METHOD AND DEVICE FOR DELAYING RIGOR MORTIS IN FISH

Abstract

A method and an apparatus for bringing fish to an under-cooled state by a sub-chilling process before processing, which prolongs rigor and allows processing of the fish in rigor providing better quality fish products.

Claims

1. A method for delaying rigor mortis in slaughtered fish, the method comprising: a) receiving slaughtered fish, b) bringing the fish to an under-cooled state in a salt-controlled and temperature-controlled solution in at least one first container, where: i) the salt concentration of the solution is set and a temperature of the solution maintained such that the temperature is higher than the freezing point of the solution, ii) providing substantially continuous movement of the fish in the solution during the step of bringing the fish to an under-cooled state, iii) maintaining the volume of the solution in the at least one container to at least 50% of the total volume of fish and solution, c) transferring the fish to a transport/storage container, where the temperature in the transport/storage container is maintained below 0 C.

2. The method according to claim 1, wherein the temperature of the solution is maintained at a temperature which is at least about 0.5 C. higher than the freezing point of the solution.

3. The method according to claim 1, wherein the temperature of the solution is maintained at a temperature which is at least about 1.0 C. higher than the freezing point of the solution, and preferably at least about 1.5 C. higher.

4. The method according to claim 1, wherein the step of bringing the fish to an under-cooled state is performed in at least two steps of: i) placing the fish in a first salt-controlled and temperature controlled solution having a salt concentration in the range from 0.1 to 10% and a temperature in the range from +1 to 3 C., where the salt concentration and set temperatures of the salt-controlled and temperature controlled solution brings the homogenous temperature of the fish to +2 to 1 C., and ii) transferring the fish to a second salt-controlled and temperature controlled solution having a salt concentration in the range from 1 to 20% and a temperature in the range from 1 to 12 C., where the salt concentration and set temperatures of the salt-controlled and temperature controlled solution brings the homogenous temperature of the fish to 0.1 to 3 C.

5. The method according to claim 1, wherein the fish is pre-cooled to a temperature of below about 6 C. and preferably below about 4 C., gutted and/or bled before step b).

6. The method according to claim 1, wherein the salt concentration and set temperatures of the salt-controlled and temperature controlled solution(s) is based on the fish species and fat content of the fish being brought to an under-cooled state.

7. The method according to claim 1, wherein time is based on the size and the quantity of the fish being cooled.

8. The method according to claim 1, wherein the at least one first container is an elongated cylindrical or semi-cylindrical tank and comprises a spiral shaped blade mounted on a rotation axis to convey the objects along the length of the tank.

9. The method according to claim 8, wherein the rotation of the spiral shaped blade provides the movement of the fish in the container.

10. The method according to claim 1, wherein the volume of the solution in the container is at least between 55% and 75% of the total volume of fish and solution.

11. The method according to claim 1, wherein the fish is maintained at between 0.5 and 2 C. during storage in step c).

12. The method according to claim 11, wherein the fish is maintained at 1 C. during storage in step c).

13. An apparatus for prolonging the rigor process in slaughtered fish, the apparatus comprising: means for transporting the slaughtered fish to a cooling device, a cooling device for bringing the slaughtered fish to an under-cooled state, said cooling device comprising: i) at least one container connected to a heat exchanger and a temperature feedback control unit, to set the temperature of a salt-controlled and temperature controlled solution in the container, and ii) stirring means for providing substantially continuous movement of the fish in the solution, one or more containers to receive and store the slaughtered fish in a under-cooled state in rigor at a temperature below 0 C. until the fish is processed.

14. The apparatus according to claim 13, wherein cooling device has more than one compartments to bring the fish to an under-cooled state in at least two steps.

15. The apparatus according to claim 13, wherein the cooling device is an elongated cylindrical or semi-cylindrical tank and comprises a spiral shaped blade mounted on a rotation axis to convey the objects along the length of the tank.

16. The apparatus according to claim 13, wherein the rotation of the spiral shaped blade provides the movement of the fish in the container.

17. The apparatus according to claim 15, wherein conveys the objects along the length of the tank and to transfer the fish from one container to another or out of the cooling device.

18. The apparatus according to claim 11, said apparatus being positioned at a fish farm where fish is brought out of aquaculture and slaughtered on site.

19. An fishing vessel for catching and slaughtering fish, said fishing vessel comprising an apparatus for prolonging the rigor process in slaughtered fish, the apparatus comprising: means for transporting the slaughtered fish to a cooling device, a cooling device for bringing the slaughtered fish to an under-cooled state, said cooling device comprising: i) at least one container connected to a heat exchanger and a temperature feedback control unit, to set the temperature of a salt-controlled and temperature controlled solution in the container, and ii) stirring means for providing substantially continuous movement of the fish in the solution, one or more containers to receive and store the slaughtered fish in a under-cooled state in rigor at a temperature below 0 C. until the fish is processed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 shows an arrangement of the vessel of the invention to facilitate pre-processing and sub-chilling of whole fish on a fishing ship.

[0024] FIG. 2 shows an arrangement of device of the invention to facilitate pre-processing and under-cooling of whole fish.

[0025] FIGS. 3A-3C show pin bone removal while salmon is in rigor and how pin bones car be removed without damaging fillet. FIG. 3A shows a salmon fillet after pin bone removal, in which the fillet looks fine and undamaged. FIG. 3B shows two bones, on top a bone removed from a salmon after traditional chilling and below a bone removed from a salmon after sub-chilling, in which no flesh is attached to the bone from the salmon chilled with sub-chilling, but flesh is attached to the salmon bone chilled with traditional chilling. FIG. 3C shows a comparison of two fillets after pin bone removal.

[0026] FIG. 4 shows temperature monitoring during transport and processing of salmon chilled by traditional method and sub-chilling method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The following definitions and embodiments relate to the method, the apparatus and the fishing vessel of the invention.

[0028] In the present context the term under-cooling or sub-chilling refers to the process or method of bringing fish to a desired temperature at or near the phase transition of freezing the fish without freezing the fish, and generally below the freezing point of water (0 C.). Furthermore, these terms refer to a fish or fish product being brought to or kept at a desired temperature at or near the phase transition of freezing the fish without freezing the fish, such as a temperature below 0 C. (sub-zero conditions), such as preferably at or below 0.2 C., or more preferably at or below 0.5 C., or at or below 0.7 C., or at or below 0.8 C., such as at or below 1.0 C., such as at or below 1.5 C.

[0029] In the present context the term fish or whole fish relates to a fish which is either freshly caught and unprocessed at all or cut and/or bled and/or gutted and/or washed and/or graded and/or de-headed and/or the tail has been removed or any combination thereof.

[0030] In the present context the terms rigor, rigor phase and rigor mortis refer to stiffening of muscles after death or slaughtering of fish. The terms are equally used for what is accomplished by the present invention, which is delaying the fish for entering rigor mortis and also keeping the fish in the rigor phase for a longer time per time unit. The term delaying rigor mortis in slaughtered fish refers to both delaying the fish for entering rigor mortis and prolonging the time the fish takes to pass through the rigor phase.

[0031] In the present context the terms substantially continuous movement refers to movement of the fish in the solution. The substantially continuous movement is provided by stirring means, such as a rotating blade in a container or any other stirring or agitating device in the container, or by circulation pumping of solution in and out of the container through via a heat exchanger, or by movement of the container it-self. Substantially continuous movement also comprises stepwise movement, e.g. a rotating blade that rotates stepwise every 1, 2 or 5 seconds, or the like, such that the mass of fish and fluid being moved is not at a standstill for any extended period of time (not more than a few seconds) and preferably continuously moving.

[0032] In an embodiment of the present invention the fish is pre-cooled before or after bleeding, before starting the process of bringing the fish to an under-cooled state.

[0033] In an embodiment of the present invention the salt concentration and set temperatures of the salt-controlled and temperature controlled solution(s) for each step in the pre-cooling and under-cooling are based on the species, size and fat content of the fish being brought to an under-cooled state.

[0034] In an embodiment of the present invention the time for each step in the pre-cooling and under-cooling is based on the species, size, as well as the fat content of the fish and the quantity of the fish being cooled. In one embodiment, freshly caught cod, slaughtered, gutted and bled is first cooled for 40-50 minutes at a set temperature of 1 C. in a solution of 3% salt concentration and then transferred to a solution of 7% salt concentration set at a temperature of 3 C. preferably for about 15 minutes. Salmon has more fat content, so slaughtered, gutted and bled salmon of same size is in one embodiment cooled for 60 minutes at a set temperature of 1 C. in a solution of 3% salt concentration and then transferred to a solution of 8% salt concentration set at a temperature of 4.5 C. for 25 minutes.

[0035] In an embodiment of the present invention a continuous movement of the fish in the solution is provided during the step of bringing the fish to an under-cooled state to prevent the fish surface of the fish from freezing and to prevent the formation of shell or crust at the surface of the fish during the cooling process. The continuous movement of the fish in the solution speeds up the cooling process and allows the use of a cooling solution at a warmer temperature, such as close to the target temperature at a certain cooling step.

[0036] In an embodiment of the present invention the fish is maintained at a temperature above freezing point of the fish, but at or near the phase transition temperature of freezing the fish without freezing the fish, such as at a temperature in the range from between about 0.5 to about 2 C. during storing, transfer and processing, such as at about 0.5 C., about 1 C., or about 1.5 C.

[0037] In an embodiment of the present invention the fish is skinned in rigor after being brought to an undercooled state and transported and/or stored according to the method of the invention.

[0038] In an embodiment of the present invention the fish undergoes pin-bone removal in rigor after being brought to an undercooled state and transported and/or stored according to the method of the invention.

[0039] In an embodiment of the present invention the apparatus is positioned at a fish farm where fish is brought out of aquaculture and slaughtered on site cooled and stored.

[0040] In an embodiment of the present invention the apparatus further comprises means for skinning the fish in rigor after the fish has been brought to an undercooled state and transported and/or stored according to the method of the invention.

[0041] In an embodiment of the present invention the fish is bled prior to the under-cooling step. The bleeding step can be allowed to occur in a container with liquid. Furthermore, the fish can be subjected to pre-cooling before or after bleeding. In a further embodiment of the present invention the steps of bleeding and undercooling take place in cooling chambers with screw conveyors. The cooling tanks of disclosed herein have one or more compartments being at least partially filled with cooling liquid and a spiral shaped blade or screw conveyor extending between the in-feed and the out-feed ends of the tank. The blade rotates and provides a rotational movement of the screw conveyor thereby conveying the food products between the in-feed and the out-feed ends of the tank. In-feed of cooling liquids of different salt concentration and temperature regulates the temperature in the tanks or in the different compartments of the tank in order to alter the temperature of the whole fish during the process of bleeding, pre-cooling and bringing the whole fish to an under-cooled state.

[0042] In an embodiment of the present invention the cooling device is an elongated cylindrical or semi-cylindrical tank and comprises a spiral shaped blade mounted on a rotation axis to convey the objects along the length of the tank. Furthermore, the rotation of the spiral shaped blade provides the movement of the fish in the container.

[0043] In an embodiment of the present invention the fish is brought to a homogenous temperature in the range between 0.2 and 4.0 C., such as a temperature in the range from about 0.5 C., such as from about 0.8 C., such as from about 1.0 C. or from about 1.2 C., to about 4.0 C., or to about 3.5 C., such to about 3.0 C., or to about 2.5 C. In the present context the term homogenous temperature refers to equalised average temperature which is measured from 0 to 120 minutes after a cooling process.

[0044] In an embodiment of the present invention the fish is stored at a temperature below 0 C. between catching and processing. For best quality of end product, the fish is bled, gutted and washed before it is processed.

[0045] In an embodiment of the present invention the fish is placed in a saline solution before processing, including de-heading, filleting and/or skinning the fish. In the present context the term saline solution relates to a salt-controlled liquid, sea water or brine having the concentration in the range between 0.01-16%. The saline solution is cooled below 0.01 C. by a refrigerating system.

[0046] In an embodiment of the present invention the temperature of the fish is in a range between 0.5 and 2.5 C. when the fish is filleted or subjected to pin-bone removal, such as at a temperature of 1.5 C. or 1 C.

[0047] In an embodiment of the present invention the cooling tank has more than one compartments to bring the fish to an under-cooled state in at least two steps, such as for performing steps i) and ii) above separately. Furthermore, a tank with a plurality of compartments may be used to bleed, pre-cool and rinse the fish prior to the step of bringing the fish to an under-cooled state.

[0048] In an embodiment of the present invention a pre-processing workstation is provided before the cooling tank to bleed and/or gut the whole fish prior to under-cooling the whole fish.

[0049] In an embodiment of the present invention a separate tank or a separate first container in the cooling tank is provided to facilitate the bleeding of the fish.

[0050] In an embodiment of the present invention the separate tanks or the compartments in the cooling tank comprise screw conveyors to transfer the whole fish from one end of a compartment to another and to transfer the fish from one compartment to another.

[0051] In an embodiment of the present invention workstations are provided after the cooling tank for one or more of filleting, skinning removing pin-bones and portioning the whole fish.

[0052] In an embodiment of the present invention the imaging means is provided for determining size, shape or colour of the whole fish prior to transferring the fish to the cooling tank.

[0053] In an embodiment of the present invention the whole fish is being transferred from the sea, lake or a sea cage, aquaculture cage, marine cage or the like bringing the fish to an undercooled state directly after slaughtering.

[0054] FIG. 1 shows an arrangement of the vessel of the invention to facilitate pre-processing and sub-chilling of whole fish on a fishing ship. The fish is brought on deck in the aft end of the ship 1 and brought to workstations 2 to gut and bleed the fish. The fish is then transported to a short cooling tank 3a, 3b, 3c with a screw blade 4 for the bleeding step. The embodiment shown in this drawing has three lines of a bleeding and undercooling tanks, the first one A for small fish, the second B for intermediate size fish and the third line C for large fish. Size determination is made by a camera 5 and the fish are directed into an appropriate lane based on this size determination. The fish is transported through the tank by the screw blade 4, which functions as a screw conveyor and slowly moves the fish from one end of the tank to another. For the bleeding step, see water may be selected saline solution. The fish is then transported to a larger tank 6a, 6b, 6c, for a first step of bringing the whole fish to an under-cooled state. In the embodiment shown in FIG. 2, the tank is divided into two compartments 7 and 8 for performing a two-step cooling of the fish. For demonstration we will follow line A (for small fish). The difference between line A, B and C is that duration of transfer in each compartment is based on the size of the fish, but the duration of transfer is regulated by the speed of the screw blade. Each compartment in the cooling tank 6 has a separate screw blade 4 and a heat exchanger (not shown) to set the temperature in each compartment. The first compartment 7 is long and has a concentration and temperature controlled saline solution with a low salt concentration at a higher temperature to allow the fish to achieve a stable homogenous/even temperature, preferably about 0.5 C. The second compartment 8 is shorter and has a concentration controlled saline solution with a higher salt concentration to bring the temperature of the fish down to about 1 to 1.5 C. based on the size and fat content of the fish.

[0055] FIG. 2 shows an arrangement of device of the invention to facilitate pre-processing and under-cooling of whole fish. It is a simple embodiment of a tank 10 with three compartments 11, 12 and 13. Each compartment in the cooling tank 10 has a separate screw blade 4 and two compartments have a heat exchanger 14 to set the temperature in each compartment. Temperature can be regulated by a combination of saline solution and heat. The middle compartment 12 is three times longer than the first 11 and the third 13 compartments. The number of compartments is not limited but this embodiment shows a tank where sea water could be pumped into the tank via inlet 15 and out through outlet 16. If the first compartment 11 is a bleeding compartment, it is important to have a good flow of liquid through the compartment. The second compartment is connected to a heat exchanger 14, but sea water or salt controlled solution can be pumped in as needed through inlet 17. This compartment brings the fish from the temperature of the sea (about 4-8 C.) to between +1 and 2 C. The third compartment is used to initiate the phase exchange and bring the fish towards 1 to 3 C. The third compartment 13 also comprises a second heat exchanger 18. Sea water or salt controlled solution can also be pumped into the third compartment as needed through inlet 19. The blade in each compartment is designed such that at the end of the compartment the blade has a curve (not shown in detail) so it pushes the fish over the edge and into the next compartment.

Example 1. Analysis of the Difference Between Sub-Chilling and Traditional Chilling of Salmon

[0056] Salmon was taken just after slaughtering and chilled either by using ice (traditional) or by the sub-chilling method of the present invention. The sub-chilled salmon was chilled in a screw-container for 1 hr in a two-step process, where it was first brought into a solution with a temperature of 1 C. and then further to 4 C. Thereafter the salmon was stored at 1.5 for 4 days. The salmon receiving traditional treatment was chilled on ice for 4 days in EPS boxes. Further processing of salmon 4 days after slaughtering showed that the fish was easy to process and had a good resistance to heading and filleting processes resulting in higher yield (Fig not shown).

[0057] Table 1 shows the temperature of the fillets after 2, 4 and 6 days as well as softness and gaping.

TABLE-US-00001 TABLE 1 Days 2 4 6 Sub Tradi- Sub Tradi- Sub Tradi- Chilled tional Chilled tional Chilled tional Temp C. 1.5 0 1.5 1 1.5 0.2 Softness 0 1 0 1 0 2 Gaping 0 2 0 3 0 4 Rigor yes No Yes No No No

[0058] The results show that the sub-chilled salmon maintains a homogenous temperature of 1.5 C., whereas the traditionally chilled salmon reaches higher temperature, becomes softer and shows increased gaping. The traditionally chilled salmon also starts to get softer, whereas the sub-chilled salmon maintains stiffness.

[0059] FIG. 3 shows pin bone removal while salmon is in rigor and how pin bones car be removed without damaging fillet. FIG. 3A shows a salmon fillet after pin bone removal. The fillet looks fine and undamaged. FIG. 3B shows two bones, on top a bone removed from a salmon after traditional chilling and below a bone removed from a salmon after sub-chilling. No flesh is attached to the bone from the salmon chilled with sub-chilling, but flesh is attached to the salmon bone chilled with traditional chilling. FIG. 3C shows a comparison of two fillets after pin bone removal. On the left is a fillet, which was chilled by traditional chilling and on the right is a fillet chilled by sub-chilling. The fillet chilled by traditional chilling is damaged after the bin bone removal, whereas the fillet chilled by sub-chilling has very little damage.

[0060] Product shelf life of the salmon was also examined based on the chilling method. Table 2 shows bacterial count comparison between salmons chilled by traditional vs. the sub-chilling method.

TABLE-US-00002 TABLE 2 Total count Black colonies/g Days Sub-Chilled Traditional Sub-Chilled Traditional 2 <10.000 20.000 <10.000 <10.000 6 <10.000 <10.000 <10.000 <10.000 10 20.000 <10.000 <10.000 <10.000 16 20.000 300.000 <10.000 30.000 21 2.100.000 39.000.000 20.000 910.000

[0061] The results show that the sub-chilling method extends shelf life dramatically.

[0062] Table 3 shows final product quality comparison between salmons chilled by traditional vs. the sub-chilling method. The slower rigor process obtained by the method of the present invention results in less drip and the fish tastes better as it retains its natural juice and flavours.

TABLE-US-00003 TABLE 3 Cooking Yield comparison Days Sub-Chilled Traditional 2 95.9% 95.0% 6 95.3% 95.6% 10 93.7% 94.2% 16 95.3% 87.0% 21 93.9% 84.8%

[0063] FIG. 4 shows temperature monitoring during transport and processing of salmon chilled by traditional method and sub-chilling method. Sub chilled salmon maintains a temperature of 1.5 C. The temperature of the fish remains stable and the salmon is in rigor throughout the whole the process. The traditionally chilled salmon never enters sub-zero conditions and takes longer to cool down.