Avaliação da composição lipídica e da capacidade antioxidante em filés de tilápias do Nilo (Oreochromis niloticus) alimentadas com diferentes fontes de ácidos graxos e antioxidantes

Abstract

The aim of this study was to evaluate the incorporation of polyunsaturated and conjugated fatty acids in tilapia fillets (Oreochromis niloticus), specifically alpha-linolenic acid (LNA) from the omega-3 series and isomers of conjugated linoleic acid (CLA) and conjugated linolenic acid (CLnA), through the supplementation of tilapia diet with chia oil (a source of LNA), concentrated of CLA (a source of CLA isomers) and tung oil (a source of CLnA isomers). Furthermore, the antioxidant capacity in tilapia fillets resulting from supplemented feeding diet containing substances which have antioxidant properties such as vitamin E, selenium and ethanolic extract of acerola fruit residue, was also evaluated. The experiment was conducted in the laboratory of Food Chemistry, Department of Chemistry of State University of Maringa, from September to December 2012. A total of 240 Nile tilapia were divided into three plastic tanks with continuous water flow and constant oxygenation. The fish spent 30 days in adaptation receiving the Control diet containing sunflower oil as the lipid source in order to obtain the zero time sample (0 days of supplementation). After this period, the different treatments were included separately: Treatment I (chia oil + tung oil + CLA + vitamin E), Treatment II (chia oil + tung oil + CLA + vitamin E + selenium) and Treatment III (sunflower oil + ethanolic extract of acerola fruit residue) during 60 days of experiment. New samples were taken at 15, 30, 45 and 60 days of supplementation, by collecting 15 fish/tank. The proximate and fatty acid compositions of all developed diets were evaluated, as well as the antioxidant capacity. In tilapia fillets from the different treatments, the fatty acids were identified and quantified in all periods of supplementation (0, 15, 30, 45 and 60 days) and the antioxidant capacity was also evaluated through the employment of DPPH, FRAP, ABTS and ORACFL assays. There was no significant difference (p>0.05) among the diets for the results of proximate composition. The fatty acid composition of the diets confirmed the transfer of the interest fatty acids, LNA and the isomers of CLA and CLnA, to TI and TII diets, as well as high amounts of linoleic acid (LA) in the Control and TIII diets, coming from the sunflower oil. The antioxidant capacity assays indicated better results in TI and TIII diets, and also showed the superiority of contribution of hydrophilic antioxidants in the total antioxidant capacity (TAC) of the diets. In fillets from the Treatments I and II were observed an increase of about 3 times in the content of LNA due to the addition of chia oil to these diets. The inclusion of concentrated of CLA to TI and TII diets resulted in the incorporation of the 18:2c9, t11 and 18:2t10, c12 isomers in tilapia fillets at higher levels than found naturally in dairy products and in meat from ruminant animals. The incorporation of conjugated linolenic acids was observed in fillets from the Treatments I and II, with a predominance of the alpha-ESA (alpha-eleostearic acid) isomer transfer, derived from tung oil added to the TI and TII diets. In fillets from the Treatment III, high levels of LA and arachidonic acid (AA), an important polyunsaturated long chain fatty acid (PUFA-LC), were verified. The application of the antioxidant capacity assays in fillet samples confirmed the superiority of TI and TIII diets in improving the antioxidant capacity of the fish. Thus, supplementation showed to be a good option for improving the nutritional value of fish fillet, contributing to the enrichment of lipid composition and antioxidant capacity of it, promoting a better product for human consumption