Spoilage of Specific Food Groups ◾ 271
growing rapidly in an environment determine the nature of the end products that are produced,
which, in turn, are associated with spoilage characteristics. An understanding of these parameters
is important in the firsthand determination of the causes of spoilage. This will be useful to investigate the cause, identify it, and take necessary corrective measures. These aspects are discussed
further in Chapter 20, using some real situations of refrigerated food products.
QUESTIONS
1. List the important psychrotrophic spoilage bacteria of raw meats and describe the metabolic
pattern and corresponding spoilage associated with each microbial genus.
2. Briefly discuss the following: (a) sources of microorganisms in low-heat-processed meat
products; (b) predominant spoilage bacteria in low-heat-processed, vacuum-packaged meat
products stored at ≤4°C; and (c) factors associated with the greening of unpackaged and
packaged meat and meat products during refrigerated storage.
3. List four microbial inhibitors in shell eggs and predominant spoilage microflora of eggs and
egg products.
4. Briefly explain the following: (a) metabolism of nutrients by predominant spoilage bacteria
while growing in fish tissues; (b) post-heat contamination and spoilage of crabmeat; and
(c) metabolism of nutrients by spoilage bacteria in shucked oysters.
5. List the predominant microflora of pasteurized milk and their sources. Discuss the reasons
for the limited shelf life of pasteurized milk.
6. Discuss the predisposing factors associated with microbial spoilage of UHP-treated milk,
sweetened condensed milk, and butter.
7. List bacteria, yeasts, and molds (two of each) associated with the spoilage of vegetables and
fruits. Discuss the major differences in spoilage by bacteria of these two groups of food. How
are ready-to-eat vegetables, fruits, and germinated seeds and beans spoiled by bacteria?
8. Discuss the influence of intrinsic factors associated with microbial spoilage of fruit drinks,
fruit juices, and vegetable juices and the nature of spoilage of these products caused by the
predominant microflora.
9. Jams, jellies, peanut butter, and salsa are not spoiled at room temperature as long as the
bottles/jars are not opened. The labels on the product, however, suggest to refrigerate the
products after opening. What could be the reasons?
10. List the similarities and differences in the microbial spoilage of (a) breads, (b) pastries,
(c) soft pastas, and (d) confectioneries.
11. List the microorganisms involved and the predisposing causes for the following spoilage
conditions: (a) gassy defect in mayonnaise, (b) gassy defect of prepared mustard, (c) gassy
defect in unripened soft cheese (such as Mexican-style cheese) and Gouda cheese, (d) bitter
taste in yogurt and Cheddar cheese, (e) tourne spoilage of wine, (f ) malolactic fermentation
in wine, and (g) sour beer.
12. List the major causes of spoilage of canned foods. Describe the factors, causative bacterial
species, and the nature of spoilage of canned foods produced by thermophilic spore formers.
References
1. Silliker, J.H., Elliot, R.P., Baird-Parker, A.C., Bryah, F.L., Christian, J.H., Clark, D.S., Roberts, T.A.
et al., Factors affecting life and death of microorganisms. In Microbial Ecology of Foods, Academic Press,
New York, 1980.
growing rapidly in an environment determine the nature of the end products that are produced,
which, in turn, are associated with spoilage characteristics. An understanding of these parameters
is important in the firsthand determination of the causes of spoilage. This will be useful to investigate the cause, identify it, and take necessary corrective measures. These aspects are discussed
further in Chapter 20, using some real situations of refrigerated food products.
QUESTIONS
1. List the important psychrotrophic spoilage bacteria of raw meats and describe the metabolic
pattern and corresponding spoilage associated with each microbial genus.
2. Briefly discuss the following: (a) sources of microorganisms in low-heat-processed meat
products; (b) predominant spoilage bacteria in low-heat-processed, vacuum-packaged meat
products stored at ≤4°C; and (c) factors associated with the greening of unpackaged and
packaged meat and meat products during refrigerated storage.
3. List four microbial inhibitors in shell eggs and predominant spoilage microflora of eggs and
egg products.
4. Briefly explain the following: (a) metabolism of nutrients by predominant spoilage bacteria
while growing in fish tissues; (b) post-heat contamination and spoilage of crabmeat; and
(c) metabolism of nutrients by spoilage bacteria in shucked oysters.
5. List the predominant microflora of pasteurized milk and their sources. Discuss the reasons
for the limited shelf life of pasteurized milk.
6. Discuss the predisposing factors associated with microbial spoilage of UHP-treated milk,
sweetened condensed milk, and butter.
7. List bacteria, yeasts, and molds (two of each) associated with the spoilage of vegetables and
fruits. Discuss the major differences in spoilage by bacteria of these two groups of food. How
are ready-to-eat vegetables, fruits, and germinated seeds and beans spoiled by bacteria?
8. Discuss the influence of intrinsic factors associated with microbial spoilage of fruit drinks,
fruit juices, and vegetable juices and the nature of spoilage of these products caused by the
predominant microflora.
9. Jams, jellies, peanut butter, and salsa are not spoiled at room temperature as long as the
bottles/jars are not opened. The labels on the product, however, suggest to refrigerate the
products after opening. What could be the reasons?
10. List the similarities and differences in the microbial spoilage of (a) breads, (b) pastries,
(c) soft pastas, and (d) confectioneries.
11. List the microorganisms involved and the predisposing causes for the following spoilage
conditions: (a) gassy defect in mayonnaise, (b) gassy defect of prepared mustard, (c) gassy
defect in unripened soft cheese (such as Mexican-style cheese) and Gouda cheese, (d) bitter
taste in yogurt and Cheddar cheese, (e) tourne spoilage of wine, (f ) malolactic fermentation
in wine, and (g) sour beer.
12. List the major causes of spoilage of canned foods. Describe the factors, causative bacterial
species, and the nature of spoilage of canned foods produced by thermophilic spore formers.
References
1. Silliker, J.H., Elliot, R.P., Baird-Parker, A.C., Bryah, F.L., Christian, J.H., Clark, D.S., Roberts, T.A.
et al., Factors affecting life and death of microorganisms. In Microbial Ecology of Foods, Academic Press,
New York, 1980.