Characterization and comparative assessment of antioxidant and ACE inhibitory activities of thornback ray gelatin hydrolysates

•Different gelatin hydrolysates from thornback ray (TRGHs) skin were prepared using various proteases;•TRGHs exhibited varying in vitro antioxidant activities depending on the test used;•TRGHs showed in vitro ACE inhibitory activity;•TRGHs could be used as ingredients to formulate functional foods. The angiotensin I-converting enzyme (ACE) inhibitory activities and antioxidant properties of thornback ray gelatin hydrolysates (TRGHs) prepared by treatment with proteolytic proteases from Bacillus subtilis A26, Raja clavata crude alkaline protease extract, Alcalase and Neutrase were investigated. All gelatin hydrolysates showed different degrees of hydrolysis and hydrophobic/hydrophilic peptides ratio. Moreover, they possess high protein content (70.04 ± 0.55–74.14 ± 0.28%). The antioxidant activity was assayed using various in vitro tests. The highest antioxidant activity was observed with hydrolysate obtained by treatment with A26 proteases (TRGH-A26) which exhibited a 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity with a concentration that produces 50% of inhibition (IC50) of 1.98 ± 0.02 mg/ml of sample, reduced the ferric ions with an absorbance at 700 nm of 0.962 ± 0.07, prevents bleaching of β-carotene with 73.02 ± 1.90% inhibition and gave an antioxidative efficacy of 180 ± 0.08 µmol/ml α-tocopherol equivalents at 5 mg/ml in the phosphomolybdenum assay. However, gelatin hydrolysate treated with Alcalase (TRGH-Alcalase) was the most potent to prevent DNA oxidation. For the ACE inhibitory activity, all hydrolysates displayed ACE-inhibitory activity. TRGH-A26 and TRGH-Alcalase exhibited the highest activity with 85 ± 0.65 and 82 ± 0.49%, respectively, at 5 mg/ml. The results revealed that TRGHs could be used as ingredients to formulate functional foods.