On September 30, 1998, the Food and Drug Administration (FDA) of the U.S. Department of Health and Human Services signed a five-year contract with the Institute of Food Technologists (IFT) to provide scientific review and analysis of issues in food safety, food processing and human health. Under the terms of the contract, FDA assigns IFT task orders, categorized as comprehensive or abbreviated reviews. IFT assembles Scientific and Technical Panels comprised of experts in the topic area to address the issues. The panels are charged with providing scientific and technical review and analysis, not with setting policy.
This report is IFT’s response to Task Order #2: Processing Parameters Needed to Control Hazards in Cold-Smoked Fish. The Background and Scope of Work that FDA provided to IFT are included. In October 1999, IFT assembled a Scientific and Technical Panel. This panel was comprised of experts in food microbiology, HACCP, and seafood microbiology. The panel met in person and via conference calls throughout 2000 and into 2001. IFT also consulted with the Science Advisory Board that advises IFT on the FDA contract and on the individual task orders
The Institute of Food Technologists greatly appreciates the efforts of the Scientific and Technical Panels, the Science Advisory Board, the many reviewers, staff and others who made this report possible. Compensation for such an effort pales in comparison to the time, effort and expertise expended.
IFT is especially grateful to the FDA staff for their tremendous cooperation, communication and assistance at every stage of this project. IFT submits this report to the agency in the hopes that the report makes a contribution to the understanding of the methods to control public health hazards that may derive from the consumption of cold-smoked fish.
Science Advisory Board
Roy G. Arnold, Ph.D.
Executive Associate Dean
College of Agricultural Science
Oregon State University
Lester M. Crawford, Ph.D., D.V.M.
Center for Food and Nutrition Policy
Ray A. Goldberg
George M. Moffett Professor of Agriculture and Business Emeritus
Harvard Business School
Marcus Karel, Ph.D.
Massachusetts Institute of Technology and Rutgers University
Sanford A. Miller, Ph.D.
Center for Food and Nutrition Policy
Martha Rhodes Roberts, Ph.D.
Deputy Commissioner for Food Safety
Dept. of Agriculture and Consumer Services State of Florida
G. Edward Schuh, Ph.D.
Freeman Chair Professor
Hubert H. Humphrey Institute of Public Affairs
University of Minnesota
Barbara O. Schneeman, Ph.D.
Professor of Nutrition
Department of Nutrition
University of California
Thomas N. Urban, Jr.
Pioneer Hi-Bred International
Institute of food technologists
Scientific and Technical Panel on Processing Parameters
Needed to Control Hazard in Cold-Smoked Fish
Panel Chair and Senior Science Advisor to the Institute of Food Technologists
Frank F. Busta, Ph.D.
University of Minnesota
Gleyn E. Bledsoe, Ph.D., C.P.A.
Northwest Indian College
George J. Flick, Jr., Ph.D.
Virginia Polytechnic Institute and State University
Lone Gram, Ph.D.
Danish Institute for Fisheries Research
Dr. Daniel Herman
National Fisheries Institute
Michael L. Jahncke, Ph.D.
Virginia Tech and
Virginia Seafood Agricultural Research and Extension Center
Lahsen H. Ababouch, Ph.D.
Fish Utilization and Marketing Service
U.S. Food and Drug Administration
John Austin, Ph.D.
Bureau of Microbial Hazards
U.S. Department of Commerce
ACME Smoked Fish
Department of Agriculture and Markets
Lester Crawford, Ph.D., D.V.M.
Brent Dixon, Ph.D.
Mel Eklund, Ph.D.
Mel Eklund Inc. and Associates
Jeffrey M. Farber, Ph.D.
Ken Gall, Ph.D.
New York Sea Grant Extension
Oregon State University
Brian Himelbloom, Ph.D.
University of Alaska, Fairbanks
Hans Henrik Huss, Ph.D.
Danish Institute for Fisheries Research
John Kaneko, Ph.D.
Pac Mar, Inc.
Roy E. Martin, Ph. D.
National Fisheries Institute
Golf Coast Research Lab
Mike Peck, Ph.D.
Institute of Food Research, Norwich
George Pigott, Ph.D.
University of Washington
Robert J. Price, Ph.D.
University of California-Davis
Barbara Rasco, Ph.D.
Washington State University
Alan Reilly, Ph.D.
Food Safety Authority of Ireland
Walter Starszkiewics, Jr., Ph.D.
U.S. Food and Drug Administration
Ewen Todd, Ph.D.
Martin Wiedman, Ph. D.
Ocean Beauty Seafoods
Virginia Polytechnic and State University
Birte Fonnesbech Vogel, Ph.D.
Danish Institute for Fisheries Research
Mike Peck, Ph.D.
Institute of Food Research
Norwich Research Park
Hans Heinrik Huss, Ph.D.
Danish Institute for Fisheries Research
Food and Drug Administration
Donald M. Kautter, Jr.
Contract Technical Officer
Division of HACCP Programs
Consumer Safety Officer
Institute of Food Technologists
Bruce R. Stillings, Ph.D.
Charles E. Manley, Ph.D.
Mary K. Schmidl, Ph.D.
Daniel E. Weber
Executive Vice President
Phillip E. Nelson, Ph.D.
2001-2002 President Elect
Jill A. Snowdon, Ph.D.
Director, Department of Science and Technology Projects
Maria P. Oria, Ph.D.
Karen Arcamonte, M.S.
Kendra Langeteig, Ph.D.
Provided by FDA to IFT
Smoking has been a popular way to preserve fish for centuries. The applications of salt, smoke and, in some products, nitrate imparts a characteristic texture and flavor that is enjoyed throughout the world. With the advent of refrigeration, these products now contain less salt and smoke and have higher concentrations of moisture. In addition, packaging systems such as vacuum packaging with high barrier films have extended shelf life.
The recent outbreak due to Listeria monocytogenes (L.m.) in hot dogs has prompted the Agency to evaluate the ready-to-eat products under its jurisdiction such as smoked fish as a potential source of this foodborne pathogen.
L.m. is a non-sporeforming, psychrotrophic bacterium that causes the disease, listeriosis. In humans, the primary manifestations of listeriosis are meningitis, abortion and prenatal septicemia. Immuno-compromised individuals, pregnant women and infants are most at risk. The estimated annual incidence of foodborne listeriosis in the United States is 1850 cases and 425 deaths. Although foodborne listeriosis is rare, the associated mortality rate is as high as 20% among those at risk.
Sporadic cases and outbreaks of listeriosis associated with seafood products have been reported: a 1980 outbreak (29 cases, 9 deaths) in New Zealand associated with fish or molluscan shellfish; an outbreak (9 cases) in Connecticut caused by contaminated shrimp; a case in which fish was implicated; a case in which smoked cod roe was implicated, 3 cases in Tasmania caused by smoked mussels, and 9 cases of listeriosis in Sweden suspected to have been caused by a gravid cold-smoked rainbow trout. FDA surveys of domestic and imported cooked, ready-to-eat seafood products found L.m. in crabmeat samples and smoked fish samples. Over 17% of the cold smoked products were positive for the organism.
The focus of this task order is on cold smoked fish. Hot smoked fish receives a cook, e.g., 62.8 °C (145 °F) for 30 minutes that should inactivate vegetative pathogens. The issue of L.m. in hot smoked fish is the need to prevent recontamination after the cook through plant sanitation and other methods. Cold smoked product, however, is not "cooked" and if the incoming product or the facility is contaminated with L.m. there is no inactivation or inhibition step. The Agency’s interest is primarily in L.m., however, other pathogens may be of concern particularly during the cold smoking at temperatures between 21.1-37.8 °C (70-100 °F), optimum temperatures for the growth of many pathogens, for extended periods of time, ranging from 12 hours to 5 days.
Recommended salt levels and heat treatments used in cold and hot smoked fish are intended to control Clostridium botulinum type E. In vacuum packaged products, 3.5% water phase salt is needed, and in air packed products, 2.5% wps. L.m., however, is relatively tolerant of salt, so concentrations adequate to control C. botulinum type E have relatively little effect. The organism can grow fairly well in cold smoked fish with 6% water phase salt at refrigerated temperatures. During hot smoking, products are normally heated to an internal temperature of 62.8 °C (145 °F) for 30 minutes to inactivate vegetative pathogens. FDA’s Fish and Fishery Products Hazards and Controls Guide recommends that during cold smoking, the smoker temperature be restricted to no more than 32.2 °C (90 °F) which is intended to allow the survival of spoilage organisms that would multiply and spoil the product before the production of C. botulinum toxin.
L.m. and non-proteolytic strains of C. botulinum are psychrotrophs and can grow at refrigeration temperatures at low as 1.1 °C (34 °F) and 3.3 °C (38 °F) respectively. Salted and/or smoked products have a longer refrigerated shelflife than raw fish, which gives extra time for psychrotrophic organisms to grow to significant levels even when stored at FDA recommended temperatures.
Because cold smoked products do not receive a heat treatment during processing adequate to inactivate vegetative pathogens, L.m., if present, may survive. There is also concern that the cold smoking process of 32.2 °C (90 °F) for times varying from 12 hours to 5 days may allow the proliferation of pathogens during the cold smoking step itself. There is a question of whether L.m., as well as toxin producers like Staphylococcus aureus and histamine producing species of bacteria may proliferate and result in food poisoning.
There is some evidence that L.m. enters the processing plant on raw material and during processing there are a number of opportunities for L.m. to be transferred from the exterior of the fish to cut surfaces of fillets, i.e., contact with contaminated skin sides, filleting knives, gloves, brine, other equipment. In addition, the interior of the fish may be inoculated with injection systems using recirculated brines. L.m. on the internal areas of the flesh will be protected from the application of smoke and the organism could multiply at temperatures used during cold smoking. There may be a bacteriocidal effect of smoke on L.m. that remains on the surface of the product.
The inhibitory effect of smoke needs to be characterized as well as the best methods for application of smoke. The inhibitory effects of salt, nitrite, and sodium lactate have been investigated and while these preservatives have little effect when used alone, there is some evidence that when used in combination, there is an inhibitory effect on low levels of L.m. Other factors that may provide an inhibitory effect include pH control, water activity, and competitive microorganisms.
In hot smoked products, L.m. is usually assumed to be a result of post processing contamination. There is some evidence that L.m. can survive on the surface of salmon fillets processed to an internal temperature of 83 °C (181 °F) without application of smoke. Other factors that may affect the survival of L.m. include the formation of a "pellicle," where the surface dries before the application of smoke which decreases the inhibitory effect of smoke. The use of liquid smoke may also provide an inhibitory effect.
FDA’s L.m. policy is based on the potentially severe public health consequences and the characteristics of the organism, i.e., the organism causes human illness, death in over 20% of the cases, can grow at refrigeration temperatures, and the infectious dose is unknown. Currently, the Agency is conducting a risk assessment on L.m.
Under the current policy, the detectable presence of L.m. in ready-to-eat food is considered to be a hazard to health. The limit of sensitivity of the analytical method is 1 colony-forming-unit (cfu) per 25 g (0.04 cfu per gram).
Because of FDA’s policy, most processors do not test their endproducts for the presence of L.m. Processors may use environmental sampling in their plants in place of and as predictors of the presence of L.m., but sampling of end product is often avoided.
FDA requests recall of any ready-to-eat food in which L.m. is detected using present methodology.
Scope of Work
(As Assigned by FDA to IFT)
Independently and not as an agent of the Government, the Contractor shall furnish the necessary materials, services, facilities, and otherwise do all things necessary for or incident to the performance of the work set forth herein.
The contractor shall review the scientific literature, shall consult with academic experts, and shall consider the requirements of other governmental bodies to address the following specific questions:
- Are the times and temperatures used during cold smoking conducive to the outgrowth of pathogens and histamine producing species of bacteria? What is the range of time and temperatures used by industry during cold smoking? Which pathogens are of concern? The contractor shall provide information on the various pathogens that might be expected to be present on seafood products. These pathogens would include but are not limited to: L.m., S. aureus, C. botulinum, organisms capable of producing histamine in scombroid species and any other organism that may serve as a foodborne pathogen. The contractor shall do an indepth review of how these organisms are inhibited (or not inhibited) in smoked fish products and define the critical control points important to each of them.
- The contractor shall do an in-depth review on the processing parameters that may contribute to L.m. contamination of product, e.g., incoming product, chlorination of rinse water, injection brining systems, recirculation of brine, etc.
- The contractor shall do an in-depth review on the options available to eliminate or inhibit those organisms of public health concern in smoked fish products. The contractor shall evaluate the various preservatives (e.g., the inhibitory effect of wood smoke, liquid smoke, salt, nitrite and sodium lactate) used alone or in combination and the levels needed as appropriate inhibitors to pathogen growth. The contractor shall include the influence of the time and method of application of such preservatives. In addition, the contractor shall evaluate the suitability of other controls (e.g., pH, water activity, competitive microflora) on the prevention of outgrowth during processing and during subsequent finished product storage.
- The contractor shall provide information on recommended levels of heat or preservatives, alone or in combination, that processors can use to establish critical limits for processing a cold smoked product that is free from L.m. and bacterial toxins. The contractor shall review appropriate corrective actions that can be taken when critical limits are exceeded.
- The contractor shall provide information on how processors can validate the adequacy of the above levels in their processing systems and how to verify that their process is adequate on an ongoing basis.
- The contractor shall evaluate the various packaging options (e.g., oxygen permeable packaging, vacuum packaging, modified atmosphere, controlled atmosphere) and their effect on the inhibition of spoilage bacteria and the outgrowth of pathogens. The contractor shall define the term oxygen permeable packaging as it relates to inhibiting the outgrowth of C. botulinum and other pathogens (e.g., what characteristics must be present for a product to be considered "air" packaged). Products packed in high barrier film without a vacuum being pulled may become anaerobic rapidly due to the growth of aerobes in the product and the subsequent production of carbon dioxide.
- The contractor shall evaluate methods to control L.m. on the incoming product. Are there good vessel/harvest/handling practices or microbiological monitoring procedures that will prevent contamination of incoming product with L.m. What are these practices and/or procedures?
- While the scope of this task order is specific to cold smoked fishery products, the contractor shall provide any information in the literature on hot smoked fish that is germane. If the contractor finds sufficient information demonstrating that the time and temperature of the hot smoke is inadequate to eliminate L.m. from hot smoked products, it shall be noted in the review.
The overall purpose of this report is to evaluate the published and unpublished data concerning likely hazards of public health concern derived from the consumption of cold-smoked fish. In 1997, the U.S. Food and Drug Administration (FDA) mandated the application of the Hazard Analysis and Critical Control Point (HACCP) principles to the processing of domestically produced and imported fishery products. Although HACCP, with its focus on science, holds great promise for minimizing the risk of foodborne disease, the application of HACCP principles to foods and food processes such as cold-smoked fish is challenging. In certain cases, no useful strategies may be available to completely eliminate the identified food safety hazards. Specifically, FDA asked the Institute of Food Technologists (IFT) selected panel to provide an in-depth review of pathogens that might be found in cold-smoked fish products, to identify processing parameters that may contribute to pathogen growth, and to review options available to eliminate or inhibit foodborne pathogens in smoked fish products. FDA also asked for a review of the safety of current fish harvesting and handling practices as well as an evaluation of packaging options and their influence on survival or growth of the organisms of concern.
To address these issues, the report begins by describing the situation with regard to the safety of consuming cold-smoked fish. Focusing attention on cold-smoked finfish, the panel reviewed the most significant and likely to occur hazards in cold-smoked products—Listeria monocytogenes, Clostridium botulinum, human parasites, and biogenic amines. For each hazard, the report evaluates the effectiveness of methods for eliminating or preventing contamination in the processing environment, identifies possible control points for each step in the process, and, where there is scientific evidence, offers processing parameters that would control the hazard. The evaluation also takes into account control points during harvesting, packaging, storage, distribution, and use by the consumer. Based on these findings, the panel offers information for reducing the risk of hazard in cold-smoked fish products. The report also identifies research needs for further investigating control methods for the hazards reviewed in this report.
Control methods for some of the hazards of the cold-smoked fish product are difficult to determine, due to the many variables and unknown factors contributing to its potential contamination (the ubiquitous pathogen L. monocytogenes is a case in point). The definitions of cold-smoked fish are, themselves, vague. The Association of Food and Drug Officials (AFDO) and Codex Alimentarius define it as follows: "Cold process smoked fish means a smoked fish that has been produced by subjecting it to smoke at a temperature where the product undergoes only incomplete heat coagulation of protein." Cold-smoked fish is categorized as "lightly preserved" in Europe. Lightly preserved fish products contain low levels of salt and added preservatives, and must be stored and distributed at refrigeration (≤ 5 °C, 41 °F) or frozen temperatures. Because it would have been almost impossible to do an in-depth review of all the different ways in which fish are cold-smoked, for the purpose of this task order the panel chose to base the discussions on the general process described in the following flowchart.
Receiving Raw Materials
Refrigerated or fresh caught
- Clean appropriately
- Wash in potable water
- Wash in potable water
Storage of Raw Materials
Separate Fish, Fillets, etc. into Batches of Uniform Size
Brining of Fish
(Liquid brine solution [bath or injection] or dry-salt mixture)
Removing Fish from Brine
Drain and/or rinse with Fresh Water
Place Fish on Hooks or Rack
- Fish arranged to allow for uniform smoke absorption, heat exposure, and dehydration
- Smoke generated, liquid or combination
- Not exceed 90 °F (32 °C) for more than 20 h
- Not exceed 50 °F (10 °C) for more than 24 h
- Not exceed 120 °F (49 °C) for more than 6 h for cold-smoked sablefis
Cool to 50 °F (10 °C) within 3 h and to 37-38 °F (3.0 - 3.3 °C) within 12 h
- Must contain 2.5% WPS
Vacuum or MA packed
- Must contain 3.5% NaCl WPS, or
- Combination of 3.0% WPS and at least 100 ppm but no more than 200 ppm sodium nitrite
Storage and Distribution
- Product must be maintained at <37 - 38 °F (3.0 - 3.3 °C) at all times
- If the species has been identified as representing a parasite hazard and the incoming raw material was not previously frozen, then product should be subjected to freezing
Cold-smoked fish products are consumed as ready-to-eat with no heat treatment. Because of the absence of a "killing" step, other parameters such as salting become of upmost importance to minimize the risk of foodborne hazards. Salting and drying are crucial steps to achieve the proper finished product water phase salt level. Drying times, after salting, range from 1 - 6 h at 20 - 28 °C (68 - 82 °F), smoking parameters at a maximum of 30 °C (86 °F) range from 3 - 6 h, and shelf life ranges from 3 to 6 weeks at 5 °C (41 °F). The recommended smoke chamber temperature combinations must not exceed 90° F (32°C) for more than 20 h, 50 °F (10 °C) for more than 24 hours, or 120 °F (48 °C) for more than 6 h (for cold-smoked sablefish). It is important that the product not be subjected to so much heat that the number of spoilage organisms is significantly reduced. Competitive inhibition may be important in cold-smoked products because the heat applied is insufficient to inactivate or damage the C. botulinum spores. However, although an important consideration, relying on the competitive flora to restrict growth of C. botulinum or to indicate spoilage before the product becomes hazardous is not an effective or reproducible control point, and cannot be trusted to control safety. According to current U.S. HACCP regulations, a suggested critical limit for air-packaged products is at least 2.5% NaCl, and for modified atmosphere-packaged products at least 3.5% NaCl, or a combination of 3.0% water phase salt and at least 100, but not more than 200 ppm, of sodium nitrite (for fish species where nitrite is permitted). All products must be maintained at 37 - 38 °F (3.0 - 3.3 °C) if no other controls are present (that is, an adequate NaCl concentration and the application of smoke). If adequate concentrations of NaCl and smoke are present, the product must be maintained at ≤ 40°F (4.4°C).
The harvesting environment is one of the factors that make it difficult for processors to control contamination in the smoked fish product. The microbial flora associated with freshly harvested fish is principally a function not of the fish species but of the environment in which the fish are caught. Although this generalization appears simple, there is great diversity in aquatic environments (that is, fresh, salt, estuarine, cold, tropical, temperate, coastal, open ocean, polluted, and pristine) and therefore the indigenous microbial populations of fish can vary significantly. The microflora on a fish product is a function of the indigenous flora and the microflora of the processing environment. Typically, the term "processing environment" is limited to that of an actual processing plant. Any handling of fish, and the associated sanitary practices from the point of harvesting, however, has the potential to contribute to the microflora on the final product. Consequently, the presence or absence of foodborne pathogens on a fish product is a function of the harvest environment, sanitary conditions, and practices associated with equipment and personnel in the processing environment, as well as any lethality associated with the actual process of preserving the fish.
The most universal means of preserving fish quality is chilling (ice or mechanical refrigeration systems). As the temperature on the surfaces of fish is reduced below optimal, bacterial growth begins to slow. Given the microbial diversity typical of fish, it is not surprising that chill temperatures impact some microbial species more dramatically than others. The growth of some species is totally inhibited while others grow, albeit more slowly. Consequently, the rather diverse microflora will shift until just a few species predominate, due to the selective pressure of the chilled environment. Furthermore, the salting, drying, and smoking processes described above often reduce the numbers of microorganisms and cause a change in the spoilage microflora. Aerobic storage of cold-smoked fish at refrigerated temperatures results in the development of spoilage microflora consisting mostly of Pseudomonas spp. and yeast. During vacuum or CO2-packing, lactic acid bacteria rapidly become the dominant microflora. The nature of the microorganisms that cause spoilage and the manner in which the interactions among the organisms influence the spoilage scenario are not yet fully understood. This is important because these spoilage bacteria may help control pathogens.
As indicated, the processes used for cold smoking of fish—from receiving the raw material to the processing, storage, and distribution of the smoked product—are not exceptionally rigorous. Thus, there is concern that some foodborne pathogens, if present, could survive. Organisms of primary concern are L. monocytogenes and C. botulinum. In addition, the extensive handling provides opportunities for other foodborne pathogens to contaminate products if insufficient attention is given to Good Manufacturing Practices (GMPs).
Listeria monocytogenes and other Listeria species have been isolated from fishery products on a regular basis since the late 1980s. Although there have not been any large outbreaks of listeriosis, sporadic cases have been linked to smoked mussels and cold-smoked trout. Listeria monocytogenes can survive the cold-smoking process and is capable of growing at the temperature-NaCl combinations of the final product, although in naturally contaminated products the growth is slow. An increase in the incidence of listeriosis over the next decades acquired from all food products is likely due to the increasing numbers of susceptible people (pregnant women, infants, the elderly, and immunocompromised). Although listeriosis occurs infrequently, at an annual rate of 2 to 10 per million, the fatality rate usually ranges from 20 - 30% in the highly susceptible groups. Consequently, keeping concentrations of L. monocytogenes in cold-smoked fish at extremely low levels is imperative to minimize the risk. To that effect, conforming to GMPs is essential.
With respect to C. botulinum, its prevalence is widespread but its incidence is low. The concerns with psychrotrophic non-proteolytic C. botulinum are not associated with the mere presence of the organism or its spores. Packaging environment and temperature significantly influence risk factors associated with C. botulinum. Because refrigeration temperatures alone will inhibit the growth of proteolytic strains, control could be established by maintaining temperatures below 3.0 - 3.3 °C (37 - 38 °F) throughout distribution, retail storage, and by the consumer. Maintaining temperatures consistently below 3.0 - 3.3 °C (37 - 38 °F) is not a realistic expectation. Consequently, a combination of both low temperature control [< 4.4 °C (40 °F)] and salt (3.5% water phase of NaCl) are vital. Because there are no reports in the scientific literature linking cold-smoked fish to an outbreak of botulism, it is assumed that the combination of NaCl and low temperature is sufficient for control of the hazard.
As the processes employed in the cold smoking of fish are not rigorous, not only are such pathogens as L. monocytogenes and C. botulinum a potential hazard, but survival of human parasites is also a distinct possibility. Fish species carrying parasites that are known to be pathogenic to humans must be frozen to a specific internal temperature and for an amount of time at some stage during processing. Farmed salmon reared on pelletized feed are not subject to the freezing requirement because the feed is considered void of parasites due to the feed processing method.
Biogenic amines, such as histamine, are by-products of bacterial growth on the surfaces of susceptible species of harvested fish and may cause scombroid toxicity. If scombrotoxin-forming fish are temperature-abused prior to cooling, levels of biogenic amines can rise. Lightly preserved fish products, such as cold-smoked fish, however, have not been linked epidemiologically to foodborne disease caused by scombroid toxicity.
In summary, the control of hazards in cold-smoked fish products requires careful attention by processors. The HACCP concept developed for controlling foodborne disease is based on a simple yet fundamental premise: "identify and control." With respect to cold-smoked fish, hazard analysis suggests that biological hazards may exist (that is, L. monocytogenes, C. botulinum), but a definitive control point is either problematic (that is, temperature control for C. botulinum); or non-existent (that is, kill step for L. monocytogenes). The concerns associated with C. botulinum in smoked fish are not new. Thus, its prescribed treatment in processing is well established. At the processing level, vacuum packaging is acceptable if barriers (that is, 3.5% NaCl, smoke, and chill temperature control) are in place. Less salt is needed to inhibit growth of the psychrotrophic (non-proteolytic) C. botulinum types B, E, and F at chilled fish temperatures than at higher temperatures. Moreover, reduced pH in combination with salt enhances the inhibition of the organism. L. monocytogenes, on the other hand, is a relatively new concern. Although much has been learned about L. monocytogenes, the dose/response relationship of the organism for humans is not yet known. The United States policy has a "zero tolerance" (non-detectable, by the current methods) for L. monocytogenes. Using a quantitative risk assessment approach, a group of researchers concluded that unless rigorously enforced, the "zero tolerance" was not better for food safety than a specification at a level of ≤ 100 per gram at time of consumption. Clearly, the United States "zero-tolerance" policy for L. monocytogenes in ready-to-eat products is a significant issue for the cold-smoked fish industry.
After numerous panel discussions and consultations with outside reviewers, the panel made conclusions on the scientific status of these important issues and listed possibilities for further research. Following is a list of the main conclusions and research areas that would need further attention.
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 °C, 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 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 needs 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 reduces 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.