Batch and Continuous Sterilization techniques

Commodity employed in food industry

1. Batch & Continuous sterilization T echniques

2. Batch sterilization: Batch sterilization can be done by injecting the steam into the medium or direct electrical heating of medium. The culture media are subjected to sterilization at 121°C, in the bioreactor for 20-60 minutes. For the direct batch sterilization, the steam should be pure, and free from all chemical additives.

3. Batch sterilization is the reduction of contaminant organisms . The batch sterilization, a system goes through 3 steps: Heating, Holding, and Cooling. The entire volume of media is sterilized at once through the use of thermal or radiation techniques.

4. The temperature is increased until it reaches the sterilization temperature where it is held for a set period of time . During this phase, most of the unwanted microorganisms are destroyed. Finally, the system is cooled to bring the sterile media back to the desired temperature.

5. There are two disadvantages of batch sterilization: 1. Damage to culture media: Alteration in nutrients, change in pH and discolouration of the culture media are common. 2. High energy consumption: All this process involves wastage of energy, and therefore batch sterilization is quite costly. It takes a few hours (2-4 hrs.) for the entire contents of the bioreactor to attain the requisite temperature (i.e. 120°C). Another 20-60 minutes for the actual process of sterilization, followed by cooling for 1-2 hours.

6. Advantages: Most widely used technique Simple operation Low risk of contamination

7. Continuous sterilization:

8. Continuous sterilization is carried out at 140°C for a very short period of time ranging from 30 to 120 seconds.  This is based on the principle that the time required for killing microorganisms is much shorter at higher temperature . 

9. In Continuous sterilization the culture medium continuously pumping holding loop. Once the media is in a holding loop, steam is injected to the system via a nozzle. The sterile culture medium again pumped into the flash cooler to bring culture medium to normal temperature. The medium stays in this loop for a predetermined holding time until the entire medium is sterile.

10. Advantages of continuous sterilization: This process involves less wastage of energy, and because sterilization complete with in short period. Low risk of contamination.

11. Disadvantages: The certain chemical compounds in the medium become precipitated (e.g., calcium phosphate, calcium oxalate) due to very high temperature. The starch-containing culture media becomes viscous in continuous sterilization and therefore is not used.

12. Sterilization of Air : Industrial fermentations are carried out under continuous aeration . Air can be sterilized by filtration, heat and UV radiation . Among these, heat and filtration are most commonly used. For an effective fermentation, the air should be completely sterile, and free from all micro­organisms and suspended particles.

13. Air sterilization by heat: In the early years, air was passed over electrically heated elements and sterilized. But this is quite expense, hence not in use these days.

14. Air sterilization by filtration: Filtration of air is the most commonly used sterilization in fermentation industries. Depth filters: Membrane cartridge filters:

15. Depth filters: When the air is passed through a glass wool (fibrous) containing depth filters the particles are trapped and removed. The air is pass through this depth filter the microbial cells are removed by physical screening or entrapment.

16. Membrane cartridge filters: Membrane filters made up of cellulose ester or nylon. Membrane cartridge filters are smaller in size, simpler for operation and replacement. Membrane cartridge filters has capability to remove Bacteriophages form air. Bacteriophages are capable of crippling the industrial fermentation. e.g., bacteriophages interfere in the production of glutamic acid by Corynebacterium glutamicum .

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