13.11

Downstream Processing

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Downstream processing begins after the production stage to recover and purify products like acids, vitamins, or antibiotics.

Centrifugation is often used as the initial step to separate cells from the medium.

For extracellular products, the supernatant is collected after centrifugation.

For intracellular products, cells are disrupted by homogenization to release their contents.

The resulting mixture is then clarified to remove solid debris using techniques like filtration, producing the crude product.

This crude product undergoes primary purification. For example, ammonium sulfate precipitation is commonly used for many protein-based products.

The precipitated product is concentrated using ultrafiltration.

Here, transmembrane pressure is applied to separate molecules by size, retaining the larger target proteins while smaller molecules pass through.

Affinity chromatography then isolates the target protein, yielding a purer product.

Finally, the purified product is stabilized through formulation, which may include adjusting pH, adding stabilizers, or lyophilizing the product.

Overview

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Downstream processing begins once fermentation is complete and involves a series of steps to recover and purify products such as acids, vitamins, antibiotics, or proteins.

Cell Harvesting
For example, for intracellular protein-based products, the first step is harvesting the cells. This is typically achieved using centrifugation or filtration to separate the cells from the liquid phase.

Cell Disruption for Intracellular Products
If the target product is intracellular, the harvested cells must be disrupted to release their contents. Common disruption methods include homogenization, sonication, and chemical lysis. These techniques release intracellular components into the liquid phase, after which the disrupted cell suspension proceeds to the clarification step.

Clarification
Clarification removes solid debris and particulate matter to produce a clear solution containing the crude product. This is done using centrifugation or depth filtration. For extracellular products, the supernatant is collected directly and subjected to clarification.

Primary Purification
The clarified liquid contains the crude product, which undergoes primary purification. A technique such as ammonium sulfate precipitation concentrates the product and reduces impurities by altering its solubility.

Concentration
After primary purification, the product is concentrated using one or more methods, including ultrafiltration, evaporation, or freeze-drying. These processes reduce the volume and increase the concentration of the product for further purification.

Purification
To achieve high purity, chromatographic techniques are employed. These include ion exchange chromatography and affinity chromatography, depending on the properties of the target molecule. In some workflows, diafiltration is also used to exchange buffer systems and remove low-molecular-weight impurities.

Formulation and Stabilization
In the final stage, the purified product is stabilized through formulation. This may involve pH adjustment, the addition of stabilizing agents, or lyophilization to preserve its activity and extend shelf life.

Transcript

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Downstream Processing

Cell Harvesting

Cell Disruption

Primary Purification

Chromatographic Techniques

Formulation Stabilization

Ammonium Sulfate Precipitation

Ultrafiltration