The skin of the rainbow trout contains many more omega-3 than the same fish fillets and stands to be a product of nutritional interest. This is revealed in a research by the Department of Agriculture, Food, Environment and Forestry conducted together with the University of Udine.
Omega-3s, as the science of nutrition has long documented, are an important ally of our health. These polyunsaturated fatty acids allow the maintenance of metabolic functions and the resolution of inflammatory processes of various nature. The human body synthesizes a small part of them. This is why it requires food containing fish or, more generally, fish products to meet its needs.
New knowledge in this field come from a study on the skin of the rainbow trout, published in “Waste and Biomass Valorization” by the aquaculture research group of the Department of Agriculture, Food, Environment and Forestry (DAGRI) of the University of Florence, in collaboration with the University of Udine [“Rainbow Trout (Oncorhynchus mykiss) Skin as Potential n-3 Fatty Acid Source” https://doi.org/10.1007/s12649-021-01384-3]. In the study, carried out as part of the project SUSHIN (SUstainable fiSH feeds INnovative ingredients) funded by Ager (AGER2-SUSHIN Cod. 2016-0112), the team found that the skin of the rainbow trout contains more omega-3 than the same fish fillets and could be appreciated again for nutritional purposes.
“The world health authorities – as the head of the aquaculture research group Prof. Giuliana Parisi explains – recommend a daily intake of about 500 mg per adult of omega-3, in particular eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), that is to say, the equivalent of 3.5 g per week. This amount is generally associated with the consumption of about 2-3 portions of 100 g of fish.”
Many species of fish are unable to produce EPA and DHA fatty acids from scratch and therefore need to get them through their diet and then accumulate them in their tissues. About 60% of the total production of fish products for human consumption comes from aquaculture, which, in turn, depends on natural resources for supplying the most noble ingredients of feed, fish meal and oil, the main source of omega-3 in the diet of carnivorous farmed fish.
“In the last 30 years, due to the depletion of natural fish stocks, ingredients of marine origin have been severely reduced and have been replaced with vegetable protein and oil sources. This change in feed has reduced the omega-3 content in farmed fish over time. As a consequence, in the near future, not only will we have to meet the demand for food of animal origin (especially fish) by a growing world population, but we will also find ourselves with food of lower nutritional quality”, says Unifi researcher Giulia Secci, among the authors of the study, together with young scholars Leonardo Bruni and Yara Husein, and Francesca Tulli, Professor in Udine.
In order to increase the supply of EPA and DHA, the path seems to be that of the valorization of by-products and the prevention of food waste. For this reason, this study aimed to characterize the fatty acid profile of the skin of the rainbow trout (Oncorhynchus mykiss) fed with alternative protein sources (meal from the larvae of the insect Hermetia illucens).
“Trout skin is a precious source of omega-3: the average content of omega-3 found in it amounts to 25% of the total fatty acids, compared to 15% in the fillets of the same animals”, Giuliana Parisi comments. “And the most important thing is that this percentage of omega-3 tends to remain constant in the skin, regardless of the diet given to animals.
It is therefore necessary to review our eating habits and to enhance this “not so noble” but extremely rich part of the fish, in order to avoid throwing away essential nutrients such as fatty acids, as well as the daily work of those who commit themselves to increasing the sustainability of the fish sector”, Parisi concludes.