Important Factors in Microbial Food Spoilage ◾ 253
Conclusion
Growth of microorganisms in food to a high level causes detectable changes in the quality of
food, which is generally termed as spoilage. Spoilage characteristics differ with the differences in
microbial type and the food component being metabolized. Different aspects of food spoilage are
discussed in this chapter. In Chapter 20, spoilage of specific food groups, the predominant microorganisms involved, and the nature of spoilage are discussed.
QUESTIONS
1. Describe when a food is considered spoiled by microorganisms. You put a packet of lunchmeat in the refrigerator two to three weeks back and forgot about it. When you opened it,
you thought it had a slightly sour odor. You asked your friends to smell it, but they said it
smelled fine. What could be the reasons for this difference?
2. You opened a 2 L bottle of a soft drink and kept it in the refrigerator and forgot about it.
After two weeks, you found some molds growing on the surface of the liquid. Describe the
sequence of events that resulted in this spoilage.
3. Discuss the significance of microbial types and numbers in food spoilage.
4. A food is usually spoiled by limited (usually one or two) types of microorganisms among the
many types initially present. Describe how this predominance is established.
5. At present, psychrotrophic bacteria seem to be the most important spoilage bacteria. Suggest
the possible reasons.
6. How can psychrotrophic bacteria be arbitrarily grouped? Give examples of two bacterial
species from each group. Also, give two examples each of thermoduric, thermophilic, and
aciduric spoilage bacteria.
7. Define aerobic respiration, anaerobic respiration, and fermentation. List four metabolites
(for each) associated with (a) odor and (b) gas formation from food nutrients.
8. Discuss the importance of preferential nutrient metabolism by microorganisms and the
nature of food spoilage from this, using meat and milk as examples.
References
1. Gill, C.O., The control of microbial spoilage in fresh meat. In Advances in Meat Research: Meat and
Poultry Microbiology, Vol. 2, Pearson, A.M. and Dutson, T.R., Eds., AVI Publishing, Westport, CN,
1986, p. 49.
2. Kraft, A.A., Health hazard vs. food spoilage. In Psychrotrophic Bacteria in Foods, CRC Press, Boca
Raton, FL, 1992, p. 113.
3. Sinell, H.J., Interacting factors affecting mixed populations. In Microbial Ecology of Foods, Vol. 1,
Silliker, J.H., Ed., Academic Press, New York, 1980, p. 215.
4. Ray, B., Foods and microorganisms of concern. In Food Biopreservatives of Microbial Origin, Ray, B. and
Daeschel, M.A., Eds., CRC Press, Boca Raton, FL, 1992, p. 25.
5. Gram, L., Ravn, L., Rasch, M., Bruhn, J.B., Christensen, A.B., and Givskov, M., Food spoilage:
Interactions between food spoilage bacteria, Int. J. Food Microbiol., 78, 79, 2002.
6. Moss, M.O., Fungi, quality and safety issues in fresh fruits and vegetables, J. Appl. Microbiol., 104,
1239–1243, 2008.
7. Stratford, M., Food and beverage spoilage yeasts. In Yeasts in Food and Beverages; Querol, A. and Fleet,
G., Eds., Springer, Berlin Heidelberg, 2006, pp. 335–379.
Conclusion
Growth of microorganisms in food to a high level causes detectable changes in the quality of
food, which is generally termed as spoilage. Spoilage characteristics differ with the differences in
microbial type and the food component being metabolized. Different aspects of food spoilage are
discussed in this chapter. In Chapter 20, spoilage of specific food groups, the predominant microorganisms involved, and the nature of spoilage are discussed.
QUESTIONS
1. Describe when a food is considered spoiled by microorganisms. You put a packet of lunchmeat in the refrigerator two to three weeks back and forgot about it. When you opened it,
you thought it had a slightly sour odor. You asked your friends to smell it, but they said it
smelled fine. What could be the reasons for this difference?
2. You opened a 2 L bottle of a soft drink and kept it in the refrigerator and forgot about it.
After two weeks, you found some molds growing on the surface of the liquid. Describe the
sequence of events that resulted in this spoilage.
3. Discuss the significance of microbial types and numbers in food spoilage.
4. A food is usually spoiled by limited (usually one or two) types of microorganisms among the
many types initially present. Describe how this predominance is established.
5. At present, psychrotrophic bacteria seem to be the most important spoilage bacteria. Suggest
the possible reasons.
6. How can psychrotrophic bacteria be arbitrarily grouped? Give examples of two bacterial
species from each group. Also, give two examples each of thermoduric, thermophilic, and
aciduric spoilage bacteria.
7. Define aerobic respiration, anaerobic respiration, and fermentation. List four metabolites
(for each) associated with (a) odor and (b) gas formation from food nutrients.
8. Discuss the importance of preferential nutrient metabolism by microorganisms and the
nature of food spoilage from this, using meat and milk as examples.
References
1. Gill, C.O., The control of microbial spoilage in fresh meat. In Advances in Meat Research: Meat and
Poultry Microbiology, Vol. 2, Pearson, A.M. and Dutson, T.R., Eds., AVI Publishing, Westport, CN,
1986, p. 49.
2. Kraft, A.A., Health hazard vs. food spoilage. In Psychrotrophic Bacteria in Foods, CRC Press, Boca
Raton, FL, 1992, p. 113.
3. Sinell, H.J., Interacting factors affecting mixed populations. In Microbial Ecology of Foods, Vol. 1,
Silliker, J.H., Ed., Academic Press, New York, 1980, p. 215.
4. Ray, B., Foods and microorganisms of concern. In Food Biopreservatives of Microbial Origin, Ray, B. and
Daeschel, M.A., Eds., CRC Press, Boca Raton, FL, 1992, p. 25.
5. Gram, L., Ravn, L., Rasch, M., Bruhn, J.B., Christensen, A.B., and Givskov, M., Food spoilage:
Interactions between food spoilage bacteria, Int. J. Food Microbiol., 78, 79, 2002.
6. Moss, M.O., Fungi, quality and safety issues in fresh fruits and vegetables, J. Appl. Microbiol., 104,
1239–1243, 2008.
7. Stratford, M., Food and beverage spoilage yeasts. In Yeasts in Food and Beverages; Querol, A. and Fleet,
G., Eds., Springer, Berlin Heidelberg, 2006, pp. 335–379.