WO1995031115A1

WO1995031115A1 - Method and apparatus for removing connective tissue-fascia and parasites from fish liver

Info

Publication number: WO1995031115A1
Application number: PCT/NO1995/000079
Authority: WO
Inventors: Asbjørn GILDBERG; Ronald Svenning
Original assignee: Harald A. Johansen A/S
Priority date: 1994-05-13
Filing date: 1995-05-12
Publication date: 1995-11-23
Also published as: AU2539195A; NO951873D0; NO951873L; EP0797393A1

Abstract

A method for treating a product, preferably removing connective tissue membranes and parasites from fish liver and an apparatus which is used to carry out the method are described.

Description

METHOD AND APPARATUS FOR REMOVING CONNECTIVE TISSUE-FASCIA AND PARASITES FROM FISH LIVER .

The present invention relates to a method and technical equipment for the performance thereof for removing connective tissue membranes and parasites from fish liver.

Nematodes, including parasites, worms and intestinal worms, have a complex life cycle and are dependent upon intermediate hosts in order to be able to infect fish. Examples of intermediate hosts include marine mammals, such as, for example, seals, whales and birds and crustaceans. In the marine environment where cod is found, these intermediate hosts are also often found and thus the basis for the possibility of the fish becoming infected. Nematodes such as Anisakis Simplex and Phocanema Decipiens sp. are often found in large numbers in codfish. The nematodes are found primarily in the abdominal cavity, the digestive organs and the liver of the fish. After the fish has been filleted, the nematodes are detected visually, optically and by means of X- ray in the muscle of the fish. Once a nematode has been detected it is removed mechanically with the aid of an knife or, for example, a water jet.

Fish liver has long been used as a major source of vitamins, and is especially rich in essential vitamins such as vitamin A, D and E. Nematodes have not caused significant problems during the production of fish-liver oil products since they disappear in the production process and are therefore not present in the end fish-liver oil product. However, recently the liver has received greater attention, as recent research is able to show that fatty acids in fact have a substantial effect against cardiovascular disease. This knowledge has led to an increased interest in consuming cod-liver oil. Canned cod liver is a product for which there is expected to be a greater demand. In this type of product the liver is packed in its natural form and it is therefore necessary to remove the nematodes, first and foremost out of aesthetic considerations. Until now it has been preferable to use liver from cod caught in geographical areas where there are few intermediate hosts for the nematodes in question. A fall in the supply of cod from these areas has made it necessary to use raw material also from areas where there are many intermediate hosts, for example, in the northerly and southerly waters of our planet, and along the coast of countries in these areas such as, for example, Lofoten and Finnmark in northern Norway. The new method and apparatus which are described below have been developed to process a product, and especially to remove nematodes from the liver in an efficient manner so that it becomes suitable for human consumption and thus can be used as a canned product.

Danish Patent Application No. 6043/69 describes a method and a means for detaching and removing the edible tissue from marine animal shells by using an aqueous bath into which the animals are dipped. The aqueous bath contains a combination of enzymes. The enzymes should preferably be in contact with the marine animals for 45 to 300 minutes. One disadvantage of this method is the large amount of time required, and the method has also shown itself to be unsuitable for removing membranes, connective tissue membranes, skin or shell from marine animals owing to the long duration of the treatment.

Norwegian Patent Application No. 852930 describes the decomposition of octopus membranes. Herein is described the use of enzymes in the octopus liver by dispersing the liver in a saline solution and subsequently separating a fatty phase and an aqueous phase or an extract of the dispersion. The extract which contains the liver enzymes is used to decompose the membranes during boiling or scolding. This method is not suitable for removing connective tissue membranes, skin or shell from marine animals other than octopus. In their article "Application of enzymes for fish processing in Iceland - present and future aspects" in Advances in fisheries technology and biotechnology for increased profitability, 1990, pages 237-250, Technomic (USA) , Stefansson, G. and Steingrimsdottir, U. describe the removal of skin, membranes and scales from fish. Enzymes isolated from cod are used, and the method is used to remove connective tissue membranes from fish liver. The method referred to here is in fact different from the method and apparatus which is o used in the present application.

The method described in IS 1447 is different from the method in the present application both with regard to the steps in the process and especially with regard to the temperatures used during the treatment . The Icelandic patent describes a three-step process wherein the liver is first treated in a water bath for 40-50 seconds at about 53°C, and is subsequently cooled in cold water (0-10°C) for about 3 minutes before the liver is enzyme-treated in an aqueous buffer solution (pH 8.5) containing proteolytic enzymes. The enzyme treatment takes place at about 15°C and has a duration of about 15 minutes. The net treatment time is about 19 minutes. The method according to the present invention differs considerably from the method in the above-mentioned Icelandic patent :

1) The preheating is effected at a higher temperature and for a shorter time. The advantage of this is that the connective tissue membrane which envelops the liver is heated o rapidly to denaturation without the liver itself being heated excessively. The liver thus maintains its structure even though the strength of the liver membrane is reduced.

2) No cooling is carried out after the preheating. The 5 liver is passed directly from the hot water bath to the enzyme bath. The enzyme bath contains no buffer salts since the enzyme preparation used has optimal activity at the natural acidity of the liver. The enzyme treatment takes place at a much higher temperature than in the above-mentioned method. This means that the duration of the enzyme treatment is about half that described in the aforementioned method.

3) The present method may include a third step comprising an after-heating at a high temperature. This step is carried out to reduce the oil content in the cleaned product, but also to inactivate process enzymes and endogenous liver enzymes which may reduce the storage stability during possible deep frozen storage. A second important effect of this step is that it causes a pasteurisation of the liver which reduces the bacteria count to a very low level .

The present invention consequently relates to a method for removing connective tissue membranes and parasites from fish liver, characterised in that the product is subjected to both chemical and mechanical treatment, in that it is treated in a drum which is submerged in a liquid bath and rotated. When the drum is submerged in the liquid bath, the product will float up and be pressed against the drum so that it is subjected to massage. The chemical treatment comprises that the product is first subjected to A) pre-heating at 60-100°C for 10-40 seconds in a hot liquid bath to denaturise the protein structures in the connective tissue membranes and the tissue structure. The product is subsequently transferred to an enzyme bath having a temperature of 40-60°C, containing 0- 10% salt, preferably 2-5% salt, and 0.01-1% of an enzyme preparation, preferably 0.02-0.2% of an enzyme preparation containing proteolytic enzymes, for 5-10 minutes. The product may subsequently be after-heated at 60-100°C for 120-240 seconds in a steam bath or a hot liquid bath to inactivate the enzyme activity and reduce the oil content before it is finally cooled in a cold liquid bath at a temperature of between 0 and 25°C, preferably 0-10°C. Alternatively, the product is subjected to B) an enzyme solution and ordinary tap water at a temperature of more than 0°C, preferably 35-90°C for 5-300 seconds, preferably 30-200 seconds, containing an enzyme concentration of 0.01-0.5 g/1, preferably 0.01-0.02 g/1. The product is subsequently transferred to a water bath at a temperature of between -2 and 100°C, preferably between 0 and 15°C, for 10-1200 seconds, preferably 600 seconds, and thereafter the liver in the drum may optionally be put into a buffer layer for temporary storage, preferably at a temperature of 1-14°C.

What is special about the present method in relation to other known methods is the rapid degradation of the connective tissue membrane of the liver and the outer part of the tissue structure of the liver with a subsequent effective release of nematodes, in particular ringworm. This property is achieved as mentioned in contrast to the other known methods by using high temperatures in the liquid-filled baths, mechanical treatment and a proteolytic enzyme preparation which is especially effective under the conditions described which make use of the natural pH of the liver and neutral water.

Before the liver is exposed to the enzyme solution in a liquid-filled bath, the liver may optionally first be treated in a heated water bath to denaturise the protein structures in the connective tissue membranes of the liver and the outer part of the tissue structure of the liver. The water bath is heated and it is preferable to use ordinary tap water at a temperature of 60-100°C. The time the liver is in the bath is adjusted according to temperature and is between 10 and 40 seconds. During this treatment the drum is rotated in the bath so that the liver in the drum is exposed to the effect of heat over the entire surface thereof. The heat-treated liver is then conveyed to the enzyme bath without any cooling or unnecessary delay. The enzyme bath is heated so that the temperature is maintained. The temperature here should be high, between 40 and 65°C, and the drum containing the liver rotates for the duration of the treatment so that the liver and the entire surface thereof is exposed in such a way that the connective tissue membranes, and to some extent the outer tissue structure of the liver, are degraded at the same time as the secondary combination of frictional forces against the perforated surfaces of the drum and liver against liver and rinsing/washing in the liquid-filled enzyme bath releases nematodes, principally ringworm. The enzyme concentration is maintained at a low level and is 0.01-1%, preferably 0.02-0.2 g/1. The enzyme preparation used is, e.g., "Arozyme" which contains proteolytic enzymes, hydrolysates and salts. Cooking salt is added to the enzyme bath so that the concentration is about 4% by weight. The liver remains in the enzyme bath for between 5 and 10 minutes, depending upon the condition of the liver, the enzyme concentration, the temperature and the conditions during preheating. The enzyme-treated liver which has been cleansed of nematodes is subsequently returned to the heat treatment bath for after-heating. During after-heating the liver is affected by the heat so that additional oil is removed and the liver's own and the added enzyme activity is inactivated, whilst the drum rotates and releases any remaining nematodes which sit deeper in the surface tissue of the liver and which are not released during the aforementioned enzyme treatment. The duration of the after-heating treatment is between 120 and 240 seconds, depending upon the condition of the liver, such as, for example, the nematode and oil content and the desired degree of inactivation. The temperature in the after-heating bath is between 60 and 100°C. The liver is then taken from the drum and placed in a buffer which is a water bath at a temperature of between 0 and 25°C, preferably 0-10°C, for cooling and temporary storage. The buffer is characterised in that the temperature in the liver is to be brought down and adjuvants may be added to stabilise the liver for storage in a frozen state.

Optionally, cod liver may be put in the drum which is then submerged in the enzyme solution in the liquid-filled bath.

In this bath the connective tissue membrane of the liver is denatured sufficiently to allow the enzyme to degrade the connective tissue membrane without the inner structure of the liver being affected to any particular extent. The enzyme solution is added to the liquid-filled water bath as mentioned above and also preferably ordinary tap water at a temperature of more than 0-90°C, preferably 50-60°C, and the time the liver remains in the bath is adjusted according to temperature and is between 5-300 seconds, preferably 60-130 seconds. During this treatment the drum is rotated in the bath so that all liver in the drum is exposed to the effects of heat and enzyme over the entire surface of the liver. The enzyme concentration is maintained at a low level and is between 0.01-0.5 g/1, preferably 0.01-0.2 g/1. This warmed and enzyme-treated liver is then passed to a water bath without cooling or unnecessary delay. The temperature in this water bath should be between -2 and +100°C, preferably 0 and 10°C. The drum containing the liver is rotated throughout the duration of the treatment so that any remaining nematodes and loose bits of connective tissue membrane are removed during the secondary combination of frictional forces against the perforated walls of the drum and liver against liver and rinsing/washing in the liquid-filled water bath. The duration of the treatment is between 10 and 1200 seconds, preferably 600 seconds, depending upon the nematode content of the liver. The liver in the drum is subsequently placed in a buffer layer for temporary storage. The buffer is characterised in that the temperature of the liver is maintained at a low level, between 1 and 14°C, preferably below +10°C. Adjuvants can be added to the liver in the buffer to stabilise it for storage in fresh or frozen state. The buffer also functions as intermediate storage so that the production can be changed from batch-by-batch processing to continuous processing and later heat treatment to regulate the oil content of the liver and to inactivate primarily the liver's own enzymes, which is important for the subsequent storage prior to later possible canning.

By means of this method, the connective tissue membranes are denatured sufficiently so that the connective tissue membrane of the liver can be degraded rapidly by the use of a proteolytic enzyme without the inner tissue structure in the liver being affected to any particular extent. During a treatment of this kind, nematodes, especially ringworm, can be effectively removed by a subsequent massage in water without the liver losing its natural shape, colour and properties. This is made possible primarily by limited duration of treatment and temperature effect, but also because the drum is designed in such a way that the liver can be massaged more effectively which allows nematodes to be removed without any damage to the liver.

The present invention also relates to an apparatus for removing connective tissue membranes and parasites from fish liver, characterised by a rotating drum (3) having an opening

(18) for introducing and removing the product, said drum (3) being rotatable and submersible in and optionally transferable between one or more baths. The apparatus has been developed so that, together with the enzymatic method, it fulfils the requirements of industrial processing in that connective tissue membranes, nematodes, especially ringworm, and oil can be released from the liver without the liver itself being damaged to any appreciable extent, and having a capacity which is satisfactory, particularly for packing and canning. When using the method and apparatus, the total process time in less than 15 minutes.

A brief description of the figures:

Figures 1A and IB illustrate an apparatus for treating a product, principally removing connective tissue membranes and parasites from fish liver.

Figure 2 shows the drum in the enzyme bath. Figure 3 shows the drum, the hatch for the introduction of the product and the closing mechanism of the drum. Figure 4 illustrates the actual drum. The apparatus consists preferably of three liquid-filled chambers and a rod-shaped drum which is mounted on a carriage and which can be transferred between the baths and the filling position 14. The drum is suspended from arms which, in addition to being capable of submerging the drum in the different baths, also allow the drum to rotate independent of the position of the drum through the chain drive 20 and motor 6. The liver which is to be cleaned is put in the drum in position 14 through the hatch 18. The hatch is hinged and is locked by means of closing mechanism 19. The drum is then raised from the filling position 14 by means of a hydraulic piston and the carriage is subsequently conveyed to the heated water bath 1 to which enzymes may optionally be added, and is then submerged in the water bath. Once submerged, the drum starts to rotate so that the liver and the entire surface thereof is subjected to the effect of heat and optional enzyme. The temperature in the water bath 1 is regulated by a supply of steam through the valve 11 which is pneumatically operated and controlled electronically in connection with a thermosensor mounted inside the water bath.

The liquid level is regulated through the overflow channel 9 between liquid baths 1 and 4 and the supply of water from water bath 2 through the overflow 8. The water is changed each time the drum containing the product is submerged in the liquid. The change of liquid has two purposes, of which one is to replace a determined amount of liquid and the other is that this liquid will convey oil and oil-containing fragments floating on the surface out through the overflow channel 9 and on to cleaning and recovery of oil. The supply of liquid is carried out in water bath 2 in such a way that the drum containing the product displaces a certain amount of water from water bath 2 to water bath 1. This transfer of liquid is achieved by virtue of the fact that there is a difference in height between liquid baths 2 and 1 and furthermore between liquid bath 2 and overflow channel 9. The change of liquid is determined through an electronically controlled supply of liquid in liquid bath 2. Each time the drum containing the product is submerged in the liquid bath 2, the drum and product will displace an amount of liquid which corresponds to the difference in volume between product and drum and the volume between the liquid surface and the overflow to liquid bath 1. The same volume will be displaced further to the overflow channel 9 the next time the drum containing the product is submerged in water bath 1. In this way the liquid baths are constantly supplied with fresh process liquid which is automatically regulated through capacity utilisation. Between liquid baths 1 and 2, there is an air-filled chamber which can be supplied with water so that a desired heat transmission between the liquid baths is maintained. The temperature in the liquid baths is regulated by means of electronic thermostats, the addition of water and cooling. The semi-circular periphery of the drum is constructed having a centre point which causes the drum to assume a spiral shape and forms a height difference in the joint between the circular and elliptical halves. The difference in height thus forms a natural carrier which allows a gentle and efficient transfer of the product each time the carrier engages the liver which because of the difference in relative density is kept floating inside the drum. In this way a complete massage of all liver is achieved without it being subjected to harsh mechanical action. The liquid level can also be regulated through the overflow 9 and the water supply 10. The change of water then takes place in that the volume of the water corresponding to the volume of the liver in the drum and the drum itself is forced out through the overflow when the drum containing liver is submerged in the water bath. As soon as the drum is raised from the water bath the refilling of water starts. When the drum is raised from the water bath 1, the carriage 5 is conveyed to the enzyme bath 2 and is submerged at the same time as the drum starts to rotate. The temperature in the enzyme bath is then constant and is regulated by supplying temperature regulated water through the valve 7 prior to the start of the enzyme treatment. The temperature in the bath is maintained through heat transmission from the water bath 1. The water in the bath is renewed when discharged through overflow 8.

The drum 3 is made of glass-blown or profiled tubes (bars) which give a rough surface sufficient to massage out impurities and in particular nematodes without any damage to the^' liver. The space between the bars is 3 mm. This space can be adapted to the individual product so that the requirements for massage are sustained without the product being squeezed or damaged when the drum is raised and transferred between the liquid baths, the loading position 14 and the emptying position 16. The drum can also be made of other materials, for example, perforated materials. When the enzyme treatment period in liquid bath 1 is completed, the drum containing the product is transferred to the liquid bath 2 for massage, release of enzyme and nematodes, and cooling. After the massage has been completed, the drum containing the product passes from liquid bath 2 to buffer 4 and the product is subsequently emptied automatically through the hatch in the drum's position 16. The liver is cooled in the water bath 4 at the same time as the water bath functions as a buffer and temporary storage for further processing.

Gradually as the connective tissue membrane of the liver is degraded this will result in the nematodes becoming detached from the liver, partly as a consequence of the friction between the liver and the rough bars, partly as a consequence of the friction between liver, and partly as a consequence of the effect of the wash. The nematodes, which are heavier than the liquid in the enzyme bath, will sink and pass out through the opening between the bars and into the bottom of the enzyme bath. Once the period in the enzyme bath is completed, the drum can be raised and the carriage 5 is conveyed back to water bath 1. The drum containing the enzyme-treated liver is then submerged once more in the water bath to inactivate the enzyme activity whilst the oil content of the liver is adjusted to the desired level. This is done by adjusting the duration of the after-heating step. The oil which is released is fed continously out from the water bath 1 through the overflow 9 and can thereafter be used as valuable fish oil . When the optional after-heating is completed and the drum raised, the carriage 5 can be conveyed further to the water bath 4. The liver is then emptied out by opening the hatch in the drum's position 16. The liver is cooled in the water bath 4, which functions simultaneously as a buffer and temporary storage for further processing or freezing.

Below are examples which elucidate the present invention.

Example 1

A cylindrical drum (length: 1.5m, diameter: 1.2m) constructed of longitudinal circular bars (diameter: 6mm, space: 3mm) .

^■ Three hundred kilos of fresh liver is supplied through a hatch in the drum. The drum is closed and submerged in a water bath at 95°C so that the entire periphery of the drum is below the level of the liquid. The drum is submerged whilst rotating (2.5 rpm) and is kept submerged for 15 seconds before it is raised and submerged in an enzyme bath. The bath contains 4% cooking salt and a preparation of proteolytic enzymes (0.1 g/1) . The enzyme bath has a temperature of 45°C. The drum is kept submerged for 5 minutes whilst being rotated before it is once more submerged in the hot water bath (95°C) . The drum is kept submerged for 2 minutes before the liver is emptied out of the drum into cold water (<10°C) . This example results in a net treatment time of 7 minutes and 15 seconds.

Example 2

This example corresponds to Example 1 with the following exceptions:

The hot water bath has a temperature of 65°C and the preheating time is 30 seconds. The enzyme bath has a temperature of 40°C and the duration of the enzyme treatment is 10 minutes. The hot water treatment after the enzyme treatment takes place at 65°C for four minutes. This example results in a net treatment time of 14 minutes and 30 seconds.

Example 3

A drum cylindrical or helical in shape (length: 1.5m, diameter: 1.2m) , constructed of longitudinal rough or profiled bars having an opening of preferably 3mm. Three hundred kilos of fish liver is supplied through a hatch. The drum is closed and submerged in a water bath at 57°C, to which 0.06% of a preparation containing proteolytic enzymes (Arozyme) is added. Once submerged, the drum is rotated (4 rpm) and is kept submerged for 80 seconds, which is sufficient to decompose the connective tissue membrane of the liver. During the massage, some of the liver's nematodes, oil and impurities will be released. Once massage has been completed, the drum containing the product is raised and submerged in a liquid bath containing water which has a temperature of +18°C. Once submerged, the drum is caused to rotate (12 rpm) . The drum is kept submerged for 4 minutes before it is raised, and the liver emptied into cold water (<15°C) . This example results in a^' net treatment time of 5 minutes and 20 seconds.

Example 4

This example corresponds to Example 3 with the following exceptions:

The enzyme bath has a temperature of 54°C and the duration of the enzyme treatment is now 130 seconds. After the enzyme treatment, the drum containing the product is submerged in the liquid-filled massage bath which has a temperature of +10°C.

The duration of the massage is now 11 minutes and the rotary speed is 8 rpm. In this example the net treatment time is 13 minutes and 10 seconds.

Claims

P a t e n t c l a i m s

^■ 1 . A method for removing connective tissue membranes and parasites from fish liver, characterised in that the product is subjected to both chemical and mechanical treatment in that it is treated in a drum which is submerged in a liquid bath and is rotated, and when the drum is submerged in the liquid bath the product will float up and be pressed against the drum in such a way that it is subjected to massage, and in that the chemical treatment comprises that the product is first subjected to

A) preheating at 60-100°C in a hot liquid bath to denature the protein structures in the connective tissue membranes and the tissue structure, the product is then transferred to an enzyme bath having temperatures of 40-60°C, containing 0-10% salt, preferably 2-5% salt, and 0.01-1% of an enzyme preparation, preferably 0.02-0.2% of an enzyme preparation containing proteolytic enzymes for 5-10 minutes, and the product may then optionally be after- heated at 60-100°C for 120-240 seconds in a steam bath or a hot liquid bath to inactivate the enzyme activity and reduce the oil content before the product is finally cooled in a cold liquid bath at a temperature of between 0 and 25°C, preferably 0-10°C, or

B) an enzyme solution and ordinary tap water at a temperature of more than 0-90°C, preferably 50-60°C, for 5-300 seconds, preferably 60-130 seconds, containing an enzyme concentration of 0.01-0.5 g/1, preferably 0.01-0.02 g/1, and then transferring the product to a water bath having a temperature of between -2 and 100°C, preferably between 0 and 10°C, for 10-1200 seconds, preferbly 600 seconds, and then the liver in the drum may optionally be placed in a buffer layer for temporary storage, at a temperature of 1-14°C, preferably less than 10°C.

2 .

The method as disclosed in Claim 1, characterised in that the enzyme preparation contains thermostable proteolytic enzymes, hydrolysates and salts.

3.

The method as disclosed in Claim 1, characterised in that adjuvants are added to the buffer to stabilise the liver during storage in a fresh or frozen state and that the buffer functions as intermediate storage.

4.

An apparatus for removing connective tissue membranes and parasites from fish liver, characterised by a rotary drum (3) having an opening (18) for introducing and removing the product, the drum (3) being rotatable and submersible and optionally transferable between one or more baths.

5. An apparatus as disclosed in Claim 4, characterised in that the semi-circular periphery of the drum (3) is constructed having a centre point which results in the drum (3) assuming a helical form and forming a height difference in the joint between the circular and elliptical halves, said difference in height forming a natural carrier which allows gentle and efficient transfer of the product each time the carrier engages the liver which owing to the difference in relative density is kept floating in the drum (3) .

6.

An apparatus as disclosed in Claim 4, characterised in that the drum (3) is cylindrical and is mounted on a carriage (5) which can be moved between the baths.

7.

An apparatus as disclosed in Claim 4, characterised in that the drum (3) is suspended from arms which are moveable between a position where the drum is above the surface of the bath and a position where the drum is wholly or partially submerged in the bath, the arms being moved between their two positions with the aid of one or more hydraulic cylinders.

8.

An apparatus as disclosed in Claim 4, characterised in that the drum (3) is rotatable independent of the position of the arms and is rotated by means of a chain drive (20) .

9.

An apparatus as disclosed in Claim 4, characterised in that the drum (3) is cylindrical and is made of glass-blown tubes having a rough surface or bars lying parallel to one another suitably spaced apart, for example, 3mm from one another, or is made of a perforated material, and is equipped with a hinged or removeable hatch over an opening in the cylindrical wall of the drum.

ιo .

An apparatus as disclosed in Claim 4, characterised in that the temperature in the water bath (1) is regulated by introducing steam through the valve (2) which is operated by compressed air and controlled electronically in connection with a thermosensor, and the liquid level is regulated through the overflow (9) and the water supply (10) .