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Title:
METHOD OF DRYING PORTION PIECES OF FISH AND MEAT PRODUCTS
Document Type and Number:
WIPO Patent Application WO/2006/068499
Kind Code:
A1
Abstract:
Method for drying of entire portion pieces of fish or meat or portion pieces of minced fish or forcemeat. The portion pieces are dried in at least one first step at atmospheric pressure and a first temperature lower than the initial freezing point of the product from a first water content typically in the range 75-85 % to a second water content typically in the range 25-40 %. Thereafter the portion pieces are dried in a consecutive step at atmospheric pressure and a temperature above the freezing point to a third water content that is typically lower than 20 %.

Inventors:
STROEMMEN INGVALD (NO)
GRANDE ANETT SPANGELO (NO)
EIKEVIK TRYGVE M (NO)
CLAUSSEN INGRID CAMILLA (NO)
JONASSEN OLA (NO)
MAGNUSSEN OLA M (NO)
GULLSVAAG PER EGIL (NO)
ALVES-FILHO ODILIO (NO)
Application Number:
PCT/NO2005/000473
Publication Date:
June 29, 2006
Filing Date:
December 22, 2005
Export Citation:
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Assignee:
NTNU TECHNOLOGY TRANSFER AS (NO)
STROEMMEN INGVALD (NO)
GRANDE ANETT SPANGELO (NO)
EIKEVIK TRYGVE M (NO)
CLAUSSEN INGRID CAMILLA (NO)
JONASSEN OLA (NO)
MAGNUSSEN OLA M (NO)
GULLSVAAG PER EGIL (NO)
ALVES-FILHO ODILIO (NO)
International Classes:
A23B4/03; A23B4/037; A23L3/40; F26B7/00; F26B21/10
Other References:
DATABASE WPI Week 200259, Derwent World Patents Index; Class D13, AN 2002-552035
Attorney, Agent or Firm:
FLUGE & OMBAL (Fredrikstad, NO)
Download PDF:
Claims:
Claims
1. Method for drying whole portion pieces offish or meat or portion pieces of minced fish or forcemeat, characterized in that the portion pieces are dried in at least one first drying step at atmospheric pressure and a first temperature lower than the initial freezing point from a first water content to a second water content and in at least one consecutive drying step at atmospheric pressure and a second temperature higher than the freezing point dried to a third water content.
2. Method as claimed in claim 1 , characterized in that the drying is conducted in one drying step at a temperature below 0 0C and one drying step at a temperature above 0 0C, that the first water content is a water content between 70 and 90 %, that the second water content is a water content between 20 and 60 % and that the final water content is a water content lower than 20 %.
3. Method as claimed in claim 1 or 2, characterized in that the first drying step is conducted in a tunnel dryer.
4. Method as claimed in any one of claims 1 3, characterized in that the first drying temperature is in the range 2 to 10 0C, preferably about 5 0C.
5. Method as claimed in any one of claims 1 4, characterized in that the second drying temperature is in the range 15 to 30 0C, preferably about 20 0C.
6. Method as claimed in any one of claims 1 5, characterized in that the first water content is about 7585 %.
7. Method as claimed in any one of claims 1 6, characterized in that the second water content is about 2540 %.
8. Method as claimed in any one of claims 1 7, characterized in that the third and final water content is in the range 515 %, preferably in the range 812 %.
9. Method as claimed in any one of claims 1 8, characterized in that the drying is conducted with air that enters the drying zone with a moisture content in the range 3050 %.
10. Method as claimed in any one of claims 1 9, characterized in that the portion pieces typically have dimensions in the range 7090 mm x 5070 mm x 520 mm.
11. Method as claimed in claim 1, characterized in that the entire drying process is conducted in a tunnel dryer with a continuous or step by step increasing temperature, the temperature being lower than the freezing point of the product for a period in the range 65 to 90 % of the drying time, more preferred for a period in the range 75 to 88 % of the drying time.
12. Method as claimed in claim 1, characterized in that the entire drying process is conducted in a belt dryer with a continuous or step by step increasing temperature, the temperature being lower than the freezing point of the product for a period in the range 65 to 90 % of the drying time, more preferred for a period in the range 75 to 88 % of the drying time.
13. Method as claimed in claim 11 or 12, characterized in that the temperature is increased step by step in 212 steps, more preferred in 28 steps.
Description:
Method of drying portion pieces of fish and meat products

The present invention concerns a method of drying whole portion pieces offish or meat or portion pieces of minced fish or forcemeat.

Background An increasing time pressure in modern society has changed peoples life and meal habits.

Contemporaiy consumers request food of a high quality and a short preparation time. This change in lifestyle has lead to an increasing demand for instant products.

Split cod is a 500 year old tradition. The present manufacture of split cod involves a number of steps. Fresh fish with a water content of 80 % are firstly salted. After the salting process that takes a few weeks the water content is reduced to about 55 %. The fish are thereafter transported to a drying plant and left for drying until a water content of about 40-45 % is reached. Thereafter a dilution process requiring 1-2 days takes place. All in all this is a time consuming and expensive process and therefore a production line that is simpler and less time consuming has been developed and the usefulness of the product has simultaneously increased. Stockfish is produced according to the old natural method. Cleaned (gutted) fish with heads removed are suspended on fish flakes for two months until the water content is about 15 %. Particularly stockfish has a varying quality due to variations in the weather.

Among the more modern methods could be mentioned that it is generally known to freeze-dry foodstuffs to obtain a better quality than with other drying methods and a more rapid processing than with traditional preparation of split cod and stockfish. As far as the inventors know there has never been developed a method to dry entire portion pieces offish or meat while preserving a quality that is close to the quality of their fresh equivalents.

Objective

It is thus an objective of the present invention to provide a method of drying products offish, meat, minced fish or forcemeat in the form of entire portion pieces, which yields products of a high quality that can rapidly be rehydrated.

It is furthermore an objective to provide a method as mentioned above which may be conducted with inexpensive means within a comparatively short period of time.

It is still further an objective to provide a method as defined above to prepare food products which, when employing relevant fresh food, may be used instead of stockfish or split cod in traditional courses or as substitution for fresh food, said products having long shelf life at room temperatures when conveniently packed.

The invention

The above mentioned objects are fulfilled by the method according to the present invention as defined by claim 1.

Preferred embodiments of the invention are disclosed by the dependent claims. According to the method of the present invention portion pieces offish or meat or portion pieces of minced fish or forcemeat are dried in two consecutive steps of which the first takes place at a temperature lower than the initial freezing point. The raw material is fresh or frozen foodstuff which is divided into pieces of a size suitable to be served. It is convenient to use pieces of a mainly uniform size since the process thus may be adapted with respect to retention time to ensure an optimal quality of the product.

The term "portion pieces" is not a clear scientific denotation, and as used herein it is meant to cover portion pieces that are typically put on a plate and served ready to eat. To fit the definition of portion piece the largest dimension should have a size of at least 40 mm and a ratio between the largest and the smallest dimension of at least 2:1. More typically portion pieces have a length in the range 70-90 mm, a width in the range 50-70 mm and a thickness in the range 5-20 mm. The size may, however, vary significantly and portion pieces of meat will often be quite thin while portion pieces offish, minced fish and forcemeat will generally be thicker. It should be emphasized that though portion pieces, such as fish fillets, often have an accurately rectangular shape the portion pieces according to the invention may as well have an oval cross-sectional shape or other cross- sectional shapes.

Different types of equipment may be used for conducting the method of the present invention but the simplest end therefore preferred method comprises use of a tunnel dryer with two or more separate chambers or zones. Another preferred embodiment involves use of a so-called belt dryer that e.g. may be arranged in a spiral or helically. It is not required with a complete isolation between the zones, it is sufficient that different zones or chambers may be operated separately with individually controlled temperature. It is thus applicable to use a tunnel dryer with a number of separate chambers separated from each adjacent chamber with whole or partial partition walls that allow "wagons" or a belt with portion pieces of raw material to pass through. The temperature can typically increase stepwise from chamber to chamber in the direction of the movement of the portion pieces through the dryer. If there as an example is 10 different chambers, a number of e.g. eight chambers may be operated at a temperature below the freezing point and two chambers at a temperature above the freezing point. An important aspect of the last chamber is to obtain a comparatively effective final frying of the product and the temperature should therefore be significantly higher than the freezing point in at least this particular chamber. The relative humidity in the dryer will also be able to affect the quality of the product as well ass the economy of the process. A convenient relative humidity for the entering air to the dryer is 30-50 %.

According to the present invention there is no need for vacuum or reduced pressure in any stage of the process. To the contrary it is preferred that the entire process takes place at ambient pressure.

In at least one step below the freezing point and preferably in the temperature range from -2 to - 10 0 C, such as about -5 0 C, an initial drying is conducted. When portion pieces enters this stage of the dryer they have a water content that is typical of the fresh product. The water content at this stage is typically between 70 and 90 % and more typically between 75 and 85 %.

When the portion pieces have been subjected to drying in one or a plural of such steps below the freezing point, the portion pieces will have a water content in the range 20-60 % and more preferred in the range 25-40 %. The portion pieces are then immediately conveyed to the next process stage which involves drying in one or a number of steps above the freezing point. The temperature in this zone will be in the range 15-30 0 C and more preferred about 20 0 C. While some products may well tolerate a temperature close to 30 0 C without experiencing a quality loss, other product need to be kept around 2O 0 C to maintain a good quality.

The product is dried to a final water content chosen with respect to a combination of economy and shelf life for the product. Generally, the lower the water content the better the shelf life of the product. The final water content will normally be lower than 20 %, more preferred in the range 5- 15 % and most preferred in the range 8-12 %.

Below the process is described in further detail with reference to he accompanying drawings, where: Figure 1 is a plot of rehydration data for a product dried in accordance with the present invention compared with a product dried above the freezing point,

Figure 2 is a bar chart of colour measurement of the product dried in accordance with the invention, compared with a product dried above the freezing point and with stockfish, and Figure 3 is a plot of not denatured protein in a product dried in accordance with the invention compared with a product dried above the freezing point.

Portion pieces of fresh fish are placed on a grating or a tray on wagons and conveyed into the drying chamber. The drying plant comprises a drying tunnel where the drying air in the first step is -5 0 C and in the second step is +20 0 C. The chambers are separated by a lock in order to maintain the different temperatures in the zones. The wagons with the fish pieces will have longer retention time in the chamber with the lower temperature. With a size of 80x65x10 mm the pieces will typically have a retention time in the cold chamber of about 4 days and in the chamber with the higher temperature of about 12 hours. In the first of these chambers the products typically are dried from about 80 % to 25-40 % water content. The drying are conducted at atmospheric pressure in both chambers. The wagons are moving through the chamber b means of suitable conveyance means such as rails or a belt. The conveyance speed in the cold chamber is adjusted so as to reach a desired water content before being transferred to the warmer chamber, e.g. a water content between 25 and

40 %. This is determined empirically for the products in question and the size of the portion pieces in question.

After completed drying the products will be porous and easily rehydratable. The products therefore should be packed in airtight packaging to avoid undesired rehydration in air. Conveniently packed the product may be stored at room temperature for several months without noticeable deterioration.

The end product is unique with respect to the ease with which it may be rehydrated in water. It is an instant fish product that needs very short time for rehydration, typically less than 3 minutes.

Examples

Experiments have been performed with fish (cod) as the raw material. In addition to a subjective assessment of the quality of the end product we have investigated the (re)hydratability of the product, its colour change and its protein content.

Rehvdratabilitv

The rehydratability of a product is a measure of how much water the product is able to absorb and thereby swell. The formula below shows the mathematical calculation of the rehydratability:

r β = -^"100% m ts r a - rehydratability [%] m w = water content in the product after reliydration fg] m ts = weight of dry substance in the product [g]

In order to draw a parallel to the original product water content, it should be emphasized that a rehydratability of 300 % corresponds to a water content of 75 % in the product (3 parts of water per 1 part of dry substance).

The pieces were weighed prior to rehydration while the dry substance is known from the drying graph. A box was filled with cold water and the portion pieces were placed in the water for different periods of time. Pieces were removed after 30 s, 1 min., 2. mins., 3 mins., 10 mins., and 20 mins. Based on the weight change the rehydratability was calculated and the rehydration graph was established. The graph is shown in Figure 1.

As shown by Fig. 1 already in 30 seconds the product has taken up a lot of water. The graph is very steep and flattens off rapidly. Already after 1 minute the rehydration graph is beyond 300%, which means that the product contains more than 75 % water. The graph shows that the product has "instant" properties and is completely rehydrated in less than 3 minutes. The properties of the comparison product are not even close to this and is only rehydratable to an extent of 50%, i.e. two parts of dry substance per one part of water.

Colour measurements

The colour of the product is seen as an important quality parameter. This is a parameter that often changes during storing and processing. The colour is important for the acceptability among consumers. The measurement apparatus used is an X-Rite ® 948 colour measurement instrument. This instrument converts colour nuances to a numeric system. The system used is Judd Hunters L*a*b- system. This is a three dimensional system in which L represents a value for lightness from 0 to 100 where 0 is darkest (black), the a value defines the position along a red-green colour axis and the b value defines the position along a yellow-blue colour axis. Four measurements were made of each piece offish and the result is given as an average of these four. Figure 2 shows colour measurements for pieces of fish dried at 20 0 C and -5 0 C. The L value increases with a drying temperature of -5 0 C compared to 20 0 C. The values of b and a decreases.

As shown by Figure 2 the product dried by the method according to the present invention maintained its lightness much more than a piece dried at a temperature above the freezing point during the entire drying period. Figure 2 for comparison also shows values for a traditional stockfish.

Protein content

The amount of protein that is extractable from a protein-rich product is a measurement of protein denaturation. Denaturing of proteins means that the protein's secondary, tertiary and quaternary structure is modified in an undesired manner while the sequence of amino acids is maintained.

Tests were made to determine how the amount of salt and water soluble proteins were investigated. The object was to see at which drying temperatures the fish is subjected most to denaturing. Figure 3 shows the protein content in fish (cod) dried at -5°C and 20 0 C respectively. Figure 3 shows that there is a much higher content of not denatured protein in fish dried with the method according to the present invention compared to fish dried entirely at a temperature above 0 0 C. The amount of salt and water soluble proteins seen in Figure 3 is a measurement of not denatured protein in the fish.

In general it was found that products dried in accordance with the present invention have a very high quality. For example when drying fresh fish it obtains a whiter colour, higher rehydratability and preserves the proteins better than fish dried above 0 0 C, cf. the above discussed measurements.

Many consumers want food with high quality and short preparation times. Products dried with the method in accordance with the present invention is well suited for bachalao type meals and meals based on stockfish. They constitute an alternative to today's traditional split cod and stockfish. The process line is shorted down and the usefulness of the product is increased.

With respect to the costs of the process, theses are related to energy consumption, time consumed, and not the least how labour demanding the process is. In all these areas the method according to the invention is good. Drying at low temperatures as an isolated element certainly is a comparatively costly step of the process and should therefore not be conducted to a higher extent than required to obtain the desired quality. The end drying at a higher temperature is significantly less expensive. By finding the optimal retention time in the low temperature zone for each product in question, the quality and the energy economical aspects can be optimally balanced. Since the entire process is rapid compared to competing methods and is well adapted to automation, it is not a labour demanding process. Compared to processes with vacuum freeze-drying the present process is much less expensive both with regard to equipment and the process as such. With vacuum freeze-drying the capacity is low and the energy consumption is high. A further advantage related to the present method is the possibility to use a temperature program. Combinations of drying temperatures that yield an optimal drying process with respect to quality and costs may then be found. In general too short or limited drying at low temperature leads to a product that is not of the finest quality while a inconveniently prolonged drying at the same temperature leads to a undesired high process cost.

In an industrial process according to the invention it may be relevant to use dryers with a significantly higher number than two temperature steps. Thus the entire drying process in a preferred embodiment of the invention may be conducted in a tunnel dryer with continuous or step by step increasing temperature, the temperature being lower than freezing point of the product for 65-90 % of the drying time and more preferred for 75 to 88 % of the drying time.

Alternatively the drying process may be conducted in a belt dryer with the same conditions as mentioned above, i.e. a continuous or step by step increasing temperature, the temperature being lower than freezing point of the product for 65-90 % of the drying time and more preferred for 75 to 88 % of the drying time.

When the temperature is increased step by step as mentioned, the number of temperature steps is typically 2-12 and more preferred 2-8 steps. Under any circumstances there will always be at least one drying step at a temperature lower than the initial freezing point of the product and at least one drying step at a temperature above the freezing point.