Impact and consequences of riboflavin deficiency on flesh quality loss in grass carp (Ctenopharyngodon idella)
Fish is one of the cheapest and promising sources of animal production. Muscle is the main edible portion of fish. The present study explored the impact of dietary riboflavin on fish flesh quality and revealed a possible role of muscle antioxidant defense in flesh quality in relation to dietary riboflavin. Young grass carp (mean weight 275.82 ± 0.57 g) were fed diets containing graded levels of riboflavin (0.63, 1.95, 3.98, 6.02, 7.96 and 10.04 mg/kg diet) for eight weeks. The results indicated that riboflavin deficiency reduced muscle nutrients (protein, lipid, flavour amino acid and total essential amino acid) deposition. Furthermore, muscle shear force, pH value, and hydroxyproline concentration were decreased by riboflavin deficiency. However, muscle cooking loss and lactic acid content were increased by riboflavin deficiency. Additionally, riboflavin deficiency increased reactive oxygen species, malondialdehyde and protein carbonyl contents. The activities of copper/zinc superoxide dismutase (CuZnSOD), glutathione reductase (GR), catalase (CAT) and glutathione peroxidase (GPx), and reduced glutathione (GSH) content were decreased by riboflavin deficiency. Moreover, the relative mRNA expression of antioxidant enzymes, including CuZnSOD, CAT, GR and GPx, as well as antioxidant-related signaling molecules, including NF-E2-related factor 2 (Nrf2) and casein kinase 2 were down-regulated when fed with riboflavin deficient diet, whereas the relative mRNA expression of Kelch-like ECH-associated protein 1b was up-regulated by riboflavin deficiency. Collectively, the present study indicated that riboflavin deficiency reduced flesh quality, partly due to the inhibition of antioxidant defense through the Nrf2 signaling pathway.