Antioxidant activity of protein hydrolysates obtained from discarded Mediterranean fish species

• The up-grading of five discarded fish species from the Mediterranean Sea was studied.
• Fish protein hydrolysates exhibiting antioxidant activity were produced.
• Highest DPPH inhibition was found for sardine (EC50 of 0.91 mg protein/mL).
• Sardine exhibited the highest chelating activity (EC50 of 0.32 mg protein/mL).
• Sardine and bogue hydrolysates presented the highest reducing power.

In this study, five discarded species in the Mediterranean Sea, namely sardine, horse mackerel, axillary seabream, bogue and small-spotted catshark, were evaluated as raw material for obtaining fish protein hydrolysates exhibiting antioxidant activity. The DH of the hydrolysates ranged from 13.2 to 21.0%, with a protein content varying from 60.7 to 89.5%. The peptide profile of all hydrolysates was very similar, except for the hydrolysate of small-spotted catshark. Their lipid content was found to be between 4.6 and 25.3%. The highest DPPH scavenging activity was found for the hydrolysates of sardine and horse mackerel with EC50 values varying from 0.91 to 1.78 mg protein/mL. Sardine and small-spotted catshark hydrolysates exhibited the highest ferrous chelating activity with an EC50 value of 0.32 mg protein/mL. Moreover, sardine and bogue hydrolysates presented the highest reducing power. Finally, a total of six antioxidant peptides were theoretically identified within the structure of myosin and actin proteins from sardine and small-spotted catshark. The potential antioxidant activity exhibited by the hydrolysates suggests that it is feasible to obtain added-value products such as natural antioxidants from these discarded species.