Dietary vitamin E further enhances the effectiveness of Clostridium autoethanogenum protein as an alternative source of soybean meal in grass carp ( Ctenopharygodon idellus) diets based on growth performance, flesh quality and antioxidant status

The effects of replacing soybean meal with Clostridium autoethanogenum protein and supplementing it with different gradients of vitamin E in grass carp diets on growth performance, flesh quality and antioxidant capacity were evaluated in a 69-day feeding trial. Five isonitrogen and isolipid diets were configured with the soybean meal-based diet (SM) served as the basal control diet, and the Clostridium autoethanogenum protein-based diet (CAP) as the treatment control diet. The CAP diet was supplemented with 80 mg/kg, 160 mg/kg and 240 mg/kg vitamin E (namely, 80VE, 160VE and 240VE), respectively. Final body weight (FBW) and specific growth rate (SGR) were significantly better in the CAP group than in the SM group (P < 0.05), and the 160 VE group was significantly better than the CAP group (P < 0.05). In terms of muscle quality, muscle fat content was significantly higher in the CAP group than in the SM group (P < 0.05), and muscle vitamin E content was significantly higher in each vitamin E-supplemented group than in the CAP group (P > 0.05). The total odor activity value in muscle in the CAP group was not significantly different from the SM group (P < 0.05), but the vitamin E-supplemented groups were significantly higher than the CAP group (P < 0.05). Muscle hardness and gumminess were significantly higher in the CAP group than the SM group and muscle shear force and gumminess were significantly higher in the 80VE group than the CAP group (P < 0.05). Muscle development-related genes in the CAP group were not significantly different from those in the SM group (P > 0.05), and Muscle Myf5 mRNA levels in the 160VE and 240VE groups were significantly higher than those in the CAP group, while the expression of MSTN genes was suppressed (P < 0.05). In terms of antioxidant properties, muscle MDA content was significantly higher in the CAP group than in the SM group (P < 0.05), and muscle MDA content was significantly lower in the 160VE and 240VE groups than in the CAP group (P < 0.05), at the same time, CAT and T-SOD activities were significantly higher (P < 0.05). In conclusion, complete replacement of soybean meal by the Clostridium autoethanogenum protein in grass carp diets promoted growth performance and muscle quality, but negatively affected antioxidant capacity, and supplementation of 160 mg/kg vitamin E in the CAP diet could further enhance growth performance and improve antioxidant capacity.