A CONTROL (fully dried or salted ﬁsh products)

Summary

Signiﬁcant hazards a r Mycotoxin formation.

Control measures

Initial level (H 0 )

r Limit spore contamination where possible.

Reduction (Σ R)

r None applicable.

Increase (Σ I) r Dry as rapidly as possible; careful control of a w during storage.

Testing

r Not required in salted ﬁsh, dried ﬁsh. Advisable for fresh water smoked

ﬁsh.

Spoilage

r Ensure rapid drying. r Avoid storage in humid areas that would allow fungal growth.

a Under particular circumstances, other hazards may need to be considered. In these products, a w is so low that bacterial pathogens or parasites are not a risk. Health hazards

primarily include mycotoxin formation.

XII Pasteurized products

A Introduction Other seafood products than the cooked, canned, or cold-smoked products, receive a heat treatment.

Several products are pasteurized and typical of such products are the hot-smoked ﬁsh and sous-vide products.

In Europe, Canada, and North America, hot-smoked fish are typically prepared from fatty species like mackerel, herring, or salmon. The fish are salted by dry-salting or brining and smoked at 60–70 ◦ C for half to one hour. Hot smoking is a common way of preserving fish in Africa and typically takes place over longer periods of time. The meat of hot-smoked fish, as opposed to cold-smoked products, appear cooked.

Recently the sous-vide (French for “under vacuum”) processing has become popular. These products are pre-cooked at temperatures between 65 ◦

C and stored under vacuum and distributed chilled. These refrigerated and processed foods with extended durability (REPFEDs) have become popular in the catering sector.

C and 90 ◦

FISH AND FISH PRODUCTS

B Saprophytes and spoilage The hot smoking of ﬁsh results in a marked reduction of bacterial numbers. If stored aerobically,

mould growth on stored smoked ﬁsh is quite common and may be a major cause for rejection of the product (Eﬁuvwevwere and Ajiboye, 1996). If stored vacuum-packed at refrigerated temperatures, very little microbial growth is seen and sensory rejection is often caused by rancidity or textural changes.

Little is know about spoilage of sous-vide ﬁsh products. Ben Embarek (1994b) found that after

C, some sous vide cooked cod developed putrid offensive off odors due to growth of spore forming Gram-positive bacteria. Similarly, clostridia have been implicated in spoilage of pasteurized crab-meat (Cockey and Chai, 1991).

3 weeks of storage at 5 ◦

C Pathogens Two bacterial pathogens are of great concern in the pasteurized ﬁsh products: Cl. botulinum and

L. monocytogenes. Botulism outbreaks from hot-smoked fish were a major problem in the sixties and seventies. The outbreaks were due to post-processing growth and toxin production by Cl. botulinum that were probably on the fish at the time of capture. The botulism cases involved hot-smoked fish, which were insufficiently heated to destroy spores of Cl. botulinum serotype E. NaCl concentrations were low and after processing the products were held at storage temperatures high enough to allow growth (Pace and Krumbiegel, 1973). Hot-smoking processes reaching temperatures of 60–92 ◦

C can inactivate spores of non-proteolytic Cl. botulinum, but were insufficient to inactivate spores of proteolytic strains (Eklund et al., 1988). The redox potential of smoked fish flesh is sufficiently low enough to permit growth of Cl. botulinum even in the presence of an oxygen containing environment. Hot- smoking may encourage Cl. botulinum growth by elimination of competing bacteria. An associate mi- croflora may sometimes enhance toxin production. Thus, Huss et al. (1980) showed that co-inoculation of hot-smoked herring with spoilage bacteria led to faster toxin formation, persumably because the spoilage bacteria used oxygen and created a favorable anaerobic atmosphere. An important risk factor is inadequate cleaning and sanitation of smoking facilities. This can allow build up of populations of Cl. botulinum , thereby ensuring recontamination of smoked fish. A post-smoking heat-pasteurization process has been described (Eklund et al., 1988). Hot-smoked fish is usually eaten without further cooking making effective control of the potential botulism hazard especially important. It has been recommended that such products be labelled to indicate the need to keep refrigerated (Eklund et al., 1988).

The D-values and z-values for L. monocytogenes are within the range reported for other foods, but are dependent on the ﬁsh species (Ben Embarek and Huss, 1993). For example, the D-values at 56 ◦

C in brined green mussels were 48.1, 16.3, 9.5, 5.5, and 1.9 min, respectively, with

C (Bremer and Osborne, 1995). Listeria monocytogenes does not appear to survive hot smoking in trout, but grew to >10 7 cfu/g when inoculated at low levels after thermal processing (Jemmi and Keusch, 1992). High NaCl levels (>5%) in combination with vacuum packaging inhibited growth in smoked salmon at 5 ◦

a z-value of 4.3 ◦

C (Peterson et al., 1993). The incidence of L. monocytogenes does not appear to reflect the smoking temperature. Heinitz and Johnson (1998) found 18% of cold-smoked fish and 8% of hot-smoked fish positive whereas a recent US study found that 3.1% of retail hot-smoked fish was positive for L. monocytogenes, which was similar to the 3.3% reported for cold-smoked fish (Kraemer, Personal communication). This indicates that post-process contamination takes place. It is noteworthy that Aero. hydrophila, a much more heat sensitive organisms, has been found in a substantial portion of hot- and cold-smoked fish products (Gobat and Jemmi, 1993), indicating significant potential for post-heating recontamination.

C, but not 10 ◦

MICROORGANISMS IN FOODS 6

A CONTROL (fully dried or salted ﬁsh products)