PRESSURE AND AUTOCLAVING

One of the essential components in the use of autoclave is pressure. Autoclaves are usually operated at a higher pressure than the environment. High pressure is needed in order to achieve the sterilizing temperature of 121 degrees centigrade. Without pressure water can only boil at 100 degrees centigrade under normal atmospheric pressure. ( Of course at higher elevation such as on mountain tops, where the atmospheric pressure is less water boils at lower temperature!)
Generally pressure of about 15 psi is required for autoclaving. This pressure is achieved by heating the water in the sealed compartment of the autoclave. High pressure is due to the built up of the steam as the water is heated. There is a pressure safety valve in autoclaves that the high pressure is not overshot. ( This explains the regular hissing sound produced during autoclaving as excess pressure is regulated)
While it is very important to build the pressure to the correct value before autoclaving is initiated, it is also important that at the end of a sterilization that the pressure is brought back to normal values before the autoclave is opened to remove the sterilized items.
Heating and cooling processes take time. Most users are impatient for the time it takes to cool and lower the pressure. Impatience often results in users trying to speed up the release of pressure by opening the release valve too quickly. This action would result in the boiling over of the contents of the flasks and test tubes which could result in the wetting of the cotton plugs and increase the possibility of contamination.
Opening the doors to quickly could result in the sudden release of internal pressure by the autoclave. This could result in scalding of the body as the hot steam rushes out. Release of pressure must be done slowly and only when it reaches zero is the door of the autoclave opened

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HIGH PRESSURE FERMENTATION TECHNOLOGY

Most fermentation studies are generally carried out under ambient pressure, despite the fact that the fermentor is often slightly positively pressurized. The slight positive pressure in most closed system fermentation studies are due to the aeration process of the fermentor, whereby air is forced to enter the broth or fermentation media for the microbial requirements. Positive pressure within the fermentation vessel is also due to the build up of back pressure due to the restriction of the exhaust gas vent.
The positive pressure is in many ways good for the fermentation process as it not only increase the solubility of air into the broth but also reduce the chances of external contaminants coming into the fermentation process. Of course there are also negative aspects of positive pressure on the fermentation process
High pressure does have the the effect of influencing the rates and direction of the metabolism of the microorganisms. This is especially so when in a particular way gases are products or side products of the pathway. High pressure in the fermentor will in a way prevent the formation or expulsion of the gaseous product into the surrounding fermentation media. This effect of preventing the release of the gaseous products will have the effect of interfering with the equilibria of the various biochemical reactions and may even result in toxicity of the internal environment of the cell and diversion of pathways.
How significant this impact will depend on many factors such as duration and intensity of the pressure applied.
One very important industrial impacts of high pressure fermentation will be on the production of organic volatiles. This is especially so in food and beverage fermentations. Often the taste, smell and characteristics of the fermentation products will determine its popularity and acceptance. If the fermented foods have lost or changed its volatile profile it might not be marketable.
While it is true these organic volatiles evaporate easily and are affected by the surrounding temperature, it is also the effect of the surrounding pressure to concentrate it within the closed fermentation system or let the valuable organic volatiles disappear into the environment.
What is important to know in detail now how does the high pressure exerted on the fermentation process affect the biochemistry and physiology of the process? Is there a way for us to control the direction of this fermentation by manipulating the fermentation pressure. Also important to know is how does high pressure fermentation in creating unwanted side side reactions or side products?
New designs in fermentors have to be created to accommodate the study on high pressure fermentation

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