Downstream Processing

Cell harvesting separates cells from the liquid medium using centrifugation or filtration. For extracellular products, the supernatant is collected directly. For intracellular products, harvested cells proceed to disruption. This initial separation is critical for recovering target molecules from fermentation broths.

Intracellular products are trapped inside cells and must be released before purification. Common disruption methods include homogenization, sonication, and chemical lysis. These techniques break open cells, releasing intracellular components into the liquid phase for subsequent clarification and purification steps.

Clarification uses centrifugation or depth filtration to remove solid debris and particulate matter, producing a clear solution containing the crude product. This step prepares the liquid for primary purification by eliminating unwanted solids while retaining dissolved target molecules and impurities.

Ammonium sulfate precipitation concentrates the target product and reduces impurities by altering protein solubility. This technique selectively precipitates proteins while leaving many contaminants in solution. The precipitated product is then collected and concentrated using ultrafiltration for further purification.

Ultrafiltration applies transmembrane pressure to separate molecules by size, retaining larger target proteins while smaller molecules and impurities pass through. This concentrates the product and removes low-molecular-weight contaminants. The process reduces volume while increasing product concentration for subsequent chromatographic purification.

Ion exchange chromatography and affinity chromatography isolate target proteins based on their chemical properties. Affinity chromatography specifically binds target molecules while impurities pass through. Diafiltration may also exchange buffer systems and remove remaining low-molecular-weight impurities for final product purity.

Formulation adjusts pH, adds stabilizing agents, or applies lyophilization to preserve product activity and extend shelf life. These final steps protect the purified product from degradation during storage and distribution. Proper formulation ensures the pharmaceutical or industrial product maintains efficacy until use.