WO2002082914A1

WO2002082914A1 - Packaged fresh fish food product and method of producing the same

Info

Publication number: WO2002082914A1
Application number: PCT/US2001/012236
Authority: WO
Inventors: Elmer F. Glabe; Victor H. Shubert; Melvin Mickevic
Original assignee: Glabe Elmer F; Shubert Victor H; Melvin Mickevic
Priority date: 2001-04-13
Filing date: 2001-04-13
Publication date: 2002-10-24

Abstract

A packaged fresh fish product -- and method of producing the same -- that has an external coating of an aqueous solution of sodium diacetate is substantially free of pathogenic bacterial species and is enclosed in a removable, airtight, film. There is no substantial penetration of the mass of the fish by said aqueous solution of sodium diacetate. The aqueous solution is retained on the external surfaces of the fish by the surface tension of the sodium diacetate solution after the fish is coated with the solution. The aqueous solution of sodium diacetate is substantially free of alkali metal lactate.

Description

PACKAGED FRESH FISH FOOD PRODUCT AND METHOD OF

PRODUCING SAME

Field of Invention

This invention relates to an improved packaged fresh fish product, and to a method of producing such a product.

Background of Invention

Numerous studies have been made by government oversight agencies such as the Food and Drug Administration, the U.S. Department of Agriculture and the Food Safety Inspection Service, as well as by fish processors, to identify species of pathogenic bacteria that have often been found in fresh fish food products and have been the cause of food poisoning outbreaks that have affected large numbers of the population. The reduction or elimination of such pathogenic bacteria has been the subject of much research and development over many years.

An important discovery ~ the use of sodium diacetate in retarding, inhibiting and preventing the growth and development of microorganisms in foodstuffs - was patented over 50 years ago in U.S. Patent No. 2,417,806, issued March 25, 1947. In the intervening years, the only instance of the use of sodium diacetate in connection with fish products of which we are aware — U.S. Patent No. 5,989,610 issued to Ruzek on November 23, 1999 - requires a very different method of treatment of the fish from the method utilized in the present invention, and thus results in a substantially different product. That patent discloses the use of an aqueous solution of a small amount of sodium diacetate, but it also (1) requires that the solution be injected within the interior of the fish product and (2) requires that a quite large amount of an alkali metal lactate be included in the aqueous solution, neither of which is a part of the present invention. Summary of the Invention

The food product of this invention comprises a dressed portion of fresh fish meat coated with an aqueous solution of sodium diacetate that is substantially free of any alkali metal lactate, and is located substantially entirely on the external surfaces of the fish portion. The coated fish portion is enclosed in a removable, airtight, packaging film.

The coating of an aqueous solution of sodium diacetate is retained on the external surfaces of the portion of the fish by the surface tension of the sodium diacetate solution after the fish is coated with the solution. If desired, the coated fish portion can be hung freely for a brief period of time to permit excess liquid to drain away.

Various concentrations of sodium diacetate contained in the aqueous solution that constitutes the coating on the fish, selected according to the degree of pathogenic bacterial contamination present in the fish, are set forth below in this specification.

This invention also includes the process of treating a dressed portion of fresh fish meat by applying to the external surfaces only of the piece of meat an aqueous solution that has an indicated concentration of sodium diacetate and is substantially free of alkali metal lactate, and then wrapping the coated fish in a removable, airtight film to produce a packaged product as described.

There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form a part of the subject matter of the claims appended hereto. It is important that the claims be regarded as including such additional subject matter insofar as it does not depart from the spirit of the present invention. Advantages of the Invention

This invention produces a dressed portion of fresh fish meat that is totally free of three very dangerous pathogenic bacteria species: o salmonella enter ides and related species; o Escheritia coli 0157/H7 and related pathogenic coliform bacteria species; and o campylobacter jejuni and related pathogenic species.

These are the "pathogenic bacterial species" referred to in this specification.

The food product of this invention is storage stable, with no reappearance of the above pathogens when the treated portion of fresh fish is held under conventional refrigeration (35 °F. to 40°F.) or frozen storage (-10°F. to 5°F.) in airtight packaging materials such as polystyrene trays wrapped in polyethylene film.

In addition to being free of the three above mentioned types of virulent pathogens, the food product of this invention is characterized by: o the enhancement of the growth of naturally occurring lactobacilli which are beneficial bacteria essential for the digestion of food; o the absence of any deleterious odor or taste in the fish meat upon preparation and cooking it for eating; and o the absence of any alteration of the natural texture of the fish meat which would make it less attractive for eating.

As indicated by the above facts, we have discovered that the coating of an aqueous solution of sodium diacetate in this invention is very effective in extending the shelf life of dressed portions of fresh fish meat, without any alkali metal lactate being present in the aqueous solution with which the fish is coated and with the coating of sodium diacetate being located substantially entirely on the external surfaces of the piece of fish rather than being injected into the fish mass. It follows that the use of this invention reduces the cost of treating the fish meat, since the very considerable cost of the alkali metal lactate is eliminated, and the texture of the fish meat is maintained.

These and other advantages of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its advantages and the specific objects attained by its use, reference should be had to the accompanying descriptive matter in which preferred embodiments of the invention are discussed.

Detailed Description of the Invention

The product of this invention comprises a dressed portion of fresh fish meat coated with an aqueous solution of sodium diacetate and enclosed in a removable, airtight, packaging film. As already pointed out, the aqueous solution is substantially free of any alkali metal lactate.

The aqueous solution of sodium diacetate extends continuously across the external surface of the dressed fish portion without any substantial penetration of the mass of the fish portion. The solution is retained on the external surfaces of the fish portion because of the surface tension of the aqueous solution after the portion of fish is coated with the solution and, if desired, is hung freely for a brief period of time to permit excess liquid to drain away.

The external surface of said coating of an aqueous solution of sodium diacetate is substantially smooth throughout. As will be understood, the surface tension of the aqueous solution will tend to produce a coating having a smooth upper boundary, while irregularities and crevices on the exposed surfaces of the portion of fresh fish being treated will produce a coating that has an irregular lower boundary and as a result is not wholly uniform in thickness. Size of Treated Portion of Fish

The conventional process for preparing dressed portions of fresh fish, commonly referred to as "fillets, " for commercial sale includes (1) removal of the skin, (2) removal of the head, tail and fins, (3) trimming, washing and chilling, (4) packaging and storing, (5) transporting and storing and (6) refrigerating and storing.

It is preferred that in the practice of the present invention the fillet to be treated should be rather large ~ as, for example, half the dressed fish. The dividing up into single servings can then be carried out in the kitchen, when the film covering the packaged product is removed, either before or after the fish is cooked.

With a larger piece of fish, the surface area of the packaged product as compared to the weight of the product is minimized. Minimizing the surface area has two desirable results. First, since the interior of a portion of fish is considered as being sterile, the smaller surface area of the larger piece of fish reduces the potential for microbiological quality problems. Second, the lower amount of sodium diacetate required to eliminate the bacterial problems makes it less likely that the sodium diacetate may produce alterations in the sensory characteristics of the fillet.

Concentration of Sodium Diacetate Solution

Depending upon the degree of pathogenic bacteria contamination of the fresh fish, satisfactory results can be obtained when the percentage by weight of sodium diacetate in the aqueous solution with which the fish portion is coated is from about 0.1 % up to about 25 % . Good results are also obtained when the percentage by weight of sodium diacetate in the aqueous solution is from about 0.1 % to about 20% . The preferred percentage of sodium diacetate in the aqueous solution is in most cases from about 10% to about 20% . The concentration of sodium diacetate employed will depend on (1) the degree of bacterial infection of the portion of fresh fish meat that is caused by processing and handling, (2) the anticipated exposure to infection of the fish after is unpackaged, (3) the anticipated length of time before cooking and (4) similar factors. In each case the sodium diacetate solution should be sufficiently concentrated to protect the fish portion from all pathogenic bacteria of the order and species of salmonella, E. coli, and campylobacter.

It is preferred that a determination first be made as to the degree of pathological bacteria contamination on the surfaces of the portion of fresh fish that is being treated, in order to determine more accurately the concentration of sodium diacetate that should be used for higher levels of contamination. The concentration of sodium diacetate should be high enough to be effective in treating the portion of fish, without incurring the expense of including substantially more of the agent than is necessary.

Application of Sodium Diacetate Solution

The coating of an aqueous solution of sodium diacetate can be applied to the portion of fish being treated by any suitable method, including dipping the dressed fish portion into the aqueous solution, or spraying or brushing the solution onto the portion of fish being treated. No matter which mechanical, pneumatic or electrical spraying device is used, it is important that it deliver a uniform mist of droplets, which will help establish a substantially uniform film of sodium diacetate solution on all external surfaces of the piece of fish being treated.

The period of time for application of the aqueous solution of sodium diacetate to the portion of fish being treated, as well as the period of time to allow excess liquid to drip away, are measured in terms of fractions of minutes or at most a few minutes.

We have found that the coating will adhere to the fish without the use of any adhesive material in the sodium diacetate solution. (As used in this specification and the appended claims, the term "adhesive material" includes an adhesive base, a potentially adhesive base, a binder, an adhesive suspending medium, a gum, other adhesive colloidal material, a gelatin or the like for adhering the sodium diacetate to the meat being treated.) However, if desired, a small amount of propylene glycol may be added to the sodium diacetate solution to stabilize the natural fish oil and thereby enhance adherence of the solution to the piece of fish being treated.

Also, if desired, a small amount of ascorbic acid (Vitamin C) may be added to the sodium diacetate solution in order to reduce oxidation of the coated fish so as to reduce the darkening of the fillet over time.

When either propylene glycol or ascorbic acid is included in the sodium diacetate solution, it will be effective in an amount from about 1 % to about 20 % by weight of the sodium diacetate that is contained in the solution.

In U.S. Patent No. 5,989,610 referred to above, the aqueous solution with which the fish meat is treated is pumped or injected directly into the mass of the portion of fish being treated. According to the discussion at Col.8, Lns.60- 65 of the '610 patent, this increases the weight of the piece of fish preferably up to about 125% of its original weight (and presumably in some cases even higher). Most of this increase in weight is water. About 5 % is represented by the humectant alkali metal lactate, which is required to tie up the water in the interior of the treated fish and prevent accumulation of purge in the ultimate packaged product. Only about 0.2% is represented by an alkali metal diacetate such as sodium diacetate. It follows that the aqueos solution that is pumped or injected directly into the fish preferably contains about 25 times as much alkali metal lactate as alkaline metal diacetate.

Two undesirable results follow from the introduction of such a large amount of water into the fish, and the use of such a large amount of the humectant, alkali metal lactate. First, injection of so much water directly into the fish meat tissue produces an undesirable change in the texture of the fish. In particular, the fish will become soft and tear easily. Second, because there is 25 times as much alkali metal lactate than alkali metal diacetate, the cost of the alkali metal lactate will run a great many times higher than the cost of the small amount of sodium diacetate that is contained in the aqueous solution with which the piece of fish is treated. Both these undesirable results are avoided in the present invention.

Packaging

A wide variety of choices for packaging exists. A styrofoam tray with an overwrap of polyethylene film is standard.

Effectiveness of Sodium Diacetate Solution

Tests that have been carried out with aqueous solutions of sodium diacetate over a broad range of concentrations demonstrate the effectiveness of sodium diacetate in inhibiting and totally eliminating pathogenic bacteria. These tests were carried out with codfish, salmon, ocean perch and catfish.

Example 1

In this Example, separate samples of codfish were treated with 0.1 %, 0.2% , 0.5% and 1.0% aqueous solutions of sodium diacetate.

Fresh cod fillets were commercially purchased and cut into small squares. The fillets were divided into two groups, one the untreated control group and the other the experimental group. Both groups were subjected to standard microbiological analysis at the beginning of the test.

A number of separate pieces of fresh fish from the untreated control group were then vacuum packed in removable, airtight, packaging film.

The fillets in the experimental group were treated by (1) dipping them separately into 0.1 % , 0.2% 0.5% , and 1.0% aqueous solutions, respectively, of sodium diacetate in four separate containers, (2) waiting 60 seconds, (3) drip draining each of the samples for 10-15 seconds and (4) then vacuum packaging the fillets separately under the same conditions as the control samples had been packaged.

The packages were held refrigerated at 4° C. for the duration of the study. On Days 1 and 5 after the preparation of the two groups of samples, packages from the untreated control group and packages from the experimental group were placed in boiling water to cook the packaged fish. The packaging was then removed, and each piece of fish was subjected to microbiological and sensory analysis.

The microbiological analysis was carried out by standard methods. The sensory testing parameters included evaluation of appearance, odor/taste, and texture of the cooked cod fillets. The sensory tests were conducted in the blind by a trained sensory panel of seven members for the tests on Day 1 and eight members for the Day 5 tests.

The microbiological data from the tests carried out on Days 1 and 5 indicate quite clearly that even at very low concentrations — preferably, with a dipping time of as much as 60 seconds — aqueous solutions of sodium diacetate have a growth-inhibiting effect on total bacterial counts on the surfaces of the treated cod fillets. The total aerobic plate count for the untreated cod rose from 3,000 per gram on Day 1 to 98,000 per gram on Day 5, while during the same period the total aerobic plate count for the cod treated with aqueous solutions of 0.2%, 0.5% and 1.0% sodium diacetate by weight, respectively, remained below 1 ,000 per gram and the total aerobic plate count for the cod treated with the 0.1 % solution rose only slightly.

Concerning changes in appearance, odor, taste and texture between Day 1 and Day 5, at least six of the eight members of the Day 5 sensory panel found significant, albeit not major, differences between the untreated control samples of cod and the samples of cod that were treated for 60 seconds with aqueous solutions of sodium diacetate of 0.2, 0.5%, and 1.0% by weight, respectively.

Example 2

The test product in this Example was commercially purchased fresh salmon fillets, cut into small squares. The test was carried out in the same manner as the cod fillets were tested in Example 1.

The microbiological data from the tests carried out on Days 1 and 5 indicate quite clearly again that even at very low concentrations — preferably, with a dipping time of as much as 60 seconds — aqueous solutions of sodium diacetate have a marked growth-inhibiting effect on total bacterial counts on the external surfaces of the treated salmon fillets. The total aerobic plate count for the untreated salmon rose from less than 1,000 per gram on Day 1 to 37,000 per gram on Day 5, while during the same period the aerobic plate count for each of the samples of the salmon treated with aqueous solutions of 0.2%, 0.5% and 1.0% sodium diacetate by weight, respectively, remained below 1,000 per gram and the aerobic plate count for the salmon treated with 0.1 % solution rose only slightly.

Concerning changes in appearance, odor, taste and texture between Day 1 and Day 5, at least six of the eight members of the Day 5 sensory panel found significant, albeit not major, differences between the untreated control samples of salmon and the samples of salmon that were treated for 60 seconds with aqueous solutions of sodium diacetate of 0.1 %, 0.2% , and 1.0% by weight, respectively.

Example 3

The test product in this Example was commercially purchased ocean perch fillets, cut into small squares. The fillets were divided into two groups, one the untreated control group and the other the experimental group. Both groups were subjected to standard microbiological analysis at the beginning of l ithe test.

A number of separate pieces of fresh fish from the untreated control group were placed in a foam tray on a paper pad and covered with a plastic film.

These fillets in the experimental group were treated by dipping them separately for 20 seconds into three separate aqueous solutions of sodium diacetate as follows:

Solution 1 ~ 5 % sodium diacetate + 1 % propylene glycol

Solution 2 - 10% sodium diacetate

Solution 3 — 15% sodium diacetate + 2% propylene glycol Each of the treated samples from the experimental group was then covered with a plastic film in the same way as the control samples were covered.

All the covered packages in both groups were held refrigerated at 38° F. for the duration of the study. On Day 15 the control group of fillets and the experimental group of treated fillets were subjected to microbiological analysis using standard methods of analysis.

The microbiological data from the tests carried out on Day 15 indicate quite clearly that aqueous solutions of 5% , 10% and 15% of sodium diacetate — preferably, with a relatively short immersion time have a marked growth- inhibiting effect on total bacterial counts. On Day 15, the total aerobic plate count for the untreated ocean perch had grown to over 3,000,000 per gram, including the following total bacteria counts for the indicated specific bacteria:

Clostridium 1,700 per gram

Streptococcus 180 per gram

Pseudomonas 93,000 per gram

Aeromonas hydrophilia 41,000 per gram

By contrast, the total aerobic plate counts for the ocean perch fillets treated with sodium diacetate aqueous solutions (referred to above as Solutions 1 , 2 and 3) were measured as 480,000, 1, 100 and 6,000 per gram, respectively, and the total aerobic plate count for the specific bacteria listed above in each case was zero. The tests in this Example 3 were repeated on Day 27 on additional samples of ocean perch with generally similar results.

Example 4

Substantially the same tests that were carried out on codfish in Example 1 were carried out on other samples of cod in this Example, with the exception that here the fillets in the experimental group were treated with a 30 second dip in a stronger concentration — 20%— sodium diacetate aqueous solution and were sampled on Days 0, 1, 2, 3, 4 and 7; the blind sensory tests were carried out by a seven-member sensory panel; and three samples instead of one were involved in the sensory tests.

The microbiological data recorded on Days 0 and 7 indicate very clearly that relatively high concentrations of aqueous solutions of sodium diacetate have a marked growth-inhibiting effect on total bacterial counts. The total aerobic plate count for the three samples of untreated cod rose by more than 2,000 times — from an average of about 15,667 per gram on Day 0 to an average of about 34,433,000 per gram on Day 7. By contrast, during the same period the total aerobic plate count for the three samples of cod treated with an aqueous solution of 20% sodium diacetate rose only about 1.5 times —from an average of about 10,733 per gram on day O to an average of about 15,733 per gram on Day 7.

Concerning appearance, odor, taste and texture, on Day 0 only 2 of the 7 judges on the sensory panel correctly determined the difference between the samples of untreated cod and the samples treated with 20% sodium diacetate solutions, while on Day 7 all of the judges correctly determined the difference.

Example 5

In this Example, farm-raised catfish fillets were purchased at a grocery store, and were tested in the same manner as the samples of ocean perch were tested in Example 3, with the exception that the concentration of sodium diacetate was greater; all the samples were first inoculated with a mixture of harmful bacteria (listeria, monocytogenes, salmonella interiditis, pseudomonas aeruginosa and E. coli 0157-H7), in order to make the tests more extreme; and the tests were performed on Days 1 , 8, 15, 22 and 29.

The sodium diacetate aqueous solutions used in this Example were the following:

Solution 1 - 20% sodium diacetate

Solution 2 - 20% sodium diacetate + 0.2% ascorbic acid + 0.2% propylene glycol

Solution 3 - 20% sodium diacetate + 2.0% ascorbic acid + 2.0% propylene glycol

The microbiological data from the tests carried out on Days, 1, 8, 15, 22, and 29 provide additional evidence that aqueous solutions of 20% sodium diacetate have a marked growth- inhibiting effect on total bacterial counts. On Day 15, for example, the total aerobic plate count for the untreated catfish fillets had grown to over 3,000,000 per gram, including the following total bacteria counts for the indicated specific bacteria:

E.coli 3,200,000 per gram

Salmonella 20,000 per gram

Listeria 6,000 per gram

By contrast, the total aerobic plate counts for the catfish fillets treated with sodium diacetate aqueous solutions (referred to above as Solutions 1, 2, and 3) were measured at 11,000, 8,000, and 16,000 per gram respectively, and the total aerobic plate count for the specific bacteria listed above was in each case zero.

Similar results were obtained when additional samples of the catfish fillets were tested on the succeeding Days 22 and 29.

While this invention has been described in connection with the best mode presently contemplated by the inventor for carrying out his invention, the preferred embodiments described are for purposes of illustration only, and are not to be construed as constituting any limitations of the invention. Modifications will be obvious to those skilled in the art, and all modifications that do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.

Claims

WE CLAIM:

1. A packaged fresh fish product which comprises

(a) a dressed portion of fresh fish meat;

(b) a coating of an aqueous solution of sodium diacetate that

(i) extends continuously across the external surfaces of said dressed fish portion without any substantial penetration of the mass of said fish portion, (ii) is retained on said external surfaces because of the surface tension of said aqueous solution after said fish portion is coated with said solution, and (iii) is substantially free of any alkali metal lactate; and

(c) a removable, airtight, packaging film wrapping around said coated fish portion.

2. The food product of claim 1 in which the external surface of said coating of an aqueous solution of sodium diacetate on said dressed fish portion is substantially smooth throughout.

3. The food product of claim 1 in which said dressed fish portion coated with an aqueous solution of sodium diacetate is hung freely for a brief period of time to permit excess liquid to drain away, before said coated fish portion is enclosed in said packaging film.

4. The food product of claim 1 in which the percentage by weight of sodium diacetate in said aqueous solution is sufficient to destroy substantially all the pathological bacteria in said food product.

5. The food product of claim 1 in which the percentage by weight of sodium diacetate in said aqueous solution is from about 0.1 % to about 25 % of the weight of said solution.

6. The food product of claim 5 in which the percentage by weight of sodium diacetate in said aqueous solution is from about 0.1 % to about 20% of the weight of said solution.

7. The food product of claim 6 in which the percentage by weight of sodium diacetate in said aqueous solution is from about 10% to about 20% of the weight of said solution.

8. The food product of claim 5, 6, or 7 in which said coating contains propylene glycol in an amount equal to about 1 % to about 20% by weight of the sodium diacetate that is contained in said solution.

9. The food product of claim 5, 6, or 7 in which said coating contains ascorbic acid in an amount equal to about 1 % to about 20% be weight of the sodium diacetate that is contained in said solution.

10. The food product of claim 1 in which said coating of an aqueous solution of sodium diacetate is applied by dipping said dressed fish portion in said aqueous solution.

11. The food product of claim 1 in which said coating of an aqueous solution of sodium diacetate is applied by spraying said aqueous solution onto said dressed fish portion.

12. The food product of claim 1 in which said coating of an aqueous solution of sodium diacetate is applied by brushing said aqueous solution onto said dressed fish portion.

13. A method of producing a packaged fresh fish product which comprises:

(a) applying to the external surfaces of a dressed portion of fresh fish meat, without causing any substantial direct penetration of the mass of said portion, an aqueous solution of sodium diacetate that is substantially free of any alkali metal lactate, to produce a coating of said aqueous solution that extends continuously across said external surfaces of said dressed fish portion; and

(b) enclosing said coated fish portion in a removable, airtight, packaging film.

14. The method of claim 13 in which the external surface of said coating of an aqueous solution of sodium diacetate that is produced as there described is substantially smooth throughout.

15. The method of claim 13 in which, after said coating of an aqueous solution of sodium diacetate is applied to said dressed portion of fish meat and before the resulting coated fish portion is enclosed in said packaging film, said coated fish portion is hung freely for a brief period of time to permit excess liquid to drain away while still leaving a coating of said aqueous solution of sodium diacetate.

16. The method of claim 13 in which the percentage by weight of sodium diacetate in said aqueous solution is sufficient to destroy substantially all the pathological bacteria in said fish portion.

17. The method of claim 13 in which the amount of sodium diacetate in said aqueous solution is from about 0.1 % to about 25 % of the weight of said solution.

18. The method of claim 17 in which the percentage by weight of sodium diacetate in said aqueous solution is from about 0.1 % to about 20% of the weight of said solution.

19. The method of claim 18 in which the percentage by weight of sodium diacetate in said aqueous solution is from about 10% to about 20% of the weight of said solution.

20. The method of claim 17, 18 or 19 in which said coating contains propylene glycol in an amount equal to about 1 % to about 20% by weight of the sodium diacetate that is contained in said solution.

21. The method of claim 17, 18, or 19 in which said coating contains ascorbic acid in an amount equal to about 1 % to about 20% by weight of the sodium diacetate that is contained in said solution.

22. The method of claim 13 in which said coating of an aqueous solution of sodium diacetate is applied by dipping said dressed fish portion in said aqueous solution.

23. The method of claim 13 in which said coating of an aqueous solution of sodium diacetate is applied by spraying said aqueous solution onto said dressed fish portion.

24. The method of claim 13 in which said coating of an aqueous solution of sodium diacetate is applied by brushing said aqueous solution onto said dressed fish portion.