Dietary histidine deficiency induced flesh quality loss associated with changes in muscle nutritive composition, antioxidant capacity, Nrf2 and TOR signaling molecules in on-growing grass carp (Ctenopharyngodon idella)

This study was a part of a larger research that involved in determination of the effects of dietary His on fish growth, health and flesh quality, and used one growth trial with our previous study which showed the growth retardation induced by dietary His deficiency. The present study was conducted to assess the effect of dietary His on flesh quality of fish and the possible role of antioxidant capacity in flesh quality in relation to dietary His. A total of 540 on-growing grass carp (Ctenopharyngodon idella) (279.8 +/- 1.07 g) were randomly fed graded levels of His at 2.0 (un-supplemented control), 3.7, 5.9, 7.9, 9.8 and 12.2 g/kg diet for 8 weeks. Results showed that compared with the dietary His level of 7.9 g/kg diet, dietary His deficiency (2.0 g/kg diet) significantly decreased nutrients contents, including protein, some essential amino acids (including lysine, methionine, threonine, leucine, histidine and arginine), lipid and unsaturated fatty acid contents in fillet of on-growing grass carp (P < .05). Meanwhile, the His-deficient diet decreased hydroxyproline contents, shear force value and pH (P < .05), whereas increased cooking loss, activities of cathepsin B and L in fish muscle (P < .05). Furthermore, malondialdehyde (MDA) and protein carbonyl contents in muscle were significantly increased by His-deficient diet (P < .05), whereas, total superoxide dismutase (T-SOD), CuZnSOD, catalase (CAT), glutathione peroxidase (GPx) activities and glutathione content in muscle of grass carp were significantly decreased by dietary His deficiency (P < .05). Additionally, the His-deficient diet down-regulated CuZnSOD, CAT, GPx, and signaling molecules Nrf2, TOR and S6K1 genes expression (P < .05), but up-regulated Keapl gene expression, total and nuclear Nrf2 protein levels, and phosphorylated TOR levels in muscle of grass carp (P < .05). In summary, the present results indicated that dietary His deficiency induced flesh quality loss partly related to the decreased nutritive compositions and antioxidant capacities through Nrf2 signaling in on-growing grass carp.