

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Different levels of purity required for different products

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Price and Production

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Low-resolution + high-throughput

High-resolution + low-throughput

Cell DisruptionPrecipitation

CentrifugationLiquid-liquid Extraction

LeachingFiltration

Supercritical Fluid ExtractionMicrofiltrationUltrafiltration

AdsorptionCrystallization

UltracentrifugationChromatography

Affinity separationElectrophoresis

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To improve the design of bioseparations, the following questions should be answered:

(1) What is the value of the product?

(2) What is an acceptable product quality?

(3) Where is the product in each process stream?

(4) Where are the impurities in each process stream?

(5) What are the unusual physicochemical properties of the product and the principal impurities?

(6) What are the economics of various alternative separations?

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Processing profile of antibiotics:

Product

Step Typical Process Conc. (g/L)

Quality (%)

Harvest broth Fermentation 0.1-5 0.1-1.0

Separation of insolubles

Filtration 1.0-5 0.2-2.0

Isolation Extraction 5-50 1-10

Purification Chromatography 50-200 50-80

Polishing Crystallization 50-200 90-100

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• Typical purification table for a protein

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Physico-chemical characteristics

• Size• Molecular weight• Diffusivity• Sedimentation coefficient• Osmotic pressure• Electrostatic charge• Solubility• Partition coefficient• Light absorption• Fluorescence

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MaterialChloride ionUreaGlucoseInsulinHuman serum albuminDextranImmunoglobulin GVirus particleBacteriaYeast cellsMammalian cell in culture

Size (microns)9.9 x 10 -5

1.6x 10 -4

8.6x 10 -4

4x 10 -3

7.2x 10 -3

lx 10 -3to 15x 10 -3

11x 10 -3

0.004 to 0.10.2 to 2.02 to 302-10

Size of Biological materials

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Table 2.3 Diffusivity of biological materialMaterialSodium chlorideUreaAcetic acidEthanolGlycerolLysozymeHuman serum albuminHuman immunoglobulin GCollagenTobacco mosaic virus

Diffusivity in water (m2/s)2.5 x 10 -9

1.35 x 10 -9

1.19 x 10 -9

8.4 x 10 -10

7.2 x 10 -10

10.4 x 10 -11

5.94 x 10 -11

4.3 x 10 -11

0.69 x 10 -11

0.46 x 10 -11