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Introduction to Fermentation Technology Fermentation word is derived from Latin verb “fervere” which means to boil. This technology has been perceived in different sense by the world of microbiologist and biochemist. For biochemists, “fermentation is a catabolic process leading to generation of energy”. Whereas, according to industrial microbiologist, “fermentation is the process of mass cultivation of micro- organisms that convert substrates into valuable products through aerobic or anaerobic route”. A general outline of the process is outlined in figure 1. Fermentation technology has wide application for the production of products such as organic solvents (acetone, alcohols), fermented beverages (wine, beer, whisky), and other products like enzymes, amino acids, vitamins, pharmaceuticals etc. The fermentation processes is dependent on microbial growth, which in turn is governed by many biochemical and physical parameters. The motive of all parameters is to provide the most suitable environment for the growth of micro-organisms. This chapter is dedicated to discuss the growth characteristics of micro-organisms, the types and needs of fermentation process and their applications.
Figure 1: Outlines of Fermentation Technology
The component parts of a fermentation process Regardless of the type of fermentation (with the possible exception of some
transformation processes) an established process may be divided into six basic component parts:
♦ The formulation of media to be used in culturing the process organism during the development of the inoculum and in the production fermenter. ♦ The sterilization of the medium, fermenters and ancillary equipment. ♦ The production of an active, pure culture in sufficient quantity to inoculate the production vessel. ♦ The growth of the organism in the production fermenter under optimum conditions for product formation. ♦ The extraction of the product and its purification. ♦ The disposal of effluents produced by the process.
Importance of Fermentation Process There are five major groups of commercially important fermentations: ♦ Those that produce microbial cells (or biomass) as the product. (Eg. SCP - Spirulina) ♦ Those that produce microbial enzymes. (Eg. Amylase, Protease, Catalase) ♦ Those that produce microbial metabolites. (Eg. Ethanol, Citric acid, Vitamins) ♦ Those that produce recombinant products. (Eg. Insulin, Human serum albumin) ♦ Those that modify a compound which is added to the fermentation the transformation process. (Eg. Steroids, antibiotics)
Microbial Growth Kinetics The most important criterion of a fermentation process is to achieve good yield of product which in turn is dependent on the proper microbial growth. The micro-organism require optimum pH, temperature, oxygen, minerals, energy source and other raw material conditions to complete their life cycle under six phases as illustrated in figure 2 and discussed below.
a) Lag phase is the no microbial growth phase, also known as acclimatization period, when the newly inoculated micro-organism adapt to their new environment and hence show no increase in number.
b) Acceleration phase is the period when microbes start increasing in number.
c) Log phase is the period when microbes demonstrated exponential increase in their number and utilizes most of the raw materials for their growth.
The figure depicts the microbial growth in a batch fermentation system where one time addition of microbial culture and sterilized media components is done. It is a closed system, where no further addition or removal of materials are followed until the all the stages of microbial life cycle are completed and product is formed. After completion, the product is removed and processed under various downstream processes. Another type of fermentation process is fed-batch, where nutrients are fed more than one times during microbial cultivation, but products are harvested only at the end of the process. This method provides opportunity to control the yield and productivity of the process by adding limiting nutrients at defined phase of cell growth. For example the substrates such as ethanol, methanol or acetic acid may be added at the later stages of cell growth to avoid their inhibitory effect at initial growth phase. The most valuable method for high turnover of industrial products is the continuous fermentation that allows continuous supply of nutrients and raw materials. To maintain a static environment inside the vessel, products are also harvested continuously from the overflow of fermenter. The exponential growth of microbes is maintained for a prolonged period which is suitable for production of primary metabolites such as organic acids, amino acids, single cell protein etc.
Classification of fermentation process Fermentation is classified as warm, cool or spontaneous as per the temperature requirement. ♦ Warm fermentation is carried out by Saccharomyces cerevisiae at 15 – 20 ˚C temperature. ♦ Cool fermentation is carried out by Saccharomyces pastorianus at around 10 ˚C temperature. ♦ Spontaneous fermentation is carried out by the wild yeast and bacteria of the oak barrels in which the fermentation takes place. There is no deliberate addition of specific yeast strain, and a mixed culture is generally employed for the fermentation.
Types of Fermentation Technology Fermentation occurs in aerobically or anaerobically. a. Aerobic fermentation: b. Anaerobic fermentation: ♦ An anaerobic fermentation is the process that occurs without atmospheric oxygen
Advantages of Fermentation Technology ♦ Preservation and enriches food, improves digestibility, and enhances the taste and flavors of foods. ♦ Potential of enhancing food safety by controlling the growth and multiplication of number of pathogens in foods. ♦ Important contribution to human nutrition, particularly in developing countries, where economic problems pose a major barrier to ensuring food safety. ♦ Low energy consumption due to the mild operating conditions relatively low capital and operating costs relative simple technologies. ♦ They cause specific and controlled changes to foods by using enzymes. ♦ Preservation and detoxification of the food. ♦ Waste treatment. ♦ Health related product.
Disadvantages of Fermentation Technology ♦ Hazardous contamination always exists in fermented food. ♦ The uneven distribution of salt in lactic acid fermentation fish products and contamination of Aspergillus flavus in traditional starter culture for rice wine and soya bean sauce result in severe food poisoning incidences. ♦ Health (obesity).
