The preparation of protein hydrolysates from black scabbardfish (Aphanopus carbo) by-products (BSB) was studied as an alternative for the upgrading of this raw material. Different levels of Protamex (TM) were used in the hydrolysate preparation and the peptides obtained and the lipids present in each of the four fractions obtained after centrifugation of the hydrolysed material were characterized. The nitrogen solubilization achieved was around 83% and degree of hydrolysis (DH) was about 57%. A high proportion of the peptides had molecular weights lower than 1000 Da. The highest percentage of oil remained in the emulsion (50-65%) and the highest percentage of free oil obtained was ca. 36%. The fatty acid profile of lipids present in the BSB and in the different fractions was similar. The triacylglycerols were dominant in all fractions and the highest percentage of phospholipids was detected in the oil from sludge and hydrolysate, followed by the emulsion but they were not present in the free oil. Cholesterol and cholesterol esters were detected in all fractions at low levels. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity and the reducing power of BSB hydrolysates increased with increasing DH. However, the hydroxyl scavenging activity decreased with DH. (C) 2009 Elsevier Ltd. All rights reserved.