Processed Meats and Seafoods
117
organisms constituted 62–95% of the biota.
69 When allowed to spoil in 100% CO 2 at 4
◦ C, the herring
fillets were dominated almost completely by lactobacilli.
69 In the case of rock cod fillets stored in
80% CO 2 + 20% air at 4
◦ C for 21 days, the biota consisted of 71–87% lactobacilli and some tancolored pseudomonads.
56 In a study of psychrotrophic Enterobacteriaceae isolated from vacuum- and
CO 2 -packaged cold-smoked salmon, Pantoea agglomerans and Serratia liquefaciens were the most
common species.
40 In this study, numbers of Enterobacteriaceae found in spoiled products ranged
from 10
3 to 1.2 × 10
7 /g, but their role in the spoilage process is unclear. A study of Pseudomonas spp.
from Mediterranean sea bream stored aerobically and under MAP conditions found Pseudomonas
lundensis and P. fluorescens to be the two dominant species during aerobic spoilage.
93 In some spoiled
fish from marine waters, Photobacterium phosphoreum is often found.
Phenethyl alcohol has been shown to be produced consistently in fish by a specific organism
designated “Achromobacter” by Chen et al.
17 and Chen and Levin.
16 The compound, along with
phenol, was recovered from a high-boiling fraction of the haddock fillets held at 2
◦ C. None of the
ten known Acinetobacter and only one of the nine known Moraxella produced phenethyl alcohol
under similar conditions. Ethanol, propanol, and iso-propanol are produced by fish spoilers, and of
244 bacteria isolated from king salmon and trout and tested in fish extracts, all produced ethanol, 241
(98.8%) produced isopropanol, and 227 (93%) produced propanol.
2
In detecting microbial fish spoilage, the reduction of TMAO to trimethylamine (TMA) has been
used with some success:
H 3 C \
Trimethylamine-N-oxide →
N − CH 3
/
H 3 C
Trimethylamine
TMAO is a normal constituent of seafish, whereas little or no TMA is found in freshly caught fish. The
presence of TMA is generally regarded to be of microbial origin, although some fish contain muscle
enzymes that reduce TMAO. Also, some TMAO may be reduced to dimethylamine. Not all bacteria
are equal in their capacity to reduce TMAO to TMA, and its reduction is pH dependent. Methods
employed to detect TMA include its extraction from fish with toluene and potassium hydroxide
followed by reaction with picric acid or its flushing from extracts and subsequent extraction by use of
alkaline permanganate solutions.
31,90 Gas chromatography was used to detect headspace TMA, and
sampling and analysis could be completed in less than 5 minutes, with results being consistent with
sensory tests.
60
The detection of CO 2 using an infrared CO 2 analyzer was suggested as a rapid method for spoilage
detection in refrigerated catfish.
18 Results by this CO 2 rate evolution method could be obtained in
less than 4 hours and they correlated well with APC data. Histamine, diamines, and total volatile
substances are used also as fish-spoilage indicators. Histamine is produced from the amino acid
histidine by microbially produced histidine decarboxylase, as noted:
Histidine −−−−−−−→
Decarboxylase
Histamine
Histamine is associated with scombroid poisoning (discussed further in Chapter 31). Cadaverine and
putrescine are the most important diamines evaluated as spoilage indicators, and they have been used
for fish as well as for meats and poultry.
117
organisms constituted 62–95% of the biota.
69 When allowed to spoil in 100% CO 2 at 4
◦ C, the herring
fillets were dominated almost completely by lactobacilli.
69 In the case of rock cod fillets stored in
80% CO 2 + 20% air at 4
◦ C for 21 days, the biota consisted of 71–87% lactobacilli and some tancolored pseudomonads.
56 In a study of psychrotrophic Enterobacteriaceae isolated from vacuum- and
CO 2 -packaged cold-smoked salmon, Pantoea agglomerans and Serratia liquefaciens were the most
common species.
40 In this study, numbers of Enterobacteriaceae found in spoiled products ranged
from 10
3 to 1.2 × 10
7 /g, but their role in the spoilage process is unclear. A study of Pseudomonas spp.
from Mediterranean sea bream stored aerobically and under MAP conditions found Pseudomonas
lundensis and P. fluorescens to be the two dominant species during aerobic spoilage.
93 In some spoiled
fish from marine waters, Photobacterium phosphoreum is often found.
Phenethyl alcohol has been shown to be produced consistently in fish by a specific organism
designated “Achromobacter” by Chen et al.
17 and Chen and Levin.
16 The compound, along with
phenol, was recovered from a high-boiling fraction of the haddock fillets held at 2
◦ C. None of the
ten known Acinetobacter and only one of the nine known Moraxella produced phenethyl alcohol
under similar conditions. Ethanol, propanol, and iso-propanol are produced by fish spoilers, and of
244 bacteria isolated from king salmon and trout and tested in fish extracts, all produced ethanol, 241
(98.8%) produced isopropanol, and 227 (93%) produced propanol.
2
In detecting microbial fish spoilage, the reduction of TMAO to trimethylamine (TMA) has been
used with some success:
H 3 C \
Trimethylamine-N-oxide →
N − CH 3
/
H 3 C
Trimethylamine
TMAO is a normal constituent of seafish, whereas little or no TMA is found in freshly caught fish. The
presence of TMA is generally regarded to be of microbial origin, although some fish contain muscle
enzymes that reduce TMAO. Also, some TMAO may be reduced to dimethylamine. Not all bacteria
are equal in their capacity to reduce TMAO to TMA, and its reduction is pH dependent. Methods
employed to detect TMA include its extraction from fish with toluene and potassium hydroxide
followed by reaction with picric acid or its flushing from extracts and subsequent extraction by use of
alkaline permanganate solutions.
31,90 Gas chromatography was used to detect headspace TMA, and
sampling and analysis could be completed in less than 5 minutes, with results being consistent with
sensory tests.
60
The detection of CO 2 using an infrared CO 2 analyzer was suggested as a rapid method for spoilage
detection in refrigerated catfish.
18 Results by this CO 2 rate evolution method could be obtained in
less than 4 hours and they correlated well with APC data. Histamine, diamines, and total volatile
substances are used also as fish-spoilage indicators. Histamine is produced from the amino acid
histidine by microbially produced histidine decarboxylase, as noted:
Histidine −−−−−−−→
Decarboxylase
Histamine
Histamine is associated with scombroid poisoning (discussed further in Chapter 31). Cadaverine and
putrescine are the most important diamines evaluated as spoilage indicators, and they have been used
for fish as well as for meats and poultry.