Technical Field : The invention refers to an improved composition of Surimi, a frozen marine product having enhanced gel strength and water holding capacity. The invention also refers to an improved process for preparing surimi having enhanced gel strength and water holding capacity.

Background and Prior art : Surimi is a frozen marine product, the consumption of which was erstwhile restricted to Japan and other far eastern societies but is now spreading and gaining popularity across the globe. Surimi is a frozen paste consisting of concentrated myofibrillar proteins of fish, protected using appropriate cryoprotectants. Surimi is a raw material in oriental marine food industries where it is utilised for conversion into products such as Kamobako, a steamed preparation. Important attributes that contribute to the superior quality of Surimi are its gel strength, water holding capacity and whiteness. These qualities have a bearing on the taste and texture of the final products made from surimi.

Surimi is produced as a result of mechanical separation of bones and skin of fish to produce a minced meat which is further processed to remove fats and water soluble substances and then subjected to cryoprotection treatment and frozen.

Surimi is generally produced by heading and gutting of the captured fish followed by mechanical descaling and deboning leading to the formation of minced meat.

The separated minced meat is subjected to a series of leaching treatments under agitation with water in special leaching tanks, during which the soluble proteins

leach out into the water. At intervals, the leaching mix is permitted to stand for dewatering and decantation of floating fats to separate the insoluble white myofrillar proteins. Cryoprotectants are added and the resultant meat is passed through a refining screen, extruded into slabs which are then frozen. This frozen meat is called surimi.

An alternative process described in WO 9911656 refers to pulverising the entire body of the captured or frozen fish followed by treating it with an acid to bring its pH down to less than 3. 0 in order to dissolve the proteins. The insoluble material and fat are separated and the solublised proteins are re-precipitated by alkali treatment and dewatered. The protein thus obtained is cryoprotected, extruded and frozen to obtain surimi.

Maintaining the superior quality of Surimi has a very important business impact as it has a significant relation to the selling price. Trawlers with on board processing facilities for surimi production are employed but with the increasing demand for the material this process is proving inadequate. Loss in freshness of the marine product leads to loss in quality of the final product. Other major factors contributing to the quality of surimi are varietal differences, delay between catching and processing, unhygienic storage and transportation and also high protease activity during storage after capture and before processing.

Ground fish meat bleached in presence of inorganic salts such as sodium chloride and simultaneously forcibly stirred are known to retain the high quality of surimi even when it has been processed from not so fresh fish meat (US 5229151). Use of transglutaminase to enhance the gel strength of surimi has been widely explored. The enzyme transglutaminase promotes cross-linking of peptide chains through the formation of epsilon-lysine bonds (Ajinomoto product literature). The addition of transglutaminase to surimi which has been shown to improve the gel strength of kamobako, a product made by cooking surimi. A number of workers have used starches and other polymers such as chitosan and polymannosylated cystatin to improve gel strength.

The above mentioned approaches have all been directed towards increasing the gel strength of surimi and do not address the property of water holding capacity of the product.

In order to increase the water holding capacity the following approaches have been taken. Yamazawa M (1991, Nippon Suisan Gakkashi, 55, (5), p 965-970) has referred to improvement of both the gel strength and water holding capacity of surimi using different types of starches. However, the amount of starch used is significantly high and replaces, a significant quantity of protein in surimi, thereby leading to a lower effective concentration of protein.

The present invention involves the use of a synergistic combination of small quantities of enzyme and polymer during the processing to give a high gel strength and enhanced water holding capacity to the Surimi obtained.

Thus, surimi that has both enhanced gel strength and water holding capacity can be obtained by using a combination of transglutaminase and use of glycol polymers during the processing of surimi..

Definition of the invention : Accordingly, the present invention provides an improved process of preparation of surimi to provide enhanced gel strength and water holding capacity to products obtained therefrom comprising : i. Separation of the protein fraction from aquatic animals ; ii. treating the protein fraction of the meat either simultaneously or sequentially in any order with transglutaminase and at least one water soluble synthetic polymer with a molecular weight of 200 to 20, 000 daltons.

According to a preferred aspect, the present invention provides an improved process of preparation of sunmi to provide enhanced gel strength and water holding capacity to products obtained therefrom comprising : i. Separation of the protein fraction from aquatic animals selected from fish, crabs, squids etc. ;

ii. treating the protein fraction of the meat either simultaneously or sequentially in any order with transglutaminase and at least one water soluble synthetic polymer with a molecular weight of 200 to 20, 000 daltons.

According to a more preferred aspect the present invention provides an improved process of preparation of surimi to provide enhanced gel strength and water holding capacity to products obtained therefrom comprising : i. Separation of the protein fraction from aquatic animals selected from fish, crabs, squids etc. ; ii. treating the protein fraction of the dewatered meat either simultaneously or sequentially in any order with 0. 2 to 20 units transglutaminase by % weight of the protein fraction and at least one water soluble polymer with a molecular weight of 2000 to 10, 000 daltons.

The protein fraction mentioned above refers to preferably fish meat that is devoid of skin, scales, membranes, bones, head, gut and fat.

Detailed description of the invention : The essential aspect of the invention is to produce surimi that is capable of providing an enhanced gel strength and water holding capacity to the products prepared therefrom. Surimi that is produced by treating protein fraction of the meat from aquatic animals after dewatering the same with transglutaminase and at least one water soluble synthetic polymer with a molecular weight 200 to 20, 000, that are essentially food grade has the ability to enhance the gel strength and water holding capacity of the products such as kamobako produced from it.

The following two processes are employed for the production of surimi.

Surimi is conventionally produced by heading and gutting of the captured fish followed by mechanical descaling and deboning leading to the formation of minced meat. The separated minced meat is subjected to a series of leaching treatments under agitation with water in special leaching tanks, during which the soluble proteins leach out into the water. At intervals the leaching mix is permitted to stand for dewatering and decantation of floating fats to separate the insoluble white myofibrillar proteins. Cryoprotectants are added and the resultant meat is passed through refining screen, extruded into slabs which are then frozen. This frozen meat is called surimi.

An alternative process refers to pulverising the entire body of the captured or frozen fish followed by treating it with an acid to bring its pH down to less than 3. 0 in order to dissolve the proteins. The insoluble material and fat are separated and the solublised proteins are re-precipitated by alkali treatment and dewatered.

The protein thus obtained is cryoprotected, extruded and frozen to obtain surimi.

The aquatic animais used for the production of surimi may be selected from fresh water or marine sources. They are generally edible fishes and other organisms

such as crabs, squids, including dark and fatty fishes. The preferred sources of fishes will however be from marine origin. The fishes generally belong to the genera Nemopterus, Johnius, Trichiurus, Theragra, Sphyraena and any other edible fish.

Transglutaminase may be obtained from any commercial source and is added at 0. 2 to 20 units transglutaminase by % weight of the protein fraction. The level of transglutaminase is preferably 1 to 10 units by % weight of the protein fraction.

One enzyme'unit'refers to 1amol of product produced per minute of reaction time.

The water soluble synthetic polymers may have a molecular weight in the range of 200-20, 000 daltons and preferably 2000-10, 000 daltons. The water soluble synthetic polymers are essentially food grade and may be selected from one or more of polyethers such as poly ethylene glycol, poly propylene glycol and others such as poly vinyl alcohol, polyvinyl pyrrolidone or a mixture thereof. The polymer is at a concentration of 0. 02 to 5% by weight of the protein fraction and is preferably at 0. 1 to 1 % by weight.

For the treatment of the protein fraction with transglutaminase and the polymer the dewatered protein fraction is selected. The protein fraction may be cryoprotected or not. The treatment of transglutaminase and the water soluble polymer is given simultaneously or sequentially in any order but is essentially

prior to the conversion of surimi into its final cooked product form such as kamobako. The temperature of treatment may range from 5-50°C. It is especially preferable to treat the protein fraction with transglutaminase and the polyether while treating the fraction with the cryoprotectants. For best results it is ensured that the transglutaminase and the polymer is blended thoroughly with the protein fraction irrespective of the stage of addition.

The surimi produced is used for making end products such as kamobako, tempura, fsh balls, fish fngers, crabsticks. It is possible to flavour the base product surimi with different flavours and shape it to desired forms.

The invention will be now be illustrated with respect to the following non-limiting examples.

Examples : Example 1 : Demonstration of the effect of transqlutaminase and Polymer : Surimi obtained from Nemopterus japonicus (Rani fish) processed by the conventional method of deheading and gutting, followed by leaching, refining, cryoprotecting and freezing was used to demonstrate the invention. One of the best grades of surimi (Control SSA) was used for comparison without giving any treatment. The other treatment procedure was as follows. 1. 5 kg of thawed surimi was taken in a laboratory mixer and 45g of sodium chloride was added to it as per the conventional requirements in making kamobako. The control (Control A) was kept untreated and transglutaminase (TG) and polyethylene glycol (PEG) individually and in combination were added at 3g each. The material was continuously mixed for 13 minutes. Part of the material was extruded into sealed sausages in a plastic film and they were cooked at 90°C for 40 minutes. To the rest of the material 20% by weight water was added and mixed for 3 minutes and this was extruded into sealed sausages in a plastic film and they were cooked at 90°C for 40 minutes. These sausages were used to determine the gel strength and water holding capacity.

The gel strength measurement : The sausages prepared as above were stored at 20oC for 15 hours. The control, and the treated sausages were kept in a metal die that permitted cutting cylindrical sections of the sausage. The penetrometer (Rheotex, Japan), was used to measure the el strength by determining the force (g. cm) required to break the surface of the sections. The material described above where 20% more water was incorporated was also measured for gel strength which would correlate with its water holding capacity.

Table 1

Treatment Normal + water (gem) (9. cm) Control A 420. 2 160. 0 Con 1 351. 50. 0 Control A + 0. 2% TG 705. 0 306. 0 Control A + 0.2% TG + 0.2% PEG 656.7 418. 7 Control SSA810. 3385. 0 The data presented in Table 1 show that although transglutaminase has the ability to improve the gel strength it is essential to use a combination of transglutaminase and polyethylene glycol to enhance both gel strength and water holding capacity. With regard to enhancing both gel strength and water holding capacity the combination of transglutaminase and polyethylene glycol is superior to even the best commercial control.

Example 2 : Effect of different molecular weight of the polymer : Following the procedure described in Example 1 the effect of various molecular weight of the polymer e. g. polyethylene glycol 400 daltons (PEG-400) and polyethylene glycol 20, 000 daltons (PEG-20, 000) was assessed for their effect on increasing gel strength and water holding capacity. Another polymer like polypropylene glycol (PPG) with a molecular weight 6000 daltons, was also tested. The corresponding controls as mentioned in Example 1, the untreated (Control A) and one of the best grades of surimi (Control SSA) were maintained for comparison and the data are presented in Table 2.

Table 2

Treatment Normal + 20% water (g.cm) (g.cm) Control A 647.5 399.0 Control + TG 942. 9 643. 9 Control + PEG-400646. 0454. 0 Control A + TG + PEG-400 1164.0 695. 0 Control A + PEG-20, 000 7316 418. 8 Control A + TG + PEG-20, 0001044. 9809. 0 Control A + PPG 731.6 419. 0 Control A + TG + PPG 1023.6 655. 0 Contro ! SSA766. 0471. 0

The data presented in Table 2 show that other polymers like polypropylene glycol are also useful in improving both gel strength and water holding capacity. The polymers with a range of molecular weights also exhibit this property.

Accordingly, the invention provides an improved surimi having enhanced gel strength and water holding capacity obtained by the incorporation of the synergistic combination the enzyme transglutaminase along with a food grade synthetic water soluble polymer during the processing.