120 Modern Food Microbiology
late stage of spoilage. A Pseudoalteromonas sp. from the marine environment around Chile was found
to be the most abundant bacterium in oysters spoiled at 18
◦ C.
78
Due to the relatively high level of glycogen, the spoilage of molluscan shellfish is basically fermentative. Several investigators, including Hunter and Linden
51 and Pottinger
75 proposed the following
pH scale as a basis for determining microbial quality in oysters:
pH 6.2–5.9
Good
pH 5.8
“off”
pH 5.7–5.5
Musty
pH 5.2 and below sour or putrid
A measure of pH decrease is apparently a better test of spoilage in oysters and other molluscan shellfish
than volatile nitrogen bases. A measure of volatile acids was attempted by Beacham
6 and found to
be unreliable as a test of oyster freshness. Although pH is regarded by many investigators as being
the best objective technique for examining the microbial quality of oysters, Abbey et al.
1 found that
organoleptic evaluations and microbial counts were more desirable indexes of microbial quality in
this product.
Clams and scallops appear to display essentially the same patterns of spoilage as do oysters, but
squid meat does not. In squid meat, volatile base nitrogen increases as spoilage occurs much in the
same manner as for the crustacean shellfish. An extensive review of fish and shellfish spoilage has
been presented by Ashie et al.
5
REFERENCES
1. Abbey, A., R.A. Kohler, and S.D. Upham. 1957. Effect of aureomycin chlortetracycline in the processing and storage of
freshly shucked oysters. Food Technol. 11:265–271.
2. Ahmed, A., and J.R. Matches. 1983. Alcohol production by fish spoilage bacteria. J. Food Protect. 46:1055–1059.
3. Allen, J.R., and E.M. Foster. 1960. Spoilage of vacuum-packed sliced processed meats during refrigerated storage. Food
Res. 25:1–7.
4. Andrews, W.H., C.R. Wilson, P.L. Poelma, and A. Romero. 1977. Bacteriological survey of the channel catfish (Ictalurus
punctalus) at the retail level. J. Food Sci. 42:359–363.
5. Ashie, I.N.A., J.P. Smith, and B.K. Simpson. 1996. Spoilage and shelf-life extension of fresh fish and shellfish. Crit. Rev.
Food Sci. Nutr. 36:87–121.
6. Beacham, L.M. 1946. A study of decomposition in canned oysters and clams. J. Assoc. Off. Anal. Chem. 29:89–92.
7. Beuret, C., A. Baumgardner, and J. Schluep. 2003. Virus-contaminated oysters: A three-month monitoring of oysters
imported to Switzerland. Appl. Environ. Microbiol. 69:2292–2297.
8. Blickstad, E., and G. Molin. 1983. The microbial flora of smoked pork loin and frankfurter sausage stored in different gas
atmospheres at 4 ◦ C. J. Appl. Bacteriol. 54:45–56.
9. Broda, D.M., P.A. Lawson, R.G. Bell, and D.R. Musgrave. 1999. Clostridium frigidicarnis sp. nov., a psychrotolerant
bacterium associated with “blown pack” spoilage of vacuum-packed meats. Int. J. Syst. Bacteriol. 49:1539–1550.
10. Broda, D.M., G.J. Saul, P.A. Lawson, R.G. Bell, and D.R. Musgrave. 2000. Clostridium gasigenes sp. nov., a psychrophile
causing spoilage of vacuum-packaged meat. Int. J. Syst. Enol. Microbiol. 50:107–118.
11. Buege, D., and J. Luchansky. 1999. Ensuring the safety of home-prepared jerky. Meat Poultry. 45(2):56, 59.
12. Calicioglu, M., N.G. Faith, D.R. Buege, and J.B. Luchansky. 1997. Viability of Escherichia coli 0157:H7 in fermented
semidry low-temperature-cooked beef summer sausage. J. Food Protect. 60:1158–1162.
13. Cavett, J.J. 1962. The microbiology of vacuum packed sliced bacon. J. Appl. Bacteriol. 25:282–289.
14. Centers for Disease Control and Prevention. 1995. Outbreak of salmonellosis associated with beef jerky—New Mexico,
1995. Morb. Mort. Wkly. Rept. 44:785–788.
late stage of spoilage. A Pseudoalteromonas sp. from the marine environment around Chile was found
to be the most abundant bacterium in oysters spoiled at 18
◦ C.
78
Due to the relatively high level of glycogen, the spoilage of molluscan shellfish is basically fermentative. Several investigators, including Hunter and Linden
51 and Pottinger
75 proposed the following
pH scale as a basis for determining microbial quality in oysters:
pH 6.2–5.9
Good
pH 5.8
“off”
pH 5.7–5.5
Musty
pH 5.2 and below sour or putrid
A measure of pH decrease is apparently a better test of spoilage in oysters and other molluscan shellfish
than volatile nitrogen bases. A measure of volatile acids was attempted by Beacham
6 and found to
be unreliable as a test of oyster freshness. Although pH is regarded by many investigators as being
the best objective technique for examining the microbial quality of oysters, Abbey et al.
1 found that
organoleptic evaluations and microbial counts were more desirable indexes of microbial quality in
this product.
Clams and scallops appear to display essentially the same patterns of spoilage as do oysters, but
squid meat does not. In squid meat, volatile base nitrogen increases as spoilage occurs much in the
same manner as for the crustacean shellfish. An extensive review of fish and shellfish spoilage has
been presented by Ashie et al.
5
REFERENCES
1. Abbey, A., R.A. Kohler, and S.D. Upham. 1957. Effect of aureomycin chlortetracycline in the processing and storage of
freshly shucked oysters. Food Technol. 11:265–271.
2. Ahmed, A., and J.R. Matches. 1983. Alcohol production by fish spoilage bacteria. J. Food Protect. 46:1055–1059.
3. Allen, J.R., and E.M. Foster. 1960. Spoilage of vacuum-packed sliced processed meats during refrigerated storage. Food
Res. 25:1–7.
4. Andrews, W.H., C.R. Wilson, P.L. Poelma, and A. Romero. 1977. Bacteriological survey of the channel catfish (Ictalurus
punctalus) at the retail level. J. Food Sci. 42:359–363.
5. Ashie, I.N.A., J.P. Smith, and B.K. Simpson. 1996. Spoilage and shelf-life extension of fresh fish and shellfish. Crit. Rev.
Food Sci. Nutr. 36:87–121.
6. Beacham, L.M. 1946. A study of decomposition in canned oysters and clams. J. Assoc. Off. Anal. Chem. 29:89–92.
7. Beuret, C., A. Baumgardner, and J. Schluep. 2003. Virus-contaminated oysters: A three-month monitoring of oysters
imported to Switzerland. Appl. Environ. Microbiol. 69:2292–2297.
8. Blickstad, E., and G. Molin. 1983. The microbial flora of smoked pork loin and frankfurter sausage stored in different gas
atmospheres at 4 ◦ C. J. Appl. Bacteriol. 54:45–56.
9. Broda, D.M., P.A. Lawson, R.G. Bell, and D.R. Musgrave. 1999. Clostridium frigidicarnis sp. nov., a psychrotolerant
bacterium associated with “blown pack” spoilage of vacuum-packed meats. Int. J. Syst. Bacteriol. 49:1539–1550.
10. Broda, D.M., G.J. Saul, P.A. Lawson, R.G. Bell, and D.R. Musgrave. 2000. Clostridium gasigenes sp. nov., a psychrophile
causing spoilage of vacuum-packaged meat. Int. J. Syst. Enol. Microbiol. 50:107–118.
11. Buege, D., and J. Luchansky. 1999. Ensuring the safety of home-prepared jerky. Meat Poultry. 45(2):56, 59.
12. Calicioglu, M., N.G. Faith, D.R. Buege, and J.B. Luchansky. 1997. Viability of Escherichia coli 0157:H7 in fermented
semidry low-temperature-cooked beef summer sausage. J. Food Protect. 60:1158–1162.
13. Cavett, J.J. 1962. The microbiology of vacuum packed sliced bacon. J. Appl. Bacteriol. 25:282–289.
14. Centers for Disease Control and Prevention. 1995. Outbreak of salmonellosis associated with beef jerky—New Mexico,
1995. Morb. Mort. Wkly. Rept. 44:785–788.