Processing Parameters Needed to Control Pathogens in Cold Smoked Fish Conclusions and Research Needs
The following conclusions are based on a thorough analysis and evaluation of the current science on control methods of human health hazards that may be associated with the consumption of cold-smoked fish.
- Given the ubiquitous nature of L. monocytogenes, the lack of listericidal steps in the cold-smoking procedure, and the ability of the organism to become established in the processing environment and re-contaminate products, it is not possible to produce cold-smoked fish consistently free of L. monocytogenes. This is not unique to cold-smoked fish because this microorganism can be isolated from a wide range of ready-to-eat (RTE) foods.
- By adhering strictly to Good Manufacturing Practices (GMPs) and Good Hygienic Practices (GHPs) it is possible to produce cold-smoked fish with low levels of L. monocytogenes, preferably at <1 cell / g at the time of production.
- Growth of L. monocytogenes in naturally contaminated fish products is significantly slower than predicted by models (using combinations of pH, NaCl, temperature, and lactate) and inoculation studies.
- Prevention of growth of L. monocytogenes in cold-smoked fish cannot be guaranteed not to occur using current combinations of NaCl and low temperature; however, growth can be prevented by freezing, by addition of certain additives (for example, nitrite), or by use of bioprotective bacterial cultures.
- If the organism cannot be eliminated and growth-inhibiting steps are not introduced, the hazard can be controlled by limiting shelf life (at 4.4° C, 40° F) to ensure that no more than 100 cells / g are present at time of consumption. Time limits may need to be established by each processor because the time limit should reflect the initial level of the organism in freshly produced product.
- Some countries, such as Australia, warn pregnant women about listeriosis and offer a list of food items to be avoided during the pregnancy. Labeling cold-smoked fish as well as other RTE foods in this risk category, indicating that these products may constitute a health hazard for immunocompromised individuals and pregnant women could be considered.
- There is no control point during the cold-smoking process that will guarantee the elimination of L. monocytogenes on the final product; however, the occurrence of L. monocytogenes on the finished cold-smoked fish products of processors can be minimized by: 1) obtaining the primary product from known sources (for example, those with a history of non-contaminated fish); 2) following strict adherence to GMPs to prevent recontamination during processing; and 3) inhibiting growth of any survivors by marketing the product frozen, or by using salt and other preservatives that can inhibit growth at refrigerated temperatures.
- Psychrotrophic C. botulinum occurs naturally in the aquatic environment, so its presence in low numbers on fresh fish must be anticipated. Spores may also be isolated infrequently from cold-smoked fish, although numbers, if present, are low. Given this low number, the probability of germination and toxin production is low but present.
- Experiments with naturally contaminated hot-smoked fish produced from fish with high levels of C. botulinum show that toxin may be formed under conditions of temperature abuse.
- Toxin production by psychrotrophic C. botulinum is controlled with a combination of a moderate level of NaCl (3.5% NaCl WPS) and storage at chill temperature (<4.4°C, <40 °F) for at least 4 wk. Based on the scientific data and because commercially produced cold-smoked fish has never been reported as a source of botulism, it is reasonable to conclude that the salt and cold keep the hazard under adequate control.
- Based on a range of model studies in broth and inoculation studies with hot- or cold-smoked fish, it can be concluded that a combination of 3.5% NaCl (as water phase salt) and chill storage (4.4 0C, 40 °F), allowing for short time periods of elevated temperatures up to 10 °C (50 °F), will prevent toxin formation in reduced oxygen packaging cold-smoked fish for several weeks beyond its sensory shelf life.
- As a general safeguard, salting to 3.5% for chilled stored cold-smoked fish is essential for reduced oxygen packaged (ROP) cold-smoked fish. In addition, the requirement for chilling with a sufficient salt concentration is an option for consideration in national or international regulations (for example, E.U. directives).
- For air-packaged products, levels of NaCl can, theoretically, be reduced; however, scientific data that support this argument do not exist and are needed before any reduction is recommended. Even when not packed under vacuum or modified atmosphere, pockets of anaerobic conditions may be created where slices of fish overlap or where aerobic spoilage bacteria consume the oxygen present.
- To control C. botulinum growth and toxin production in ROP products the following considerations are indicated: 1) A minimum 3.5% water phase salt concentration in the thickest part of the fillet for vacuum or modified atmosphere packaged fish, or a combination of at least 3% water phase salt and a nitrite level of 100-200 ppm is necessary for the control of C botulinum growth and toxin formation (Note: nitrite is not allowed in products sold in Europe, and is only allowed in the United States for sable, salmon, shad, chub, and tuna). 2) Packages containing refrigerated, cold-smoked fish should be labeled, "Keep Refrigerated at 40: F (4.4 :C) or below. 3) Packages containing frozen, cold-smoked fish should be labeled, "This product must remain frozen until thawed at refrigeration temperatures and shall not be refrozen," and 4) Products should not be packaged in reduced oxygen packaging by the retailer.
- The majority of species that are cold-smoked have not been identified by the scientific community as causing scombrotoxin illness. Therefore, the risk of foodborne illness is limited in the majority of cold-smoked products available in the marketplace.
- Only relatively high and sometimes controversial concentrations of histamine have usually resulted in illness. The contribution of other biogenic amines to the onset of symptoms is not well understood.
- Most scombrotoxin results from extrinsic, rather than intrinsic, spoilage through the growth of certain bacteria, generally members of the family Enterobactericae. Some bacteria are capable of producing greater quantities of decarboxylase enzymes than others.
- Certain processing operations, such as freezing, salting, or smoking may be capable of inhibiting or inactivating biogenic amine-producing microorganisms; however, microorganism growth with potential toxin production may occur after thawing and post-processing.
- Under certain conditions addition of lactic acid-producing microorganisms suppresses the growth of biogenic amine-forming microorganisms.
- Vacuum packaging does not prevent growth of biogenic amine-forming microorganisms.
- While biogenic amine-forming microorganisms may grow at refrigeration temperatures, generally the minimal temperature for growth is lower than the minimal temperature for toxin production.
- The most effective methods of preventing biogenic amine formation are handling and processing under sanitary conditions, rapid cooling of the fish, and continued refrigeration from harvest through consumption.
- To minimize the level of biogenic amines in species susceptible to histamine formation, temperature control is important throughout the process, particularly during the storage and transportation before cold-smoking, the cooling step, and the final product storage, distribution, retail, and consumer steps. The temperatures required for the control of C. botulinum may be appropriate to control production of biogenic amines.
- Much of the published scientific research on scombrotoxin utilized fish samples obtained from processing facilities and retail food stores. Only a limited number of studies followed samples from harvest through analysis. Also, sensory analyses were not always incorporated into microbiological and analytical chemical studies. There is a lack of reports describing comprehensive and integrated projects.
- Some of the fish species used for cold-smoked processing are either intermediate or final hosts to parasites. For this reason, assuring the harvesting of parasite-free fish in the wild is difficult.
- Some aquacultured fish are considered free of parasites (if their feeding regime has not been supplemented with raw fish) because their diet can be controlled using net-pens, closed recycled systems or an equivalent system, and commercially pelleted diets; consequently, these control measures must be carefully considered and applied. An analysis of the potential control points for parasites in aquacultured fish is beyond the scope of this report.
- Freezing raw fish prior to smoking remains the most effective way to insure that viable parasites are not present in cold-smoked products consumed by the public. It is essential, therefore, that raw fish potentially containing viable parasites be frozen and held in that state for a period of time that assures destruction of all viable parasites in that fish species.
The following is a list of research areas that the panel suggests need further attention:
- Conduct epidemiological investigations to determine if and to what extent cold-smoked fish is involved in cases of listeriosis. Despite prediction of a risk, only a limited number of cases have been associated with cold-smoked fish.
- Assess virulence potential of L. monocytogenes isolated from cold-smoked fish.
- Measure behavior of L. monocytogenes in naturally contaminated products. Listeria monocytogenes appears to grow more slowly and to lower numbers than anticipated based on model predictions and inoculation trials. An understanding of which factors cause these differences may be used to design appropriate control measures in the product.
- Determine the robustness and applicability of alternative growth inhibitory measures such as bioprotective cultures, bacteriocins, lactate and others.
- Determine how L. monocytogenes becomes established in smoke houses and processing facilities. Several studies show that particular DNA types become established in niches in the processing environments. Research is needed to evaluate what parameters determine which types reside whether it be particular adhesion properties, or particular resistance properties, or other factors.
- Investigate the source of contamination in smoke houses and processing environments in order to introduce procedures specifically targeted at eliminating or limiting introduction of the organism.
- Identify GMP practices that would minimize the contamination and growth of L. monocytogenes.
- Determine the effectiveness of intervention strategies to reduce or eliminate L. monocytogenes, such as using chlorinated water to thaw and rinse incoming fish, and for rinsing fish following the brining operation.
- Develop cleaning and disinfection procedures targeted at adhered or established cells for removal of L. monocytogenes from surfaces.
- Determine if particular types of surfaces reduce numbers of adhering L. monocytogenes or if particular treatments (that is, spraying with lactic acid bacteria or lactate) can reduce surface contamination by minimizing adhesion and biofilm formation.
- Evaluate the robustness and sensory acceptability of the various procedures under investigation (that is, bioprotection, lactate, and so on) for the elimination of the possibility of growth in the product.
- Determine the effect of post-processing methods such as irradiation and high pressure to eliminate L. monocytogenes in cold smoked fish.
- Evaluate growth and toxin production in naturally contaminated cold-smoked fish products to validate models and predictions for growth and toxin production.
- Determine the influence of redox potential, various concentrations of trimethylamine oxide (TMAO), and NaCl on toxin production by psychrotrophic C. botulinum in gadoid and non-gadoid species.
- Determine the potential facilitation by TMAO on formation of nitrosamines, if nitrite is added, during cold-smoking.
- Identify processing conditions and gas transmission rates of films under various time and temperature conditions for products to be considered "air packaged." Determine the Oxygen Transmission Rate (OTR) needed for a product with 2.5% salt concentration to provide equivalent safety compared with cold-smoked reduced oxygen-packaged products (ROP).
- Conduct challenge studies on air-packaged, cold-smoked fish in films with OTRs between 7,000 and 10,000 cc / m2 / 24 h and compare to unpackaged cold-smoked fish.
- Establish minimum water phase salt concentrations required to inhibit growth and toxin formation by C. botulinum in air-packaged and unpackaged cold-smoked fish.
- Determine the shelf life of the product relative to product quality as well as safety under different packaging methods and storage temperatures.
- Determine appropriate sell-by dates and evaluate the use of time-temperature indicators to ensure a safe product.
- Determine the influence of ROP on the inhibition of biogenic amine production by gram-negative bacteria.
- Define the minimum temperatures for growth and biogenic amine production of biogenic amine-forming microorganisms.
- Identify practical temperatures that would minimize the levels of biogenic amines in all steps of the production chain and in the final product.
- Determine the effect of salt and redox potential on the formation of biogenic amines on the final product.
- Determine the impact of the inter-relationship(s) among histamine, putrescine, cadaverine, and perhaps other biogenic amine concentrations in scombrotoxin and their effects on subsequent host responses.
- Investigate the effects of various cold-smoked fish processes (water phase salt concentrations, process times and temperatures) on biogenic amine formation.
- practical methods for cold-smoked fish processors to determine the histamine/scombrotoxin risk in the raw material used for smoking.
- Apply new processes, such as irradiation, modified atmospheres, or high pressure, to reduce specific groups of microorganisms to determine if control of those responsible for biogenic amine formation reduce the hazard.
- Evaluate the effects of harvesting methods and post-harvest handling practices on biogenic amine formation under varying environmental conditions.
- Identify specific methods for representative and effective sampling and for accurate and precise analysis of biogenic amines.
- Describe possible alternative freezing procedures that are or could be effective for inactivation of various fish parasites.
- Establish the kinetics and lethal effect of specific regimes of freezing on various fish parasites.
- Evaluate alternative processing procedures, such as high pressure and X-ray or e-beam irradiation for control of various fish parasites.
- Investigate the possible human health risks of allergic reactions due to parasite antigens remaining after freezing the fish to inactivate the live parasites.