Dietary protein source affects the susceptibility to lipid peroxidation ofrainbow trout (Oncorhynchus mykiss) and sea bass (Dicentrarchus labrax) muscle

This study was designed to explore the effect of protein source on muscle s usceptibility to lipid peroxidation in two representative species of fish f armed for human consumption: the freshwater rainbow trout and the seawater European sea bass. Four isoproteic diets (digestible protein in the range 3 66 to 392 for rainbow trout and 391 to 415 g/kg for European sea bass) were formulated to contain one of the following as the main protein source:fish meal, warm water alcohol-extracted or toasted soya protein concentrates or maize gluten meal. Highest daily growth indices were always achieved using the diets based on fish meal as the main source of protein (P < 0(.)05). F ish of both species given diets containing maize gluten and the toasted soy a protein concentrate showed slowest growth. The depressant growth effect o f the vegetable protein concentrates was greater in sea bass than in rainbo w trout. Dietary treatment was not correlated with any significant effect o n whole-body composition or intramuscular fat content except for ash concen tration in European sea bass. Under conditions of forced peroxidation in vi tro for 240 min, muscle specimens of trout and sea bass given diets contain ing fish protein as the main source of protein showed the highest peroxidat ion levels (P < 0.05); while the lowest peroxidation values were found in f ish given maize gluten-containing diets (P < 0(.)05). In the present case, the partial substitution of fish meal with vegetable proteins in diets led to a lower susceptibility of fish flesh to peroxidation. This finding may h ave applications in the production of fish of improved quality and longer s helf life.