Iodine enrichment of rainbow trout flesh by dietary supplementation with the red seaweed Gracilaria vermiculophylla Luísa M.P. Valente a,b, ⁎, Paulo Rema c , V. Ferraro d , M. Pintado d , Isabel Sousa-Pinto a,e , Luís M. Cunha f , M.B. Oliveira g , Mariana Araújo a,g a CIIMAR/CIMAR — Centro Interdisciplinar de Investigação Marinha e Ambiental, Universidade do Porto, Rua dos Bragas 289, 4050-123 Porto, Portugal b ICBAS — Instituto de Ciências Biomédicas de Abel Salazar, Universidade do Porto, Rua de Jorge Viterbo Ferreira 228, 4050-313 Porto, Portugal c CECAV/UTAD — Universidade de Trás-os-Montes e Alto Douro, Quinta de Prados, Apartado 1013, 5001-801 Vila Real, Portugal d CBQF — Centro de Biotecnologia e Química Fina, Laboratório Associado, Escola Superior de Biotecnologia, Universidade Católica Portuguesa/Centro Regional do Porto, Rua Arquitecto Lobão Vidal, Apartado 2511, 4202-401 Porto, Portugal e FCUP — Departamento de Biologia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal f LAQV, REQUIMTE, Faculdade de Ciências, Universidade do Porto, Campus Agrário de Vairão, Rua Padre Armando Quintas, 7, 4485-661 Vila do Conde, Portugal g LAQV, REQUIMTE, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira 228, 4050-313 Porto, Portugal abstract article info Article history: Received 26 February 2015 Received in revised form 1 May 2015 Accepted 2 May 2015 Available online 7 May 2015 Keywords: Flesh quality IMTA-cultivated seaweed Sensory analysis Functional food The effects of different dietary inclusion levels (0, 5 and 10%) of IMTA-cultivated Gracilaria vermiculophylla on rainbow trout growth performance and flesh quality traits were evaluated. Flesh chemical composition (mois- ture, protein, lipid, vitamin E and iodine contents), sensory attributes and instrumental color were determined after a feeding period of 91 days with the experimental diets. The antioxidant activity of muscle carotenoids and hydrolysates was also determined by the 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) methods. By the end of the experiment, fish fed CTRL or G5 diet reached similar body weight (215–220 g), but fish fed G10 weighed significantly less (167 g). Seaweed inclusion in- creased flesh moisture and decreased lipid content, with significant differences between the G5 and CTRL groups. Vitamin E content varied among treatments with CTRL fed fish presenting the highest levels of α-tocopherol. Io- dine levels in the flesh increased with the seaweed inclusion, with fish fed G5 doubling its iodine content (214.5 μg/kg) in relation to the CTRL (111.7 μg/kg). Instrumental color showed that cooked fillets from fish fed seaweed-rich diets were more luminous (L*), less yellowish (b*) and more reddish (a*) than the CTRL. The sen- sory evaluation showed that fish fed with seaweed had juicier fillets than the CTRL with G5 presenting the most intense (pinkish) color. The instrumental differences are balanced in such a way that the sensory panel perceived G5 as the sample with higher color intensity. Muscle carotenoid extracts presented no significant antioxidant ac- tivity through the ABTS and DPPH assays, whereas muscle hydrolysates showed similar antioxidant activity in all dietary treatments (ca. 33% through DPPH assay). The inclusion of Gracilaria sp. meal in diets for rainbow trout seems to be possible for up to 5%, as higher inclusion levels resulted in significantly smaller fish. The sensory panel perceived G5 as the sample with higher color inten- sity and juicier than the CTRL. Moreover, flesh iodine content doubled in fish fed G5, confirming seaweed as a nat- ural and effective tool to increase the nutritional value of rainbow trout. Statement of relevance/impact of your paper to the general field of commercial aquaculture This paper is relevant for the aquafeed industry and fish consumers. Fish meal has traditionally been the major dietary protein source for fish, but its reduction in aquafeeds is now a priority goal for the further expansion and sustainability of farmed fish production. Seaweeds may act as nutrient supply in fish, which in turn could ul- timately function as vehicle of valuable compounds in human nutrition. This paper shows that 5% Gracilaria sp. meal can be a natural and effective tool to increase the nutritional value of rainbow trout flesh without impacting growth. © 2015 Elsevier B.V. All rights reserved. Aquaculture 446 (2015) 132–139 ⁎ Corresponding author at: CIIMAR/CIMAR — Centro Interdisciplinar de Investigação Marinha e Ambiental, Rua dos Bragas, 289, 4050-123 Porto, Portugal. E-mail address: lvalente@icbas.up.pt (L.M.P. Valente). http://dx.doi.org/10.1016/j.aquaculture.2015.05.004 0044-8486/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online