GB2366985A - Elimination of bacterial comtamination in cold processed fish products - Google Patents

Abstract

A method of treating seafood to remove or kill pathogenic microbes comprising providing seafood and an aqueous solution having a pH of at least 9.5, and contacting the seafood with the aqueous solution such that all of the exterior and other accessible portions of the seafood are exposed to the solution, wherein the entire surface of the seafood is exposed to the aqueous solution for at least a time sufficient to kill or remove the microbes. Hydrated lime is the preferred chemical for raising the pH. The seafood may be provided frozen and subsequently deglazed prior to contacting with the aqueous solution.

Description

ELIMINATION OF BACTERIAL CONTAMINATION IN COLD PROCESSED FISH PRODUCTS BACKGROUND OF THE INVENTION The invention relates generally to the decontamination of seafood for human consumption, particularly seafood products that are not subjected to a bactericidal heating step such as cooking.

Microbial contamination of food is a significant public health issue. Those infected can suffer from vomiting, nausea, and diarrhea. Although many organisms are implicated in food poisoning, Listeria poses particular problems because it can grow and multiply at low storage temperatures. The genus Listeria includes 6 different species, but only L. monocytogenes is consistently associated with human illness (Hitchins, 1998, Listeria monocytogenes. Ch. 10.

In Food and Drug Administration Bacteriological Analytical Manual, 8th ed. (revision A), (CD-ROM version), RL. Merker (Ed.), AOAC International, Gaithersburg, MD).

L. monocytogenes is widespread in nature and has been isolated from soil, vegetation, marine sediments and water. It has been identified as the cause of listeriosis in humans. Severe listeriosis can cause meningitis, abortions, septicemia and a number of other maladies, some of which may lead to death. Those at highest risk include cancer patients, individuals taking drugs that affect the body's immune system, alcoholics, pregnant women and their fetuses, infants, elderly persons, persons with low stomach acidity, and individuals with AIDS.

Listeria is unusual in that it can grow and multiply at normal refrigeration temperatures and can survive both freezing and relatively high cooking temperatures. Temperatures of at least 70oC throughout a food for at least two minutes are required to reduce numbers of Listeria. The bacteria to grow and multiply at temperatures between 1 to 44 C. Those who process, manufacture, handle or store foods intended for consumption without further cooking or processing must ensure that effective Listeria control measures are maintained. Ideally, cross contamination is eliminated from the environment through suitable design of equipment and appropriate sanitation procedures; contamination from contact surfaces and staff practices is minimized. However, it is difficult to completely remove Listeria from food products that are not cooked, and if the contamination comes from the food itself, rather than the preparation environment, elimination of Listeria has proven to be inordinately difficult without cooking.

The greatest threat oflisteriosis is from ready-to-eat products that do not require further cooking at home. Foodstuffs that can be contaminated include meats, unpasteurized milk, vegetables and seafood. Foods that require no further heat treatment or processing prior to being eaten, such as cold smoked salmon, or lox, and have a longer shelf life are particularly dangerous if contaminated. L. monocytogenes in raw food that will be cooked before consumption is less of a concern to the food industry since the bacteria are killed during cooking. Regarding seafood, L. monocytogenes has been isolated from raw fish, cooked crabs, raw and cooked shrimp, raw lobster, surimi and smoked fish (Ward et aI., (eds. ) 1997 Hazards Found in Seafoods, Appendix

III. In HA CCP : HazardAnalysis aK Critical Control Point Training Curriculum, 2nd ed., p. 173188, UNC-SG-96-02, North Carolina Sea Grant, Raleigh, NC.). The FDA has published guidelines pertaining to LM levels in fish products (FDA & EPA guidance levels, Appendix 5. In Fish and Fishery Products Hazards and Controls Guide, 2'eu., p. 245-248. Department of Health and Human Services, Public Health Service, Food and Drug Administration, Center for Food Safety and Applied Nutrition, Office of Seafood, Washington, DC (1998)).

A need exists for a method to eliminate contaminating microbes from seafood products, especially those which are not subjected to a cooking step. Such a method must not damage or alter the taste, texture, or appearance of the product.

SUMMARY OF THE INVENTION The methods of the invention provide safe, uncontaminated uncooked fish products, such as cold-smoked salmon, which are unaltered with respect to taste, texture, and appearance. The invention features a method of treating seafood to remove or kill pathogenic microbes which comprises providing seafood, preferably fish, and exposing the seafood to an aqueous solution having a pH of at least about 9.5, so that all of the exterior and other accessible portions of the seafood (e. g. , gills, oral cavity, etc. ) are exposed to the solution for at least a time sufficient to kill or remove any pathogenic microbes that are present so that they are not detectable using standard testing methods (e. g. , specific culture methods, nucleic acid, or protein/antibody tests). In preferred embodiments, the pH of the solution is at least about 10. 5, preferably at least about 11.5, and more preferably at least about 12.5. An advantage of the method is that it can be used on any seafood item, preferably intact seafood such as fish, to non-toxically render the seafood safe for consumption, even if it is not to be cooked or heat treated later.

In a preferred embodiment, the method of decontaminating the seafood/fish involves placing the fish into a container with the high pH aqueous solution, and agitating the container or the fish at least once during the contacting period by shaking or stirring such that any part of the fish that is in physical contact with another object is moved and exposed to the solution. In this way, even if multiple fish are being treated at once, each fish is uniformly covered with the high pH aqueous solution and contaminated surfaces are exposed. The treatment can then kill or wash off all pathogenic microbes on the surface of the fish, in its slime, on and under the scales and on the skin.

The methods of the invention are ideally suited for eliminating Listeria monocytogenes contamination, and when used on whole undressed or whole dressed fish, do not change the texture or appearance of the meat at all. This is useful for cold-smoked salmon products, for example, which do not have a heat-treatment or cooking step, and where it is extremely important to remove all surface pathogens prior to curing/brining and packaging.

While exposure to high pH solution can kill L. monocytogenes in under 15 minutes (e. g., at pH 12.5), preferably the exposure time is at least 15 minutes, more preferably at least one hour, and most preferably at least 2 hours. Longer exposure times have the advantage of accounting for variables such as the effect of natural acidity in fish skin on the solution and permitting portions of skin that were blocked to be exposed for an adequate time once the fish are agitated.

There is no disadvantage in using longer exposure times, because although the skin darkens and dulls, the meat inside is unaffected by the process and retains its color and quality.

An additional feature of the methods of the invention is the addition of an optional deglazing process, particularly useful for frozen fish and those with thick slime layers. The deglazing process comprises an additional step where the surface of the fish, including the skin, is at least partially thawed, so that ice on the surface of the fish and at least some slime is removed. This thawing step comprises exposure to a deglazing liquid, which is preferably an aqueous solution such as water, more preferably warm water, most preferably between about 68 of and 72 of when first placed in contact with the fish. The seafood is exposed to this liquid for at least the time necessary to thaw any superficial ice (if the fish are frozen) and the skin, about at least 15 minutes, and more preferably at least between 20 and 40 minutes. The liquid is then drained, taking ice and at least some of the slime with it. The advantage of this deglazing process is that some of the slime is removed, allowing the subsequent high pH solution easier access to the fish scales and skin, and enhancing the bactericidal treatment of the high pH solution.

DESCRIPTION OF THE DRAWING FIG. 1 is a graph of the relationship between time and Listeria cell death on salmon skin treated with high pH compared to controls. Open circles represent the number of viable Listeria monocytogenes colonies per ml over the time in minutes in the control group (incubated in sterile water at pH 7); closed circles represent the number of viable Listeria monocytogenes colonies per ml over time in the group treated with high pH solution (hydrated lime in water at pH 12.4).

DETAILED DESCRIPTION OF THE INVENTION It has been discovered that pathogenic bacteria on seafood, particularly Listeria monocytogenes on fish, can be removed or killed by treatment with a high pH solution. The methods of the invention are ideal for use prior to curing, flavoring, or packaging steps, especially in products which are not heat treated or cooked either before or after sale to the final consumer, such as cold-smoked salmon.

Bacterial contamination can be detected on food by several testing methods. A negative test result has no impact on subsequent sales of the food product, but a positive test often results in destruction of the food product as unfit for consumption. Contamination of foods by environmental bacteria, for example Listeria monocytogenes, is a common cause of contamination of certain food products, for example seafood and dairy products.

In order to discover the methods of prevention and eradication of the invention, an in-depth testing program was implemented to determine the sources of pathogens, particularly Listeria, in an actual smoked fish operation. Environmental factors and inadequate sanitation (e. g. , floor drains, employees carrying bacteria into the plant on their clothes or shoes, etc. ) were evaluated. Test on thousands of samples of equipment through finished products led to the conclusion that the biggest source of contamination is the fish itself. Listeria contamination is found on the skin, on and under the scales, and in the slime of the live fish. The meat of the intact fish is not exposed to the pathogen, but when the meat of the fish is exposed during processing, and live Listeria is present on the skin, the meat can become contaminated.

However, before the fish is split and the meat exposed, Listeria present on the skin will not contaminate the meat. Therefore, the methods of the invention were developed to remove or kill the Listeria on the skin of the fish so the meat can then be processed without contamination.

This is especially critical for cold smoked products, because unlike hot smoking (which cooks the product), there is no bactericidal step in cold smoking to destroy the Listeria. It is therefore desirable to kill or remove the bacteria, rather than just slow or inhibit their growth, since during

storage or consumer handling prior to consumption, bacteria from contaminated product could resume growth. The description below generally pertains to fish, but the methods of the invention can be used on any seafood product which has exterior or superficial microbial contamination, or on exposed meat surfaces where superficial protein denaturation/discoloration does not adversely affect the product quality or appearance.

Special techniques were developed to sample the fish prior to processing to determine whether Listeria was present on the skin. Sampling of fish prior to processing is more economical than sampling finished product, which must be destroyed if found to be contaminated. Samples of fresh or frozen pre-processed fish were obtained by scraping bits of skin, scales, and slime off of fish, or rinsing the fish and filtering out scales and other skinassociated debris. These samples were then tested for the presence of Listeria. These tests showed that Listeria was present in approximately 50% of wild salmon, particularly those caught in hatcheries (e. g. , near the spawning location). There was a correlation between fish that had large amounts of slime on the skin and incidents of positive tests. Listeria was also found to be present in approximately 60% of farm raised salmon, in spite of better handling and never coming into direct contact with the dirty streams that wild salmon are exposed to. By"slime" is meant the natural mucous layer which is secreted by all fish. The slime can form a coating on the fish which resists bactericidal chemicals like chorine and efforts to wash off by scrubbing.

However, because of the sporadic and unpredictable nature of the contamination, a method was required that can be used to treat all fish without any adverse effects on the product.

The methods of the invention can be used with fresh or previously frozen seafood, such as fish, preferably in their whole (intact or unsplit) form or after gutting and cleaning (dressing).

It is not necessary to know in advance whether or not the fish or seafood is actually contaminated.

Because contamination is not apparent by visual inspection, the treatment can be used on all fish prior to processing.

The treatment comprises an optional"deglazing"process if the fish are frozen ; then exposure to an aqueous solution of at least pH 9.5, or preferably greater (more preferably pH 12.5) for a time sufficient to kill or wash off adherent pathogenic microbes; and agitation or stirring of the seafood and/or high pH solution to infuse all superficial and exposed parts of the seafood.

The deglazing process is intended to thaw the ice on the outside of the fish and the superficial layer of the fish (e. g. , the skin) so that external ice is removed (if the fish are frozen), and to remove some or all of the natural slime layer on the fish. If the fish are fresh rather than

frozen, a pre-rinse step accomplishes removal of at least some of the slime. The pre-rinse can be achieved by spraying the fish with an aqueous solution, or immersing the fish. The deglazing or pre-rinse processes remove slime whether the fish is frozen or fresh, although it is more often used on frozen fish. The superficial thawing also helps prevent multiple frozen fish in a tank from freezing together and preventing the high pH solution from reaching the frozen patches.

In the pre-rinse or deglazing process, fish are exposed to an initial water bath for a time sufficient to remove the ice and/or slime, and thaw the skin portion of the fish if frozen. Although not necessary in many situations, this step is useful on heavily frozen or slimy fish to remove enough of the slime layer coating the fish so that the high pH treatment solution can easily reach all exposed surfaces of the fish, including under the scales and all of the skin, where Listeria and other contaminating microbes are found. Certain fish (for example, salmon returning to freshwater streams to spawn) tend to have a thicker coating of slime, and removing some or all of this coating makes is faster and easier to decontaminate the fish using the high pH treatment.

The optional deglazing or pre-rinse can be done in any temperature of water or aqueous solution that is above freezing for a time sufficient to defrost the skin of the fish (if frozen), and can be done by any means appropriate to achieve the goals of defrosting and/or removing slime.

Such means include immersion in a bath, spraying the fish with aqueous solution, or dunking the fish into a solution one or several times. Preferably, the water for deglazing is warm, more preferably between about 68-72 of, and preferably the fish are immersed in a bath of this warm water for at least 10 minutes, more preferably between about 20-30 minutes. The water is then drained away from the fish, taking with it the glaze and at least some of the slime from the fish.

The temperature of the solution used for pre-rinsing is generally cool, to prevent warming the flesh of the fish, preferably under about 50 of. more preferably under about 40 of.

If used without an initial deglazing or pre-rinse step, the high pH treatment itself also tends to remove the slime layer, especially if the slime layer on the fish is not particularly thick.

The high pH treatment solution comprises an aqueous solution having a pH high enough to kill microbes, particularly Listeria, upon exposure. An additional benefit of using the solution is that it can wash away adherent bacteria as well as kill them. The fish is exposed to the high pH solution by immersion in a bath, spraying the fish with aqueous solution, or dunking the fish into a solution one or several times. Immersion for a period of time is the preferred mode of treating the fish. Preferably, the fish are treated in their whole undressed or dressed form. Fillets exposed to the high pH solution tend to discolor on the exposed surface of the meat (due to protein

denaturation caused by the elevated pH). Where appearance of the product is important, it is preferable to treat the intact fish and fillet it subsequent to the treatment.

The antimicrobial (bactericidal) effect of the solution is related to the time of exposure, and the time requirement is affected by such things as the slime layer, ice, or other physical obstacles that may prevent direct access of the solution to the skin and scales of the fish. Thus, it is critical that the entire fish be exposed to the solution, as by complete submersion in the solution. A pH of 9.5 or above has a bactericidal effect on Listeria and other pathogenic microbes associated with seafood, and pH values higher than this kill these microbes in less time. Preferably, the pH used is above 9.5, more preferably above pH 10.5, more preferably above pH 11.5 and most preferably above pH 12.5. At a preferred pH of 12.5, for example, exposure of the fish skin for 15 minutes to the high pH solution has been found to kill all colony forming units on the exposed skin (see Example 1 below). In a large-scale plant environment, for example, where many fish are treated at one time in a single container, it is preferable to use a longer time period to ensure adequate exposure of all parts of each fish to the high pH solution.

This is to account for variables such as the inherent acidity of fish skin altering the pH to some extent, fish touching during treatment and preventing the solution from reaching those parts of the fish for a period of time, etc. At pH 9.5, a period of several days to two weeks is preferred to eliminate Listeria or other microbial contamination, and at pH 12.5 or higher, a period of more than 15 minutes, more preferably over one hour, is all that is necessary. Because the product is not harmed by exposure to the high pH treatment, an exposure time of at least about 2 hours is more preferred, and exposure times of from 12-24 hours are quite suitable.

Exposure to the solution renders salmon skin a dark, dull color, and this provides a visual method to check that all parts of the fish were uniformly exposed to the solution and were thus adequately treated. This visual inspection does not necessarily dispense with the need to test samples with bacteriological methods, but readily identifies product which has not been adequately treated.

Because a plant setting usually requires the processing of large numbers of fish, fish are handled in lots or groups rather than individually. The treatment methods of the invention are suited to treating as many fish concurrently as necessary. For example, many fish can be piled into large vats for both the deglazing/pre-rinse processes, if used, and the high pH treatment process, preferably so that all parts of all fish are completely submerged throughout the processes. However, as such high concentrations of fish almost always lead to fish-to-fish contact, a risk remains that not all exposed surfaces of every fish will be treated. It is also

possible that the vats can be overloaded, so that parts of some fish are sticking out of the solution. To avoid problems of certain fish being incompletely treated with the high pH solution, the containers in which the fish are treated are periodically agitated by any suitable means, such as stirring or shaking, that will dislodge the fish from their positions. In large containers, such agitation can be achieved by movement of the container by heavy equipment, such as a forklift. Alternatively, a large stirring implement can be inserted into the container and manually operated. It is important to leave enough free space in the container, regardless of its size, to allow some movement of the fish when the container is agitated or stirred. Thus, there is an upper limit to the number of fish that should be placed in each container that is dictated by the ability of the fish to move relative to one another upon shaking, preferably to move freely within the container and remain submerged at all times.

Chemicals suitable for use in elevating the pH of solutions used in treating seafood according to the methods of the invention are those that are approved by the FDA as food grade.

Such chemicals can be selected from sources such as the Food Chemicals Codex (4"'ed., 1996 ; and the First Supplement to the fourth edition (1997) ) published by the Food and Nutrition Board of the Institute of Medicine and supported by the U. S. Food and Drug Administration.

Appropriate chemicals are those which are food grade, and basic when dissolved in water, for example hydrated lime (calcium hydroxide), sodium hydroxide, magnesium hydroxide, or potassium hydroxide (available from sources such as Van Waters and Rogers, Los Angeles, CA; or Spectrum Chemical Mfg. Corp. , Gardena, CA). Any food grade base can be used, however.

Enough of the selected chemical is dissolved in the aqueous treatment solution so that the pH is raised to the desired level. A buffering agent can be added as well to stabilize the pH, but the seafood itself generally provides some buffering. For example, about 1-2 lobs. of hydrated lime added to a tank that is 32"x 60"x 18"and which holds about 250 lobs. of seafood raises the pH of the solution to at least about 12.5. This amount of lime is sufficient to maintain the pH at or about the same pH throughout even 18 hour or longer treatment periods.

To identify whether or not the treatment has been effective, or whether treatment is necessary (e. g. , whether the fish are infected with Listeria), the whole fish or subsequent product can be tested by methods known in the art. One method for identifying L. monocytogenes in food products is to sample the food item (the samples are composited, if required, according to compliance instructions). Analytical portions (25 g) are enriched for Listeria species in selective enrichment broth at 30 C for 48 hours. The enrichment culture is streaked at 24 and 48 hours on two different, but complementary, differential selective agars to isolate Listeria species. Isolates

are purified on nonselective agar and speciated directly by a battery of conventional tests or by such tests in kit form, or are preliminarily identified as members of the genus Listeria by genus specific rapid test ELISA or DNA probe kits. Alternatively, isolate cultures are rapidly speciated, within 1 hour, as L. moiiocytogenes (or not L. monocytogenes) by a chemiluminescent labeled DNA probe kit or by equivalent L. monocytogenes specific DNA probes or probe kits. Serotyping, virulence testing, and enumeration of Listeria by direct plating on selective agar or by MPN enrichment and selection are optional methods. Several rapid DNA probe and ELISA kits can be used in the generic or specific identification of Listeria isolates on selective isolation or purification agars, such as listed in the table below.

Table 1. Commercial test products for L. monocytogenes.

Test Analytical Technique Approx. Total Supplier Test Timet AccuPROBE## Listeria monocytogenes Nucleic acid hybridization 18-48h Gen-OProbe, San Diego, CA Culture Identification Test Web : www. gen-probe. com API LISTERIA Used to identify Listeria spp. Biochemical reactions 18-24 h ioMerieux Inc., Hazelwood, MO Assurance isteria EIA2 [Used to identify Enzyme immunoassay 50 h BioControl Systems, Inc., Bellevue Listeria spp. including L. monocytogenes WA 98005 BAX## for Genus Listeria Polymerase chain reaction 45 h Qualicon, Inc. Wilmington, DE BAX## for Screening/L. monocytogenes Polymerase chain reaction 45 h qualicon, Inc.

Oynabcads anti-Listeria [Used to identify L. immunomagnetic Separation 48 h Oynal Inc., Lake Success, NY 1042 nonocytogenes Web: www.dynal.no/ EIAFoss Listeria Combination ELISA and 48 h Foss North America, Inc., Eden mmunornagnetic separation raine, MN 3ENE-TRAK Listerza monocytogenes Assay Nucleic acid hybridization 48 h GENE-TRAK Systems, Hopkinton, MA 3ENE-TRAK Listena Species Assay nucleic acid hybridization 48 h GENE-TRAK Systems SO-GRID Method for Listeria spp. Membrane filtration 24 h A Life Sciences, Inc. , San Diego, : A isteria ulture 24 h contamination Sciences LLC madison, WI Listeria RapidTest2 [Used to identify Listeria EIA 42 h O xoid, Inc, Nepean, Ontario spp. including L monocytogenes Canada Listeria-TekTMTM2 ELISA 48 h Organon Teknika Corp.

Durham, NC ListerTestTMTM2 immunomagnetic separation 24 h secam, L. P., Watertown, MA (Used to identify L monocytogenes Web www.vicam com Microbact 12L2 [used to identify Listeria spp.] Biochemical identification system 4-24h BioControl Systems, Inc

Test Analytical Technique Approx. Total Supplier Test Time' Probeha PCR System (Used to identify L Polymerase chain reaction 30 h BioControl Systems, Inc monocytogenes] Reveal## for Listeria2 [Used to identify Listeria Sandwich ELISA 48 h Neogen Corporation, Lanisng, MI spp Web www. neogen.com rECRA Listeria Visual Immuno Assay2 ELISA 48 h ntemational BioProducts Used to identify Listeria spp. Redmond, WA Vidas Li S2 (Used to identify L moncoytogenes] Enzyme linked fluorescent assay 48 h ioMéérieux Inc.

Vidas LMO [Used to identify L enzyme linked fluorescent assay 48 h ioMeérieux Inc rnonocytogenes] VIP for Listeria2 [Used to identify Listeria spp. [Visua immunoprecipitate 48 h BioControl Systems, Inc. including L monocytogenes 'Includes enrichment 2AOAC The following Examples are intended to be illustrative and are not intended to limit the invention in any way.

Example 1 : Bactericidal Effect of High pH Solutions on Listeria in Fresh Fish Skin The purpose of this study was to examine the effects of high pH water on Listeria A 48 hour broth culture of Listeria monocytogenes was diluted out to a concentration of approximately 1,200 cells per milliliter. One milliliter of the cell suspension was pipetted onto the surface of a fish skin (25 grams), and spread out evenly. The skin set for 15 minutes to allow the Listeria cells to acclimate to the new environment. A separate skin was inoculated similarly to act as a control. One skin was placed into 250 mL of high pH water (initial pH 12.39), prepared by mixing 16 oz. water and 0.0025 Ibs. of hydrated lime. The control skin was placed into 250 mL of sterile water (pH 7.00). Each sample was tested for Listeria count and pH. At 1, 3,5, 7,9, 11 and 15 minutes, a Listeria count and pH measurement was taken. The results are shown in FIG. 1 and Table 2.

Table 2 Control* Test Time L mono/ml L. monolml pH 0 13 0 12.39 1 12 0 12. 21 3 12.17 5 12.35 7 12.34 9 13 8 123 11 11 2 12. 22 15 13 0 12. 25 *Control sample maintained pH 7.00 Following this immersion, the skins were tested for the presence of live (colony forming) units of L. monocytogenes by culturing methods specific for Listeria. As seen in Fig. 1, the Listeria cells on the skins in the high pH water require at least 2-3 minutes before they are released into the surrounding solution. After release, the cell counts drop steadily for approximately 10 minutes. Viable Listeria appear to disappear at the 15 minute mark. The control sample maintained a steady viable count. The pH of the test sample showed some fluctuations, which had minimal, if any, effect on the counts.

Example 2: Sample Protocol to Treat Frozen Fish 1) Dump frozen dressed fish into tank. Add no more than can easily be moved or rotated in the tank. For a tank of 31"x 60"x 18", this is about 250 lbs. of fish.

2) Pre-rinse-frozen fish a) Fill tank with warm water (between about 68-70OF) in order to melt the glaze, and loosen the slime. b) When skins are thawed, in approximately 30 minutes, drain water.

3) Add hydrated lime or other alkaline food grade ingredient to tank in an amount sufficient to raise the pH the desired amount. Amount of lime will vary according to size of tank. For a tank of the above dimensions, 1-2 pounds of lime is more than sufficient to maintain a pH of at least about 12.5. Fill tank with water, ensure even dissolution and distribution of lime and complete coverage of fish.

4) pH level-the kill rate has a time/pH level relationship.

A pH level of 12.5 requires less than 2 hrs. to kill pathogens Add sufficient lime to tank to bring pH level to 12.5. Test pH level after lime is dissolved and tank is full of water. Do not allow water to overflow the tank, thereby diluting the solution.

S) Exposure-Entire exterior of fish, including gills and fins, must be exposed to solution in order to be effective. There should be no ice left in the solution or on the fish at the end of the defrost period, if a deglazing step is used, or the fish can stick together. The fish must be completely submerged throughout process, or for at least enough time to kill pathogenic microbes. In order to ensure that all surfaces contact the solution for a sufficient period of time needed to kill the pathogens, the fish must be stirred and rotated periodically using a sanitary paddle or other device.

6) Time-The fish can be held in this solution overnight, which is more than sufficient to ensure a complete pathogen kill. Although much less time is required, defrosting of frozen fish is done overnight (12-18 hours), so fish are left in the high pH solution for this time period without any adverse effects to the product.

7) Rinse-The next morning, drain the solution and rinse remaining lime off the fish with clean water.

It is critical to monitor the treatment process at steps 4,5, and 6 above. The pH level must not be allowed to fall below the bactericidal level, and an excess of lime is used to ensure that the pH does not drop. The entire fish must be exposed to the high pH solution for a sufficient time to kill pathogenic microbes. This is best done by ensuring that the tank is not overloaded with fish, so that fins, tails, or other parts do not stick out, and so that the fish move freely relative to each other when the tank is agitated. The tank is stirred twice at hourly intervals before it is left for the night, and then stirred again first thing in the morning to ensure that all parts of the fish are exposed to the solution.

The preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described methods may be practiced without meaningfully departing from the principles, spirit and scope of this invention.

Accordingly, the foregoing description should not be read as pertaining only to the precise methods described, but rather should be read consistent with and as support to the following claims which are to have their fullest and fair scope.

Claims (27)

CLAIMS :

1. A method of treating seafood to remove or kill pathogenic microbes, the method comprising: providing seafood; providing an aqueous solution having a pH of at least 9.5 ; and contacting the seafood with the aqueous solution such that all of the exterior and other accessible portions of the seafood are exposed to the solution, wherein the entire surface of the seafood is exposed to the aqueous solution for at least a time sufficient to kill or remove the microbes to an undetectable level.

2. The method of claim 1 wherein the seafood is fish.

3. The method of claim 2 wherein the contacting of the fish with the aqueous solution is effected by placing the fish into a container with the solution, and agitating the container or the fish at least once during the contacting period such that any part of the fish that is in physical contact with another object is moved and exposed to the solution.

4. The method of claim 2 wherein the fish is whole or dressed.

5. The method of claim 1 wherein the microbe is Listeria monocytogenes.

6. The method of claim 2 wherein the microbe is Listeria monocytogenes

7. The method of claim 2 wherein the pH of the aqueous solution is at least 10.5.

8. The method of claim 2 wherein the pH of the aqueous solution is at least 11.5.

9. The method of claim 2 wherein the pH of the aqueous solution is at least 12.5.

10. The method of claim 2 wherein the contacting time is at least 15 minutes.

11. The method of claim 2 wherein the contacting time is at least one hour.

12. The method of claim 2 wherein the fish provided are frozen, the method further comprising a deglazing process prior to contacting the fish with the aqueous solution, wherein during the deglazing process, the surface of the fish including the skin is at least partially thawed, so that ice on the surface of the fish and at least some slime is removed.

13. The method of claim 2 wherein the fish provided are fresh, the method further comprising a pre-rinse process prior to contacting the fish with the aqueous solution to remove slime, the pre-rinse selected from spraying with an aqueous solution and immersing in a bath.

14. The method of claim 12 wherein the deglazing process comprises exposure to a deglazing liquid.

15. The method of claim 14 wherein the deglazing liquid is between about 680 F and 72 OF when placed in contact with the fish.

16. The method of claim 14 wherein the fish are placed in the bath for between about 15 and 40 minutes.

17. The method of claim 1 wherein the pH is elevated by addition of hydrated lime.

18. The method of claim 3 wherein the agitation is done by at least one of stirring the fish in the container and shaking the container.

19. The method of claim I wherein the contacting of the seafood with the aqueous solution is effected by placing the seafood into a container with the solution, and agitating the container or the seafood at least once during the contacting period such that any part of the seafood that is in physical contact with another object is moved and exposed to the solution.

20. The method of claim 1 wherein the pH of the aqueous solution is at least 10.5.

21. The method of claim 1 wherein the pH of the aqueous solution is at least 12.5.

22. The method of claim 1 wherein the contacting time is at least 15 minutes.

23. The method of claim 1 wherein the exposure time is at least one hour.

24. The method of claim 1 wherein the seafood is provided frozen, the method further comprising a deglazing process prior to contacting the seafood with the aqueous solution, wherein during the deglazing process, the surface of the seafood is at least partially thawed, so that ice on the surface of the seafood is removed.

25. The method of claim 24 wherein the deglazing process comprises exposure to a deglazing liquid selected from a spray or an immersion bath.

26. The method of claim 1 wherein the pH is elevated by addition of hydrated lime.

27. The method of claim 19 wherein the agitation is done by at least one of stirring the seafood in the container and shaking the container.