Fermentation has many important uses in industry. Though the word fermentation can have stricter definitions, when speaking of it in industrial fermentation it more loosely refers to the breakdown of organic substances and re-assembly into other substances. Somewhat paradoxically, fermenter culture in industrial capacity often refers to highly oxygenated and aerobic growth conditions, whereas fermentation in the biochemical context is a strictly anaerobic process.
Ancient fermented food processes, such as making bread, wine, cheese, curds, idli, dosa, etc., can be dated to more than 6,000 yr ago. They were developed long before man had any knowledge of the existence of the microorganisms involved. Also, fermentation is a powerful economic incentive for semi-industrialized countries, in their willingness to produce bio-ethanol.
Pharmaceuticals and the biotechnology industry
There are 5 major groups of commercially important fermentation:
- Microbial cells or biomass as the product, e.g. bakers yeast, lactobacillus, etc.
- Microbial enzymes: catalase, amylase, protease, pectinase, glucose isomerase, cellulase, hemicellulase, lipase, lactase, streptokinase, etc.
- Microbial metabolites :
- Recombinant products: insulin, HBV, interferon, GCSF, streptokinase
- Biotransformations: phenyl acetyl carbinol, steroid biotransformation, etc.
Nutrient sources for industrial fermentation
Growth media are required for industrial fermentation, since any microbe requires water, oxygen, an energy source, a carbon source, a nitrogen source and micronutrients for growth.
Carbon & energy source + nitrogen source + O2 + other requirements → Biomass + Product + byproducts + CO2 + H2O + heat
|Glucose||corn sugar, starch, cellulose|
|Sucrose||sugarcane, sugar beet molasses|
|Protein||soybean meal, cornsteep liquor, distillers' solubles|
|Ammonia||pure ammonia or ammonium salts|
|Phosphorus source||phosphate salts|
Trace elements: Fe, Zn, Cu, Mn, Mo, Co
Antifoaming agents : Esters, fatty acids, silicones, sulphonates, polypropylene
Buffers: Calcium carbonate, phosphates
Precursors: Directly incorporated into the desired product: Phenyl ethylamine into Benzyl penicillin, Phenyl acetic acid into Penicillin G
Inducers: The majority of the enzymes used in industrial fermentation are inducible and are synthesized in response of inducers: e.g. starch for amylases, maltose for pollulanase, pectin for pectinase,olive oil and tween are also used at times.
In the process of sewage disposal, sewage is digested by enzymes secreted by bacteria. Solid organic matters are broken down into harmless, soluble substances and carbon dioxide. Liquids that result are disinfected to remove pathogens before being discharged into rivers or the sea or can be used as liquid fertilisers. Digested solids, known also as sludge, is dried and used as fertilisers. Gaseous by-products such as methane, can be utilised as biogas to fuel generators. One advantage of bacterial digestion is that it reduces the bulk and odour of sewage, thus reducing space needed for dumping, on the other hand, a major disadvantage of bacterial digestion in sewage disposal is that it is a very slow process.
Phases of microbial growth
When a particular organism is introduced into a selected growth medium, the medium is inoculated with the particular organism. Growth of the inoculum does not occur immediately, but takes a little while. This is the period of adaptation, called the lag phase. Following the lag phase, the rate of growth of the organism steadily increases, for a certain period--this period is the log or exponential phase. After a certain time of exponential phase, the rate of growth slows down, due to the continuously falling concentrations of nutrients and/or a continuously increasing (accumulating) concentrations of toxic substances. This phase, where the increase of the rate of growth is checked, is the deceleration phase. After the deceleration phase, growth ceases and the culture enters a stationary phase or a steady state. The biomass remains constant, except when certain accumulated chemicals in the culture lyse the cells (chemolysis). Unless other micro-organisms contaminate the culture, the chemical constitution remains unchanged. Mutation of the organism in the culture can also be a source of contamination, called internal contamination.
- Schuytser, M.A.I., 2003, Solid state fermentation, PhD Thesis, Wageningen UR
- Biochemical Engineering Fundamentals by J.E. Bailey and P.F. Ollis, McGraw Hill Publication
- Principles of fermentation technology by Stansbury, P.F., A. Whitaker and S.J. Hall, 1997