Abstract
This study was conducted to examine the effects of dietary valine on the physical and flavor characteristics, fatty acid (FA) profile, antioxidant status and Nrf2-dependent antioxidant enzyme gene expression in the muscle of young grass carp (Ctenopharyngodon idella) fed increasing levels of valine (4.3, 8.0, 10.6, 13.1, 16.9 and 19.1 g/kg) for 8 weeks. Compared with the control group, the group fed valine showed improved physical characteristics of fish fillets (increased relative shear force, hydroxyproline, protein and lipid levels and decreased cathepsin B and L activities, as well as cooking loss, were observed). Moreover, valine improved the flavor of young grass carp fillets by increasing the amino acid (AA) concentration in fish muscle (increased aspartic acid, threonine, glutamine, cystine, methionine, leucine, tyrosine, phenylalanine, lysine, histidine, arginine and valine concentrations were observed). Additionally, optimal valine supplementation increased the potential health benefits to humans by decreasing the saturated FA (C15:0 and C16:0) concentration and increasing the unsaturated FA (monounsaturated FAs (MUFAs), such as C16:1, C18:1c+t and C20:1, and polyunsaturated FAs (PUFAs), such as C18:3n-3, C20:2 and C22:6) concentration. In addition, the reduced glutathione (GSH) content and the activities of Cu/Zn superoxide dismutase (SOD1), catalase (CAT) and Selenium-dependent glutathione peroxydase (Se-GPx) increased under valine supplementation (P < 0.05). Furthermore, the SOD1, CAT and Se-GPx mRNA levels increased with dietary valine levels, possibly due to the up-regulation of NF-E2-related factor 2 (Nrf2), target of rapamycin (TOR) and ribosomal protein S6 kinase 1 (S6K1) and the down-regulation of Kelch-like-ECH-associated protein 1 (Keap1) in muscle (P < 0.05). In conclusion, valine improved the physical and flavor characteristics, FA profile, and antioxidant status and regulated the expression of the antioxidant enzyme genes Nrf2, Keap1, TOR and S6K1 in fish fillets.
Highlights
In China, farmed fish account for more than 70% of the total food fish supply [1]
We investigated the effects of valine on the physical and flavor (AA) characteristics, fatty acid (FA) profile, antioxidant status and NF-E2-related factor 2 (Nrf2)-dependent antioxidant enzyme gene expression in the muscle of grass carp; this information could be used to preliminarily identify a valine-dependent mechanism that improves fillet quality
The present study showed that valine increased the protein-bound amino acid (AA) in muscle such as aspartic acid, threonine, glutamine, cystine, methionine, leucine, tyrosine, phenylalanine, lysine, histidine, arginine and valine contents, suggesting that valine may have partially improved the flavor of young grass carp fillets by altering the AA concentration in the fish muscle
Summary
In China, farmed fish account for more than 70% of the total food fish supply [1]. Grass carp is a native Chinese freshwater fish that is widely cultured in China because of its good taste and high nutritional value [2]. It has been reported that valine is a major substrate for the synthesis of α-melanocyte-stimulating hormone (α-MSH) in fish [9] In both keratinocytes and melanocytes, α-MSH significantly improves antioxidant status and increases γ-glutamylcysteine-synthetase and glutathione (GSH)-S- transferase Pi gene expression [10]. The growth and development of these organs depend on the structural integrity of cells and have been associated with antioxidant defenses [14] Based on these studies, we speculate that dietary valine may influence flesh quality parameters and warrants further investigation. Jian), an optimum valine diet increases the Na+, K+-ATPase activity [22] These data suggest that valine may affect the AA content in fish, but no studies have investigated this hypothesis. These data indicate that valine might affect FA content and requires further investigation
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