Biomedical Engineering Reference
In-Depth Information
7 Fermentation
Mark R. Wilkins and Hasan Atiyeh
From ancient times man has used microorganisms to produce valuable products. The first
instances of the use of microbiology were the production of bread with yeast, followed
closely by beer and wine fermentation. Fermented milk products such as yogurt, kefir, and
ghee are found throughout the world. Though the mechanisms behind the production of
these products have only been understood for the last 100-150 years, their importance in
preserving foods and beverages from spoilage and the prevention of food-borne diseases has
long been appreciated.
In addition to food products, microorganisms have also played an important role in the
production of industrial chemicals and pharmaceuticals. Many products, such as acetone,
butanol, glycerol and ethanol, were exclusively produced from microbial fermentations
during the two World Wars due to lack of petroleum and other raw materials. As the Second
World War ended and the price of petroleum declined, petrochemical methods of producing
these and other chemicals emerged as cheaper alternatives to microbial production methods;
thus, microbial chemical production methods were abandoned.
In recent years, the price of petroleum has increased again. As emerging economies
such as China and India increase their demand for petroleum and put more pressure on
petroleum prices and supplies, the need for alternative chemical production methods using
renewable resources has been recognized by governments and industries throughout the
world. Also, the recognition of carbon dioxide (CO 2 ) emissions from combustion of fossil
fuels as a cause of global climate change has further highlighted the need for production
methods that produce less carbon dioxide. As a result of increased petroleum prices and
awareness of the role of carbon dioxide in climate change, microbial-based chemical
production processes that were previously abandoned have become the subject of intense
research and development effort.
The word fermentation conventionally is used in several different ways. However, in this
chapter it will be used only in the strict definition of anaerobic and/or microaerobic microbial
processes. Anaerobic processes are those where oxygen is not present and microaerobic
processes are those where oxygen is present at concentrations much lower than those in air
(21% by volume). Some discussion of aerobic alternatives to fermentation processes will
also be discussed.
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