Isolation and characterization of acid soluble collagens and pepsin soluble collagens from the skin and bone of Spanish mackerel (Scomberomorous niphonius)

The objective of this study was to extract and characterize acid soluble collagens (ASCs) and pepsin soluble collagens (PSCs) from the skin and bone of Spanish mackerel (Scomberomorous niphonius) and to provide a simultaneous comparison of the four collagens. The yields of ASC-S (ASC from skin), PSC-S (PSC from skin), ASC-B (ASC from bone) and PSC-B (PSC from bone) were 13.68 ± 0.35, 3.49 ± 0.24, 12.54 ± 0.83 and 14.27 ± 0.66% (on wet weight basis), respectively. The four collagens contained glycine (341.6–352.6 residues/1000 residues) as the major amino acid and the contents of imino acids were between 177.1 and 184.3 residues/1000 residues. Amino acid composition, SDS-PAGE and FTIR confirmed that ASC-S, ASC-B and PSC-B were mainly composed of type I collagen with slight molecular structure differences, and PSCs had lower content of high-molecular weight cross-links than that of ASCs. The denaturation temperatures of ASC-S, PSC-S, ASC-B and PSC-B were 15.12, 14.66, 18.02 and 16.85 °C, respectively, which were much lower than those of collagens from the mammalian and tropical fish species due to low imino acid contents. All the collagens were soluble at acidic pH (1–4) and lost their solubility when the NaCl concentrations were above 2% (w/v). The four lyophilized collagens displayed a uniform and regular network ultrastructure based on the ultrastructural analysis. The isolated collagens from Spanish mackerel could serve as an alternative source of collagens for further application in food and neutraceutical industries.