Comment réduire le taux de contaminants environnementaux dans les huiles de poisson sans en affecter les caractéristiques nutritionnelles ?

Crude fish oil is an important ingredient in fish feed for fish farming; it can be used as functional food or neutraceutical (cod liver oil, EPA/DHA concentrates) or incorporated in healthy foods after refining. Major components of fish oil have positive nutritional properties. Polyunsaturated fatty acids can go up to 40% with variable proportions of EPA (C20:5) and DHA (C22-6) [ω-3 fatty acids]. Content of fat soluble vitamins is usually high. Unfortunately, fish oil is also sensitive to degradation products (polymeric and oxidized fat, increased polar content, off-flavor problems…). The beneficial nutritional properties of fish oil are in great contrast with the presence of heavy metals and persistent organic pollutants (POPs) such as polychlorinated dibenzo-dioxins and -furans (PCDDs/PCDFs) and polychlorinated biphenyls (PCBs), mainly originating from the environment. Usual steps for fish oil refining are neutralization, bleaching, winterization (optional) and deodorization. Processing difficulties consist in finding the best operating conditions for an effective removal of unwanted contaminants and a maximal preservation of the nutritional qualities (processing duality). In this work, different adsorbents (filter aid, silica powder, bleaching earth and active carbon) were tested for the best removal of PCDDs/PCDFs and PCBs; it was shown that filter aid, silica and bleaching earth have no significant effect on decontamination while removal of majority non ortho PCBs and PCDDs/PCDFs was possible with active carbon. Mono-ortho PCBs were significantly less absorbed by active carbon. Deodorization was further investigated. Processing temperature had a very pronounced effect on the reduction of PCDDs/PCDFs and PCBs. Already at 210 °C, all of them were removed efficiently to a level below the limit set by European Legislation. But temperature increase was limited by the risk of degradation of EPA/DHA (ω-3). Combination of active carbon treatment and deodorization was shown to be the best compromise to remove majority of the contaminants and to preserve the nutritional quality of fish oil. At low active carbon dosage and deodorization temperature below 200 °C, the total contamination level of PCDDs/PCDFs and PCBs can be reduced below level imposed by European Legislation.