WO1991001089A1

WO1991001089A1 - De-bacterialized fish and improved method for the production of same

Info

Publication number: WO1991001089A1
Application number: PCT/NO1990/000120
Authority: WO
Inventors: Bjørn HENRIKSEN; Johann Olafsson
Original assignee: Henriksen Bjoern; Johann Olafsson
Priority date: 1989-07-17
Filing date: 1990-07-17
Publication date: 1991-02-07
Also published as: EP0483231A1; IS3604A7; AU6048890A; CA2063706A1; JPH05503416A

Abstract

This invention is a method for obtaining a considerable increase in the storage life of raw produce such as fish, shellfish and meat without the addition of preservatives. The raw produce (fish fillet) is immersed in a flavoured solution containing salt or other spices or spice mixture. In two opposing walls of the tub are placed a pair of electromagnets to which a chopped DC-voltage is applied. The fillet is then rinsed in well circulating water and is air-dried in a special room. The fillet is vacuumized and heated up to between 80 and 90 °C and maintained at this temperature for a period of time varying between 10 to 145 minutes according to the type of raw produce. The fillet is then refrigerated to a temperature below 5 °C.

Description

DE-BACTERIA IZED FISH AND IMPROVED METHOD FOR THE PRODUCTION OF SAME

The invention relates to a method consisting of pre- and post-treatment of vacuum-packed fish, shellfish and meat with an aim to increase storage life consi¬ derably and to preserve all the natural nutrients and fatty substances intact.

Throughout the ages long-term storage of foodstuffs has preoccupied mankind for simple reasons of survival, and out of the need to store large catches and crops of various foodstuffs so as to portion these out over a certain period of time. It is necessary to have a ready supply of food in store for the seasons when such foodstuffs cannot be fished, hunted or harvested. One of the problems of long-term storage of foodstuffs is the loss of quality related to the storage time. This is particularly relevant as regards long-term storage of fresh fish, shellfish and meat. Numerous methods are used to increase the storage life of foodstuffs, for example frying, boiling, curing, chemical additives, refrigeration, deep-freezing, radiation treatment, etc.

Many such converting methods alter the consistency of the raw produce to a state which is no longer raw. This will therefore limit the variations available when preparing the produce for a meal. (A boiled fish can no longer be fried, and vice versa). Chemical additives and radiation treatment may have adverse effects on the produce, and the produce's smell, taste and consistency will no longer have the qualities expected from the raw produce. Many preserving methods are such that the nature of the raw produce's quality will be altered.

Suppliers and consumers wish for a considerably longer storage life for raw produce without this affecting the taste, smell and nutritive value of the produce, that is to say its quality. The use of chemical additives to prolong storage life being a health hazard, such methods cannot be considered as a valid alternative in this case. Prolonging storage life will have major economic benefits as regards wastage, sales price and profitability.

Use of the method here disclosed for preserving raw fish, shellfish and meat gives a storage life which is 2 to 3 times longer than that obtained by today's known methods. An increase in storage life is achieved without the addition of chemicals or the use of radiation, and without any other prerequisite than low temperature for storage of the product.

The aim is achieved by starting with raw produce of the highest quality. The raw produce is_vacuum packed, then the package is heated up to a temperature necessary to kill the bacteria which may induce deterioration of the produce.

The details of the method will appear from the description which follows. In the following description of the method for long-term converting of fresh foodstuffs, a raw fish fillet is used as an example, but the method gives good results if applied to larger pieces of fish, shellfish or meat. Application of the method on the fish fillet involves the following process:

1) The cell walls in the flesh of the fish are altered so as to prevent penetration of decay- generating bacteria into the cell.

2) The structure of the enzymes inside the cell is altered so that the cell itself is prevented from initiating self-destructive activity. The clean-cut fish fillet arrives from the inspection table on a conveyor belt and is immersed for 10 to 30 minutes into a subcooled flavoured fluid consisting of a saturated spice solution. This may be sea salt, mineral salt (calcium chloride), spice salt, sugar- salt, a herb mixture, etc. The purpose of thi£ is to provide the fish fillet with a flavour additive, to provide the basis for an irreversible alteration of the cell walls (sealing), and to alter the enzyme structure so as to prevent decay inside the cells. To initiate this structure-altering process, a chopped DC-voltage is applied to a set of electromagnets placed in two opposing vertical walls of the tub of flavoured solution. This voltage is applied to the flavoured solution for up to 4 minutes. The chopped frequency can be altered, which means that treatment can be suited to various types of produce such as fish, meat, etc. to obtain the best possible results. This treatment of the fish while in the electrolytic solution alters the trace elements in the cell so that enzyme activity which generates decay in the fish is brought to a halt. In addition, the electrolytic treatment modifies the salts in the flavoured solution so that the external trace elements will also inhibit decay- initiating enzyme activity inside the cells. Combined with the osmotic balance between the solution and the cell structure, the voltage applied also causes desirable alterations in the fish fillet and inhibits penetration of the cell wall. (A beneficial side effect is the destruction of a number of bacteria on the fish fillet surface).

This is of decisive importance for the preserving process. If the salt flavour is to be reduced to a minimum or totally removed, the fish fillet may be flushed in distilled water after leaving the flavoured electrolytic solution. After they have been taken up from the flavoured electrolytic solution, the fish fillets are drained and air-dried in a closed room before being packed in plastic bags, and the packs are vacuumized individually or collectively. The fish fillets are vacuumized at 7 kg vacuum pressure minimum. This will prevent the growth of aerobic bacteria (bacteria which need oxygen to survive) and will also maintain enzyme inhibition. Vacuumization also contributes to stabilizing the product. The vacuumized fish fillets are then heated up to a temperature of between 80 and 90°C. The length of treatment may vary from 10 minutes to 2 hours and 25 minutes according to the type of raw produce used. The heat treatment (converting process) also deprives anaerobic bacteria (those which can survive without oxygen) of their basis for growth.

Traditional boiling or poaching of fresh fish fillets causes the cells to burst and the flesh of the fish becomes an easier target for bacteria. This form of heat treatment does not make the cells burst and the bacteria are not only destroyed, but also lose a great deal of their basis for growth. The heating process may be slow or rapid.

When the desired temperature within the interval mentioned has been obtained, it is maintained constant for a certain period of time. The time and temperature will depend on the raw produce, its shape, size, the type of fish and fat contents, etc. For example, the optimal temperature for salmon is 84°C for 17 minutes. The example is given for a 300-gram piece of skinned and boned salmon fillet.

Enzyme activity in the fish fillet has now ceased, oxidation has been prevented and the fish fillet has been de-bacterialized. All decay-initiating activity has thus been brought to a halt. When the ^ ;t treatment process is over, the fish fillets are refrigerated to a temperature below 5°C.

After this treatment, the fish fillets are neither raw nor boiled in consistency. However, their taste, smell and consistency will appear as those of readily eatable raw produce. The nutrient contents is also that of raw fish.

The finished product will have a storage life of at least 12 weeks in refrigerated storage. The product may be warmed up, fried, grilled, baked in a crust, coated in bread crumbs, marinated, deep-fried, or prepared in a microwave oven. The product may also be eaten cold straight out of the pack. If the pack is warmed up unopened, the product will taste like freshly boiled fish.

Claims

C L A I M S

1. An improved method for de-bacterializing raw fish, shellfish and meat (raw produce) c h a r a c t e r i z e d in that the raw produce is immersed in a flavoured solution consisting of a saturated salt and/or spice solution, remains in said solution for a period of time between 10 and 30 minutes where it is subjected to the influence of electromagnets placed on two walls of the tub when to said electromagnets is applied a chopped DC- voltage for 4 minutes of the immersion time, after which the raw produce is removed from the solution and drained and air-dried in a closed room, then hermetically packed in an gas and fluid-tight package, vacuumized and heated up to a temperature in a range of 80 to 90"C and is maintained at that temperature for a period of time between 10 and 145 minutes, and is thereafter refrigerated to a temperature below 5°C.

2. An improved method for de-bacterializing raw fish, shellfish and meat in accordance with claim 1 c h a r a c t e r i z e d in that the flavoured solution contains one or several of such substances as sea salt, herb mixture, mineral salt (calcium chloride), herb salt, sugar salt, etc.

3. An improved method of the previous claims c h a r a c t e r i z e d in that flavouring substances may be added to the raw produce in any known manner during the smoke-curing process, after immersion in the flavoured solution but before packaging.