Microorganisms may be cultured commercially in order to obtain a substance that they produce
They must be able to:
- Produce the substance in large quantities in a small amount of time
- Be available in pure culture, & be genetically stable
- Grow rapidly in large-scale culture
- Not be harmful to humans
- Be capable of easy removal from culture
- Grow on readily available & cheap raw materials
- Have growth conditions that do not require extremes of temperature
Yeasts are widely cultured commercially, & are used in the production of:
- Food substances in their own right, & in bread production
- Beers, ales, lagers & wines, & alcohol as a biofuel
There are two main types of process for the production:
1. Batch processes: raw materials & microbes are placed together in a container vessel.
The microbes are then allowed to grow to their maximum population size, then the fermenter is emptied & the products are extracted & purified
2. Continuous process: the nutrients are continually inputted into the fermentation vessel & the material is continually removed & processed.
This may be more economical, as it doesn’t have to be shut down on a regular basis
In order to develop a large industrial fermentation process, four main stages are required:
1. Isolation of microorganism: organism must be able to be purified easily & give the optimum product yield
2. Culture preparation: master culture is stored by freeze-drying (lyophilising) in a small space.
Small samples are taken from master culture in order to produce stock cultures, from which working cultures can subsequently be produced
3. Laboratory scale (200cm3 fermenter): optimum conditions are determined using a small-scale fermenter
4. Pilot plant (200 to 500 dm3 fermenter): laboratory fermenter is scaled up to make sure that it works on a larger scale.
There may be problems with heating/aeration, which may require electric mixers & cooling mechanisms
Enzymes are produced using submerged culture techniques.
They are produced on a commercial scale when the organism is in the post-exponential growth phase. In downstream processing:
- The mixture of nutrient broth, cells and extracellular enzymes is filtered and centrifuged to remove cellular material
- The liquid enzyme mixture is concentrated by evaporation, to give the bulk enzyme
The bulk enzyme may be:
- Concentrated by chromatography to give the pure enzyme
- Added to stabilisers to give the bulk liquid enzyme
- Precipitated and filtered, then sprayed and grinded to give the powdered enzyme
Immobilised enzymes are widely used commercially – they can be immobilised in three ways:
1. Cross linkage: the enzymes are linked together by gluteraldehyde, to form a mesh. This may damage some enzymes, but those that are not damaged remain very active
2. Entrapment: the enzymes are trapped in gel microcapsules or in a fibrous polymer mesh. This does not damage the enzymes, but may slow their action due to the substrate having to diffuse in
3. Adsorption: the enzymes are held by weak bonds on the surface of an adsorbing agent (e.g. glass bead, carbon particle, collagen).
The enzymes easily come into contact with the substrate, but it is expensive, and the enzymes may become detached