Evaluations of the nutritional value of Jatropha curcas protein isolate in common carp (Cyprinus carpio L.)

Jatropha curcas seeds are rich in oil and protein. The oil is used for biodiesel production. Jatropha seed cake (JSC) obtained after oil extraction is rich in protein; however, it is toxic (phorbol esters content 1.3 mg/g) and consists of 50–60% shells, which are indigestible. The principle of isoelectric precipitation was used to obtain Jatropha protein isolate (JPI) from JSC and it was detoxified (DJPI). Carp (n = 45, 20.3 ± 0.13 g) were randomly distributed into five groups with three replicates and for 12‐week fed iso‐nitrogenous diets (crude protein 38%): Control [fishmeal (FM)‐based protein]; J₅₀ and J₇₅ (50% and 75% of FM protein replaced by DJPI); S₅₀ and S₇₅ (50% and 75% of FM protein replaced by soy protein isolate). Growth performance and nutrient utilisation parameters were highest in S₇₅ group and not significantly different to those in J₅₀ and S₅₀ groups but were significantly higher than those for all other groups. Similar trend was observed for protein and energy digestibilities of experimental diets, whereas opposite trend was observed for the feed to gain ratio. Activities of intestinal digestive enzymes did not different significantly between the five groups. In conclusion, DJPI is a good quality protein source for carp.