Patent Application
20080286407
1. Field of the Invention
The invention relates to a method of preserving fish, more particularly to a method of producing fish meat having fresh color.
2. Description of the Related Art
In general, fish meat tissues are vulnerable to bacterial decomposition. The meat of freshly caught fish is likely to decay under room temperature, and fats of fish are prone to oxidization and acidification, so that the color of fish is adversely affected. To preserve the fresh color of fish, fish have to be processed quickly after they are caught.
Referring to
In the cleansing step 10, a live fish to be processed is moved to a fish tank containing clean water, and is kept there for at least 12 hours to allow the fish to discharge most of the excremental wastes in its body into the fish tank.
In the cutting step 11, the cleansed live fish is immersed in a solution containing sodium hypochlorite or chlorite for about 10 minutes so as to disinfect the surface of the fish. The fish is then washed in clean water to remove the sodium hypochlorite or chlorite therefrom. Then, the fish is killed instantly by cutting the throat of the fish using a knife, or by subjecting the fish to carbon monoxide. Thereafter, the fish is bled and filleted, the fish skin and the spine are removed, and edges of the meat pieces are trimmed to obtain a neat appearance.
In the color enhancing step 12, the meat pieces are placed in a gas-tight bag, and carbon monoxide gas is introduced into the bag for a period of time. For a meat piece of 200 g, the meat piece is placed in an environment of carbon monoxide for 40-60 minutes to allow the meat pigment myoglobin in the fish meat to react with the carbon monoxide so as to produce a bright pink or red color in the fish meat.
In the disinfecting step 13, the color enhanced meat pieces are immersed in a solution containing sodium hypochlorite or chlorite for about 1 minute. Then, the meat pieces are washed in clean water to remove residual sodium hypochlorite or chlorite so as to achieve surface disinfection. Since the color enhancing step 12 takes a relatively long time to conduct, bacteria may breed on the surface of the meat pieces. Therefore, the disinfecting step 13 is mainly intended to destroy the bacteria that breed during the color enhancing step 12.
In the ozone sterilizing step 14, the meat pieces are immersed in a sterilizing tank containing ozone (O3) for some time for sterilization. Thereafter, the meat pieces are removed and wiped dry.
In the grading step 15, the meat pieces are graded by weight so as to facilitate determination of the time required for subsequent freezing and packaging processing.
In the ultraviolet sterilizing step 16, the meat pieces are subjected to ultraviolet irradiation for sterilization purposes. This step is performed to kill bacteria that may breed on the meat pieces during the grading step 15 so as to prolong the shelf life of the meat pieces.
In the vacuum packaging step 17, the meat pieces thus sterilized are packed into packaging bags, and air within the packaging bags is evacuated to form a vacuum therein.
In the quick-freezing step 18, the packaging bags with the meat pieces are placed in a freezer at a temperature lower than −30° C. to quick-freeze the meat pieces.
In the packaging and freezing step 19, the frozen meat pieces are packed in Styrofoam® containers and stored in a freezer.
For a meat piece of 200 g, the time required for performing step 11 through step 13 is about 60-80 minutes, the time required for performing step 14 through step 17 is about 30-40 minutes, and the time required for performing steps 18 and 19 is about 90-100 minutes, adding up to a total of at least 3 hours.
It is apparent from the foregoing that the conventional method of preserving fresh color of fish has several disadvantages:
1. Prolonged processing time affects freshness of fish meat: To allow the myoglobin in fish meat to sufficiently react with carbon monoxide, the color enhancing step 12 generally takes at least 40 minutes to complete. For bigger or thicker meat pieces, the time will be longer. Therefore, the disinfecting step 13 is necessary to kill the bacteria generated during the color enhancing step 12. In so doing, the texture of the fish meat is also affected adversely, thereby reducing freshness of the fish meat and increasing the likelihood of food poisoning.
2. Potential health hazard: As the meat pieces show a bright pink or red color after being subjected to the carbon monoxide color enhancing treatment, the natural color of the fish meat is masked. Thus, consumers are unable to judge the freshness of the meat pieces by their appearance or color, and may unknowingly consume spoiled or toxic fish meat that threatens health.
3. Fish protein is likely to degrade, and bleeding is incomplete: As the live fish is instantly killed in the cutting step 11, the protein in the fish starts to degrade at the instant the fish is dead. Degraded protein generates toxic histamine that may endanger consumer's health when ingested. In addition, as the fish is instantly put to death and its nervous system virtually stops functioning, bleeding of the fish cannot be thoroughly done.
4. Packaged meat pieces tend to be compressed to result in impaired appearance: As the meat pieces are packaged in vacuum bags in the vacuum packaging step 17, the meat pieces may be compressed by the packaging bag so that residual blood in the capillaries on the surface of the meat pieces is forced out, which gradually becomes dark in color and mars the appearance of the packaged meat pieces.
Therefore, the object of the present invention is to provide a method of producing fish meat having fresh color so as to retard degradation of fish protein, shorten processing time, and retain the fresh color of fish meat for a relatively long period of time.
Accordingly, a method of producing fish meat having fresh color of this invention comprises:
placing live fish in a state of unconsciousness by blocking the conduction of nerve pulses along a nervous system of the fish;
bleeding the fish and cutting meat pieces from the fish while the fish is unconscious;
sterilizing the meat pieces;
placing the sterilized meat pieces in an oxygen-free environment to preserve the original color of the meat pieces;
freezing the meat pieces; and
packaging the frozen meat pieces.
Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiment with reference to the accompanying drawings, of which:
Referring to
In the cleansing step 2, a live fish to be processed is moved to a fish tank containing clean water, and is kept there for at least 12 hours to allow the fish to discharge most of the excremental wastes in its body into the fish tank.
In the cutting step 3, the cleansed live fish is first subjected to a surface disinfecting treatment by immersing the live fish in a solution containing sodium hypochlorite or chlorite so as to disinfect the surface of the fish. Sodium hypochlorite is commonly referred to as a bleaching agent, which can destroy protein of microorganisms to thereby kill bacteria, fungi and viruses. Chlorite is a highly effective oxidizing agent, which can adhere to and penetrate cell walls of microorganisms to oxidize mercapto-containing enzymes therein to thereby destroy the same. The live fish is removed from the solution after about 10 minutes, and is washed in clean water to remove residual sodium hypochlorite and chlorite therefrom.
Thereafter, a pointed rod is used to sever or destroy nerves in the spine or spinal column of the fish so as to block the conduction of nerve pulses along the nervous system of the fish, thereby placing the live fish in a state of unconsciousness such that the fish is unable to struggle. At this point, the fish can be subjected to bleeding and cutting or filleting. Since the fish is merely unconscious and is still alive, the fish muscles will still twitch, and the fish can be bled substantially thoroughly so that the fish meat is comparatively whiter or clearer in appearance. Alternatively, the live fish can be rendered unconscious by putting the fish temporarily in an environment such that the fish suffers from oxygen deficiency and the conduction of nerves pulses is blocked. In an example, a lot of fish is put into a bucket of cold water with a temperature of about 5° C. Due to coldness of the water, the respiratory system of the fish gradually fails so that the fish suffers from deficiency of oxygen and becomes unconscious. When the fish no longer wriggles, the fish can be subjected to bleeding and filleting. During filleting, the fish is skinned, the spine is removed, and meat pieces are cut from the fish. Thereafter, edges of the meat pieces are trimmed to obtain a neat appearance.
In the sterilizing step 4, the meat pieces are immersed in a low-temperature ozone sterilizing tank at a temperature within a range from 0° C. to 5° C. for sterilization for 30 seconds. Thereafter, the meat pieces are removed and wiped dry.
In the grading and placement step 5, the meat pieces are graded according to the weight thereof. The purpose of grading the meat pieces is to determine the time needed for freezing the meat pieces and the packaging operation. The heavier the meat pieces, the longer the time required to freeze the meat pieces. Thereafter, a plurality of meat pieces of the same grade are arranged on a tray, and the tray with the meat pieces is placed in a sealable gas-tight bag. The meat pieces should be arranged in such a manner that they do not overlap so that the meat pieces will not stick together upon freezing.
In the color fixing step 6, the meat pieces are placed in an oxygen-free environment so as to be isolated from ambient air. In the preferred embodiment, the oxygen-free environment is an environment filled with nitrogen, or an inert gas. In actual practice, before sealing, the gas-tight bag is filled with nitrogen, which forces out the air in the gas-tight bag, thereby isolating the meat pieces in the gas-tight bag completely from the ambient air.
In the quick-freezing step 7, the packaged meat pieces are placed in a freezer at a temperature below −30° C. so as to quick-freeze the meat pieces to thereby ensure freshness. Preferably, the meat pieces are frozen to a temperature below −35° C.
It is noted that the color fixing step 6 and the quick-freezing step 7 can be implemented in an assembly line having a conveyor belt. That is, trays with properly arranged meat pieces are placed on a conveyor belt to be transported to a cavity filled with nitrogen so as to expel the air in the gas-tight bags, and are further transported to the freezer for quick freezing. Thus, automated processing can be achieved to save manpower resources and operational time.
In the packaging step 8, the frozen meat pieces are subjected to ultraviolet sterilization for 80˜100 seconds. Thereafter, the frozen meat pieces are packed into a packaging bag, and air in the packaging bag is evacuated such that the volume of the packaging bag is reduced to 5% to 15% of an original volume of the packaging bag, thereby achieving a semi-vacuum state. Preferably, the volume of the packaging bag is reduced to about 10% of the original volume of the packaging bag. Thereafter, the packaging bag containing the meat pieces is placed in a Styrofoam® box for subsequent freezing. The purpose of leaving a small amount of air in the packaging bag is to prevent the packaging bag from adhering to and compressing the meat pieces. With the presence of a small amount of air in the packaging bag, the surface of the meat pieces can be kept intact. Certainly, nitrogen or an inert gas can be introduced into the packaging bag in place of air so as to provide a substantially oxygen-free environment.
With the present invention, for a fish meat piece of 200 g, the time needed to perform steps 3, 4 and 5 is about 20˜30 minutes. Filling the gas-tight bag with nitrogen in the color fixing step 6 takes only about several seconds, and steps 7 and 8 require about 90˜100 minutes to perform. Therefore, processing of a meat piece of 200 g can be completed in about 2 hours.
It is apparent from the foregoing that the present invention provides several advantages over the prior art in actual practice.
1. The processing time can be reduced considerably to ensure the freshness of fish meat: Since the nitrogen treatment can be completed in just several seconds, the fish meat can be isolated from ambient air so that the natural white or pink color of the fish meat can be maintained, which is very different from the prior art which utilizes carbon monoxide as a color enhancing agent and which requires a period of reaction time of about 40˜60 minutes to allow the carbon monoxide to exert its full effect. Besides, in the prior art, the time required for carbon monoxide to react will increase with an increase in the weight of the fish meat. Furthermore, as the color fixing step 6 in the present invention is extremely short, the fish meat can be directly subjected to quick-freezing without going through a disinfecting step, which is required in the prior art. In other words, the disinfecting step 13 (see
2. Spoilage of the fish meat can be easily identified to ensure food safety: Unlike the prior art which uses carbon monoxide to create a bright red color in the fish and to mask the natural color of the fish meat, in the present invention, since nitrogen is used to isolate the fish meat from ambient air in the color fixing step 6, the natural white or pink color of the fish meat can be maintained for a relatively long period of time. Thus, consumers can readily identify the freshness of the fish meat by looking, and can avoid eating spoiled fish meat, or fish meat that starts to develop toxics.
3. The natural white or pink color of the fish meat can be retained for a relatively long period of time while delaying degradation of fish protein: Since the live fish is bled and filleted after being rendered unconscious in step 2, bleeding can be done substantially thoroughly to help retain the original white or pink color of the fish meat. Besides, since death of the fish is delayed, degradation of the fish protein can be retarded as well.
4. The appearance of the fish meat will not be adversely affected by packaging: Since a small amount of air is retained in the packaging bag in step 8, the packaging bag will not adhere to the fish meat to compress the capillaries on the surface of the fish meat, thereby preserving the surface of the fish meat intact.
While the present invention has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this invention is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.
