Fundamental Food Microbiology, Third Edition - Fuad Fathir

MICROBIAL METABOLISM OF FOOD COMPONENTS 91
Geotrichum, and Penicillium. Oxidative enzymes are produced mainly by the molds.
Both groups of enzymes are associated with food spoilage, but oxidative enzymes
are also important for desirable flavor in mold-ripened cheeses.
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VI. CONCLUSION
Microbial growth in food is accomplished through the metabolism of food nutrients,
principally the metabolizable carbohydrates, proteins, and lipids. Many metabolic
pathways can be used, which are determined by the nature and concentration of a
nutrient, the microbial type, and the oxidation–reduction potential of the food environment.
Many types of end products are produced during metabolism of the nutrients,
which, depending on the chemical nature, are associated with food spoilage,
food poisoning, or production of fermented food. Some are also used to improve
texture and flavor of foods. The metabolic end products are also useful to identify
unknown microbial isolates from a food. As long as the physical and nutritional
environments are maintained, bacterial cells continue to multiply, generating energy
and cellular materials through the metabolic processes. However, a change in the
environment can cause some species to shut down the cell multiplication cycle and
trigger the sporulation cycle, in which a cell is differentiated as an endospore. This
survival strategy under unfavorable conditions and its importance in food microbiology
are discussed in Chapter 8.
REFERENCES
1. Lengeler, J.W., Drews, G., and Schlegel, H.C., Biology of the Prokaryotes, Blackwell
Science, New York, 1999, pp. 59, 110, 163.
2. Gottschalk, G., Bacterial Metabolism, 2nd ed., Academic Press, New York, 1986, pp.
13, 96, 141, 210.
3. Rose, A.H., Chemical Microbiology, Butterworths, London, 1965, pp. 79, 85, 94.
4. Sneath, P.H.A., Ed., Bergey's Manual of Systemic Bacteriology, Williams & Wilkins,
Baltimore, 1986.
5. Gunsalus, I.C. and Stanier, R.Y., Eds., The Bacteria, Vol. II, Academic Press, New
York, 1961, pp. 59, 151.
QUESTIONS
1. Discuss the major differences among aerobic respiration, anaerobic respiration,
and fermentation of food nutrients by microorganisms.
2. Discuss how aerobes, anaerobes, and facultative anaerobes differ from each other
in their ability to transfer electrons by different acceptors.
3. A facultative bacterial species is growing anaerobically in the following foods:
one rich in carbohydrates but low in proteins, the second rich in proteins but low
in carbohydrates, and the third rich in both. Also, the carbohydrates and proteins