pH
Bacteria can grow at high pH (8.5-11.5) are called alkaliphiles. Acidophiles are those that grow at low pH (0.5-5). However, most microbes need near neutral conditions for optimum growth. Keeping pH constant can be difficult, so to check it, a pH meter or pH probe may be used to regulate it.
Water Activity
Like all organisms, microbes are sensitive to the osmolarity of the surrounding medium; at low osmolarity, water will be accumulated in the cell and at high osmolarity water will be lost. Lysis of the cell at low osmolarity is prevented by the presence of the cell wall. Growth at high osmolarity is dependent on whether the microbe has the ability to maintain a high osmolarity within the cell without damaging cellular metabolism.
In the laboratory, water activity and pH are controlled by the composition of the medium. Incubators are used to provide the correct temperature. Aeration to provide adequate O2 levels is normally achieved by shaking liquid cultures or by providing large surfaces of solid medium. Anaerobic conditions can be obtained b simply filling a bottle to the top with medium so that there is not much room for air, but for more stringent anaerobes, a reducing agent such as thioglycolate may be added to the medium.
Apparatus
The techniques applied and apparatus used in micro-organisms play an important part in the outcome of the product. These techniques may include stirring, fermentation and the extraction of the product. For an industry to achieve optimum condition to grow micro-organisms; the environment in which they are grown should be free from any sort of contamination but 100% contamination is very hard to achieve. However, by using the aseptic techniques it can help to minimise the chances.
Biotechnology
Bacteria have been used for thousands of years in the manufacture of a wide range of products, and this is called biotechnology. However, in the last 30 years or so, there have been many changes, such as how most industrial microbial processes are carried out. Fermenters are used, which allow for processes to be controlled to maximize production and reduce failure from contamination.
For example, vinegar is now produced by the aerobic conversion of ethanol to acetic acid by Acetobacter and Glucobacter. Vinegar can also be produced from any alcoholic liquor such as wine or cider. The traditional open-vat system was originally used, which required alcoholic liquor to be placed in shallow vats than allow considerable exposure to air.
Fermentation
Fermentation reactions lead to only a limited oxidation of an organic substrate. They do not need aerobic conditions because the required oxidant is an organic molecule which is produced by the fermentation process itself. Because the substrate is only partially oxidised, much of its potential energy remains locked up in the fermentation process.
Fermentation is a typically bacterial process, although brewer’s yeast is an exception to this rule. Although bacteria are able to ferment a variety of organic substances, most can utilise glucose. Different fermentations produce a wise range of end-products, some of which are commercially valuable. For example, dairy products such as cheese and yoghurt are produced by the activity of bacteria – Lacotbacillus and Streptococcus, which produce lactic acid as a fermentation product.
Industrial fermentation may be divided into two types: batch fermentation and continous fermentation.
Batch Fermentation
A tank of fermenter is filled with the prepared mash of raw materials to be fermented. The temperature and pH for microbial fermentation is properly adjusted, and occasionally nutritive supplements are added to the prepared mash. The mash is steam sterilized in a pure culture process. The inoculum of a pure culture is added to the fermenter, from a separate pure culture vessel.
Fermentation proceeds, and after the proper time the contents of the fermenter, are taken out for further processing. The fermenter is cleaned and the process is repeated. Thus each fermentation is a discontinuous process divided into batches.
Continuous Fermentation
In continuous fermentation, the substrate is added to the fermenter contillously at a fixed rate. This maintains the organisms in the logarithmic growth phase. The fermentation products are taken out continuously. The design and arrangements for continuous fermentation, are some what complex.
http://www.microbiologyprocedure.com/industrial-microbiology/continuous-fermentation-process.htm
