Characterization of acid-and pepsin-soluble collagens from spines and skulls of skipjack tuna(Katsuwonus pelamis)

Acid-soluble collagen(ASC) and pepsin-soluble collagen(PSC) from the spine(ASC-SP and PSC-SP) and skull(ASC-SK and PSC-SK) of the skipjack tuna,Katsuwonus pelamis,were successfully isolated and characterized.The yields of ASC-SP,PSC-SP,ASC-SK and PSC-SK were(2.47±0.39)%,(5.62±0.82)%,(3.57±0.40)%,and(6.71±0.81)%,respectively,on the basis of dry weight.The four collagens contained Gly(330.2-339.1 residues/1 000 residues) as the major amino acid,and their imino acid contents were between 168.8 and 178.2 residues/1 000 residues.Amino acid composition,SDS-PAGE,and FTIR investigations confirmed that ASC-SP and ASC-SK were mainly composed of type I collagen,and had higher contents of high-molecular weight cross-links than those of PSC-SK and PSC-SP.The FTIR investigation also certified all the collagens had triple helical structure.The denaturation temperatures of ASC-SK,PSC-SK,ASC-SP,and PSC-SP were 17.8,16.6,17.6,and 16.5℃,respectively.All isolated collagens were soluble at acidic pH(1-5) and lost their solubilities when the NaCl concentration was above 2%(W/V).The isolated collagens from the spines and skulls of skipjack tuna could serve as an alternative source of collagens for further application in food,cosmetic,biomedical,and pharmaceutical industries.