Collagenous proteins from black-barred halfbeak skin as a source of gelatin and bioactive peptides

In the current study, gelatin was extracted from black-barred halfbeak (Hemiramphus far) skin by successive alkaline and acid treatments and then hydrolyzed with Purafect®. The black-barred halfbeak gelatin (BG) and its hydrolysate (BGH) were characterized and compared to the commercial bovine gelatin (CG). Samples were evaluated for their antioxidant, antibacterial and angiotensin I-converting enzyme (ACE) inhibitory activities. Results obtained using size exclusion chromatography showed that BG contained lower level of high molecular weight proteins, compared to CG. In addition, the amino acids composition revealed that BG contained lower level of imino acids (Pro+Hpx), compared to CG. These differences reflect the variations observed in the gel strength and gelling and melting temperatures of both skin gelatins. Furthermore, high similarities were observed between CG and BG in terms of their Fourier transform infrared (FTIR) spectra, while their amino acid compositions were quite different. BGH, with a degree of hydrolysis of 12.5%, showed high antioxidant potential that was assessed by the scavenging activity, reducing power, oxygen radical absorbance capacity, β-carotene bleaching protection and lipid per-oxidation inhibition assays. In addition, BGH sample exhibited antibacterial activity against different Gram+ and Gram- bacteria. The ACE-inhibitory activity was also investigated. BGH showed an inhibitory effect of 80.76%, while BG inhibited the ACE only by 36.51% at 1 mg/ml. Thus, black-barred halfbeak gelatin represents a promising source of antioxidant, ACE-inhibitory and antimicrobial peptides that might prevent humans from several diseases.