Lipid characterization and properties of protein hydrolysates obtained from discarded Mediterranean fish species

Discards are an important fraction of the by-products produced by the fishing industry. As a consequence of their low commercial acceptance, it is necessary to provide added value to these underutilized materials. In this study the lipid fraction of three discarded fish species in the western Mediterranean Sea, namely sardine (Sardina pilchardus), mackerel (Scomber colias) and horse mackerel (Trachurus trachurus), was characterized and the angiotensin I-converting enzyme (ACE)-inhibitory and antioxidative activities of their protein hydrolysates were evaluated.

Processing of these biomaterials led to oils with a high content of omega-3 polyunsaturated fatty acids (PUFAs), ranging from 220.5 g kg(-1) for horse mackerel to 306.0 g kg(-1) for sardine. Regarding the protein fraction, most of the hydrolysates presented ACE inhibition values higher than 60%, corresponding to IC50 values varying from 345 µg protein mL(-1) for mackerel to 400 µg protein mL(-1) for sardine. Moreover, most of the hydrolysates exhibited acceptable antioxidative activity, namely 35-45% inhibition of 1,1-diphenyl-2-picrylhydrazyl (DPPH).

This study suggests that the three discarded species evaluated are valuable raw materials for the production of bioactive ingredients such as omega-3 PUFAs and protein hydrolysates exhibiting antihypertensive and antioxidative activities.