72 ◾ Fundamental Food Microbiology
QUESTIONS
1. List the intrinsic and extrinsic factors necessary for growth of microorganisms in a food.
2. What are the major nutrients in food that are metabolized by the microorganisms? List the
major groups of carbohydrates present in foods. List the carbohydrates in milk and meat, the
pentoses in plant foods, and an oligosaccharide in plant foods.
3. Discuss how bacteria are able to metabolize large molecules of carbohydrates, proteins, and
lipids. How do molds differ from bacteria in the metabolism of these molecules?
4. Discuss the importance of antimicrobials in foods that can adversely affect microbial growth.
5. Define A W and explain the desorption and adsorption processes of moisture in a food.
Discuss the importance of A W in microbial growth. How do halophilic, osmophilic, and
xerophilic microorganisms differ in minimum A W needed for growth?
6. Define pH and discuss factors that influence the pH of a food. Discuss the role of pH on
microbial growth. How does a bacterial cell maintain a high intracellular pH (6.0) while
growing in a low-pH (5.0) environment? Give examples of an aciduric bacterium and an
acid-tolerant bacterium.
7. Define redox potential and discuss how it influences microbial growth in a food. How can
microorganisms be grouped on the basis of their growth capabilities at different redox potentials and oxygen availabilities?
8. How are microorganisms grouped on the basis of their temperature of growth and survival?
Discuss the significance of psychrotrophic and thermoduric microorganisms in the processing and refrigerated storage of foods.
9. What is quorum sensing? How does quorum sensing affect bacterial growth in foods?
References
1. Lengeler, J.W., Drews, G., and Schlegel, H.G., Biology of the Prokaryotes, Blackwell Science, New York,
1999, pp. 80, 110.
2. Potter, N.N., Food Science, 2nd ed., AVI Publishing, Westport, CT, 1973, p. 36.
3. Conner, D.E., Naturally occurring compounds, in Antimicrobials in Foods, 2nd ed., Davidson, P.M.,
and Branen, A.L., Eds., Marcel Dekker, New York, 1993, p. 441.
4. Sperber, W.H., Influence of water activity of foodborne bacteria: A review, J. Food Prot., 46, 142, 1983.
5. Troller, J.A., Water relations to foodborne bacterial pathogens: An update, J. Food Prot., 49, 656, 1986.
6. Beuchat, L.R., Influence of water activity on growth, metabolic activities and survival of yeasts, J. Food
Prot., 46, 135, 1983.
7. Christian, J.H.B., Reduced water activity, in Microbial Ecology of Foods, Vol. 1, Silliker, J.H., Ed.,
Academic Press, New York, 1980, p. 70.
8. Corlett, D.A., Jr. and Brown, M.H., pH and acidity, in Microbial Ecology of Foods, Vol. 1, Silliker, J.H.,
Ed., Academic Press, New York, 1980, p. 92.
9. Baird-Parker, A.C., Organic acids, in Microbial Ecology of Foods, Vol. 1, Silliker, J.H., Ed., Academic
Press, New York, 1980, p. 126.
10. Brown, M.H. and Emberger, O., Oxidation reduction potential, in Microbial Ecology of Foods, Vol. 1,
Silliker, J.H., Ed., Academic Press, New York, 1980, p. 112.
11. Olson, J.C., Jr. and Nottingham, P.M., Temperature, in Microbial Ecology of Foods, Vol. 1, Silliker, J.H.,
Ed., Academic Press, New York, 1980, p. 1.
12. Skandamis, P.N. and Nychas, G.-J.E., Quorum sensing in the context of food microbiology, Appl.
Environ. Microbiol., 78, 5473–5482, 2012.
13. Antunes, L.C.M., Ferreira, R.B.R., Buckner, M.M.C., and Finlay, B.B., Quorum sensing in bacterial
virulence, Microbiology, 156, 2271–2282, 2010.
QUESTIONS
1. List the intrinsic and extrinsic factors necessary for growth of microorganisms in a food.
2. What are the major nutrients in food that are metabolized by the microorganisms? List the
major groups of carbohydrates present in foods. List the carbohydrates in milk and meat, the
pentoses in plant foods, and an oligosaccharide in plant foods.
3. Discuss how bacteria are able to metabolize large molecules of carbohydrates, proteins, and
lipids. How do molds differ from bacteria in the metabolism of these molecules?
4. Discuss the importance of antimicrobials in foods that can adversely affect microbial growth.
5. Define A W and explain the desorption and adsorption processes of moisture in a food.
Discuss the importance of A W in microbial growth. How do halophilic, osmophilic, and
xerophilic microorganisms differ in minimum A W needed for growth?
6. Define pH and discuss factors that influence the pH of a food. Discuss the role of pH on
microbial growth. How does a bacterial cell maintain a high intracellular pH (6.0) while
growing in a low-pH (5.0) environment? Give examples of an aciduric bacterium and an
acid-tolerant bacterium.
7. Define redox potential and discuss how it influences microbial growth in a food. How can
microorganisms be grouped on the basis of their growth capabilities at different redox potentials and oxygen availabilities?
8. How are microorganisms grouped on the basis of their temperature of growth and survival?
Discuss the significance of psychrotrophic and thermoduric microorganisms in the processing and refrigerated storage of foods.
9. What is quorum sensing? How does quorum sensing affect bacterial growth in foods?
References
1. Lengeler, J.W., Drews, G., and Schlegel, H.G., Biology of the Prokaryotes, Blackwell Science, New York,
1999, pp. 80, 110.
2. Potter, N.N., Food Science, 2nd ed., AVI Publishing, Westport, CT, 1973, p. 36.
3. Conner, D.E., Naturally occurring compounds, in Antimicrobials in Foods, 2nd ed., Davidson, P.M.,
and Branen, A.L., Eds., Marcel Dekker, New York, 1993, p. 441.
4. Sperber, W.H., Influence of water activity of foodborne bacteria: A review, J. Food Prot., 46, 142, 1983.
5. Troller, J.A., Water relations to foodborne bacterial pathogens: An update, J. Food Prot., 49, 656, 1986.
6. Beuchat, L.R., Influence of water activity on growth, metabolic activities and survival of yeasts, J. Food
Prot., 46, 135, 1983.
7. Christian, J.H.B., Reduced water activity, in Microbial Ecology of Foods, Vol. 1, Silliker, J.H., Ed.,
Academic Press, New York, 1980, p. 70.
8. Corlett, D.A., Jr. and Brown, M.H., pH and acidity, in Microbial Ecology of Foods, Vol. 1, Silliker, J.H.,
Ed., Academic Press, New York, 1980, p. 92.
9. Baird-Parker, A.C., Organic acids, in Microbial Ecology of Foods, Vol. 1, Silliker, J.H., Ed., Academic
Press, New York, 1980, p. 126.
10. Brown, M.H. and Emberger, O., Oxidation reduction potential, in Microbial Ecology of Foods, Vol. 1,
Silliker, J.H., Ed., Academic Press, New York, 1980, p. 112.
11. Olson, J.C., Jr. and Nottingham, P.M., Temperature, in Microbial Ecology of Foods, Vol. 1, Silliker, J.H.,
Ed., Academic Press, New York, 1980, p. 1.
12. Skandamis, P.N. and Nychas, G.-J.E., Quorum sensing in the context of food microbiology, Appl.
Environ. Microbiol., 78, 5473–5482, 2012.
13. Antunes, L.C.M., Ferreira, R.B.R., Buckner, M.M.C., and Finlay, B.B., Quorum sensing in bacterial
virulence, Microbiology, 156, 2271–2282, 2010.