Fermentation:
The conventional definition of fermentation is the breakdown (metabolism) of
the larger molecules, for example carbohydrates, into simpler ones under the
influence of microorganisms for their enzymes. In a microbiological way,
fermentation is defined as, any process for the production of useful products
through culture of microorganisms, whereas in a biochemical sense, this would
mean the numerous oxidation-reduction reactions in which organic
compounds used as source of carbon and energy, act as acceptors or donors of
hydrogen ions. Although, fermentation was implied for example for brewing and wine
production from ancient times and during the end of fifteenth century,
brewing became partially industrialized in Britain. In the 19th century CagniardLatour and Schwan reported that the fermentation of wine and beer is
accomplished by yeast cells. Finally it was Pasteur who observed that
microorganism are associated with fermentation and are causing many
diseases in human beings.
At present, there are more than one million microorganisms known to be
present in nature out of which about a few hundred species synthesize the
useful products some of these important microorganisms are enumerated as;
Algae: Chlorella sorokiniara, Spiruline maxima.
Fungi: Aspergillus,Fusarium,Moniliforme,Gibberella,pencilliumchrysogenium,
P.n otatum,Rhizopus,T.reesei etc.
Actinomycetes: Micromonospora purpurea,Nocardia mediterrnei etc.
Bacteria: Clostridium acticum, Pseudomonas denitrificans, Bacillus substilis,
Bacillus polymyxa, Acetobacter lacti, Acetobacter woodi etc.
Factors that influence fermentation:
It is essential to maintain optimal growth environment in the reaction vessel
for maximum product formation. Maximal efficiency of the formation can be
achieved by continuously monitoring the variables such as the pH, temp,
dissolved oxygen, adequate mixing nutrient concentration, and foam
formation. Improved sensors are now available for continuous and automated
monitoring of these variables (i.e., on line measurement of pH)
1. pH: Most of the micro organisms employed in fermentation grow optimally
between pH 5.5 and 8.5 in the bioreactor, as the microorganisms grow, they
release metabolites into the medium which change pH. Therefore, the pH of
the medium should be continuously monitored and maintained at the optimal
level. This can be done by the addition of acid or alkaline base (as needed) and
a thorough mixing of fermentation contents (sometimes an acid or alkaline
medium components can be used to correct pH, besides providing nutrients to
the growing microorganism.)
2.Temperature: Temperature control is absolutely essential for a good
fermentation process. Lower temperature causes reduced product formation
while higher temperature adversely affects the growth of microorganisms. The
bioreactors are normally equipped with heating and cooling systems that can
be used as per the requirement, to maintain the reaction vessel at optimum
temp.
3. Dissolved O2: O2 is sparingly soluble in H2O(0.0084 g/l at 25C). Continuous
supply of O2 in the form of sterilized air is carried out by introducing air into the
bioreactor in the form of bubbles. Continuous monitoring of dissolved O2 conc.
is done in the bioreactor for optimal product formation.
4. Adequate mixing: Continuous and adequate mixing of the microbial cultures
ensure optimal supply of nutrients and O2, besides preventing the
accumulation of toxic metabolic byproducts. Good mixing (by agitation) also
