It is known that fresh fish, shellfish and meat lose their freshness after a period of storage if no measures are taken. After some time, the raw material becomes putrid and unsuitable as human food. To keep the fresh condition under a longer period of time it is necessary to take measures to preserve the raw material.

To increase the storage stability of different food hitherto different preserva- tion agents have been used, such as bactericidal agents, antibiotics, radia- tion etc. Another well-known method is deep-freezing, wherein the raw ma- terial is rapidly frozen to a temperature typically between -20°C and -40°C.

A drawback when using preservation agents in the form of bactericidal agents and such is, however, that it is difficult to avoid that the quality of the raw material decreases, for example smell and taste changes. Moreover, the added agent must of course be harmless to humans. Furthermore, the added agents must not be too expensive, which would make the process un- economical. As regards deep freezing, it is often difficult to keep the raw material at the low temperature from the time the fish has been captured until it is delivered to the consumer. If the temperature increases the preser- vation effect decreases, after which the process of decomposition starts. Even if it is possible to keep the low temperature during freezing, the raw material is impaired by the freezing and thawing process, respectively, which sometimes gives impaired characteristics regarding consistency.

From WO 88/09620 a cooling liquid for fresh fish is known. It comprises the following components: water; one or more inorganic salts, preferably NaCl; one or more polyols, preferably glycerol; and ascorbic acid. By using this cooling liquid the fish can be cooled to - 10C to -20C without freezing of the fishmeat. The purpose with this cooling liquid is thus to lower the freezing point so that the fish does not become frozen at the storage temperature used.

It is known that antioxidants, such as ascorbic acid, increase the storage stability of food. However, the increase in storage stability is very short and not an alternative to deep-freezing.

The applicant is not aware of any satisfactory process for treatment of fish which gives the fish longer storage stability at normal refrigerator tempera- ture, i. e. +4"C to +80C, which is the storage temperature available to the consumers in their homes besides freezer temperature.

Summary of the invention Therefore, it was the object of the present invention to provide a rapid, sim- ple and cheap process to preserve the fresh condition of food, such as fish, shellfish and meat, under a longer period of time at storage in temperatures above 0°C.

The present invention provides a method of treating fresh food, such as fish, shellfish and meat, to improve its storage stability so that the smell, consis- tency and taste of the food is preserved during a longer period of time. The process is characterized in that the fresh food is treated with a solution comprising at least two antioxidants having different antioxidative charac- teristics, i.e. different oxidation rates. By using these different antioxidants a prolonged antioxidative effect is provided.

The anitoxidants are chosen from antioxidants having rapid, intermediate, and slow oxidation rates, respectively.

Preferably, the antioxidants according to the invention are selected from the following: ascorbic acid, astaxanthin, sodium ascorbate, calcium ascorbate, ascorbylic palmitate, ascorbylic stearate, tocopherol-rich extracts, a-tocopherol, y- tocopherol, b-tocopherol, propyl gallate, octyl gallate, dodecyl gallate, isoascorbic acid, sodium isoascorbate, butyl hydroxy anisol (BHA), butyl hy- droxy toluene (BHT), lecithin, sodium lactate, potassium lactate, calcium lactate, citric acid, sodium citrate 5, potassium citrates, calcium citrates, L- tartaric acid, sodium tartrates, potassium tartrates, sodium potassium tar- trates, phosphoric acid, sodium phosphates, potassium phosphates, cal- cium phosphates, sodium malate, sodium hydrogen malate, potassium malate, calcium malate, calcium hydrogen malate, metatartaric acid, cal- ciumtartrate, adipic acid, sodium adipate, potassium adipate, succinic acid, triammonium citrate, calcium disodium-EDTA, ubiquinon.

A presently preferred antioxidant is green tea which in itself shows a spec- trum of antioxaditive characteristics.

The solution used in the process according to the invention may be a water solution, wherein water soluble antioxidantes are used, or an oil solution, wherein fat soluble antioxidantes are used. The oil solution may comprise any edible oil, for example rape-oil.

The solution is added to the food by dipping, painting or spraying, wherein the latter has given especially good results for water solutions.

According to a preferred embodiment of the invention the solution also com- prises antioxidative mineral agent(s), such as zinc and selenium, which has the additional function of stabilizing the solution, i. e. gives longer storage stability of the food.

The preferred food for treatment according to the invention is all kinds of fish.

Detailed description of the invention The invention will now be described closer in relation to some non-limiting examples. While the examples relate to fish, it is realised that the invention also can be applied to other kinds of food such as meat.

In the examples the antioxidant solutions were used containing representa- tive examples from rapid, intermediate and slow acting antioxidants. Pref- erably, a member from each of these groups is present. It is realised that the choice is dependant on the raw material, i. e. the food to be treated. For ex- ample, the size of the antioxidant will influence its penetration depth into the selected raw material.

Water soluble antioxidant solution Ascorbic acid 20 g/L Zinc 1.8 g/L Selenium 2 mg/ L Water to desired volume Fat soluble antioxidant solution Tocopherol 40 g/L Ubiquinon 12 g/L Selenium 2 mg/L Rape-oil to desired volume These concentrations have proven to be suitable but are only exemplifying.

The storage stability of these solutions was larger than when the respective antioxidant was used separately. This shows that the process of the inven- tion provides a synergistic antioxidative effect in the purpose of giving food increased storage stability.

Example 1 The treated food was filleted fresh whitefish having a weight of 300-400 g.

Water-soluble antioxidant solution was added on both sides of the fish, after which it was kept, together with an untreated control, in a refrigerator at +7"C to +80 C. The storage stability was judged after the levels of smell and consistency.

Results: Untreated fish (control): consistency impairment after 5 days, smell impair- ment after 6 days.

Treated fish: consistency impairment after 8 days, smell impairment after 9 days.

The results from example 1 show that the fish treated according to the in- vention exhibited about 50% better storage stability.

Example 2 The treated food was filleted fresh whitefish having a weight of 700-800 g.

Water-soluble and oil-soluble antioxidant solution, respectively, were added on both sides of the fish, after which it was kept, together with an untreated control, in a cold-storage room at +2"C to +4"C. The storage stability was judged after the levels of smell.

Results: Untreated fish (control): smell impairment after 8 days.

Treated fish (water-solution) : smell impairment after 11 days.

Treated fish (oil-solution) : smell impairment after 10 days.

The results show a clear improvement for the water-solution and the oil- solution, respectively, regarding storage stability whereby the former showed a somewhat better effect.

Example 3 The treated food was about 48 hours old (since the capture) filleted Baltic herring having a weight of about 100 g per fish. Water-soluble and oil- soluble antioxidant solution, respectively, were added to both sides of the fish, after which it was kept, together with an untreated control, in a refrig- erator at about +6"C. The storage stability was judged after the levels of con- sistency and smell.

Results: Untreated fish (control): consistency impairment after 5 days, smell impair- ment after 5-6 days.

Treated fish (water-solution): consistency impairment after 7 days, smell im- pairment after 8 days.

Treated fish (oil-solution): consistency impairment after 6 days, smell im- pairment after 7 days.

The results show a clear improvement for the treated fish, wherein better results were obtained for the water-solution than for the oil-solution.

Example 4 Water soluble antioxidant solution: Green tea 10 g dry leaves/2 dl H20 Zinc 1.8 gel Selenium 2 mg/L The treated food was frozen and thawn shrimps. Antioxidant solution was sprayed on the shrimps. Controls were sprayed with the same amount of water. The specimens were kept in a cold storage room at +20C to +40 C.

Results: Untreated shrimps (control): smell impairment after 3 days.

Treated shrimps (tea-solution): smell impairment after 8 days.

In summary, the experimental results show that the process according to the invention provides clearly improved storage stability of fresh food.