The concentrated product is now purified and formulated to make it stable.
This is the last stage in downstream processing. Purification is more important because the product must have to be free from impurities if it has to be used in any further biological synthesis or other applications. The purified product is then made stable by implementing few processes because the end product must not be volatile in nature and must have to be suitable for transportation and future usage.
The purification process in downstream processing is primarily chromatography. It is a method involved in the separation of closely related compounds from a mixture. It consists of 2 phases: stationary and mobile. Chromatography is of several types
- Gel-filtration Chromatography (Also known as size-exclusion chromatography)
- Ion-exchange Chromatography
- Affinity Chromatography
- Hydrophobic Interaction Chromatography
The formulation is the process of maintaining the activity and the stability of the product in the course of storage and processing. In downstream processing, the formulation of low molecular weight products is achieved by simply taking out water from them. Thus the concentration process is the formulation process in the case of low molecular weight product downstream processing. For small molecules, it is formulated by adding some salts.
High molecular weight products such as proteins tend to lose its activity because of its high molecular weight. In order to make it stable special treatment has to be given. The products used to make the proteins stable are sucrose, sodium chloride, polymers and polyhydric alcohols. They can be formulated either in the form of a solution, suspension or dry powders.
Drying: It is an essential process in the formulation of the product. Drying acts as the final touch in downstream processing. The addition of heat takes away the moisture from the wet product. This is the concept of drying. There are 3 commercially available dryers: Spray drying, Freeze drying, lyophilization.