What is sterilization?Why sterilization is required?
Sterilization is technique to make anything free from organisms either by removing them or killing them.
The removal or killing all organisms from fermentation medium is the main aim of the sterilization process or else the contaminant will deteriorate the process.
Contaminant can enter into the fermenter from various points or sight like
- Improper sterilization of media
- Partial sterilization of air
- Cooling water system
- Through out-lets, in-lets or other openings
- Faulty inoculum procedure
- Due to faulty process used for pretreatment of crude ingredients
- Due to leakage in design of fermenter
If any foreign microorganism invades, the fermentation process then product will not be produce.
Thus, it is very necessary to sterilize the medium and other materials so that only required organisms, which we inoculate, will grow and give high yield of fermentation product. Thus, process of sterilization plays vital role in the fermentation processes.
We have discussed importance of sterilization. Following are the consequences of contamination of fermenter.
- The medium would have to support the growth of both the production organism and the contaminant resulting in a loss of productivity
- If the fermentation is a continuous one then the contaminant may outgrow the production organism and displace it from the fermentation
- The foreign organism may contaminate the final product for example single-cell protein where the cells separated from the broth constitute the product
- The contaminant may produce compounds, which make subsequent extraction of the final product difficult
- The contaminant may degrade the desired product this is common in bacterial contamination of antibiotic fermentations where the contaminant would have to be resistant to the normal inhibitory effects of the antibiotic and degradation of the antibiotic is a common resistance mechanism for example, the degradation of beta lactam antibiotics by beta lactamase producing bacteria
- Contamination of a bacterial fermentation with phage could result in the lysis of the culture
- Using a pure inoculum to start the fermentation
- Sterilizing the medium to be employed
- Sterilizing the fermenter vessel
- Sterilizing everything that is used during the process
- Maintaining aseptic conditions during the fermentation
Microorganisms will be removed by sterilization process which otherwise will create problem in fermentation process.
There are two main methods for the sterilization.
- Destruction of microorganism
- Removal of microorganism
Sterilization is carry out by many methods like
- Ultra sonic treatment
- Heat treatment
- Chemical treatment
The extent to which this procedure adoptsdetermine by the likely probability of contamination and the nature of its consequences.
Microbes that may contaminate the fermenter vessel include bacteria, fungi, protozoa, spores, and phages.
Destruction of microbes may be achieve by either chemical or physical methods.
The common physical agent is Moist Heat
- Moist heat is the satisfactory sterilization process in industry
- Removal of microorganisms done by filtration
- Various kinds of filters are available for this purpose
- Size of microorganism
- Effectiveness of filter
- Types of fermentation process
- Time of fermentation process
- Type and magnitude of contamination of the other article
Some fermentations are described as 'protected' - that is, the medium may be utilized by only a very limited range of microorganisms or the growth of the process organism may result in the development of selective growth conditions such as a reduction in pH.
The brewing of beer falls into this category hop resins tend to inhibit the growth of many micro-organisms and the growth of brewing yeasts tends to decrease the pH of the medium. Thus, brewing worts are boiled but not necessarily sterilized and, the fermenters are thoroughly clean with disinfectant solution but are not necessarily sterile. Also the precautions used in the development of inoculum for brewing are far less stringent than for example in an antibiotic fermentation.
However the vast majorities of fermentations are not 'protected' and if contaminated would suffer some of the consequences previously listed.
Which article to be sterilize?
- Sterilization is required for Media, Air, Fermenter, Feed and additives
- Different articles are sterilize by different methods
- Heat labile (Serum, blood or animal tissue) medium is sterilized by filter
- Heat stable media is sterilize by steam under pressure
- Air is mainly sterilized by filter
- Continuous sterilization process or
- Batch sterilization process