Abstract:
The present invention is a process and an apparatus for efficiently separating fine bones from fish flakes wherein fish flakes are dispersed after dehydration or dehydrated after dispersion, and separated using a sieve with a plate with slits formed thereon.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a process and an apparatus for separating fine bones from fish flakes. 
     DESCRIPTION OF THE RELATED ARTS 
     There have been conventionally employed processes for utillizing fish caught in large quantities such as Alaska pollack, Atka mackerels, Saffron cod, Hoki, Rattails, Pacific cod, Pacific salmon. Among them, processes for separating fine bones to be used as foods comprises mainly selecting refined meat and used as food materials such as frozen SURIMI (ground frozen fish), KAMABOKO (fish jelly), DENBU, SOBORO, OYAKO-ZUKE and the like. 
     The demand for fish flakes has been increasing. However, any one of the processes are not suitable for producing them. 
     For example, the process for producing frozen SURIMI comprises separating meat by a meat separator, rinsing in water, then removing impurities such as fine bones, scales and the like by a refiner, compressing and dehydrating and freezing with sugars and phosphate. 
     The above process is a mass production process which provides products completely free from impurities such as fine bones, but involves problems. That is, when the dehydrated meat before adding sugars and phosphate is steamed and flaked, the product is like fine fibers or tangles of fibers which had been once fined down, resulting in unpleasant taste and unsuitable mouthfeel for foodstuff. 
     DENBU is prepared by powdering dried fish or salted and dried fish, and then by separating meat fibers from fine bones by wind force. Such process is disadvantageous because it provides product which appears flake but dried, that is process capability is too small for separating fine bones. 
     SOBORO and OYAKO-ZUKE are long-established foods, SOBORO is prepared by cutting Pacific cod, Alaska pollack or the like into three portions (two fillets and flesh-webbed skeleton), skinning, removing belly meat as well as fine bones present at the boundary between belly and back, steaming only back meat and crumbling to flake, adding soy sauce, mirin (sweet sake used as seasoning) and the like and boiling down. OYAKO-ZUKE is prepared by adding fish eggs to the above flakes and pickling in vinegar. 
     However, such processes are inevitably accompanied with the problem of the presence of fine bones no matter how carefully treated. Accordingly, the operation of removing fine bones by manual labor in the final step is required. These methods provide good products with less impurities, but all of them rely on manual labor and are not suitable for mass production. 
     Among the prior arts, as mentioned above, mass productive methods disadvantageously provides products with unsuitable qualities for flakes, while processes which provides products with suitable qualities depends on manual labor and are not suitable for mass production. 
     Further, as an apparatus for separating fine bones, Japanese Patent Publication No. 43327/1981 discloses an apparatus for electrically separating dried fish flakes from bone. The method is not a method to separate fine bones from wet fish flakes, which is one of the characteristics of the present invention. 
     When we eat boiled or roasted fish, we use chop sticks and pick out a piece of meat, which is ideal as a fish flake. Removing fine bones is extremely important in the process for production of products which we can directly eat. 
     For example, Alaska pollack has long and hard bones at the root of the fins (dorsal fin, pectoral fin, ventral fin, caudal fin) and between the meats under them in addition to the backbone, further it has long bones in the wall of the visceral cavity. 
     There are many thin bones of 10-30 mm length at the junction of back and belly meat. The bones of fin are readilly removed at the stage of the treatment of fish body and skinning, and the backbone at the stage of collecting meat after steaming. But the probability that fine bones in junction of back and belly meat are present in the flakes is extremely high. About fifty of fine bones are present per head of Alaska pollack. Accordingly, about ten Alaska pollacks are required to produce 1 kg of flakes, accompanied with about 500 fine bones present therein on calculation. 
     Actually, the number of fine bones present therein is less than the above value since some may be removed at the stage of the treatment of fish body. On calculation, however, about 500,000 fine bones are present in products when 1 ton of flakes are produced. When the flakes are white like fine bones, it is extremely difficult to distinguish bones from flakes and impossible to completely remove fine bones by manual labor. 
     In case of Alaska pollack, the color of flake is white like that of fine bones, furthermore the fine bones are thin, hard, pointed and sticks like a needle. Therefore, it is dangerous that they are present in food and accidentally eaten. 
     It is quite difficult to completely eliminate fine bones, which is required for production of foodstuff. It applies to other kinds of fish such as Atka mackerels, Saffron cod, Hoki, Rattails, Pacific cod, Pacific salmon and the like. 
     The production of flakes of Alaska pollack which is cheap and caught in large quantities has not been industrialized. It is partly because the effective methoes for elimination of fine bones have not been developed. Accordingly, the processes and apparatus to effectively eliminate fine bones from wet fish flakes by a process which can be applied for mass production are eagerly expected. 
     SUMMARY OF THE INVENTION 
     The present inventor has studied intensively on a method and an apparatus for separating fish flakes into meat and fine bones to solve the above problems. As the result, I have succeeded in effectively separating meat from fine bones by dispersing fish flakes after dehydration or dehydrating after dispersion, and separating by a sieve using a plate on which slits are formed, and have attained the present invention. 
     That is, the present invention is (a) a method for separating fine bones from fish flakes, which is characterized by conducting the following two steps in succession: 
     (i) the first step wherein fish flakes collected from prepared, skinned and heated fish are dispersed after dehydration by compression or centrifugation, or dehydrated by compression or centrifugation after dispersion; 
     (ii) the second step wherein meat is separated from fine bones by a sieve using a plate on which slits are formed. 
     The present invention is (b) a process for separating fine bones from fish flakes according to the above (a), wherein heating in the first step is conducted in an acidic buffer solution which is adjusted to pH 3-6. 
     Further, the present invention is (c) a process for separating fine bones from fish flakes according to the above (a) wherein dispersion in the first step is conducted using a way of bubbled water jetting or a rolling mean. 
     The present invention is (d) a process for separating fine bones from fish flakes according to the above (a), wherein the slit of the plate is 0.5-5 mm width, 3-100 mm length and arranged in lengthwise, crosswise or right inclined or left inclined directions, or a combination of two or more of them. 
     The present invention is (e) a process for separating fine bones from fish flakes according to any one of the above methods (a)-(d), wherein clogging is prevented by drawing the plate by suction or blowing air against the plate. 
     The present invention is (f) an apparatus for separating fine bones from fish flakes which is equipped with a way of bubbled water jetting or a rolling mean and a sieve to separate fine bones from fish flakes using a plate on which slits are formed. 
     The present invention is (g) a sieve for separating fine bones from fish flakes which comprises a rotatable cylindrical member on which slits of 0.5-5 mm width, 3-100 mm length are arranged in lengthwise, crosswise, right inclined or left inclined direction, or a combination of two or more of them. 
     The present invention will be explained in detail. The kinds of fish to which the process of the present invention can be applied are not particularly limited, but it is advantageous to apply it to fish which can be caught in large quantities such as Alaska pollack, Atka mackerels, Saffron cod, Hoki, Rattails, Pacific cod, Pacific salmon and the like from the economical point of view. 
     When the method of the present invention is carried out, the raw material fish is first prepared, skinned and heated. In this case, the term &#34;to prepare&#34; means to remove the portions, for example, head, tail, fin, viscera, which are not used for production of fish flakes, and there are no particular limitation to the conditions for preparation or skinning. It suffices that not so many fine bones are left. 
     But heating should be conducted under the conditions sufficient for heat denaturation of the meat. 
     Heating is conducted in an acidic buffer solution adjusted to pH 3-6 to enhance the yield of the fish flakes and to improve preservability, and further to improve qualities such as mouthfeel. 
     The acidic buffer solution which can be advantageously used includes, for example, a mixture of one or two of the compounds selected from the group consisting of citric acid, gluconic acid, succinic acid, tartaric acid, lactic acid, malic acid, fumaric acid, acetic acid, adipic acid, and aqueous solution of their salts. 
     When the process of the present invention is carried out, the pH of the acidic buffer solution is preferably from 3 to 6. When pH is less than 3, the yield of the fish flakes which is finally obtained is disadvantageously decreased. In addition, it is not preferable from the viewpoint of taste, that is the acidity of the product become stronger. On the other hand, when the acidic buffer solution at pH more than 6 is used, the yield of the fish flakes is also disadvantageously decreased. 
     The concentration of the buffer varies depending on the acidity of the buffer, and types and quality of the fish. For example, when citric acid and sodium citrate are used in a combination in the acidic aqueous buffer, it is preferable to adjust pH in the range from 3 to 6 using about 5-50 mmol of the solution. 
     Subsequently, meat is collected, and dispersed after dehydration, or dehydrated after dispersion to give fine flakes. When large fish such as Pacific salmon is used, it is preferably dispersed after roughly dehydrated. However, the meat is often collected as lumps and it is difficult to disperse them. Accordingly, it is preferable to conduct rolling using a rolling mill or the like, followed by various kinds of dispersion treatment. 
     The examples of the rolling mill are ilustrated in FIGS. 5 and 6. 
     When Alaska pollack is used, the fish body is often small, so it is preferable to be dehydrated after dispersion. It is preferable to disperse by means, for example, jetting bubbled water. 
     It is preferable to jet bubbled water to the obtained fish flakes to disperse the muscle fibers as fine flakes, and at the same time, make them float on the surface of the water to separate large bones. As the bubble generator, for example, a commercially available bubble generator, for bath can be used. Thus, separation of fine bones in the next step can be quite effectively conducted. 
     Subsequently, the fish flakes are lightly compressed or centrifuged to dehydrate (to drain off water). Such dehydration is not necessarily conducted under severe conditions. It is sufficient that the product may not adhere but can be crumbled in hands as if it is almost dry. 
     Finally, fine bones are separated from meat using, for example, a metal plate with holes punched thereon as a sieve. The holes should be most preferably slits. Circle or other shapes are not preferable because the meat may pass through or the fine bones may insufficiently pass through the holes. 
     The preferably size of the slit is about 0.5-5 mm width and 3-100 mm length. The sieve with the slits of the above size which are arranged in lengthwise, crosswise, right inclined or left inclined direction, or a combination of two or more of them are advantageously used because they provides the highest efficiency of separation of fine bones. 
     Further, in the step for separation of fine bones, the first discharged flakes which once pass through a sieve can be directly provided as a product. The flakes may be subjected to another separation step. Alternatively, the first sieve passed flakes containing many fine bones may be subjected to a step for separation of fine bones again to enhance yield of fish flakes. 
     The sieve may be prepared using a plastic plate with slits formed thereon. 
     When the apparatus of the present invention is set working according to the method of the present invention, fine bones or fish flakes may adhere to the plate with slits formed thereon, resulting in clogging. For maintaining the separation ability of fine bones, it is necessary to prevent such clogging. Such clogging can be prevented by drawing by suction from discharged side or blowing air from sieve passed side to discharged side. 
     The intensity of suction, or the amount, intensity, temperature, humidity of the blowing air may be properly selected depending on the types, conditions of the flakes, and may not be generalized. 
     As explained above, the present invention is conducted to effectively separate fine bones from fish flakes with many fine bones present therein by quite simple operations, giving a chance for fish which can be caught in large quantities such as Alaska pollack, Saffron cod, Atka mackerels, Hoki, Rattails, Pacific cod, Pacific salmon and the like to be used as food materials. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of the step for separation of fine bones from fish flakes according to the present invention, FIGS. 2 and 3 are a side view and a development of a sieve for separation of fine bones according to the present invention, 
     FIGS. 4a-4d are enlarged views of slits formed on a sieve, 
     FIG. 5 is a plane view of a rolling mill, and 
     FIG. 6 is a side view of a rolling mill. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Examples of the present invention will be explained with the reference to the attached drawings, but the present invention is not limited to them. 
     The term &#34;%&#34; herein used means percent by weight unless othersise indicated. 
     In FIG. 1, a is fish flakes, 1 is a tank in which fish flakes are charged, 2 is a bubble generator of a way of bubbled water jetting to put bubbled water in the tank, 3 is a screw press of dehydration means to dehydrate the fish flakes discharged from the tank, b is a dehydrated flake discharged from the screw press, 4 is a first sieve to separate fine bones from the dehydrated flakes, c is a first discharged flake after separation of fine bones by a first sieve, d is a first sieve passed flake which passes through the slits of the first sieve, 5 is a conveyer to convey the first sieve passed flakes, 6 is a second sieve to further separate fine bone from the first sieve passed flake, e is a second discharged flake after separation of fine bones using a second sieve, f is a second sieved flake which passes through the slits of the second sieve. 
     In FIGS. 2-4d, 10 is an example of a sieve for separation of fine bones which is cylindrical and rotates by a motor (not shown) and divided by quarters of circumference (α1-α4), on which slits in different direction are formed, that is, slits arranged in lengthwise direction 10a, crosswise direction 10b, right inclined direction 10c and left inclined direction 10d are formed in parts α1, α2, α3 and α4, respectively. 
     The arrangement of these slits are not limited to the case of the circumferentially divided cylinder. The slits arranged in various directions may be optionally combined. 
     EXAMPLE 1 
     (1) 100 Alaska pollacks were used as raw materials. The heads, viscera, pectoral and caudal fins were cut off, and the fishes were immersed in a hot water at 100° C. for about one minute, pulled up and skinned by gently rubbing with a wooden spatula. 
     (2) Subsequently, dorsal and ventral fins were removed, and the fishes were washed with water and smothered with a steam at 95° C. for 15 minutes. 
     (3) The smothered fish bodies were gently rubbed aginst a screen (15 mm square) to give fish flakes a through the screen. The resultant was fell into a tank 1 in FIG. 1, bubbled water was jetted by a bubble generator 2, and the floated fish flakes a were dehydrated by a screw press 3 to give dehydrated flakes b. 
     (4) Further, the dehydrated flakes b were put through a first sieve 4 which is a rotary sieve having a structure shown in FIGS. 2 and 3 to give 9,500 g of the objective fish flakes free from fine bones as first discharged flakes c. 
     The resulting fish flakes had natural mouthfeel suitable for various kinds of food. 
     The amount of the first sieve passed flakes d containing many fine bones were 1,500 g and 1,360 of fine bones were contained therein. 
     Subsequently, the first sieve passed flakes d conveyed by a conveyer 5 were sieved again in the same manner as the above (4) using the said rotary sieve 6 having a structure shown in FIGS. 2 and 3 with slits of 1 mm width and 5 mm length formed thereon, to give 1,100 g of the objective fish flakes containing less fine bones as second discharged flakes e. The number of fine bones contained therein was five. 
     The second sieve passed flakes f were 300 g and 1,230 fine bones were contained therein. 
     EXAMPLE 2 
     After the same operations of (1)-(3) of the above Example 1 were carried out, 
     (4) the resultant was put through a rotary sieve having a structure shown in FIGS. 2 and 3 with slits of 4 mm width and 30 mm length formed thereon to give 9,900 g of the objective fish flakes containing less fine bones as first discharged flakes. Six fine bones were contained therein. 
     The amount of the first sieve passed flakes containing many fine bones was 1,100 g and 1,350 fine bones were contained therein. 
     Subsequently, the first sieve passed flakes were sieved again in the same manner as that in the above (4) using a rotary sieve having a structure shown in FIGS. 2 and 3 with slits of 1 mm width and 5 mm length formed thereon, to give 7,000 g of the objective flakes containing less fish bones as second discharged flakes and 2,900 g of second sieve passed flakes containing five bones. 
     Further, the first sieve passed flake was sieved again in the same manner as that in the above (4) using the above rotary sieve shown in FIGS. 2 and 3 with slits of 0.8 mm width and 5 mm length formed thereon to give 900 g of the objective fish flakes containing less fine bones as second discharged flakes. There were no fine bones contained therein. 
     The second sieve passed flakes were 500 g and 1,350 fine bones were contained therein. 
     EXAMPLE 3 
     (1) Seven divisions of frozen dressed Alaska pollack (10 kg for each division) were defrosted overnight, heated by blowing steam onto the surface, then skin and fins were removed. Thus the raw material for each experimental division was prepared. 
     (2) Subsequently, an aqueous solution with composition shown in Table 1 (30 liter was boiled, and Alaska pollack after above treatment (1) was put is said solution, boiled for 5 minutes, and the fish body was gently rubbed aginst a screen (15 mm square) to make meat into flakes to give fish flakes before separation of fine bones for each experimental division. 
     
                       TABLE 1______________________________________  CompositionExperimental    Citric Acid               Sodium Citrate                           pH of AqueousDivision (g)        (g)         Solution______________________________________a         0          0          6.75b        460        140         3.01c        518         70         2.50d        129        474         5.11e         32         38         4.35f         81         96         4.20g        162        192         4.11______________________________________ 
    
     (3) Further, fish flakes before separation of fine bones containing about 500 fine bones per kg which were obtained in the above (2) were dehydrated by compression, put through a first sieve 4, a rotary sieve having a structure shown in FIGS. 2 and 3 with slits of 3 mm width and 20 mm length formed thereon, to give fish flakes after separation of fine bones for each experimental division. The amount of the obtained flakes, the number of fine bones contained in 1 kg of flakes and acidic taste of the product are shown in Table 2. 
     
                                           TABLE 2__________________________________________________________________________  Amount of Flake Before               Remaining Fine Bones After                             Acidic taste of FlakeExperimental  Separation of Fine Bones               Separation of Fine Bones                             After SeparationDivision  (kg)         (per kg)      of Fine Bones__________________________________________________________________________a      3.2          70            -b      3.7          32            +c      3.9          41            +d      3.7          45            -e      3.8          35            -f      4.3           9            -g      4.1          20            +__________________________________________________________________________ 
    
     EXAMPLE 4 
     Pacific salmon was cut into three portions (two fillets and flesh webbed skelton), boiled in a boiling water for 10 minutes, long and thin bones at the wall of visceral cavity were removed using a wooden spatula, gently compressed to dehydrate. Thus 10 kg of flake before separation with moisture content of 66.3% was obtained. 
     The resulting flakes were divided in two divisions (5 kg for each). 
     The first portion was passed through a rolling mill which is effective to disperse fish flakes collected from a large fish into fine flakes. 
     The above rolling mill will be explained the reference to the attached FIG. 5 (a plain view) and FIG. 6 (a side view). 
     The rolling mill has two roller of about 400 mm width and about 100 mm in diameter made from plastic or the like which arranged at interval of α. In the present example, three sets of rollers, rollers 20a and 20b, 30a and 30b, and 40a and 40b were arranged in three layers. 
     In this case, the intervals α between rollers 20a and 20b, 30a and 30b, and 40a and 40b are 20 mm, 10 mm and 6 mm, respectively. 
     In FIGS. 5 and 6, 21a, 21b, 31a, 31b, 41a or 41b is a rotation axis of each roller, 22a, 22b, 32a, 32b, 42a or 42b is a gear of each roller, 23, 33 and 43 are sprockets, 50 is a chain to be engaged with each sprocket, 51-54 are guides of the chain 50. 
     Running of said roller of the rolling mill is not shown, it can be performed by manual labor using handle or by motive power. 
     Cogged belts and the like may be used instead of the chain. 
     When fish flakes are rolled in the top rollers 20a and 20b  of such roller, fish flakes are dispersed and discharged between the bottom rollers 40a and 40b. 
     Subsequently, fine bones were separated from the dispersed fish flakes using a first sieve 4 to give 4.6 kg of first discharged flakes. 
     As a control, the second division was directly put through a first sieve 4 to separate fine bones to give 4.6 kg of first discharged flakes. 
     The number of fine bones in the first discharged flakes of each division after separation was measured and shown in Table 3. 
     
                       TABLE 3______________________________________      Number of Fine Bones in 1 kg      of Flakes______________________________________First Division         3Second Division        21______________________________________ 
    
     REFERENCE EXAMPLE 1 
     In the same manner as that in Example 1, except that (3) dispersion and floating operation by bubbled water were not carried out, fish flake were obtained. The items are shown below. 
     
         ______________________________________          CollectedFlake          amount    Number of Fine Bones______________________________________First Discharged Flake          9,400 g     40First Sieve Passed Flake          1,500 g   1,420______________________________________ 
    
     The result of the second sieving conducted in the same manner as that in Example 1 using the first sieve passed flakes is shown below. 
     
         ______________________________________          CollectedFlake          amount    Number of Fine Bones______________________________________Second Discharged Flake          1,100 g      6Second Sieve Passed Flake            400 g   1,360______________________________________