The use of an inorganic and organic acid-based preservative as storage control for fish-offal
Published:August 14, 2009
By:Friedrich Weißbach and Christian Lückstädt
Acid preservation of fish and fish viscera to produce fish silage is common practice. The final product has been widely used in fish feed and as a feed component for fur animals. In many European countries it is a commonly used method of preserving fish-by-products, using formic acid or its salts to keep the fish silage stable. However, due to regulatory restriction and the limited tolerance to formic acid in fur animals such as mink and foxes, the accepted practice of preparing fish silage with formic acid treatment is not always possible. The objective of the present study was therefore to investigate the effect of a new chemical preservation method which excludes the use of formic acid.
The efficacy of a liquid blend of sodium disulphite, hexamethylenetetramine and sodium benzoate was evaluated when prepared in aqueous solution by a special procedure (FURMIX, patent pending). This preservative was added to nearly 10 tonnes of roughly minced Baltic herring (Clupea harengus) which was previously acidified by adding 13 litres of concentrated sulphuric acid per tonne. The product blend was applied at a rate of 20 litres per tonne. The storage trial was carried out under European summer conditions (approximately 20°C) in an open container and lasted for 3 months. The following parameters were tested after one month and at the end of the trial (Table 1): bacterial counts, mould count, pH and total volatile nitrogen (TVN). TVN is often used as an indication of the freshness of fish raw material. The main constituents of TVN are trimethylamine and ammonia. Trimethylamine originates from bacterial decomposition and its presence in raw fish is thus taken as an indication of bacterial growth, while ammonia arises from the breakdown of amino acids - thus reducing the quality of the available protein. Levels of around 75 mg TVN per 100 g fish mass are regarded by the industry as limits for good quality fish silage.
Table 1: Quality parameters of treated fish silage stored over 3 months
Duration of storage
Target figures
1 month
3 month
Aerobic bacteria (cfu/g)
<10,000
<10,000
<5,000,000
Salmonella (cfu/10 g)
0
0
0
Moulds (cfu/g)
<1,000
<100
n.d.
pH
3.9
4.1
<4.8
TVN (mg/100 g)
46
55
<75
n.d. - not defined
The results clearly indicate that due to the addition of sulphuric acid and the unique acid-salt blend, the fish silage derived from herring can be kept stable and in good quality for at least three months for further feed processes.
The main reason for shifting from organic acids, like formic acid, for the preparation of fish silage was the limited tolerance of formic acid in fur animals. In order to achieve a stable fish silage a pH-level between pH 3.5-4 has to be achieved. For this the amount of formic acid needed, exceeds the tolerance of fur animals and feed refusal is often the case. Therefore an alternative method to preserve fish waste which should be fed to fur animals was needed. We have shown in the listed abstract from the Aquaculture America 2009 proceedings that the decribed method with sulphite, HMT and benzoate is a possible alternative.
On the other hand - acidified raw materials are not only preserved, but will have also an beneficial impact on the animals fed upon. The use of acidifers is already common in pigs, while the application in poultry and fish is increasing. Christiansen and Lückstädt (2008) reported for instance the beneficial effects of acidified fishmeal on Salmon growth. Currently, trials with tilapia and catfish are carried out.
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Okpaikhian Michael
5 de septiembre de 2009
Good article about the use of organic acids. I think ur finding is explicit and good. your tabular presentation shows that preservation is possible in all continents since worked with european condition of close to summer. GOOD but my question is can suh fish preserved through this means be used fishmeal for young animal such as chicks and juveniles catfish. what could be the the side effect of this product considering its process of preservation.THANKS
What i understand is The aim of diverging preservative from organic acids to sodium disuphide and hexamethylene tetraamine was to be safe the fishsilage for both fish and fur animals.Privious method invlve 13 Litter per ton of H2So4 ,and new reagent of 20 l / t was not outstanding according to me,because hexamethylene tetraamine is a chelating agent and most proble Mutagent, so it must be notice this compound is highly reactive with proteins ,if some part of the compound in silage is not degraded it might be utilised in fur animals,.sumrising there should be differnt stratigies against differnt microbes ie Some bacteria could be controled by Toxic protene,and host specific viruses ,and some mold could be damaged by some bacteria along with previous methods used in egyptian age should be remodelld.
Thanks
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