Question

for ster i l izat ion of fermentat ion equipment the method followed is

Answer 1

Sterilization of Culture Media and Gases:

For successful fermentation, it is absolutely essential to ensure:

a. Sterility of the media containing the nutrients.

 

b. Sterility of incoming and outgoing air.

c. Sterility of the bioreactor.

d. Prevention of contamination during fermentation.

A bioreactor can be sterilized by destroying the organisms by heat/chemicals/radiation or sometimes by physical procedures such as filtration.

Sterilization of media and air are discussed below:

1. Sterilization of Culture Media:

The constituents of culture media, water and containers contribute to the contamination by vegetative cells and spores. The media must be free from contamination before use in fermentation. Sterilization of the media is most commonly achieved by applying heat and to a lesser extent by other means (physical methods, chemical treatment, and radiation).

Heat sterilization:

Heat is the most widely used sterilization technique. The quality and quantity of contamination (i.e., the type and load of microorganisms), composition of the media and its pH and size of the suspended particles are the important factors that influence the success of heat sterilization.

In general, vegetative cells are destroyed at lower temperature in a short time (around 60°C in 5-10 minutes). However, destruction of spores requires higher temperature and relatively longer time (around 80°C for 15-20 minutes). Spores of Bacillus stearothermophilus are the most heat resistant. In fact, this organism is exploited for testing the sterility of fermentation equipment.

Physical methods:

The physical methods such as filtration, centrifugation, and adsorption (to ion-exchangers or activated carbon) are in use. Among these, filtration is most widely used. Certain constituents (vitamins, blood components, antibiotics) of culture media are heat labile and therefore, are destroyed by heat sterilization. Such components of the medium are completely dissolved (absolutely essential or else they will be removed along with microorganisms) and then subjected to filter sterilization.

There are a couple of limitations of filtration technique:

1. Application of high pressure in filtration is unsuitable for industries.