Thursday, July 5, 2007

What is shake flask fermentation?

Shake Flask Fermentation

Shake flask fermentation is nothing but the fermentation carried out in a shake flasks, in particular Erlenmeyer flask.

The standard 250 ml Erlenmeyer flask is cheap and simple; most of the shaker tables designed to use these flasks although there are tables which can be adapted to allow other shapes or bigger flasks.

Baffles have been used in shake flasks to assist in the OTR, as well as preventing vortex formation, but there are only really suitable for low-volume short-term fermentations because of splashing which leads to the cotton-wool plug becoming damp preventing free flow oxygen.

Different plugs can be made of cotton-wool, glass wool, polyurethane foam, gauze or synthetic fibrous material. (An aluminium foil cup can sometimes be used in conjunction with these plugs). The plug has to be prevent airborne microorganisms from getting into the medium while at the same time allowing free flow of air into the flask, and for this reason it must not be allowed to become wet.

Shake Flasks and Bottles

These pieces of glassware can vary in size and form and in some instances have been designed and developed for specialist application.

Shake Flask Volume

The lower the volume of medium in a shake flask, the better will be the OTR (Oxygen Transport Rate). The minimum volume that can be practically obtained (e.g. 50 ml in a 250 ml shake flask) should give the best OTR and hence the best results. This will also be dependent on sample volume. Very low volumes can only be used for short-term fermentations, otherwise the medium will evaporate and the nutrients would become too concentrated for the culture to perform satisfactorily.

Shaker Tables

Shaker tables were designed to assist with oxygen transfer. These tables are designed to run for long periods of time and be free from vibration. The tables are driven by a motor, and normally a rotary shaking action or reciprocating shaking action is produced.

These shakers have to be robust and reliable with no vibration and silent running conditions. One can have a more sophisticated shaker by having an incubator shaking cabinet for shake-flask fermentation in a precisely defined environment. These cabinets can control the temperature, illumination, gaseous levels, and humidity.

Increasing the speed of a shaker can increase the oxygen transfer rate of a particular flask, therefore the optimum speed for that flask and culture has to be found by trial and error.

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