Gelatins and antioxidant peptides from Skipjack tuna (Katsuwonus pelamis) skins: Purification, characterization, and cytoprotection on ultraviolet-A injured human skin fibroblasts

For full use of Skipjack tuna (Katsuwonus pelamis) canning by-products, gelatins (STG) were extracted from tuna skins using acid (STG-A), enzyme (STG-E) and hot water (STG-H) methods with yields of 65.30 ± 1.56%, 39.83 ± 1.61%, and 50.97 ± 1.44%, respectively. Due to the high imino acid contents (228, 216, and 213 residues/1000 residues for STG-A, STG-E, and STG-H, respectively), STG-A showed the highest transparency and gel strength properties. Amino acid analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), ultraviolet (UV) and Fourier transform infrared spectroscopy (FTIR) analysis confirmed that STG-A, STG-E, and STG-H kept the main structure of type I collagen, but enzyme and hot water extraction methods showed much stronger hydrolysis ability on α and β chains. Moreover, neutrase hydrolysate (STG-AH) of STG-A showed the highest 1,1-diphenyl-2-picrylhydrazyl radical (DPPH•) scavenging activity and the fraction STG-AH-І (<3.5 kDa) from STG-AH prepared by ultrafiltration could significantly protect human skin fibroblasts (HSFBs) against ultraviolet-A (UVA) injury. Furthermore, nineteen peptides with high antioxidant activity were purified from STG-AH-І and identified. These results suggested that STG-AH and its derived antioxidant peptides could serve as potential ingredients applied in health benefiting products for preventing UVA injury.