Technical field

The invention relates to a food package, comprising fish and a sorbent, wherein the sorbent is attached to the package and is capable of adsorbing volatile organic substances. The invention also relates to methods for packaging and storing fish, to sorbent devices and uses of sorbents or sorbent devices.

State of the art Fish storage and transportation presents great challenges to the food industry due to the perishable nature of the fish. Fish is an important food source for the human diet due to the high content of polyunsaturated fatty acids, which cannot be synthesized in the human body. However, because seafood has a high content of polyunsaturated lipids, oxidative reactions are much more important as shelf life limiters in fish compared with other flesh meat. Like mammalian flesh, fish spoils through the combined effects of chemical reactions, continuing activity of its own enzymes (autolysis of cells) and bacterial growth. However, in fish, metabolism and the commensal bacterial flora of their skin and intestines are adapted to lower temperature than mammals, with catabolic activities continuing even in chilled conditions.

Methods have been developed in the art to extend the shelf life of fish. These involve rapid chilling and ice storage, the use of organic acids, antimicrobials, modified atmosphere packaging (MAP), ionizing radiation, salting combined with low irradiation and vacuum-packaging and salting combined with essential oil compounds as preservatives.

Modified atmosphere packaging coupled with storage at low temperatures i.e. 0-1 °C is considered as the most widely used commercial method used for fish preservation. However, although CO2 can effectively inhibit the growth of several microorganisms, there is a major concern regarding the limited effects on autolysis, since autolysis is the major cause of spoilage of fish stored at temperature close to 0°C. Other newly developed fish preservation technologies include the use of electrolyzed NaCI solution and essential oil compounds and low-dose irradiation in the range of 1— 3 kGy. Synergistic treatments may be complementary to the already existing methods of fish preservation.

There is thus an ongoing need for new and improved efficient methods for extending the shelf life of fish, which overcome the above-mentioned problems.

Problem underlying the invention

The problem underlying the invention is to provide packages, methods, devices and uses, which overcome the above-mentioned problems.

The invention shall provide improved devices and methods for extending the shelf life of fish. Specifically, devices and methods shall be provided, which are efficient and easy to apply. The freshness and shelf life of the fish shall be maintained for an extended time.

The devices and methods shall be applicable in industrial and retail food packaging and storing. They shall be in accordance with health and environment-related requirements and regulations for food applications. Specifically, the method and device shall avoid potentially hazardous substances or treatments, for example with harsh chemicals or heavy metals. It is another problem underlying the invention to provide devices and methods which decrease or delay the development of odours of fish products.

Disclosure of the invention

Surprisingly, the problem underlying the invention is solved by devices, methods and uses according to the claims. Further inventive embodiments are described in the description. Subject of the invention is a food package, comprising fish and a sorbent, wherein the sorbent is attached to the food package and is capable of adsorbing volatile organic substances. Preferably, the sorbent adsorbs volatile organic substances released from the fish. Preferably, the volatile substances are those which decrease the shelf life of the fish.

The food package of the invention comprises fish. Preferably, the fish is raw fish. In other words, it is not boiled, cooked or subjected to another equivalent heat treatment. In another embodiment, the fish is smoked fish. Preferably, the fish is not frozen. In this embodiment, the fish should be fresh fish. The fish may be marine or freshwater fish. Since the package comprises a food, the fish is not alive any more.

In a preferred embodiment, the fish is the only food or the main food ingredient in the package. In another embodiment, the package comprises fish in combination with other food components. For example, the food may be a fish dish, such as sushi.

The package may be any package, which is used in the art for packaging fish. The food package can be non-permeable or permeable for gases and/or liquids. It is preferred that the package is non-permeable for gases and/or liquids. In other words, the package should seal the fish inside from the surrounding. The interior might comprise a specific atmosphere for prolonging the shelf life of the fish. For example, the atmosphere may be reduced in oxygen or free of oxygen, or the packaging may be a modified atmosphere packaging (MAP).

The food package may be any known package, such as a container, wrap, box or bag. The packaging walls may be composed of foil, plastic, glass, cardboard or the like. The package might be additionally sealed with foliage. The inventive sorbent device may also be positioned in a storage room, such as a warehouse.

The sorbent is attached to the food package in a manner, such that volatile substances released from the fish can diffuse to the sorbent. Preferably, the sorbent is positioned inside the package. However, the sorbent can also be attached to the outside, if the package is gas-permeable or if openings are provided, through which volatile substances can diffuse towards the sorbent. In a preferred embodiment of the invention, the sorbent is not in physical contact with the fish. In other words, the sorbent is separated from the fish. Preferably, the sorbent and the fish are spaced apart from each other by separation means, such as an interior gas-permeable wall or a sorbent package. The sorbent could also be fixed to a package side wall with tape. Thereby, leakage of the sorbent, or particles of the sorbent, into the food product can be avoided.

The sorbent adsorbs volatile organic substances. Upon storage, fish releases volatile organic substances, such as amines, aldehydes and ketones. According to the invention, it was found that by decreasing the overall level of volatile organic substances released from the fish, the freshness and shelf life can be prolonged. Specifically, the odour, colour, texture and/or taste of the fish are maintained for a longer time. Without being bound to theory, at least some released volatile organic substances seem to exert a negative effect on the fish, which reduces freshness and enhances spoilage. Preferably, the sorbent is selected to adsorb organic amines, aldehydes, ketones and related substances.

In principle, any known sorbents can be used which efficiently adsorb volatile organic substances released from fish upon storing. The sorbent may be adapted to the specific fish. The sorbent may be an adsorbent or an absorbent. Adsorbents bind molecules to their surface, whereas absorbents incorporate substances of another physical state into their internal volume. According to the invention, the sorbent is preferably an adsorbent.

In a preferred embodiment of the invention, the sorbent comprises carbon and/or zeolite. Preferably, the sorbent comprises or consists of activated carbon (activated charcoal, activated coal). Activated charcoal (AC) is a porous material mainly composed of carbon, which is widely used as an adsorbent. It is formed via a controlled process that involves homogenization, carbonization, volatilization of inorganic impurities and graphitization. The physical properties of this depend on its source and subsequent treatment. AC has a complex surface structure containing a wide range of functional groups, including phenolic, carboxylic, carbonylic, aldehydic, etheric, peroxidic, quinine and lactone groups. The binding mechanisms include hydrophobic interactions, charge-transfer complexation, hydrogen bonding, cation exchange and other specific interactions. Activated charcoal has a very fine network of pores, an extraordinarily large surface area and volume that gives it a unique adsorption capacity. Activated carbon may be obtained from coal or coconut shells.

Zeolites are another class of sorbent materials with similar adsorption mechanism to AC, high crystallinity and an open pore system readily accessible to small molecules. Common types of zeolites are stilbite (STI, a natural zeolite) and modified stilbites, like H-STI and Na-STI.

The sorbent may be used of any applicable form. Preferably, the sorbent is a powder, granulate or a block material. Depending on the physical form, the sorbent may be embedded in or part of the sorbent device. The sorbent may be used as part of a sorbent device. In other words, it may be used in combination with other means, such as storing means. In a preferred embodiment of a useful sorbent device, the sorbent is included in a sorbent container, such as a pad, sachet or box. The container may be gas-permeable, such that the volatile organic compounds can diffuse to the sorbent. For example, a sorbent device may comprise activated carbon as a powder or granulate in a pad or sachet. The sorbent device or sorbent container is attached to the food package.

Another preferred embodiment of the invention is a sorbent device, in which the sorbent is attached to a carrier. Preferably, this sorbent device comprises in addition a sorbent container, in which the carrier with the sorbent is included. It was surprisingly found that it is possible to adhere a sorbent, such as activated carbon or zeolite, firmly to a carrier. In the inventive sorbent device, volatile organic substances can contact the sorbent and be removed from the fish package interior.

The carrier might be porous or non-porous. For example, the carrier may be a paper, cardboard, polymer film or foil, a membrane or the like.

In a specific embodiment of the invention, the carrier is a porous carrier. When using such a porous carrier, the volatile substances may diffuse freely to the sorbent through the carrier. Preferably, the carrier is a non-woven or a polymer foam.

In a preferred embodiment, the carrier is a non-woven. Preferably, the non-woven consists of or comprises polymer fibers and/or filaments. The polymer is preferably an organic polymer. The fibers and/or filaments may be natural and/or synthetic. The natural fibers or filaments may be cellulose or derivatives thereof. The synthetic organic polymer may be a polyolefin, such as polyethylene and polypropylene, or polyester. The non-woven may have a thickness below 5 mm. Preferably, the basis weight of the non-woven is from 50 to 250 g/m ² . The amount of sorbent attached to the non-woven may be from 20 to 200 g/m ² . The polymer foam is preferably a polyurethane foam. The pore size of the carrier, for example the non-woven or polymer foam, is selected such that the free diffusion of volatile organic substances is still possible. The material of the carrier should be inert, such that it does not interfere with the volatile organic substances physically or chemically.

In a preferred embodiment of the invention, the sorbent is attached to the carrier with a binder. Another subject of the invention is thus a sorbent device for increasing the shelf life of fish, comprising a sorbent, which is capable of adsorbing volatile organic substances, and a carrier, wherein the sorbent is attached to the carrier with a binder. In this embodiment, the sorbent is preferably provided in particulate form. It was found that a sorbent powder, such as activated carbon or zeolite, can be adhered to a carrier with a binder whilst maintaining excellent sorbent properties.

Preferably, the binder is applied in a relatively thin layer. The binder may be applied to the carrier as an adhesive layer prior to adding the sorbent. Alternatively, the carrier may be impregnated with a binder solution, which comprises the sorbent. When applying only a thin binder layer, the sorbent and carrier are not sealed by the binder and the sorbent can still access the volatile organic substances in the atmosphere. Preferably, the binder and sorbent are applied together from an aqueous solution or suspension. This is advantageous for environmental and cost reasons, because organic solvents can be avoided. The aqueous solution or suspension may comprise additives, such as wetting agents and stabilizers. In a preferred embodiment of the invention, the binder is cross-linked. When cross- linking the binder, it is possible to obtain a highly porous binder network, or matrix, which tightly binds the binder to the carrier without inhibiting or significantly decreasing the sorbent function. In a preferred embodiment of the invention, the binder consists of or comprises polyacrylate and/or polymethacrylate and/or polybutadiene. In another embodiment, the polymeric binder comprises monomeric acrylate and/or methacrylate and/or butadiene subunits as part of a copolymer with other monomers. In other embodiments of the invention, the binder is another adhesive polymer, such as a polyester or polyamide.

The inventive sorbent device may also be obtained by applying a sorbent to a carrier and subsequently adhering both to each other with a binder, preferably a binder solution. After applying the binder, the binder may be cross-linked.

Alternatively, the carrier may be brought into contact with a mixture of the sorbent and the binder. For example, the carrier may be impregnated with a solution, suspension or emulsion which comprises the sorbent and the binder. After or during drying, the binder may be cross-linked.

Preferably, the inventive sorbent device has a shape which is adapted to the specific use. The shape may be regular, for example square or round, or a shape adapted to a pocket or cavity in the food package.

Another subject of the invention is a method for packaging and/or storing fish, comprising

(a) providing fish in a package, and

(b) providing a sorbent, which is capable of adsorbing volatile organic substances, wherein the sorbent is attached to the package.

When the method is a method for packaging fish, it comprises positioning the fish inside the package and attaching the sorbent to the package. Subsequently, the package should be sealed. When the method is a method for storing fish, the fish should be stored for an extended time, for example at least 24 hours. The packaging and/or storing should be carried out under appropriate conditions, for example reduced temperature, absence of light, etc. In principle, the inventive method for improving the shelf life may be combined with other known methods for improving the shelf-life, such as rapid chilling and ice storage, the use of organic acids, antimicrobials, modified atmosphere packaging (MAP), ionizing radiation, salting combined with low irradiation and vacuum-packaging and salting combined with essential oil compounds as preservatives. In a preferred embodiment of the invention, the method is a method for extending the shelf life and/or freshness of the fish. Preferably, the shelf life of the fish is extended for at least 10%, compared to a package which does not comprise an inventive sorbent. Methods for evaluating the freshness of fish are known in the art and may comprise sensory evaluation, microbial methods or measurements of physical changes, such as fish structure or colour.

According to the invention, it was found that especially long term storage of the fish can be improved significantly. It was found that the quality of the fish can be increased especially upon storage after at least 6 days after packing or more, or after at least 10 days after packing or more, or after at least 14 days after packing or more. The method and devices of the invention of the invention are especially applicable for increasing quality of the fish within 6 to 20 days after packing, more specifically within 10 to 18 days after packing, or especially between 14 and 16 days after packing.

According to the invention, it was found that depleting the atmosphere of volatile organic compounds increases the shelf life. Preferably, the atmosphere is depleted of amines, such as trimethylamine (TMA). Without being bound by theory, the production of TMA may be dependent at least partially upon the bacterial population, as its concentrations in the muscle increases in the same exponential manner as bacteria growth. TMA can be measured with related substances, the total volatile base, which includes ammonia and dimethylamine.

Another subject of the invention is the use of a sorbent, which is capable of adsorbing volatile organic substances, or a sorbent device of the invention, for increasing the shelf life and/or freshness of fish. The inventive devices, methods and uses solve the problem underlying the invention. According to the invention, the shelf life of fish is extended in a relatively simple and cost-efficient manner. The method is applicable for industrial and retail food-packaging and storing and does not make use of potentially hazardous substances, such as heavy metals. The sorbent does not interfere with the fish and can simply be discarded after use or may remain in the package.

Examples:

Example 1 : Preparation of sorbent device

An aqueous solution was prepared where the powdered activated carbon (sourced from coconut shells or coal) was mechanically mixed with water along with a wetting agent, stabilizer and acrylate or butadiene based cross linking polymer binder. When sufficiently homogenous, the mix was pressurized and applied using a gas propellant to the surface of a carrier. The carrier was a needle punched polyester based non-woven, a reticulated or non-reticulated polyurethane foam, or a bonded non-woven, which was bonded with another binder. The non-woven used had a thickness of no greater that 5mm and a weight in the range of 50 g/m ² - 250 g/m ² . The amount and penetration of this composition applied to the surface varies depending on the application, ranging from a surface treatment on one side of the material to total penetration of the composition through the material on both sides. The applied mass could vary from 20 g/m ² to 200 g/m ² and will be adapted to the applications requirement. After application of the sorbent, the device was heated to a temperature in excess of 100°C to drive off any moisture and to complete the cross linking of the binding agent with the carbon and carrier.

Example 2: Preparation of sachet

The sorbent device prepared according to example 1 was converted by slitting, punching or other means to a regular shaped (square, circular or other form) individual item, ranging from 0.0004 m ² to 0.01 m ² , which was then enclosed within a 20 micron thick polypropylene perforated air permeable film. Enclosure was achieved by heat sealing, but could also have been achieved through adhesion, ultrasonic sealing or another means. Example 3: Preparation of food container

The sachet of example 2 was placed in a moulded plastic fish packaging tray after the fish had been placed in the tray first. Loose within the pack or adhered to the internal surface, the sachet avoided excess moisture while present in the pack. Once film sealed with heat against the atmosphere and with the tray and fish being flushed with a modified atmosphere, the process of packaging the fish was complete. Examples 4 and 5: Testing of fish shelf life

Storage trials were conducted with an inventive food package (example 5) which comprised salmon and the sachet of example 3. A comparative trial (example 4) was carried out with a food package, which comprised salmon but did not comprise a sachet. Both salmon samples were left with the skin on and packaged using MAP (modified atmosphere packing). The trials were performed under controlled conditions, emulating the normal storage life of a sample when it is commercially sold. This included temperature monitoring and sample dwell time among other parameters. During this storage period, samples were taken periodically by a professional body for testing. All tests were carried out by the professional body, which is familiar with such testing on a regular basis and does so according to accepted industry standards. This testing was to assess any extension to the life of the packaged fish. Samples were evaluated for odour, colour, texture and taste, respectively. A calibrated taste test panel conducted the assessment of fish samples over a number of days marking each sample on its organoleptic criteria. Overall scores between 0 and 10 points were noted and evaluated as "good" (8-10 points), "medium" (5 to 7 points) or "poor" (0 to 4 points). Samples were evaluated after every two days except at day 4, which was a Sunday. The results are summarized in Figures 1 and 2. Graphical assessments are shown in figure 2. It can be seen that over a period of 16 days the results of testing diverge significantly when the carbon sachet is introduced. Viewing the results on an individual basis of odour, colour, texture and taste the following becomes apparent. Smell is a test criterion critical in measuring the shelf life of the product and the area where the sachet is expected to have most impact. The odour of the fish, when stored in combination with the sachet, never alters from typical after 6 days showing that there is no degradation in the smell of the fish. However, for the comparative package without the inventive sachet, the odour begins to be negatively assessed after the 6th day, losing its "typical" rating at points and acquiring a rating of "strong" or "ammonia" based scent.

Reviewing the results from the texture and taste sections of testing, it can be seen again that around the 14 and 16 day mark, the inventive combination packs show a better level of evaluation with the fish still being classed as "good" and "moist" when in combination with the inventive carbon sachet, while without it the classification tends to drop to "flaky" or "poor"

With these results gathered, it is clear that the inventive sachet provides a marked improvement on the condition of the fish after an extended number of days.