2 [a] State the effects of sterilization on mixing in a batch bioreactor Nyataka

Question

2 [a] State the effects of sterilization on mixing in a batch bioreactor Nyatakan kesan pensterilan ke atas percampuran di dalam bioreaktor kelompok. 5 marks/markah) For the inactivation of B. subtilis spores, A-9.5 x 1037 min., and E-687 kcal/mol. Assuming that a liquid containing these spores is instantaneously sterilized at 115°C, calculate the time required to give a destruction ratio of 106 [b] Untuk ketidakaktifan spora B. subtilis, A-9.5 x 10 min, dan E -68.7 kkal/mol. Andaikan cecair itu mengandungi spora yang boleh disteril dengan serta merta pada 115"C, kirakan masa yang diperlu untuk menghasilkan nisbah kemusnahan 10 5 marks/markah)

Explanation / Answer

[a] Main aim of batch sterilization process is still to attain the necessary chance of getting sterility with the least change in nutrient value of the medium. Continuous sterilization process is better than batch sterilization process in avoiding the damage of nutrients than a continuous sterilization process.The maximum temperature, which is possible in batch sterilization, is 121°C therefore a method adopted so that medium exposed to this high temperature for a short period.High temperature and short time sterilization attained by taking into consideration the heating and cooling time of the batch sterilization.Deindoerfer and Humphrey (1959) offered a method to evaluate the role of heating and cooling periods in sterilization process.

The following point should take into consideration for a batch sterilization process

1. How much temperature of the fermentation medium is increased during heating or decreased during cooling periods of the batch sterilization

2. The initially number of micro-organisms in the medium

3. The thermal death rate of the selected organism

Requisite Del factor is design by knowing the initial number of organisms in the medium and the danger of contamination. Commonly accepted threat of contamination is one in 1000, which means number of living organisms after time t is 0.001. For example if any unsterile broth contain 1011 number of cells then Del factor for that situation is 32.2

However, the killing of cells take place during both the heating period and cooling period of the sterilization process in addition to during holding period at 121°C

So, Del factor can be overall = heating +holding +cooling

Knowing the temperature and time required to reach that temperature during heating period and cooling period of sterilization process it is possible to determine the overall Del factor by these periods

Thus, from the Del factors contributed by heating and cooling periods, it is possible to estimate the holding time that may be required for overall Del factor Batch sterilization Methods The batch sterilization of the medium for fermentation achieved either in the fermentation vessel or in a separate mash cooker. Richards (1966) considered the relative merits of in situ medium sterilization and the use of a special vessel.

Advantages of a separate medium sterilization vessel

The medium sterilized in a cooker in a more concentrated form than would be used in the fermentation and then diluted in the fermenter with sterile water prior to inoculation. This would allow the construction of smaller cookers One cooker may be used to serve several fermenters and the medium may be sterilized as the fermenters are being cleaned and prepared for the next fermentation, thus saving time between fermentations In some fermentation, the medium is at its most viscous during sterilization and the power requirements for agitation increased lessen by aeration. Fermenter equipped with a powerful motor would provide sterile medium for several fermenters The fermenter spared the corrosion, which may occur with medium at high temperature.

Disadvantages of a separate medium sterilization vessel

The cost of constructing a batch medium sterilizer is much the same as that for the fermenter.

If a cooker serves a large number of fermenters complex pipe work would be necessary to transport the sterile medium, with the inherent dangers of contamination.

Mechanical failure in a cooker supplying medium to several fermenters would render all the fermenters temporarily redundant (unneeded). The provision of contingency equipment may be prohibitively costly The design of continuous sterilization.

Advantages of batch sterilization over continuous sterilization

1. Lesser assetsapparatusexpenditure

2. Less chance of contamination - processes require the aseptic inoculums transfer of the sterile broth to the sterile vessel

3. Easier manual control

4. Easier to use with media having a high amount of solid material

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