The partial substitution of digestible protein with gelatinized starch as an energy source reduces susceptibility to lipid oxidation in rainbow trout(Oncorhynchus mykiss) and sea bass (Dicentrarchus labrax) muscle

We evaluated the influence of dietary gelatinized starch and protein on the fatty acid composition of muscle in rainbow trout and European sea bass an d on the susceptibility of flesh to lipid peroxidation. The possibility tha t flesh peroxidation could be accounted for by lipogenesis and the depositi on of fat was also explored. The inclusion of gelatinized starch in the die t of rainbow trout improved growth with respect to that observed in fish fe d crude starch (P < .001). This was especially noticeable at the lowest con centration of dietary protein tested (P = .037), suggesting that gelatinize d starch may partially replace protein in the production of energy without inducing a negative effect on growth. However, in European sea bass, the ge latinization of starch and dietary protein concentration showed no signific ant effect on final body weight. The intramuscular neutral lipid concentrat ion of the sea bass was reduced by the gelatinization of dietary starch (P = .034). The highest dietary protein concentration increased the proportion of saturated fatty acids in the neutral (P = .0742) and polar (P = .0033) lipid fractions. The dietary inclusion of high levels of protein in rainbow trout led to a lower concentration of total (n-3) (P = .0457) and (n-6) (P = .0522) fatty acids and a higher concentration of total monounsaturated f atty acids (P = .0006). The inclusion of gelatinized starch led to a lower concentration of(n-3) fatty acids (P = .0034) and a higher concentration of saturated fatty acids (P = .0007). The polar fraction was hardly affected by the same treatment. A significantly lower susceptibility of the dorsal m uscle to oxidation was observed in groups of European sea bass fed gelatini zed starch (P < .01). A similar trend was observed in rainbow trout, althou gh differences were not significant. The findings suggest that the digestib le protein concentration of nutrient-dense diets for rainbow trout and Euro pean sea bass can be reduced with a beneficial effect on tissue lipid oxida tion and no negative effects on growth and muscle composition.