Dr. Nermin Hassan Ibrahim Ass. Prof. of Medical Microbiology and Immunology

Because we want to know how to inhibit or stop bacteria growth and want to control their metabolism to prolong shelf- life of food products.

 The Greek metabole, meaning change  It is the totality of an organism's chemical processes to maintain life. - Catabolism - Anabolism

C Sugar, Lipid Energy, Biosynthesis N Protein Biosynthesis O Air Energy

Overview of fermentation products formed from pyruvic acid by different bacteria

 1- Single cell protein  2- Production of baker’s yeast  3- Fermented foods  4- Organic acids  5. Biofuels  6. Amino Acids  7. Production of enzymes  8. Peptide hormones  9. Antibiotic Production

 The term ‘Single Cell Protein’ (SCP) = protein derived from microorganisms.  It was recognized that protein malnutrition is usually far more severe than that of other foods.  SCP would replace the need to increase proteins from plants such as oil beans or from animals such as fish. 8

 the limitations of conventional sources of proteins were recognized. These include: A. possible crop failure due to unfavorable climatic conditions in the case of plants; B. the need to allow a time lapse for the refreshment of stock in the case of fish; C. The limited land available for farming in the case of plant and cattle production.  On the other hand the production of SCP has many advantages : A. It was not subject to the changes of the weather and can be produced every minute of the year. B. Microorganisms have a much more rapid growth than plants or animals. C. waste products can be turned into food in the production of SCP. 9

 One of the most obvious is that many developing countries, where protein malnutrition actually exists, lack the expertise and/or the financial resources to develop the highly capital intensive fermentation industries involved.  Other criticisms of SCP are that microorganisms contain high levels of RNA and that its consumption could lead to uric acid accumulation, kidney stone formation and gout.  There was concern with the possibility of the presence of carcinogenic compounds in petroleum-grown SCP.  the concern was over the safe content the polycyclic aromatic hydrocarbons, fatty acids containing odd-numbered carbon skeletons and the presence of n-paraffins carried over from protein-grown yeasts fed to farm animals. 10

 A wide variety of substrates have been used for SCP production, they include hydrocarbons, alcohols, and wastes from various sources. 1. Hydrocarbons  methane has been most widely studied.  Others include propane and butane.  The major source of liquid hydrocarbons is crude petroleum. These hydrocarbons were first studied as a source of microbial vitamins and lipids 11

2. Alcohols Me thanol and ethanol are alternatives to petroleum based substrates.  Methanol Methanol is suitable as a substrate for SCP for the following reasons: (a) it is highly soluble in water (b) the explosion hazard of methanol is minimized in comparison with methane-oxygen mixtures; (c) it is readily available in a wide range of hydrocarbon sources (d) it requires less oxygen than methane for metabolism by micro- organisms and hence a lower cooling load; (e) it is not utilized by many organisms. 12

 Ethanol  Ethanol may be produced by the fermentative activity of yeasts. In the synthetic process however, it is produced by the hydration of ethylene.  Ethanol has the following advantages:  (a) Since it is already consumed in alcoholic beverages it is not quite as suspect a substrate for SCP as are gas oil and n-paraffins.  (b) It is like methanol, highly miscible with water  (c) Ethanol in contrast with methane can be more safely stored and transported  (d) As it is non-toxic it can be more easily handled.  (e) Ethanol is partially oxidized. For this reason, the fermentation of ethanol for SCP production requires comparatively less oxygen and hence releases considerably less heat than if it were unsaturated.  The major disadvantage in using ethanol for SCP production is that it is expensive. 13

3. Waste Products A. Plant/wood wastes: These are cellulose containing materials. B. Starch-wastes: Starch-containing wastes from rice, or potatoes, manufacturing industry are relatively easy to utilize in SCP production in comparison with cellulosic agricultural wastes. C. Dairy wastes: Whey is a by-product of the dairy industry resulting from the removal of proteins (and fat) in cheese manufacture. Saccharomyces fragilis is grown in it for a high- quality edible food yeast. 14

C. Wastes from chemical industries. D. Miscellaneous substrates: Molasses the by- product of the sugar industry is a well- known raw material for microbial industries. A wide variety of substrates may be used for SCP production. These include coffee wastes, coconut wastes, palm-oil wastes 15

 organisms to be used in SCP production should have the following properties: (a) Absence of pathogenicity and toxicity (b) Protein quality and content (c) Digestibility and organoleptic qualities (d) Adaptability to unusual environmental conditions 16

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 The nutritional value of SCP depends on the composition of the microbial cells used especially their protein, amino acid, vitamin, and mineral contents.  These to some extent also depend on the conditions of growth of the organism. 19

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