Due to the growth of omega-3 supplementation in human nutrition, the recovery of omega-3 Fatty Acids (FA’s) derived from the oil of harvested fish has grown significantly in the past few years. Many fish species are used as an omega-3 (FA) source, including the oils derived from salmon, herring, sardines, anchovy, mackerel, and tuna. Fish oil can be separated by methods such as a wet reduction process, enzymatic or autolytic (silage) processes, dry rendering, solvent or supercritical fluid extraction. Some of these extraction processes create fish meal proteins as a by-product of the fish oil extraction. These fish meals can then be sold in animal feed and pet food applications. The process of extraction can take place on shore, or sometimes on a processing vessel at sea. These products and processes have been the subject of many safety issues due to the volatility and stability of the proteins in question.

Spontaneous ignition of fishmeal has resulted in accidents and fires in fishmeal storage, both on land and in vessels at sea. The heating of fishmeal is due to atmospheric oxidation. The chemical process is complex and involves a series of reactions within the fish meal and it’s fatty acids. These spontaneous ignition fishmeal fires are caused by the heat generated through fermentation or oxidation. The contributing FAs include mono- and especially polyunsaturated FAs (MUFAs and PUFAs, respectively), which appear at a concentration of 63–79.5% in Atlantic salmon. One of the main disadvantages of PUFAs is their low oxidative and thermal stability. The rate of oxidation of such FAs (especially at higher temperatures) drastically increases with the increasing number of double bonds present, even by few thousand times. The relative oxidation rate of α-linolenic acid (an omega-3 FA) is 2500 times higher in comparison with saturated stearic acid. Light (photo-oxidation) and the presence of heavy metal ions contribute to the initiation of auto-oxidation.

Thermal degradation or fragmentation of these intermediates leads to odor-active carbonyl compounds such as aldehydes, ketones, alcohols and esters, aldehydic acids, alkanes and alkenes. In fish oil, the main odoriferous compounds resulting from oxidation are propanal, pent-1-en-3-one, hex-3-enal, and pent-1-en-3-ol.

The fishmeal industry sought to resolve the dual problem of odor and fires by modifying the product to render it inert or less susceptible to oxidation. This was achieved by the addition of antioxidant during the production of the meal. The stabilization of fish oils like Salmon oil can be simply performed by using Natural antioxidants. Tocopherol blends, such as FoodSafe Technologies™ SafeNature™ Marine product line are the most appropriate due to their lipophilic characteristics. Use of synthetic antioxidant BHT blends like EntendOx™ Marine are ideal for fish meal feed applications.

The timing of the process of adding antioxidants to fish meals and fish oil is as critical as the addition of the antioxidant itself. Antioxidant are used up as treated fishmeal ages. If an insufficient quantity is added at the time of production, it will be used up before the condition of the fishmeal has been stabilized. As a result, at some stage after production, oxidation will start, producing substantial quantities of heat and the risk of a serious rise in temperature in the affected meal. However, this will not be evident for some time after loading. For production processes that have longer duration, a two-step addition of antioxidants is encouraged, once at the stage of production of the meal (and the fish oil), and second application after time has absorbed the efficacy of the initial antioxidant application. The timing of this second application can be determined best by shelf-life trial applications and treatments of the targeted fish species product.

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