Fermentation preparation

Inoculum

To start a fermentation, you need a preculture with a certain number of healthy cells as an inoculum. A culture used to inoculate (inoculum) for fermentation should meet the following criteria:

• Healthy and in an active state to minimize lag phase time

• Free of contamination

• Suitable morphological form

• Available in sufficient volume

• Retain its product-forming capabilities

Avoid contamination

One of the worst things that can happen during fermentation experiments is to detect contaminants. Contaminants are unwanted microorganisms that compete with the original strain over nutrients, and disrupt the experiment. Contaminants can be detected microscopically, or from the dataset. A contaminant will often grow rapidly, thereby giving rise to very high CO₂-levels, and a high biomass concentration relative to the product. It is extremely important to prevent contamination; therefore, the bioreactor must be sterilized before starting with the fermentation.

Fermentors or bioreactors can be sterilized with or without the medium. Bioreactors are normally sterilized by heating the jacket or coil of the bioreactor using steam in the vessel. For sterilization, steam pressure inside the vessel is 15 psi and held for 20 min. After sterilization complete, it is important to maintain positive pressure inside the vessel; otherwise, a vacuum may develop and unsterile air be drawn into the vessel.