NO313857B1 - Method and materials for inhibiting gas silage development in fish silage - Google Patents

Description

The present invention relates to a method for preventing gas development in fish silage, as well as a fish silage liquid.

Within the fishing industry, it has for a long time been a major problem that, in connection with the production and transport of fish silage, large quantities of unidentified gas are formed in the silage.

Fish silage is a product made by adding acids to whole fish or parts thereof.

The product can be purified or fractionated to increase the quality, and the silage can be dewatered to varying degrees.

The problem of gas formation occurs with several silage suppliers. The problem has been greatest and most frequent in the summer months, and until now it has been of the opinion that the gas formation could be related to how much fish bone was mixed in the silage.

Under acidic conditions and with bone-rich waste, there is a risk that carbonate in fish bones is dissolved during the release of CC>2 and the consumption of protons (=acid) with the subsequent increase in pH, according to the following reaction:

However, the inventors of the present invention have studied the problem of gas formation in<*>fish silage in more detail, and our preliminary conclusion is that other factors make a greater contribution to gas formation. As can be seen from the experiments below, we have concluded that microorganisms are the origin of the gas formation, and the present invention thus provides methods and materials for inhibiting microbial growth in the fish silage.

The present invention thus includes a method for preventing gas development in fish silage, characterized in that an anti-microbial agent is added to the fish silage in an amount from 0.01 - 10% by weight, more preferably in an amount from 0, 1-1% by weight, and most preferably about 0.5% by weight.

Further embodiments of the method are specified in claims 2-10.

Furthermore, the present invention comprises a fish ensiling liquid as stated in claim 11.

A series of tests were carried out to identify and solve the problem. Since there was no clear understanding of what caused the gas production, the strategy was to first characterize the silage chemically, as well as microbiologically in addition to determining which gas was produced. On behalf of Hordafor AS, the tests have been carried out by Norconserv v/Torstein Skåra.

Example 1

Gas development - silage.

Samples of bone-rich silage were collected from Sotra Fiskeindustri on 10 June 1998. 3 samples were packed in plastic bags and sealed under vacuum.

One sample (No. 1) was stored at room temperature, one (No. 2) was incubated at 20°C and one (No. 2) at 5°C. In samples no. 1 and 2, there was clear gas development (several times the volume of the silage) after 2-3 days. Initial gas samples taken from sample No. 1 indicated that the gas did not contain CO2. However, this was disproved by analysis of gas from sample no. 2, on GC-MS, and an external gas analysis instrument - which reported >50% CO2. We therefore have reason to believe that the gas mainly consists of CO2.

Example 2

Composition - Analysis results.

According to the result from example 1, we could not give a clear explanation of what developed the gas in the silage. An analysis of the silage itself was therefore carried out, which in sample 2 gave the following results:

The analysis results show that the pH in the silage is so low that we expect it to be a preservative in itself. On the other hand, due to the large amount of nutrients found in silage, microbial growth and activity can be expected. On a general basis, one would expect that lactic acid bacteria and/or yeast could grow at low pH values. The results show that this is not the case for the analyzed sample quantity.

However, it cannot be ruled out that specially adapted bacteria will be able to adapt to this acidic environment.

Example 3

Gas development in silage. Change of storage temperature.

Sample no. 3 was, as indicated in example 1, stored at 5°C. After 14 days of storage at this temperature, we still could not observe gas evolution.

After 14 days the temperature was then increased to 20°C. After a few hours, a significant gas development occurred, as approximately 3 times as much gas (volume) as the volume of the silage was formed in the bag. It was assumed that this gas formation was the chemical process as described above, as the bag with the sample material was sealed so that no new microorganisms could be absorbed. The fact that the silage is packed in tight packaging can help to stabilize the equilibrium:

However, based on this experiment, we cannot exclude that the growth of microorganisms is the cause, as the reason for low or no gas formation at 5°C may be due to the microorganisms in question having a low activity and growth rate at this temperature, although this would be somewhat surprising.

Example 4

Addition of preservative - sodium benzoate.

In order to possibly exclude microbial causes, an experiment was carried out with the addition of a preservative to the silage. If the preservative had an effect on gas production, it would be a clear indication that the problems were caused by microbial growth.

A sample of silage was again collected at Sotra Fiskeindustri on 22 September 1998. The sample was divided into 5 portions of 200 ml and packed in plastic bags under soft vacuum. 5 g of benzoic acid was added to 2 of the bags. 2 bags, one with and one without benzoic acid were then incubated at 20°C. After a few days, we could observe gas development in the bag without added benzoic acid. Approximately 3 times as much gas (volume) was formed as the volume of the silage. However, there was no gas development in the bags with added sodium benzoate. In other words, there was much that indicated that the gas production was connected with microbial growth.

Example 5

Identification of gas-producing organism.

In order to clarify whether the gas formation could really be explained on the basis of microbial growth, a smear was now taken directly from one of the bags that had developed gas. Due to the low pH in the silage, samples were also sown on media with pH 3.5 and 5.5. Examination of direct smears under a microscope gave no clear indications of causation. And cultivation on dishes gave no growth of either lactic acid bacteria or yeast. Sowing on anaerobic medium, however, gave a clear growth of gram positive rods, and initially we assumed that these could be Clostridia or Leuconostoc. Isolated colonies were propagated and species determined, and we have initially concluded that the gas formation is caused by bacteria of the Clostridium type, and probably by Clostridium botulinum.

Example 6

Effect of different concentrations of sodium benzoate on development of gas in silage.

Samples of silage were collected from Sotra Fiskeindustri on 26 April 1999. The samples were packed in portions of 200 ml (95% vacuum). 2 units of each variant were packed, according to table 1.

After 2 days, there was clear gas evolution in the samples without added preservative, stored at 20°C. Also in the sample to which lg/kg and 2g/kg were added, respectively, there were signs of gas formation (bubbles), while the samples with more sodium benzoate were without signs of gas formation.

After 5 days, approx. 1 liter of gas in both bags of silage without added preservative, while there was little or no sign of gas formation in any of the other bags. We therefore cannot rule out that even lower levels than 1 g of sodium benzoate per kg of silage may be sufficient to prevent gas formation at 20°C.

The conclusion is that both sodium benzoate and potassium sorbate inhibit gas development in the silage.

Based on the experiments above, we have surprisingly shown that the gas formation is microbially conditioned, and probably caused by the species-specific Clostridium bacterium. Based on this, we would expect that all preservatives, i.e. agents that extend the food's shelf life by inhibiting deterioration caused by microorganisms, will inhibit gas development in silage.

It also appears that gas formation is temperature-dependent, so that problems will preferably arise in the summer months. And one possibility to reduce gas formation would obviously be to keep the temperature at, for example, +5°C. In practical terms, this is not entirely simple and it may thus seem simpler and less resource-intensive to use a preservative.

Sodium benzoate is in the "positive list" for fish and other aquatic products from 1991. Benzoic acid is poorly soluble, so salts are often used, e.g. benzoate. Benzoic acid has a better antibacterial effect than sorbic acid, because it helps to prevent the bacteria from utilizing the water phase in the products. It also has an inhibitory effect on yeast, but is less effective when it comes to preventing mould. Benzoic acid has the greatest effect in the pH range 3-4, but can also be used in slightly acidic products with a pH up to pH 6. In a food context, it is approved for use in fish, herring and shellfish products, jams and marmalades, vegetable products, soft drinks and juice.

One can therefore think of several different solutions:

1. After one silage has started to "boil", i.e. develop gas, adding an agent that kills microorganisms, such as a bactericide, will stop the growth of the gas-producing bacteria, and thus the gas production. Thus, one can imagine a contingency situation, where sodium benzoate, for example, is added to the plant when "boiling" occurs, i.e. when it is necessary. 2. You can protect yourself against the phenomenon by adding sodium benzoate directly to the ensiling liquid, so that there is a lower concentration of a bactericidal agent in the store all the time during the production of the silage. For example, so that the concentration of sodium benzoate in finished silage is approx. 5 g/kg. 3. Furthermore, in the experiments explained above, we have shown that gas development is temperature-dependent, and production and transport of the silage at a reduced temperature will thus inhibit gas development. 4. A combination of (a) lowered temperature and (b) addition of an agent that prevents the growth of microorganisms can be used.

We have started testing several different preservatives to find out which ones are best suited, as well as which concentrations and temperatures should most appropriately be used. The experiments are carried out both in the laboratory and on a large scale. However, we would like to note that the actual solution to the problem lay in the identification that microorganisms, and then probably bacteria, are the real cause of the gas formation. Once the causal relationship has been proven, it is relatively easy for the person skilled in the field to find the preservatives that should be used, as well as concentration ranges, incubation conditions, etc.

Claims (13)

1. Method for preventing gas development in fish silage, characterized in that an anti-microbial agent is added to the fish silage in an amount from 0.01-10% by weight, more preferably in an amount from 0.1-1% by weight , and most preferably about 0.5% by weight. 2. Method in accordance with claim 1, characterized in that the agent is a bactericidal agent. 3. Method in accordance with one of claims 1-2, characterized in that the agent is a preservative that is approved for use in pre-products. 4. Method in accordance with claim 3, characterized in that the agent is an agent selected from the group consisting of benzoic acid and its salts such as sodium, potassium and calcium benzoate, potassium sorbate, sorbic acid, sodium sorbate, acetic acid, potassium acetate, sodium acetate, calcium acetate, lactic acid, citric acid, sulfuric acid, hydrochloric acid, phosphoric acid, , p-hydroxybenzoic acid esters, Na-, Ca-, and K-propionate. 5. Method in accordance with claim 1, characterized in that the agent is added to the silage as gas formation in the fish silage has been identified. 6. Method in accordance with claim 5, characterized in that the agent is sodium benzoate. 7. Method in accordance with claim 1, characterized in that the agent is added together with the ensiling liquid. 8. Method in accordance with one of claims 1-7, characterized in that the production and storage of the fish silage takes place at a reduced temperature, preferably at approx. 5°C. 9. Method in accordance with one of claims 1-8, characterized in that in connection with the production or storage of fish silage (a) an agent is added that prevents bacterial growth and (b) that the silage is stored/incubated at a reduced temperature. 10. Method in accordance with claim 9, characterized in that the agent is sodium benzoate in a concentration of 0.1 gram/kilogram, more preferably 1 gram/kilogram, and that the temperature is in the range 0-20°C, more preferably about 5°C . 11. Fish ensiling liquid, characterized in that it comprises (a) formic acid, (b) antioxidant and (c) an agent that inhibits microbial growth. 12. Fish silage liquid in accordance with claim 11, characterized in that the agent which inhibits microbial growth is a bactericidal agent. 13 Fish ensiling liquid in accordance with claim 11, characterized in that the agent is selected from the group consisting of sodium, potassium and calcium benzoate, potassium sorbate, sorbic acid, sodium sorbate, acetic acid, potassium acetate, sodium acetate, calcium acetate, lactic acid, citric acid, sulfuric acid, hydrochloric acid, phosphoric acid, p-hydroxybenzoic acid esters, Na-, Ca- and K-propionate.