- Microbiologists use the term fermentation in total two different contexts.
- First, in metabolism, fermentation refers to energy-generating processes wherever organic compounds act as both electron donor and acceptor.
- Second, within the context of industrial microbiology, the term also refers to the growth of huge quantities of cells under aerobic or anaerobic conditions, within a vessel referred to as a fermenter or bioreactor.
- Apart from their use for cell cultivation, and for live vegetative cell and spore biotransformations, similar vessels are used in processes involving cell-free and immobilized enzyme transformations.
- However, here we will be considering fermenters for microbial, plant and animal cell culture.
- Although we will be primarily examining conventional fermenters, it must be remembered that, particularly with the advent of recombinant DNA technology, alternate systems for producing specific cell products are now available.
- Monoclonal antibodies are already extracted from the pathology fluid of rodents, vaccines can be produced in fruit or in sheep’s milk (e.g. Synthesis of malaria vaccine in bananas) and many other recombinant products may be manufactured in agricultural plants.
- Although solid-substrate fermentations are operated, most fermentations use liquid media, often referred to as broth, under aerobic or anaerobic conditions.
- Some, like beer and wine fermentations, are nonstirred, non-aerated and are not operated aseptically, whereas many others are stirred, aerated and aseptic.
- Fermentations are also broadly classified according to the organization of the biological phase, whether it is in suspension or in the form of a supported film.
- For suspended growth, the cells are freely dispersed in the growth medium and interact as individual or flocculated units.
- These systems may appear simple, but in reality nutrient and oxygen gradients may develop.
- In supported growth, the cells develop as a biofilm, normally on an inert support material and result in the formation of a complex interacting community of cells.
- Supported growth systems can be subdivided into fixed film processes, where the medium flows over the static support material; and fluidized expanded systems, where particles of support material are suspended in a liquid medium.
- Also, some microorganisms can be grown as unattached surface films at a liquid–air interface.