Comparative study on acid-soluble and pepsin-soluble collagens from skin and swim bladder of grass carp (Ctenopharyngodon idella).

BACKGROUND: Collagen has a wide range of applications in food, biomedical and pharmaceutical products. RESULTS: The collagens in grass carp (Ctenopharyngodon idella) skin and swim bladder were extracted using acetic acid and pepsin. Higher yield of pepsin-soluble collagen (PSC) was obtained from skin (178 g kg(-1)) than from swim bladder (114 g kg(-1)). Not surprisingly, yields of PSC from skin and swim bladder were also higher than those of acid-soluble collagen (ASC) from the same organs (89 and 51 g kg(-1)). Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) profiles showed that ASC and PSC were type I collagens, with PSC containing a higher proportion of α components than ASC. Fourier transform infrared spectra revealed that ASC and PSC were very similar in their protein secondary structures. Scanning electron micrographs showed that the collagens had a spongy structure, with more pores being obtained in swim bladder than in skin collagens. The collagens showed high solubility in the acidic pH range. However, their solubility decreased in the presence of NaCl at concentrations above 20 g kg(-1). CONCLUSION: Collagens were successfully extracted from the skin and swim bladder of grass carp. These fish by-products could serve as an alternative source of collagens for a wide variety of applications in the food and nutraceutical industries.