Micro-organisms processes

Enzymes are proteins of high molecular weight and possess exceptionally high catalytic properties. These are important to plant and animal life processes. An enzyme, E, is a protein or protein-like substance with catalytic properties. A substrate, S, is the substance that is chemically transformed at an accelerated rate because of the action of the enzyme on it. Most enzymes are normally named in terms of the reactions they catalyze. In practice, a suffice -ase is added to the substrate on which die enzyme acts. Eor example, die enzyme dial catalyzes die decomposition of urea is urease, the enzyme dial acts on uric acid is uricase, and die enzyme present in die micro-organism dial converts glucose to gluconolactone is glucose oxidase. The diree major types of enzyme reaction are ... 

There are many reactions in which the products formed often act as catalysts for the reaction. The reaction rate accelerates as the reaction continues, and this process is referred to as autocatalysis. The reaction rate is proportional to a product concentration raised to a positive exponent for an autocatalytic reaction. Examples of this type of reaction are the hydrolysis of several esters. This is because the acids formed by the reaction give rise to hydrogen ions that act as catalysts for subsequent reactions. The fermentation reaction that involves the action of a micro-organism on an organic feedstock is a significant autocatalytic reaction. 

Within the chemical industry, micro-organisms and enzymes are often used as catalysts. It is possible for a unit operation in an essentially chemical production process to be a biochemically catalysed step giving rise to a mixed chemical/biochemical production process. The products of these reactions include organic chemicals, solvents, polymers, pharmaceuticals, and purfumes. Mixed chemical/biochemical production processes are continuously innovated and optimised, mainly for economical reasons. 

Micro-organisms with resistance to environmental stresses such as solvents, extremes of pH, high salt concentration, and having broad temperature and dissolved oxygen optima are more suited to process applications. Improved process instrumentation and... 

We have seen that both the maintenance energy requirement and the P/O quotient of the process micro-organism influences the rate of product formation. In the following sections we will consider how these two factors can be determined, together with the maximum biomass yield. 

In this chapter we examine the processes that have been developed to produce micro-organisms as a source of food protein. We will examine the reasons why micro-organisms have been considered as alternative protein sources, the substrates on which they have been grown, the various process technologies developed and the comparative economics of these processes. One process will be examined in depth, to illustrate how a team composed of such diverse people as microbiologists, process engineers, patent lawyers and cost analysts work together to develop a marketable product. 

We have seen that only certain micro-organisms that conform to nutritional and safety requirements are suitable for food or feed, and that food has more strict requirements than feed. In addition, for use as food, SCP should have a reduced nudeic add content and should be palatable. Most often this means that its use is limited to processed foods, in which food technologists can produce acceptable tastes, smells and textures. 

Finally the word fermentation will be used in its industrial sense, that is a commercially viable process in which a micro-organism produces a required product or change. 

The first of the antibiotics that found practical use as a therapeutic was penicillin. The success of penicillin initiated a vast screening process all over the world, which resulted in the isolation of a large number of antibiotic substances from various natural sources. Many of these compounds were produced by micro-organisms and prove to be lethal for other micro-organisms. Many of these compounds were also very toxic to humans and could not be used therapeutically. Nevertheless a large number of classes of useful compounds were produced. The chemical structures of members of some of the most important classes are shown in Figure 6.1. 

For a high-quality product, the substrate itself must be relatively pure to minimise carryover of impurities to the final product Most industrial process micro-organisms produce optimal yields of exopolysaccharides from carbohydrate and the most commonly used substrates for industrial production are ... 

Considerable interest arose during the 1970 s and 1980 s in the use of micro-organisms to produce useful fatty adds and related compounds from hydrocarbons derived from the petroleum industry. During this period, a large number of patents were granted in Europe, USA and Japan protecting processes leading to the production of alkanols, alkyl oxides, ketones, alkanoic adds, alkane dioic acids and surfactants from hydrocarbons. Many of these processes involved the use of bacteria and yeasts associated with hydrocarbon catabolism. 

Addition of antibiotics to the fermentation broth may be used to avoid problems associated with growth revertants (eg auxotrophic back mutation) ensure that genetic material (eg plasmid DNA) is maintained within the process micro-organism. 

Potential effects on the micro-organisms used for industrial food processing... 

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