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Angiotensin I-converting enzyme (ACE) inhibitory peptides have been searched in thornback ray (Raja clavata) muscle hydrolysed with Bacillus subtilis A26 proteases until a hydrolysis degree of 18.35%. The hydrolysate showed an IC50 of 0.83 mg mL−1. To identify peptides responsible for this activity, the extract was eluted through size-exclusion chromatography and fractions collected. The highest ACE inhibitory activity was found for fractions F2 and F3 which had IC50 of 0.42 and 0.51 mg mL−1, respectively. These fractions were analysed by nano-liquid chromatography coupled to tandem mass spectrometry (nLC-MS/MS). A total of 131 and 108 peptide sequences mainly derived from actin, myosin heavy chain and procollagen alpha 1 chain proteins were identified in fractions F2 and F3, respectively. FQPSF and LKYPI showed the best results with an IC50 of 12.56 and 27.07 μM, respectively. These results prove the potential of thornback ray muscle hydrolysate as a source of ACE inhibitory peptides., This work was funded by a grant from the Ministry of Higher Education and Scientific Research of Tunisia and grant Prometeo/2012/001 from Conselleria d´Educació Cultura i Sport of Generalitat Valenciana, both are acknowledged. JAEDOC- CSIC postdoctoral contract cofounded by ESF to L.M. is also acknowledged

Summary The sensory determination of ammonia in raw, steamed and boiled ray wings using a scoring system appeared to be a valuable method of quality assessment. The borderline of acceptability was reached after 10 (±1) days in ice. A combination of the steaming and boiling tests (with addition of acetic acid and salt) was useful to confirm definite spoilage or to indicate the approach to the borderline of acceptability. The chemical determination of ammonia appeared to be a useful objective method in addition to the organoleptic tests. Thornback ray was borderline at a concentration of 60–70 mg N. From the other related parameters determined (urea, pH, redox potential, total bacterial count, α-amino nitrogen) only pH appeared to be of value.