PURE CULTURE VERSUS MIXED CULTURE FERMENTATIONS

In the fermentation industry, we normally encounter two types of fermentation such as:
1 Mixed culture fermentations
2) Pure culture fermentations


MIXED CULTURE FERMENTATIONS

In mixed culture fermentations, the fermentation process is considered as septic fermentation and involves more than one species of microorganisms. Generally mixed culture fermentation involves many types of microorganisms for the fermentation process is to complete its fermentation.

The most common types of mixed culture fermentations are always associated with food or even beverage fermentation. In these fermentations, the inocula are usually introduced "naturally" and these fermentations usually show the phenomenon of microbial succession in which different types of microorganisms will predominate as the fermentation progresses. Sewage treatment is also an example of mixed culture fermentation.

Complexity of mixed culture fermentations are usually brought about by the complexity of the substrate composition. The breakdown of the complex substrate require various array of microorganisms to act upon it. In the process of breaking down the complex substrate with the chemistry of the substrate changing and the environmental parameters changing as product of microbial metabolism, certain species are suppressed while certain species will exploit the new conditions


PURE CULTURE FERMENTATIONS
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Pure culture fermentations are fermentations being carried out only by one type of microorganisms throughout the fermentation process. Of course in nature pure culture fermentations rarely occurs as there are always the presence of many types of microorganisms in nature and that inter species competition is a very strong force to contend with.

Pure culture fermentations are only carried out by the fermentation industries interested only in obtaining fermentation products of that particular microorganisms and not others.

In fact the presence of other microorganisms in the fermentation is actively prevented and these unwanted microorganisms are called as microbial contaminants which can affect the desired fermentation process negatively.

As we have said earlier here, pure culture fermentations in nature is not normal or usual. In order for the industrial fermentations to carry out pure culture fermentations, they have to carry out certain steps such as:

1) Obtaining pure culture or strains of the desired microorganism
2) Build up sufficient biomass for the fermentation process of the desired microorganism
3) Prepare sterile media that can only be inoculated by the desired microorganism
4) Prevent the unwanted entry of any other undesired microorganisms throughout the fermentation process, from upstream, right down to downstream processing

Aseptic techniques and maintaining stringent aseptic integrity of the fermentor and the fermentation system is essential for the success of the pure culture fermentations