II) Shake Culture:

It is very simple and effective system of suspension culture. In this method, single cells and cell aggregates in fixed volume of liquid medium are placed in conical flask. Conical flasks are mounted with the help of clip on a horizontal large square plate of an orbital platform shaker. The square plate moves by a circular motion at 60-180 rpm.

III) Spinning Culture:

Large volume of cell suspension may be cultured in 10L,bottles which are rotated in a culture spinner at 120 rpm at an angle of 45 0.

IV) Stirred Culture:

This system is also used for large scale batch culture. In this method, the large culture vessel is not rotated but the cell suspension inside the vessel is kept dispersed continuously by bubbling sterile air through culture medium. The use of an internal magnetic stirrer is the most convenient way to agitate the culture medium safely. Magnetic stirrer revolves at 200-600 rpm. The culture vessel is a 5-10 litres round bottom flask.

B) Continuous Culture System:

In this system, the old liquid medium is continuously replaced by the fresh liquid medium to stabilize the physiological stage of the growing cells. Normally, the liquid medium is not changed until the depletion of some nutrients in the medium and the cells are kept in the same medium for a certain period. As a result, the active growth phase of the cell declines the depletion of nutrient. The cells passing through out flowing medium are separated mechanically and reintroduced in the culture.

I) Chemostats:

In this system, cultures vessels are generally cylindrical or circular in shape and posses inlet and outlet pores for aeration and for introduction of and removal of cells and medium. The liquid medium containing the cell is stirred by a magnetic stirrer. The introduction of fresh sterile medium, which is pumped in at a constant rate into the vessel is balanced by the displacement of an equal volume of spent or old medium and cells.  Such a system can be maintained in a steady state so that new cells are produced by division at a rate which compensate the number lost in outflow of spent medium.

II) Turbostats:

In this system, the input of medium is intermittent as it is mainly required to control the rise in turbidity due to cell growth. The turbidity of a suspension culture medium changes rapidly when cells increase in number due to their steady state growth. The changes in turbidity of the culture medium can be measured by the changes of optical density of the medium. In Turbostats an automatic monitoring unit is connected with the culture vessel and such unit adjusts the medium flow in such a way as to maintain the optical density or PH at chosen, present level.

23)Fermentation Biotechnology: principles, processes and products A general definition of fermentation is an energy-yielding anaerobic metabolic process in which organisms convert nutrients (typically carbohydrates) to alcohols and acids (lactic acid and acetic acid).

The most commonly known definition for fermentation is the conversion of sugar to alcohol, using yeast, under anaerobic conditions, as in the production of beer or wine, vinegars and cider. 

However, in biotechnology, the term is used more loosely to refer to growth of microorganisms on food, under either aerobic or anaerobic conditions.

Fermentation tanks, also called bioreactors, used for industrial fermentation processes are glass, metal or plastic tanks, equipped with gages and settings to control aeration, stir rate, temperature, pH and other parameters of interest. Units can be small enough for bench-top applications (5-10 L) or up to 10,000 L in capacity for large-scale industrial applications. Fermentation units such as these are used in the pharmaceutical industry for the growth of specialized pure cultures of bacteria, fungi and yeast, and the production ofenzymes and drugs.

Microbial fermentations may be classified into the following major

group^:^

(i) Those that produce microbial cells (biomass) as the product.

(ii) Those that produce microbial metabolites.

(iii) Those that produce microbial enzymes.

(iv) Those that modify a compound which is added to the fermenta-

tion - the transformation processes.

(v) Those that produce recombinant products.

Before the fermentation is started the medium must be formulated and sterilized, the fermenter sterilized, and a starter culture must be available in sufficient quantity and in the correct physiological state to inoculate the production fermenter. Downstream of the fermenter the product has to be purified and further processed and the effluents produced by the process have to be treated.