Antioxidants and Fishmeal
Securing Quality and Optimising the Utilisation of a Finite Resource
- Fishmeal is a natural product which contains oil and therefore omega-3 fatty acids at significant levels
- Due to their chemical properties, fats 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 is critical from a farmed animal’s nutritional perspective. Physically, there are hazards attached to oxidation as a process (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
- There are two important frameworks for how antioxidants are managed in fishmeal, one relating to stabilisation, transportation and shipping safety, the other relating to animal feed and food safety
- 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
Fishmeal is a brown powder obtained after cooking, pressing, drying and milling of fresh raw fish and/or food fish trimmings and other byproducts. It is known, and highly regarded in animal and aquafeeds for its high protein content of usually >65% dry matter, and comparatively high digestibility.
Fishmeal contains fish oil
Although fish oil is generated in the same process and is manufactured as a separate product, fishmeal retains a proportion of the oil at significant levels, generally comprising approximately 8-12% of the fishmeal by weight. (there is some variability in this figure, especially with some byproduct meals, notably white fishmeals) 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 is a reflection of the composition of that resource. That raw material differs according to whether it is sourced from capture fisheries byproduct, aquaculture byproduct, or whole fish (usually small pelagic fish species). All these materials vary with regard to their proximate composition, i.e. carrying different protein, water, ash and fat contents. The total content of fat in fishmeal will clearly therefore show some differences, but not only the total fats present in fish differs from one species to another, but there are also important differences in the fatty acid profile of the oils in different species and therefore fishmeals, as there are in fish oil products themselves.
Fishmeal is rich in the Omega-3 long chain polyunsaturated fatty acids
Those oils therefore vary in absolute level and profile, but one thing they do have in common is the presence of comparatively high levels of omega-3 long-chain polyunsaturated fatty acids . Those include the important eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), 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. Although there are some developments in the production of long chain omega-3 oils through mechanisms such as genetic modification of plants or the farming of marine algae, annual supply of omega-3 oils at this stage is a finite resource obtained from reduction fisheries, and increasingly from trimmings. It is therefore important to protect the limited annual supply of these materials as far as possible.
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 is usually accompanied by self-heating of the substrate, which can generate temperatures within the milieu that are significantly higher than ambient conditions, thus carrying 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 achieving temperature increase under limiting conditions and ultimately presenting 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.
Antioxidants used as stabilisers
Mitigation of that risk since the 1950s has been through the addition of effective antioxidants which stabilise the product. This was an early breakthrough for the fishmeal industry as the inclusion of antioxidants at the end of the manufacturing process was 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 effectively to stabilise fishmeal, including ethoxyquin, butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), tocopherols (with, or without rosemary extract). Of these ethoxyquin has been perhaps the most 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.
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 International Maritime Organisation Codes and Conventions for packaged goods (IMDG) and bulk cargoes (IMSBC) specify minimum limits for antioxidant inclusions in fishmeal prior to shipping. This is an affective way of ensuring stability of the fishmeal during transport, hence safety, and is based on known concentrations of antioxidants above which fishmeal is assumed to be stable under normal 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.
At the time of writing (March 2020) there is an increasing focus on the use and safety of antioxidants in food and feed, which has been active over the last decade or so and 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.
 Meade, T. L., A New Development in Fishmeal Processing, Feedstuffs, May 19, 1956