Antioxidants and Fishmeal

Securing Quality and Optimising the Utilisation of a Finite Resource

In Brief:

  • Fishmeal is a natural product which contains lipids (fats) and can contain omega-3 fatty acids at significant levels.
  • Due to their chemical properties, the fats and in particular the omega-3 fatty acids in fishmeal are prone to oxidation.
  • Oxidation of the fats in fishmeal may cause the loss of some of the important omega-3 fatty acids, which are valuable nutritional components. Physically, there are hazards that can arise from uncontrolled oxidation as a process, which can in some circumstances lead to spontaneous combustion.
  • Mitigation of these risks has been through the addition of effective antioxidants, which both stabilise the product and secure the full nutritional value in fishmeal, is critical.
  • There are two important regulatory frameworks for how antioxidants are managed in fishmeal. One relating to stabilisation, transportation, and shipping safety, and the other relating to animal feed and food safety.
  • Most jurisdictions around the world regulate the use of antioxidants, whether at the level of feed ingredient (i.e. the fishmeal), or at the level of compound feed, or sometimes both, and are usually based on the setting of a maximum limit for antioxidant concentration.  The European Commission’s legislation is perhaps some of the strictest in the world.
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Fishmeal is a brown powder obtained after cooking, pressing, drying, and milling of fresh raw fish and/or food fish trimmings and other fish byproducts.  It is highly regarded in animal and aquafeeds for its high protein content of usually >65% dry matter, comparatively high digestibility, and importantly is highly palatable characteristics. 

Fishmeal contains fish oil

Fish oil is generated as a co-product during the same process as fishmeal and is manufactured as a separate product. However, fishmeal retains a proportion of the oil at significant levels, generally comprising approximately 8-12% of the fishmeal by weight.  The presence of oil in the fishmeal product has consequences for how fishmeal is handled and used during storage and transport, and within animal and aquafeed formulations.

The oil in fishmeal varies according to the raw material used in production and reflects the composition of that resource. Raw material differences occur according to whether they are sourced from capture fisheries byproduct, aquaculture byproduct, or whole fish (usually small pelagic fish species).  Each of these materials vary with regards to their composition, i.e. comprising different protein, water, ash and fat contents. There can be variation not only in the total content of fat in fishmeal, but there are also important differences in the fatty acid profile of the oils among the different species and raw materials and therefore subsequently the fishmeals produced, as there are in fish oil products themselves. 

Fishmeal is rich in Omega-3 long chain polyunsaturated fatty acids

Fats in fishmeals have comparatively high levels of omega-3 long-chain polyunsaturated fatty acids relative to other types of protein sources.  Those omega-3 fatty acids include the important eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) fatty acids, which are both nutritionally and economically valuable, conferring health benefits to the consumer via the end product of farming, but also to the farmed animals themselves.

In turn, meat, fish, and egg products from farmed animals fed high omega-3 fishmeal are functional foods which benefit human health.  The annual supply of omega-3 oils from fishery resources at this stage is a finite resource., Though increasingly we are seeing growing production from trimmings from wild-catch and aquaculture to the extent now that more than 50% of global fish oil production is from such circular resources. It is therefore important to continue to capture all the supply of these materials as far as possible to ensure we maximise the use of all fish harvested whether wild or farmed. 

Fats in fishmeal are prone to oxidation

Due to their chemical properties, Omega-3 long chain polyunsaturated fatty acids (including EPA and DHA) are prone to oxidation, which results in rancidity and is both a quality and a safety issue. Chemically, oxidation of the fats in fishmeal may cause the loss of some of the important fatty acids, and that is obviously critical from a farmed animal’s nutritional perspective.  Physically, there are also hazards attached to oxidation as a process, since it can be accompanied by self-heating of the substrate, which can generate temperatures that are significantly higher than ambient conditions, and have the potential to lead to combustion if not managed and controlled.

In the early days of the fishmeal industry, oxidation was managed through the curing of fishmeal.  Curing was essentially a process of allowing oxidation under controlled conditions, thereby managing any temperature increase under safe conditions and ultimately producing a stable product for transportation to worldwide markets. The globally traded nature of fishmeal required effective management of the risk of combustion, since geographically lengthy supply chains (both then, and now) result in substantial periods in cargo holds of ships. To allow for better management of this oxidation activity, antioxidants were developed that allowed a greater degree of control of the fishmeal stability.  

Antioxidants used as stabilisers

Mitigation of that risk since the 1950s[1] has been through the addition of effective antioxidants which aim to stabilise the product. This was an early breakthrough for the fishmeal industry as the inclusion of antioxidants at the end of the manufacturing process provided a way of achieving a stable fishmeal product, that also secured and protected the full nutritional value in marine ingredients that enhanced their use in animal feed formulations.

Several antioxidants have been used to effectively to stabilise fishmeal, including ethoxyquin, butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and tocopherols (with, or without rosemary extract).  Of these ethoxyquin has been perhaps the most widely used, and its efficacy is such that some researchers have regarded it as the benchmark against which the fishmeal stabilising effect of other antioxidants is measured. However, recent evidence has shown that the materials from which ethoxyquin is made is carcinogenic, though ethoxyquin itself is not2. This concern about residual levels of the materials (para-phenetidine) have led to the ban in using ethoxyquin in Europe through the implementation of Regulation (EU) 2022/1375 of the European Commission3.

Regulatory framework

In terms of regulation of the use of antioxidants there are two important frameworks for how these compounds are managed in fishmeal, one relating to stabilisation, transportation, and shipping safety, the other relating to animal feed and food safety.  The United Nations International Maritime Organisation (IMO) has Codes and Conventions for packaged goods (IMDG) and bulk cargoes (IMSBC), each of which specify minimum limits for antioxidant inclusions in fishmeal prior to shipping.  This is an effective way of ensuring stability of the fishmeal during transport, hence safety, and is based on known concentrations of antioxidants above which fishmeal has been demonstrated to be stable under certain conditions. On the feed and food safety side, the emphasis is on achieving levels which are set below maximum limits, based on science that informs on safety risks, thereby driving the inclusion rate for antioxidants downwards towards a minimum.  We therefore have competing systems that drive inclusions of antioxidants in different directions for fishmeal, a situation which the fishmeal industry must balance in relation to continuing to providing safe, nutritious products. 

Since 2015 there has been a focus on the use and safety of antioxidants in food and feed, which is reflected in a review of several antioxidants in the European Commission’s feed additive legislation. Most, if not all, jurisdictions around the world regulate the use of antioxidants, whether at the level of feed ingredient (i.e. the fishmeal), or at the level of compound feed, or sometimes both, and are usually based on the setting of a maximum limit for antioxidant concentration.  The European Commission’s legislation is perhaps some of the strictest in the world, and the current position with feed additives may be accessed through the Commission’s webpage for the European Union Register of Feed Additives, here.

[1]  Meade, T. L.,  A New Development in Fishmeal Processing, Feedstuffs, May 19, 1956

[2] https://www.efsa.europa.eu/en/efsajournal/pub/7166

[3] https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32022R1375