Seasonal variation of acid-soluble collagens extracted from the swim bladders and skins of bighead carp (Hypophthalmichthys nobilis) and grass carp (Ctenopharyngodon idella)

This study investigated the seasonal variation in the physicochemical properties of acid-soluble collagens (ASC) from the scales and skins of bighead carp and grass carp. The electrophoresis patterns of protein fraction and peptide hydrolysis treated by V8 protease were characterized using gel electrophoresis. Changes in thermostability were measured using differential scanning calorimetry, and collagen fibrils in vitro were observed using transmission electron microscopy. The ASC were mainly determined as type I collagens with triple helical structures. For collagens from the same tissue of the same fish species, similar protein fraction patterns and peptide hydrolysis patterns were observed, and the amino acid contents also showed no clear pattern of change with season. The thermal transition temperature of ASC showed a maximum seasonal variation of 0.5 °C, with no systematic pattern. The collagens could assemble into fibrils in vitro, and the d-periodicities of the fibrils showed no significant seasonal variation. The results suggested that the skins and swim bladders of two major freshwater species were reasonably stable as an alternative collagen source for year-round production.