PROCESS TO PRODUCE PASTEURIZED SHRIMP AND SHELLFISH

Abstract

A system and method are disclosed for processing packaged seafood containing shrimp or other non-crab shellfish species. Embodiments of the disclosed method provide a pasteurized shellfish product having a longer refrigerated shelf-life than experienced with conventional shellfish processing methods, and the shellfish product produced retains more of its original sensory qualities, such as texture, flavor and odor, than are retained by shellfish made according to current processing methods.

Claims

1. A pasteurized, packaged, seafood product comprising a pasteurized seafood comprising shrimp or non-crab shellfish in a sealed container that retains its natural flavor and texture after processing, wherein said seafood product is organoleptically stable for a time within the range of about 9-18 months when stored at refrigeration conditions of 40 F. or less without the risk of C. botulinum growth or toxin formation.

2. The packaged seafood product of claim 1, wherein the non-crab shellfish comprises mussels, clams, scallops, crayfish, or squid.

3. The packaged seafood product of claim 2, wherein the seafood comprises cleaned shrimp, mussels, clams, or scallops that is substantially shell-free.

4. The packaged seafood product of claim 3, wherein the seafood comprises shrimp or mussels.

5. The packaged seafood product of claim 1, wherein the container further includes a packing brine having a salt concentration between 1.25 and 2.0 wt % NaCl and is in an amount sufficient to displace substantially all air from said container.

6. The packaged seafood product of claim 5, wherein the packing brine in the container has salt at a concentration between 1.50 and 2.0 wt % NaCl.

7. The packaged seafood product of claim 5, wherein the packing brine in the container is substantially clear in the container.

8. The packaged seafood product of claim 1 wherein the seafood is packaged in a plastic can with a seal-top lid.

9. A pasteurized product according to claim 1 wherein said product has been prepared by a process comprising the following steps: cooking uncooked seafood selected from the group consisting of shrimp and non-crab shellfish at a first, selected, cooking temperature that is not higher than 190 F. for a time sufficient to cook the seafood to a uniform temperature, substantially uniformly coagulate proteins in the seafood, and reach an internal cooking temperature to obtain cooked seafood; immediately and rapidly cooling the cooked seafood with a cold brine containing 1.25-2 wt % salt to a temperature that is about 40 F. or less and that is sufficiently low to stop the cooking process and produce cooled, cooked, seafood; rinsing the cooled, cooked, seafood with a brine rinsing solution to remove any coagulated proteins released during the cooking step; packaging the cooled, rinsed, cooked, seafood in a soft, semi-rigid, or rigid container that is conducive to rapid heat penetration and that is suitable to withstand pasteurization temperatures; when using a rigid or semi-rigid container, filling the container of cooled, rinsed, cooked, seafood with a packing brine in an amount sufficient to submerge the cooled, rinsed, cooked, seafood completely; sealing the container of cooled, rinsed, cooked, seafood; pasteurizing the container of cooled, rinsed, cooked, seafood at a pasteurizing temperature by heating the packaged seafood to an internal pasteurizing temperature that is not more than 190 F. and that is not higher than said internal cooking temperature to thereby inhibit the release of protein from the packaged seafood, said pasteurizing step occurring for a time sufficient to achieve control of nonproteolytic C. botulinum type B in the package; and immediately and rapidly cooling the pasteurized, packaged, seafood by immersing the pasteurized, packaged, seafood container in a cold-water bath to stop pasteurization and produce a packaged, pasteurized, seafood product that is stable for about 9-18 months when stored at refrigeration conditions of 40 F. or less.

10. The packaged seafood product of claim 9, wherein the cooking occurs in a cooking brine having a concentration of salt within the range of about 1.25 wt % to 2.0 wt %.

11. The packaged seafood product of claim 9, wherein the cooking step comprises: heating said uncooked seafood in a high humidity atmosphere having a relative humidity of 85-100% at a temperature within the range of 180 to 190 F.

12. The packaged seafood product of claim 9, wherein the process further comprises: pre-treating the uncooked seafood by submerging the raw, peeled, or unpeeled seafood in an unheated, pre-treating brine solution and/or a water retention aid prior to the cooking step.

13. The packaged seafood product of claim 9, wherein said cooking step is at a temperature within the range of 180 F. to 190 F., and wherein said pasteurizing temperature is within the range of 180 F. to 190 F. and is selected so that the pasteurization temperature does not exceed the cooking temperature.

14. The packaged seafood product of claim 9 wherein the seafood is selected from the group consisting of shrimp, mussels, clams, scallops, crayfish, squid, and lobster.

15. The packaged seafood product of claim 14 wherein the seafood is selected from the group consisting of shrimp, mussels, clams, and scallops.

16. The packaged seafood product of claim 15 wherein the seafood is selected from the group consisting of shrimp, mussels, and scallops.

17. The packaged seafood product of claim 16 wherein the seafood is selected from the group consisting of shrimp and mussels.

18. The packaged seafood product of claim 1 wherein the seafood is vacuum sealed in a heat-resistant, plastic pouch.

19. The packaged seafood product of claim 1 wherein the seafood is cleaned, substantially the whole edible meat portion, and substantially shell-free.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0035] The FIGURE is a schematic diagram of the apparatus in one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0036] The method of the invention results in a packaged, pasteurized, shellfish having an extended shelf-life under refrigeration conditions where the shellfish has and retains a near-fresh flavor and texture similar to a freshly prepared shellfish.

[0037] The process of the invention is particularly directed to cooking and packaging non-crab shellfish such as shrimp, clams, scallops, mussels, crayfish, squid and lobster. Preferably, the non-crab shellfish is cleaned and deveined, if suitable, and substantially shell-free but otherwise whole rather than diced or finely subdivided. The raw shellfish used for the present invention can be fresh or may be a previously frozen shellfish that was pre-treated with a brine or phosphate solution prior to freezing.

[0038] The shellfish can be immersed in an aqueous medium in the package, and the package can be clear so as to provide the consumer with a view of the packaged seafood. Such packaging is discouraged where the brine is cloudy or the processed seafood is unattractive. With the present invention, however, the invention produces a packaged product where the aqueous medium remains clear or substantially clear after pasteurization and during storage. The result is a visually appealing, imminently saleable, refrigerated seafood product with an extended storage life.

[0039] The method of the invention pretreats raw shellfish meats in salt brine (1-2.5% w/v) or solution of salt brine and food phosphates or other water-holding additives. The addition of salt ions (sodium and chloride) opens the protein structure to improve water bonding. This step is optional for osmoregulating species, such as clams and mussels, which may have a naturally elevated salt ion content.

[0040] The method of the invention cooks the shellfish at a first temperature and for a period of time sufficient to fully cook the shellfish without excessive unnecessary denaturation of the proteins. The cooked shellfish is then packaged in a closed container and heat pasteurized at a second temperature that is not higher than the first temperature, i.e., the 2.sup.nd temperature is the same or lower than the 1.sup.st temperature. The closed container can include a brine solution as an aqueous storage medium in an amount to cover the shellfish entirely during storage.

[0041] In one embodiment of the invention, the raw, uncooked shellfish is converted into a refrigerator-stable, pasteurized, packaged product with a multi-step process based on a cooking step that is at least as high as a subsequent pasteurization step. This sequence of heating steps allows the proteins in the shellfish to become fully cooked and coagulated in the relatively short cooking step so that the additional heating and holding time of the later pasteurizing step does not cause additional purge, shrinkage or protein curd that would adversely affect the marketability of the product. In a preferred embodiment, (step 1) the uncooked shellfish is cooked by immersion in a heated first brine solution having a salt (NaCl) concentration of not more than 2 wt %, preferably within the range of 1.25-2 wt % and more preferably within the range of 1.5-1.75 wt %, and a temperature within the range of at least 180 F. and not more than 190 F. for a time shorter than the later pasteurization step but for a sufficient time to fully cook the shellfish to a uniform temperature and to coagulate the proteins. The shellfish is preferably cooked to coagulate the proteins substantially uniformly throughout the shellfish. The precise cooking time for the specific shellfish and size is preferably established from heat penetration tests of the product and equipment using no more than the existing skill level within the art so as to achieve an internal end-point temperature of the cooked shellfish that is equal to or slightly higher than the internal end-point temperature attained during the later pasteurization step.

[0042] At the end of the cooking step, (step 2) the shellfish is rapidly cooled to stop the cooking process. Preferably, the cooked shellfish is quickly cooled to a temperature below approximately 40 F. such as by immersing the cooked shrimp pieces in a cold, second brine solution such as an ice water bath containing not more than 2 wt % salt, preferably salt within the range of 1.25-2 wt % and more preferably 1.5-1.75 wt % salt.

[0043] The cooled, cooked shellfish is then (optional step 3) rinsed with a brine to remove any curd or solids on the cooked shrimp.

[0044] The clean, cooked shellfish is then (step 4) placed in a sealable container which contains, or to which is added, a third brine solution. This third brine solution preferably has not more than 2 wt % salt, preferably 1.25-2 wt % and more preferably 1.5-1.75 wt % salt, and its use is optional when using vacuum-sealed, flexible, packaging. Preferably, the third brine solution is added to the container in an amount that is sufficient to cover the shellfish so that the shellfish remains submerged in the solution during later pasteurization and storage. The covering third brine solution also significantly increases heat transfer rates (heating in the packaging occurs via convection rather than conduction only) throughout the package for a more efficient pasteurization step and improved sensory quality of the product.

[0045] The packaged shellfish is then (step 5) heat pasteurized by uniformly heating the container to a temperature of up to 190 F. but provided that the pasteurization temperature is not more than the cooking temperature. The heat pasteurizing is carried out for a longer time than the cooking step and that is sufficient in duration to pasteurize the shellfish within the container according to the government standards.

[0046] As soon as the required pasteurizing temperature and time are attained, (step 6) the packaged shellfish is rapidly cooled to refrigeration temperature of about 40 F. or lower.

[0047] Exemplary embodiments of the present invention are specifically described below based on examples, but the scope of the present invention is in no way limited to the embodiments and examples expressly disclosed. Those of skill in the art will understand that additions, revisions and other modifications to certain expressed details of the exemplary embodiments described herein can be made without departing from the spirit and scope of the invention.

[0048] In accordance with exemplary embodiments, overcoming some or all of the previously described quality defects in properly pasteurized shrimp and other shellfish products prepared in accordance with conventional methods includes one or more specific process steps which are described in further detail below. These steps include pretreating the shrimp or other shellfish with salt and, optionally, other water retention aides, cooking the shrimp or other shellfish, adding brine to rigid and semi-rigid containersa step which is optional when the shellfish product is packaged in vacuum sealed bags or pouchesselecting the appropriate container, and pasteurization heating and cooling using the appropriate equipment.

[0049] In accordance with at least one embodiment of the invention each of the process steps and features outlined above are addressed by utilizing a system of procedures and controls that produce finished refrigerated, pasteurized shrimp and other shellfish products possessing a number of desirable attributes. The resulting pasteurized products are stable under refrigeration for extended periods of time. For example, shrimp and other shellfish processed in accordance with embodiments of the invention are plump and typically fill the container in which they are packaged with minimal shrinkage. Additionally, the meat of shellfish products processed according to embodiments of the invention are tender and possess a sweet aroma and flavor characteristic of the particular type of shellfish and/or species. Clear brine within the package also results which permits high visibility of the shellfish which improves visual appeal to the consumer. Lastly, processing shellfish products in accordance with the invention produces a packaged product that has a 9-18 month refrigerated shelf-life.

[0050] As disclosed in Tables 2-6, the process of the invention described herein and the product made by this process are not merely the application of traditional crab processing methods to shrimp and non-crab shellfish.

TABLE-US-00002 TABLE 2 Cooking Methods Food Product Cooking/Cooling Effects Swimming crabs Traditionally, pressurized No negative effects, crabmeat steam at 240-250 F.; cooked is tolerant of high heat crabs are air cooled prior exposures to refrigeration Shrimp and other shellfish Traditionally, atmospheric Moderate shrinkage; steam or boiling at 212 F. to acceptable sensory quality achieve minimum internal but unsuitable for listericidal kill according to pasteurization-clouding of the US FDA requirement = brine and/or curd formation several thousand times less heat exposure than crab cook Shellfish processed according Pretreatment with salt; Greater cook shrinkage than to Invention cooked in sub-190 F. brine or Traditional method but Steam/air mixture held sensory quality retained sufficiently long to achieve without protein purge, an internal meat formation of unsightly curd, temperature equal to or or weight loss during higher than that achieved subsequent pasteurization during subsequent pasteurization, significantly hotter than achieved by traditional shrimp cook; cook stopped rapidly by quick chilling once internal temperature is reached

TABLE-US-00003 TABLE 3 Packing Food Product Packing Effects Swimming crabs Metal or plastic cans; No negative effects; crabmeat geometry unimportant tolerant of relatively high heat exposures Shrimp and other shellfish N/A; packaging suitable for N/A Pasteurization is not used Shellfish processed according Thin profile packaging Thin profile packaging to Invention suitable for pasteurization shortens pasteurization times increases heating and cooling resulting in reduced rates shrinkage, improved sensory quality, and controlled final drained weights

TABLE-US-00004 TABLE 4 Use of Packing Brine Food Product Tradition Effects Swimming crabs N/A; crabmeat tolerates Crabmeat in liquid results in pasteurization without use of unacceptable sensory quality; packing brines packing brines are traditionally used by canning industry, not for pasteurization Shrimp and other shellfish N/A, shrimp is not N/A traditionally pasteurized Shellfish processed according Covering pre-cooked packed Salt ions and reduced heat to Invention shrimp with brine exposures retain fresh-like significantly increases heat sensory properties, reduce transfer rates shortening shrinkage and optimize final pasteurization schedules; salt product drained weights ions penetrate meats

TABLE-US-00005 TABLE 5 Pasteurization (Heating and Cooling) Food Product Tradition Effects Swimming crabs Crabmeat must be processed Little or no negative impact to FDA requirement for on sensory quality destruction of Clostridium botulinum type E Shrimp and other shellfish N/A, shrimp and other non- N/A crab shellfish are not traditionally pasteurized Shellfish processed according Non-crabmeat seafoods must Near fresh cooked sensory to Invention be processed to FDA properties but only when requirement for destruction of invention procedures are nonproteolytic Clostridium followed botulinum type B, requiring more heat exposure than for crabmeat

TABLE-US-00006 TABLE 6 Impact of Traditional Crab Processing on Shrimp Traditional Crab Processing Impact on Shrimp and Other Shellfish Pressurized steam cooking of crabs at 240-250 Severe shrinkage, toughening; shrimp F.; cooked crabs are air cooled prior to muscle subject to excessive cross-linking refrigeration (crabs) and dehydration Packing in metal or plastic cans (crabs) Traditional thick profile cans result in excessive shrinkage, toughening and reduced weight of drained final products Pasteurization (heating and cooling) Shrimp and other shellfish must be processed more extensively than crabmeat to achieve C. botulinum control; good sensory quality is possible only according to the method of the present invention

[0051] The invention is directed to a method of producing a packaged shellfish that is stable for about 9-18 months when stored under refrigeration of about 40 F. or less and the pasteurized, packaged, shrimp and non-crab shellfish product that can be produced by the process of the invention.

[0052] The method of the invention in one embodiment includes the steps of quickly cooking the shellfish in a pre-heated aqueous brine solution to obtain a cooked shellfish. The shellfish is heated at sub-boiling temperatures for a sufficient time for the shellfish to reach an internal temperature that is substantially equal to the temperature of the heated cooking brine Pt brine) solution. The raw and uncooked shellfish is heated for a time sufficient to cook the shellfish uniformly without excessive heating beyond that necessary to reach the internal temperature corresponding to the temperature of the heated first brine solution, thereby preventing overcooking that can result in a tough, rubbery texture. The cooking step can be carried out for a time sufficient to coagulate the proteins fully without excessive heating or overcooking.

[0053] The heated first brine solution has a salt concentration that limits the amount of salt absorbed by the shellfish. In one embodiment of the invention, the heated bring solution has a non-zero salt (NaCl) concentration of not more than 2 wt %. The heated brine solution preferably has a salt concentration of 1.25 to 2.0 wt %, and more preferably about 1.5 to 1.75 wt %. In one embodiment, the brine solution has a NaCl concentration of about 1.6 to 1.7 wt %.

[0054] The cooking temperature of the raw, uncooked shellfish in one embodiment does not exceed about 190 F. so that the internal temperature of the resulting cooked shellfish at no time exceeds 190 F. to limit the extent of protein denaturation. The cooking temperature is preferably about 180 to 190 F. The maximum temperature of 190 F. avoids or inhibits excessive cooking and protein denaturation so that the shellfish retains sufficient water, texture and organoleptic properties during storage after pasteurization.

[0055] The ratio of the weight or volume of the shellfish to the volume of the heated brine solution is selected to enable the shellfish to reach an internal temperature of the heated brine solution rapidly to minimize the temperature drop or reduction upon immersion of the quantity of shellfish in the brine solution, to enable the shellfish to reach the desired internal temperature quickly to provide a uniformly cooked shellfish, and to minimize the heating or cooking time. The shellfish is fully cooked in the cooking step.

[0056] The sodium chloride concentration of the brine solution in the cooking step (first brine) is a non-zero amount that is preferably not more than about 2 wt % and at least about 1.25 wt %, preferably within the range of 1.5-1.75 wt %. It has been found that the salt concentration in the 1.25-2 wt % range retains a desirable product flavor and textural attributes while protecting the shellfish muscle from dehydration, and so that the subsequent pasteurizing step does not cause excessive release of liquid or solids from the shellfish. The inventors have found that pasteurizing the shellfish at a temperature not higher than the cooking temperature inhibits the release of excess liquid and solids from the shellfish during the pasteurizing step that can otherwise result in liquid in the container becoming cloudy or forming proteinaceous particulates and sediment during storage.

[0057] The shrimp or other shellfish are preferably cooked (a) directly in a preheated brine solution before packing/pasteurizing, or (b) by pre-brining the raw shellfish in an unheated brine and then cooking the brined shellfish in a high humidity (for example, 85-100% relative humidity at a temperature of 180 F. to 190 F. by mixing air and steam) cooker, such as a steam-air oven. The brine used as the cooking medium or as the pre-brining treatment has a salt concentration within the range of 1-2 wt %, preferably 1.25 to 2.0 wt % NaCl, more preferably within the range of 1.50 to 2.0 wt %, and most preferably within the range of 1.50 to 1.75 wt % salt.

[0058] According to a preferred embodiment of the process of the invention, raw shrimp that is either peeled or unpeeled is submerged in a preheated 1-2 wt %, preferably 1.25-2.0 wt % sodium chloride solution, i.e., a first brine, to cook the shrimp. Preferably, the cooking brine contains sodium chloride as substantially the only salt.

[0059] The first brine solution or other heating medium in the cooking step is maintained at a temperature of about 180 F. to 190 F., and ideally about 185 F. to 188 F. According to this embodiment, the cooking step is continued until the internal temperature of the shellfish product reaches the temperature of the cooking medium, i.e., the brine or other heating medium. In one embodiment of this invention, the cooking temperature closely approaches, or slightly exceeds, the temperature that the shellfish will reach when pasteurized in the subsequent pasteurization step. In one embodiment, the shellfish is cooked to an internal temperature at least as high as the subsequent pasteurizing step.

[0060] When the shellfish product reaches the desired internal temperature pursuant to the cooking step of not higher than 190 F., the shellfish is immediately transferred to a cooling liquid, such as an ice bath, or refrigerated bath, shower, spray or slush, i.e., a mixture of water and ice, to quickly remove the heat and chill the shellfish and stop the cooking process. To assist in removing the heat even more quickly, the ice slush or refrigerated bath is agitated, e.g., either manually, through injection of air or other gas, or with mechanized assistance to facilitate heat transfer and maintain a more even temperature distribution within the slush, bath or spray. According to this embodiment, the ice slush or refrigerated cooling medium also contains 1.25-2.0 wt % NaCl, and ideally 1.50-1.75 wt % NaCl. The addition of salt to the ice slush or other cooling medium minimizes absorption of water by the shellfish which, being weakly bound, would be released or cook out during the subsequent pasteurization step, described below or during storage. Maintaining an elevated ion concentration within the shellfish muscle optimizes water holding capacity.

[0061] The cooling liquid is typically maintained at a temperature of 35 F. or lower. The cooling liquid provides a heat exchange medium to stop the cooking process quickly. The cooling liquid also washes and removes any solids, such as coagulated proteins released during the cooking process. According to further aspects of this embodiment the shellfish meat should be chilled to 40 F. after cooking or below before further handling.

[0062] After chilling, the shellfish should be rinsed at least once with a second brine having a salt concentration within the range of 1.25-2.0 wt % and preferably within the range of 1.50-1.75 wt % salt to remove any remaining solids or expressed proteins. This rinsing can be accomplished by submersing the shellfish in brine or passing the shellfish through a spray or shower of brine.

[0063] The cooked, cooled, and washed shellfish are then packed to the desired amount, e.g., desired weight, in pasteurizable packaging that is appropriate for rapid heat-transfer, such as rigid and semi-rigid containers that are preferably wider than they are tall, or pouches or bags. One such suitable container is the model ES 40106 S/T 6 oz. container with the LPF 402,401 FPPO Bowl lid by King Plastics, Inc., but other suitable containers with various capacities and lids can also be used in accordance with embodiments of the invention.

[0064] If packaged in a pouch, no packing brine is required but is allowed, and the packaged shellfish are stored at a refrigeration temperature and preferably at a refrigeration temperature within the range of 32 F. to 36 F. until they are pasteurized. The flexible pouches or bags are made, for example, of boilable, heat resistant plastic or foil laminate, and can be vacuum sealed according to known methods. The pouches or bags are vacuum sealed with or without added brine or other aqueous storage medium. The vacuum sealed pouches allow direct heating of a thin layer of shellfish though the pouch and therefore the need for added liquid or brine is dependent on the specific shellfish and product thickness. This embodiment produces rapid and uniform heating to a pasteurizing temperature and for a time sufficient to achieve the necessary heat exposure with or without the need for packaging in aqueous brine solution. As with other types of packaging, the pasteurizing temperature is preferably at least 185 F. and not higher than the maximum temperature achieved during cooking.

[0065] If a rigid container is used, a packing brine is preferably added to facilitate heat transfer within the container. The container is filled with an aqueous storage liquid, preferably a packing brine having a NaCl concentration of about 1 wt % to 2 wt %, preferably about 1.25 wt % to 2.0 wt %, and most preferably about 1.50 wt % to 1.75 wt %. The packing brine displaces air from the interstitial spaces and fills the container to submerge the shellfish completely during the pasteurizing step and during storage. The packing brine rapidly conducts heat from the container wall to heat the shellfish quickly and uniformly to the pasteurizing temperature to pasteurize the shellfish without excessive, prolonged, or uneven heating. The aqueous brine solution enables rapid pasteurization while protecting proteins from excessive denaturation. The brine solution also increases and stabilizes the drained net weight of the final, packed, pasteurized, shellfish product which represents a significant commercial and consumer improvement over alternative methods.

[0066] In the embodiments in which rigid or semi-rigid containers are used, the previously packed containers containing the shellfish are filled to the brim with a 1-2 wt %, preferably 1.25-2.0 wt %, and more preferably a 1.50-1.75 wt %, brine solution. The containers are then closed and sealed or seamed. The closed containers are hermetically sealed. The filled and seamed/sealed packaging is then transferred to the pasteurizing step and loaded into highly perforated pasteurization baskets.

[0067] The sealed containers are heated at a pasteurizing temperature for a time sufficient to pasteurize the shellfish in the container. In one embodiment, the sealed containers are placed in a hot water bath to heat the container, the shellfish and the aqueous storage medium to a temperature of up to 190 F. and not higher than the temperature of the cooking step. Typically, the pasteurizing temperature is at least 185 F. and not exceeding 190 F.

[0068] In a further embodiment of the invention, the raw shellfish (such as shrimp and non-crab shellfish) can be pre-treated prior to the cooking step by submerging the shellfish in a pre-treatment solution of a water retention additive, such as sodium tripolyphosphate, other phosphate, non-phosphate blend or other additive or additive blend such as sodium bicarbonate or proteins that increase the water holding capacity of shellfish muscle. Preferably, the pre-treatment solution is functionally equivalent to a sodium tripolyphosphate concentration of less than or equal to about 4.0 wt % of the polyphosphate or its functional equivalent if other water retention additives are used. One example of a water retention additive that does not contain phosphates is sold under the trade name Seafood Blend by A&B Chemical Company. Additionally, the length of time the raw shellfish is submerged in the pre-treatment solution is limited to that necessary to achieve a post-treatment shellfish weight gain of less than 20 percent, and ideally not exceeding 16 percent. This optional soak and pre-treatment step has been found to further improve the moisture retention and texture of the final shellfish product. In one embodiment, the pre-treatment solution containing water retention additives also contains 1.0-2.0 wt % sodium chloride.

[0069] The shellfish that is pretreated with the water retention additive solution can be then cooked in steam/air mixture as an alternative to hot brine at a temperature of not higher than 190 F. and preferably at a temperature range of about 180 F. to 190 F. The cooking atmosphere preferably has a high humidity in a range of about 85-100% relative humidity. The relative humidity can be obtained from a mixture of steam and air to maintain the cooking atmosphere at a temperature of about 180-190 F. As in the previous embodiment, the shellfish is held in the cooking atmosphere for a time sufficient for the shellfish to reach an internal temperature equal to the cooking atmosphere and not higher than 190 F. As in the previous embodiments, the shellfish at the end of the cooking step is immediately placed in a cooling liquid and rinsed with the brine solution to remove any solids on the surface of the shellfish, such as proteins that cook out of the shellfish. The resulting cooked shellfish should weigh approximately 10 percent of what the raw shellfish did prior to any pretreatment. The cooked shellfish is then packaged and pasteurized as in the previous embodiment.

[0070] A further step in accordance with one or more embodiments of the invention is the pasteurization step after the cooking step and after the packaging step. More particularly, the pasteurization step according to the present embodiment can involve submersing the packaged shellfish product, typically held in a pasteurization basket, in a tightly controlled, uniformly agitated hot water bath to provide rapid and uniform heating while minimizing excessive heat exposure, to a pasteurizing temperature and for a time sufficient for the shellfish to achieve the necessary microbiological lethality.

[0071] The pasteurizing temperature is preferably at least 185 F. and not higher than the maximum cooking temperature used. In one embodiment, the shellfish is pasteurized at a temperature not higher than 190 F. The water temperature according to this embodiment is controlled between 185 F. and 190 F. to achieve rapid heating in a range sufficient for targeted microbial kill (6D process for non-proteolytic C. botulinum type B) while holding the shrimp and other shellfish muscle at or below the final internal temperature achieved during the cooking step.

[0072] Maintaining the pasteurizing temperature at or below the pre-cooking temperature assists in maintaining the clear packing brine in the packaging containing the pasteurized finished shellfish product as well as preventing the formation of protein curd which, if present, would reduce visual appeal whether or not a brine is used. Higher pasteurizing temperatures above the cooking temperature and/or prolonged cooking or pasteurization times are detrimental to the texture, appearance and other sensory attributes of the final shellfish product. Pasteurizing at a temperature above the cooking temperature can cause the release of proteins or other solids from the shellfish that can cause the brine solution in the container to become cloudy. Maintaining the pasteurizing temperature below the cooking temperature inhibits the release of proteins into the brine and maintains the brine solution in a clear state.

[0073] When the pasteurization is completed, the packages of pasteurized shellfish are immediately and quickly chilled to 40 F. or below to stop the pasteurization process and to stop any further cooking. In one embodiment, the packages after the pasteurization heating step are transferred from the basket to an agitated ice slush or refrigerated bath and cooled to less than or equal to 40 F. A chilled liquid bath, such as an agitated ice bath have been found to quickly cool the packaged shellfish. The containers of pasteurized shellfish are then stored, shipped and warehoused at between 32 F. and 38 F. for optimal shelf-life.

[0074] The method of the invention for processing shrimp and other shellfish prolongs the shelf-life of processed shellfish and also renders it more appealing to the various senses of the consumer. It has been found that the cooking in brine at a temperature not higher than 190 F., packaging in a container and pasteurizing at a temperature not higher than the cooking temperature maintains a clear brine solution in the container and maintains the desirable flavor and texture without the shellfish becoming tough or rubbery.

[0075] During the cooking step, which according to at least one exemplary embodiment, includes submersing the shellfish in a hot 1.25-2.0 wt % brine at sub-boiling temperatures of not higher than 190 F., or pre-soaking shellfish in 1.25-2.0 wt % brine and/or 2.0-3.0 wt % phosphate solution, prior to cooking at temperatures below that of atmospheric steam (212 F.), the amount of protein denaturation with associated dehydration of the muscle tissue is minimized. When dissolved in water, sodium chloride has unique properties that interact with the muscle proteins of the shellfish. In particular, sodium ions are positively charged, and chloride ions are negatively charged. The proteins found in the meat of the shellfish also have charged groups, with certain moieties being positively charged and others being negatively charged. Also, other sections of the shellfish proteins are often found to have a neutral charge. Dissimilarly charged groups, i.e., positive and negative, repel each other in water, which itself is a bipolar molecule. This holds the native proteins in the shellfish open as they interact with the water. When cations and anions, such as sodium and chloride ions, are present, they too interact with groups of opposite charge in a dynamic balance of ions and charged molecules competing for charged sites.

[0076] These forces of attraction and repulsion are counterbalanced by physicochemical interferences, as large ions, e.g., chloride, are less able to penetrate niches in the protein tertiary and quaternary structure than are small ions, e.g., sodium. This dynamic interaction directly affects the water retention capacity, texture and loss of small molecular weight, flavor and odor compounds of the shellfish. The addition of dissolved table salt to the system, as described above in accordance with various steps of one or more embodiments, contributes ions that enhance the ability of the shrimp and other shellfish muscle proteins to open and chemically interact, or bond, with water. When the concentrations of sodium and/or chloride ions are too high, for example, greater than 5-6 wt % NaCl, a condition known as salting out occurs, whereby ionic interferences are overcome and both ions, i.e., sodium and chloride, neutralize the charged groups within the proteins, causing them to collapse and interact with other regions of the protein, predominantly through hydrophobic interactions, rather than with water. This exclusion of water, known as dehydration, and the formation of inter-protein bonds are responsible for the often severe shrinkage and toughening of muscle foods like shrimp and other shellfish, a problem often encountered by conventional shellfish processing methods.

[0077] Consequently, the use of the proper concentration of salt brine during cooking and inside the container during storage, as described above in accordance with the invention, is important to the sensory attributes of pasteurized shrimp and other shellfish. The use of salt, phosphate or other additives in concentrations greater than those provided in accordance with the embodiments disclosed herein, for example, more than 2.0 wt % NaCl, can also have the undesirable effects of either toughening or solubilizing proteins, some of which then migrate, e.g., cook-out, into the brine or as protein curd onto the surface of the shellfish particularly in the subsequent pasteurization step. The pre-treatment of the shellfish with the brine and/or phosphate solution before cooking is preferably less than 3 hours. Preferably the treatment time is sufficient to pre-treat the shellfish without causing an unnatural appearance, for example a translucent glassy quality, or rubbery or tough texture during cooking, pasteurization or storage.

[0078] Rigid and semi-rigid packages, such as plastic containers of shrimp and other shellfish in brine serve another important function, i.e., significantly increasing heat penetration rates during pasteurization. Dry-packed foods heat predominantly by conduction, which typically takes a relatively long time. Heating of brine-packed or water-packed foods in containers having a high surface area to volume ratio, such as those with such a ratio of greater than 5, more preferably those with a ratio within the range of 6-15, is assisted by convection currents which flow between food particulates, significantly speeding the pasteurization process and thereby further minimizing undesirable sensory changes in the shellfish.

[0079] The use of brine as a packing medium in the product containers according to embodiments of the invention greatly facilitates pasteurization heating and cooling rates of the shellfish, e.g., in the rigid and/or semi-rigid containers, and results in a more favorable final product. Shellfish that are vacuum packed in flexible pouches or bags may not require the addition of brine prior to sealing due to reduced interstitial spaces between shellfish pieces and the rapid heat transfer rates attainable when thinly packed, for example to thicknesses less than or equal to 1.5 inches.

[0080] It is further preferable that the cooking and pasteurization equipment used in accordance with the embodiments of the invention disclosed herein be designed and operated to achieve uniformly rapid heat transfer rates to and from the shellfish product. This will ensure optimal finished product quality. Further, it is desired that heat accumulation (nonproteolytic C. botulinum lethalities) in the shellfish product during pasteurization be accomplished within and not more than about 75 minutes of submersion for many species of shellfish and preferably within and not more than about 65 minutes for shrimp at a pasteurization temperature of about 180 F. to 190 F. and preferably about 185 F. to 190 F.

[0081] The relationship between cooking temperature and pasteurization temperature is an important feature of the invention. Shellfish, like other muscle foods, consist of numerous proteins possessing different properties including a range of coagulation temperatures. As raw meats are heated, certain proteins begin to coagulate and turn opaque at temperatures just below approximately 130 F. while others may require temperatures of 180-190 F. to fully coagulate. If shellfish are cooked to an end-point temperature which is below the maximum temperature they reach during pasteurization, i.e., the pasteurization temperature is higher than the cooking temperature, any uncoagulated protein that cooks out into the pasteurized container will coagulate on the surface of the pasteurized shellfish as curd or in the brine as fine cloudy or milky particulates. This results in a very unappealing product that is unsuitable for retail sale. Rinsing of cooked shrimp and other shellfish, such as a 1.25-2.0 wt % NaCl solution in accordance with embodiments of the invention, e.g., prior to packing, removes surface particulates, i.e., small meat pieces and curd formed from solubilized protein, that would further cloud the brine or form sediment in finished products. Additionally, the pasteurization temperature is selected to be a temperature sufficient to obtain target lethalities and desirable product sensory attributes without causing uncoagulated proteins or other substances to cook out of the shellfish into the package during pasteurization. In one embodiment of the invention, the pasteurization temperature is not higher than the cooking temperature.

[0082] The apparatus for carrying out the method of the invention and for producing the storage stable shellfish is shown in the FIGURE. In the embodiment shown, the apparatus 10 is a batch or continuous process for obtaining a packaged shellfish that is stable under refrigeration for at least 9 months and up to 18 months.

[0083] The apparatus 10 includes an optional pre-treatment bath 12 containing a sufficient amount of a water retention additive solution. The raw shellfish, such as shrimp, are immersed in the pre-treatment solution for sufficient time to pre-treat the shellfish.

[0084] The pre-treated shellfish are then transferred to a cooking apparatus 14. The pre-cooking apparatus contains a brine solution having a non-zero sodium chloride concentration of not more than 2.0 wt %. The brine is maintained at a constant temperature sufficient to cook the shellfish by immersing the shellfish in the heated brine solution. In one embodiment, the pre-cooking apparatus includes a heat source to heat the brine solution to a temperature of about 180 F. to about 190 F.

[0085] The cooking apparatus is connected to a chilling apparatus 16 to immediately chill the shellfish at the end of the cooking step to stop the cooking process quickly. The chilling apparatus can include a spray or shower of cooling medium, such as water or brine spray. In one embodiment, the cooling medium is an aqueous bath where the shellfish is immediately immersed in the aqueous bath. The aqueous bath can be an ice bath or ice/water mixture such as an ice slush. The aqueous cooling medium can have a non-zero sodium chloride concentration of not more than 2.0 wt %.

[0086] The chilled, cooked shellfish is then transferred to an optional rinse apparatus 18. The rinse apparatus can be spray or a bath containing an aqueous rinse having a sodium chloride concentration of not more than 2.0 wt %.

[0087] The rinsed shellfish is then transferred to a packaging apparatus 20. The apparatus 20 places the cooked shellfish in a suitable package that is able to withstand the pasteurizing temperatures. The packaging can be a flexible pouch or bag that can be vacuum sealed with or without an aqueous packaging medium. The packaging can also be a rigid container that can be closed and sealed. In one embodiment, the rigid container is filled with an aqueous packing medium to displace substantially all of the air from the container prior to closing, sealing/seaming and pasteurizing. The packing medium can be water or, preferably, a salt solution.

[0088] The packaged shellfish is then transferred to the pasteurizing apparatus 22 where the container and the shellfish are quickly heated to a pasteurizing temperature and held at that temperature. In one embodiment, the pasteurizing apparatus is a heated aqueous bath. The containers can be placed in a suitable partitioned basket or rack and immersed in the heated bath for sufficient time to pasteurize the shellfish. The containers are then transferred to a chilling apparatus 24, such as a cooled aqueous medium to lower the temperature of the container and the shellfish and quickly stop any further pasteurization or cooking.

Examples

Example 1

[0089] The following is one example of the process for producing a packaged shrimp that is stable at refrigeration temperatures. [0090] 1. Frozen raw shrimp that was pretreated with water retention additives, such as a blend of food phosphates, prior to freezing was thawed. [0091] 2. The thawed shrimp was cooked in a highly perforated basket in an agitated hot brine (1.65 percent NaCl) at 187 F. Cooking continues until the internal shrimp temperature reaches 186.5 F. as determined by internal probes or by previous study, approximately 7 minutes for 41/50 count shrimp. [0092] 3. Immediately cool the shrimp by immersing in an agitated brine bath (1.65 percent NaCl) chilled mechanically or with ice. [0093] 4. Rinse the cooked shrimp twice by immersing in 1.65 wt % brine solutions to remove fine proteinaceous particulates from shrimp surface. [0094] 5. Pack the cooked shrimp in King Plastics 40106 clear, flat, plastic, containers to 6 ounces net weight, arranging shrimp in the containers for optimal visual consumer appeal. This round container is made of polypropylene, has a volume of 6.5 fl. oz., and is 4 inches in diameter with lid by 1 11/16 inches high. This container has a surface area to volume ratio of about 9 in.sup.1.) [0095] 6. Fill the packed containers to the brim with 1.65 wt % brine. [0096] 7. Seam the containers with easy open lids according to manufacturer's specifications. [0097] 8. Place the sealed containers in a highly perforated pasteurization basket with separators and top plate designed for this container. [0098] 9. Submerge the basket of containers in an agitated hot water bath pasteurizer at 186 F., and process for the time necessary to meet FDA requirements for control of non-proteolytic Clostridium botulinum type B bacteria. This time is determined by routine heat penetration studies performed under commercial conditions. [0099] 10. Immediately transfer the basket of hot containers to an agitated, ice-chilled water bath and cool until the internal temperature of the shrimp reaches 40 F. or below, as measured by a temperature probe inserted into the container center. [0100] 11. Immediately remove the containers of finished pasteurized shrimp from the basket and move to refrigerated storage at less than or equal to 36 F. Refrigeration temperatures are maintained during storage, shipment and distribution.

Example 2

[0101] To determine the sensory effects of the example 1 process compared to shrimp processed by more traditional methods, a sensory panel was convened in the sensory evaluation facility of the Center for Food Science and Technology, University of Maryland Eastern Shore in Princess Anne, Md. Treatments were prepared to evaluate the panelist's relative preferences for shrimp made according to example 1 of the present application, two currently available commercial products possessing extended shelf-lives (frozen shrimp ring and canned shrimp), and two shrimp treatments processed with some, but not all, of the procedures identified in the present application.

[0102] Specifically, the five treatments in Table 7 were prepared in advance of holding the sensory panel session:

TABLE-US-00007 TABLE 7 Sample Treatment A Shrimp (block frozen Ecuador aquacultured shrimp) that was cooked, packed and pasteurized according to example 1. B Cooked shrimp from a commercial shrimp ring purchased at a local supermarket (Thailand aquacultured). C Commercially cooked frozen shrimp purchased at a local supermarket and pasteurized with a packing brine like sample A (IQF Vietnam aquacultured, BAP certified). D Same as treatment C but pasteurized without a packing brine (requiring a 50 percent extension of pasteurization heating time). E Commercial, canned, shelf-stable, medium shrimp purchased at a local supermarket.

[0103] Except for treatment E, two shrimps from each treatment were placed in plastic sample cups coded with a random three-digit code (one of three code numbers per treatment produced by a random number generator). Canned shrimp were very small, as are most canned shrimp since the texture, flavor and appearance of larger shrimp would be severely degraded by the more extensive canning process required. Consequently, about four shrimps were placed in each cup for treatment E. The coded sample cups were placed randomly in a circle on a round white paper plate along with a cocktail pick for presentation to the panelists.

[0104] Ten panelists consisting of university students, technicians and faculty were told they would be evaluating cooked cocktail shrimp. They were asked to rank the five samples from most preferred to least preferred for appearance, odor, texture (mouthfeel), and flavor. Only shrimp were coded and sampled, not cocktail sauces or packing brines, and so the cloudiness of brine was not a factor judged by panelists.

[0105] Panelists were provided a score sheet, pen, fresh water and a spittle cup. The panelist's rank scores were summed and analyzed for significance according to Kahan et al. Expanded tables for determining significance of differences for ranked data, J. Food Technology 27(5), pp. 61, 64, 68 (1973). For example, if a sample was ranked first (most preferred) of the five samples by eight panelists and ranked second by two panelists, rank sum=12 (rank 18 panelists+rank 22 panelists). Referring to Kahan, et al., this result would be significant at the 99 percent confidence level (p<0.01). That is, the high preference ranking for this process treatment compared to the other treatments would have less than a one percent probability of being due to chance.

[0106] Plastic containers of the three pasteurized treatments had been previously packed with 1802 g of shrimp, filled with packing brine, or not, depending on the treatment, and seamed immediately prior to pasteurization. Five days after pasteurization, containers of each pasteurized treatment were randomly selected, drained of any brines/liquids by dumping the container contents into a colander for one minute, and the shrimp weighed. Shrimp weight, in grams, was recorded and the shrimp percent yield and shrinkage associated with pasteurization were calculated.

[0107] The ranks for each of the five treatment groups are shown in Table 8.

TABLE-US-00008 TABLE 8 Sensory preference rankings for five treatments by attribute. Attribute Treatment Preference Rank Significance Appearance A 2 *** B 1 p < 0.01* C 3 *** D 4 *** E 5 p < 0.01** Odor A 1 p < 0.05* B 4 *** C 3 *** D 2 *** E 5 p < 0.01** Texture A 1 p < 0.05* B 4 p < 0.05** C 2 *** D 3 *** E 5 p < 0.01** Flavor A 1 p < 0.0l* B 4 *** C 7 *** D 3 *** E 5 p < 0.01**

[0108] The process of Example 1 produced a sensory profile that the panelists significantly preferred to all other treatments for odor, texture and flavor. All panelists ranked the example 1 shrimp first for flavor, the only treatment so consistently ranked for any attribute. It ranked second to shrimp ring shrimp in appearance, a product that is stored and distributed frozen. The shrimp ring shrimp and canned shrimp were ranked significantly lower than the example 1 shrimp and other treatments for texture.

[0109] The canned shrimp were ranked lowest of the treatments for all sensory attributes. Although packing brines or liquid released from the shrimp during pasteurization were not evaluated by panelists, appreciable cloudiness was observed in these liquids for all pasteurized and canned shrimp except those receiving the full example 1 process. Sediment (particulates) in this liquid was most pronounced in treatment D, shrimp commercially cooked (likely a minimal listericidal cook, the industry standard) and pasteurized without a packing brine. In the absence of packing brine, heat penetration rates are slowed, necessitating more extensive heating during pasteurization for treatment D.

[0110] The plastic containers were all packed tightly to the same net weight of shrimp (1802 g) and were visually similar prior to seaming and pasteurization. Shrimp shrinkage and release of protein (cloudy brine/liquid) was visibly evident for the pasteurized shrimp treatments that did not receive the example 1 process. These observations were supported by the drained weight yields and shrink percentages reported in Table 9.

TABLE-US-00009 TABLE 9 Shrimp yields and shrinkage of pasteurized treatments Fill weight, g Drained weight, g Yield/shrink Treatment Before pasteurization After pasteurization percent A 180 145 80.5/19.5 C 180 118 65.5/34.5 D 180 112 62.2/37.8

[0111] The results in Table 9 indicate that the initial cooking method had an especially large impact on shrimp shrinkage and release of liquid and protein during pasteurization, with the example 1 shrimp retaining most of their original size, weight and appearance, and the commercially cooked shrimp exhibiting pronounced shrinkage.

[0112] While various features and embodiments of the invention are disclosed herein, it will be understood that various changes and modifications can be made without departing from the scope of the claims as defined in the appended claims.