METHOD FOR ENZYME MATURING OF FISH

Abstract: A method of rapid enzyme maturing of fish, particularly herring, with a suitable salt content for instant consumption, by which the fish is filleted, skinned, trimmed and made open to diffusion by deep-freezing, optionally by salting or vacuum treatment, before, during or after filleting. The fillets are exposed to a brine having a temperature below 10<o> C, preferably below 5<o> C, and having a salt content which will give a salt concentration of from 4 to 8%, preferably 6%, in the finished matured fillet product. The brine further contains from 0 to 8% of sugar, seasonings and other substances that can have an influence on the taste of the products. The enzymes needed for the maturing process are added in the form of viscera, particularly appendixes (Pylorus caecae) in a natural, preferably finely divided form, or in the form of commercially available water soluble proteolytic enzymes or enzyme preparations. When an optimal product quality is obtained, which occurs after a maturing period of from 1 to 5 days, the enzyme activity is disrupted by deep-freezing or chemical inactivation in a manner known per se.

Description: METHOD FOR ENZYME MATURING OF FISH The present invention concerns a method for rapid enzyme maturing of fish, particularly herring, in which the biogchemical reaction conditions in the herring muscle tissue (fillet) is optimized by con¬ trolling the parameters that are vital for the course and speed of the reaction. The methods in use at the present time for the pro¬ duction of fermented fish products such as salted herring and pickled herring are both cumbersome and time consuming, or the additives used in the process are not allowed in accordance with the Food Industry Act. In the conventional and commonly used process for salt maturing of e.g. pickled herring, the usual method consists in cutting off the herring head and then placing the fish in barrels with successive additon of 12 - 15% salt, 0 - 8% sugar, natural mix¬ tures and sometimes saltpetre in order to attain a colour reaction. The salt is used mainly for preservering. The high salt concentration causes the proteins to denaturate with liberation of water. The herring then becomes stiff. In order to obtain a satisfactory consistence and O PI taste, the herring needs a maturing period of 3 to 7 months. During this time the protein molecules are - broken down by enzymes that are present, into water soluble compounds, whereby the smooth consistence and aroma typical for this product is obtained. The salt content of the edible parts of the herring, i.e. the fillet, is in this condition too concen¬ trated for direct consumption. The salt content must, therefore, be reduced by leaching with water to 5 - 8%, preferably 6%, salt in the fillet in order to make it edible. By further processing of pickled herring to e.g. small fillets of pickled herring special attention must be paid to the salt content of the fillet by admixture of salt to the spiced sauce. Further processing of the herring results in large amounts of salty fillet waste. This cannot be used, thus further processing of conventional decapitated pickled herring results in great waste problems. It is well known that enzymes from the herrings vicera and in particular from the appendix are responsible for the biochemical maturing processes occuring in the herring. The rate by which the enzymes break down herring muscle tissue is influenced by several factors, but particularly by the salt content and temperature of the ambient medium. Increased salt content has an inhibitive effect, whereas an increase of tempera¬ ture accelerates the reactions within certain limits. Several methods are previously known for controlling the maturing process of the herring. Thus, from Norwegian Patent No. 131629 a method is known which is characterized by adding to the herring a chemically cleaned and dried enzyme preparation (enzyme concentrate) derived from fish viscera, the added amount of enzyme preparation being 0.1 - 5.0 kg per 100 kg of herring. It is evident that the aim of the invention is to control the maturing process when the raw material is caught during the time of year ' when there is too little enzyme activity in the vicera of the herring to enable a normal maturing. From the description it is also clear that the ma¬ turing is accomplished by using the traditional amounts of salt, sugar and saltpetre. The described method has considerable drawbacks. The process for the production of the enzyme preparation is both complicated and expensive. Besides, no adven- tages are gained in the finished product seen in re¬ lation to products obtained by conventional methods. Thus, the product has to be leached with water before use, and further processing results in the same amounts of waste products. From Norwegian Patent No. 1248811 a method is known for salting and maturing of fish, in which the most important aim is to achieve a product with a salt OMPI content suitable for direct consumption. The invention is charachterized thereby that the maturing takes place in a brine which apart from a salt content of 8 - 20% also contains up to 3% delta-lactone of gluconic acid. The distinct draw¬ back of the method is demonstrated thereby that the addition of delta-lactone of gluconic acid to nutrients is not permitted by the law. It is the object of the present invention to avoid the drawbacks of the conventional methods as well as of the more recent methods of maturing fish, particularly herring. Thus, the objects of the invention are to achieve: - A rational production with a marked reduction of the long maturing period characteristic of both the conventional method and the more recent methods, from a period of up to 7 months to a period of about 24 hours. An improved utiliaztion of the resources by en- abling byproducts such as roe and milt to be used as human food and other wastes to be used as a valuable fodder product, in particular for breed fish. - A direct production of a ready for consumption fillet product having an adequate salt content, which preferably is 6%. - A steady employment in the production, without peaks resulting from seasonal variations in the fishing. - A higher degree of processing of the raw materials for further processing. According to the invention these objects are achieved by there being used as raw material a frozen or salted skinned fillet or similar parts of frozen herring. This implies that byproducts and waste products are removed in a fresh condition before the salting and maturing process is started. Simultaneously the basis is laid for the subsequent high speed process inasmuch as only those parts of the herring which will constitute the finished product, i.e. the fillets, take part in the process. On the basis of the content of water and dry material in the fillets a predetermination is made of the additives required to give the desired degree of maturation, salt content, suger content and spice flavor in the finished matured product. Firstly, this involves that the amounts of enzyme preparation, salt and other substances added to the reaction medium, i.e. the brine, are calculated on the basis of the total water content in herring and brine, the solved substances being evenly distribu- ted in the total amount of water by the time when the quality of the product is optimal and the maturing process is stopped by deep-freezing or in- activation of the enzymes in manner known per se. However, an optimal reaction rate presupposes an optimal diffusion rate for all substances supposed to diffuse into the cellular tissue and take part in the fermenting and flavouring process. These conditions are fulfilled in accordance with the invention by the above-mentioned deep-freezing of the raw material before the process is started and or by use of a high vacuum - at the latest at the time when the fillet is exposed to the brine. Salt saturating can also be used. Thereby, a cell bursting is achieved in the -tissue, and this in¬ creases the diffusion rate considerably. Further¬ more, all physical obstacles to penetration of the substances, such as skin and other membranes, are removed, so that the cleaned fillet is exposed directly to the brine, in which the substances which are to penetrate into the fillet, are supposed to be present in a solved condition or in any other state in which they are easily available, e.g. σolloidally dispersed. The enzyme amount necessary to catalyze the bio¬ chemical degradation processes in the conven- tional method of maturing herring is given by the natural content of digestive enzymes in the herring. These enzymes are found especially in O PI the appendix of the herring of the quality normally used for salted herring and pickled herring and remain in the herring during the salting. This means that the maturing process of the inven¬ tion is catalyzed by the amount of appendix accumu¬ lated during the filleting operation. This amount or a corresponding amount of appendix from other fish can be preserved in a frozen state until required. This amount is then later used in the natural state and in the same porportion as normally found in the herring. Alternatively, corresponding amounts of commercially available protolytic enzymes or enzyme preparations as determined by standard measuring methods can be used. By adding the appendixes directly to the brine in the natural state, preferably in a σolloidally dispersed state or other easily available state, the enzymes are instantly dissolved in the brine. Thus the degradation processes can commence imme¬ diately at the upper surface of the fillets. Simul¬ taneously, however, according to the invention the salt concentration at the upper surface of the fillets will be at a maxium and consequently also the salt denaturation of the proteins. Thereby, the enzyme activity will be slowed down and kept in balance so that the cellular tissue will not decom¬ pose from said upper surface. The surprising effect of the invention is due to the fact that the balance is best achieved with the salt OMPI content in the ambient medium which gives the fi- nished matured fillet product the preferred salt con¬ tent of about 6%. For further control of the rate of the maturing pro- cess and in order to minimize the growth of microor¬ ganisms the temperature of the ambient medium is reduced to less than 10°C, preferably to less than 5°C, before the enzyme preparation is added. Since the salt molecules are smaller than the other molecule disperse and ion disperse substances that are of importance in the process, the former will penetrate into the tissue first, if they are not already existent from before and will gradually denaturate the proteins. Then the much -larger enzyme molecules will penetrate and denaturate the proteins to a sufficient extent to achieve the typical smooth consistence and aroma. In this way the balance between the denaturating effect of the electrolytes on the proteins and the solubilizing effect of the enzymes on said proteins is maintained throughout the fillets during the maturation period. Simultaneously, also a biological balance is main¬ tained. The electrolyte concentration is not suffi- ciently high to prevent growth of microorganisms, but in combination with the low temperature needed to control the enzyme activity, growth of unwanted mircroorganisms is kept down during the short matu¬ ration period of 1 - 5 days. The particular fact that salt as described penetrates into the fillet OMPI and denaturates the proteins before the larger enzyme molecules can do it, implies that, according to the invention and as already mentioned, there may be used a salt preserved, but non-matured raw material. The salt content in the fillet at the beginning of the process is higher than at the end of the pro¬ cess, since all soluble substances are then.evenly distributed in the water. In accordance with the in- vention the total salt content in the total amount of water present is a decisive factor for the end re¬ sult. The risk of uneven maturing can be avoided by keep¬ ing the temperature of the ambient medium suffici- ently low to substantially slow down the degradation process or to stop them until the salt content, the water content and the enzyme concentration are evened out, whereupon the temperature is raised, and the bio¬ chemical changes occur as prescribed. The following example illustrates a typical practical embodiment of the method of the invention:- 10 kg of frozen skinned fillet of herring con¬ taining 60% water was added to a brine con¬ taining 600 g of defrozen and finely divided Pylorus caecea (appendixes) having been removed from the herring after filleting and frozen. 1600 g of salt, 800 g of sugar and seasoning ex¬ tracts in 10 liters of water had previously been dissolved in the brine. After standing for 5 days at 3°C the herring was fully matured and had a smooth consistence and a good aroma. The fillets of pickled herring were frozen and were later tested " by "Hermetikkindustriens Kontrollinstitutt" (The Control Institute for the Canning Industry) in the town of Stavanger, and were rated as "good products". Due to the low salt content of 5,9%, the herring was later classified as "well suited for direct con¬ sumption". The same test has been repeated a number of times both with natural and finely divided Pylorus cacea from various sorts of fish, and even with commer¬ cially available proteolytic enzyme preparations. The enzyme concentration and temperature of the am¬ bient medium influence the maturing period within certain limits. A maturing period down to 24 hours has been achieved for salted herring, by optimizing these parameters. The enzyme quality used is significant to some extent for the sort of taste to be achieved, but that para- meter is not critical for the practical use of the invention. OMPI

Claims: Patent claims 1. A method of enzyme maturing of fish, particularly herring, characterized by making the cellular tissue of the fish open to diffusion by freezing, vacuum treatment, salting and removal of body parts, preferably to form a trimmed and skinned fillet; adding to the fish an amount of salt and sugar to give from 4 to 8%, preferably 6%, of salt and from 0 to 8% of sugar in the muscle tissue of the fillets, based on a presumed even distribution thereof in the total amount of water in muslce tissue and brine; adding to the fillets the enzymes needed for the maturing process in the form of viscera, particularly appendixes (Pylorus caecae) in a natural, preferably finely divided form, or in the form of commercially available water soluble proteolytic enzymes or enzyme preparations; adding other substances assumed to penetrate into the cellular tissue, such as spices, in a solved or easily soluble form; and maintaining the temperature between 1.00 CC aanndd tthhee ffrreeeezziinngg point of the cryohydrate >f the aqueous phase. 2. A method according to claim 1, characterized by maintianing the temperature of fish and brine at a low level at which the enzyme quality, as long as the diffusion of substances that are important to the maturing process is taking place; then in¬ creasing the temperature to any desired level at which the enzymes present are capable of cata- - Ε E lyzing the hydrolysis process - according to their specific activities and a rate depending on the temperature selected - to the extent re¬ quired to obtain the desired product quality; and then disrupting the enzyme activity. 3. A method according to claim 1 or 2, characterized by disrupting the enzyme activity by deep¬ freezing or chemical inactivation in a manner known per se. 4. A method according to claim 1, characterized in that the viscera from the filleting of herring or other fish, particularly the appendixes, are used directly, in untreated or finely divided form, or are preserved by deep-freezing or in any other suitable manner until needed.

Inventors: OPSHAUG KJELL ROLF
Applicants: OPSHAUG KJELL ROLF
Application year: 1982
Main classification: A23B4
IPC codes: A23B4, A23L1