Abstract: In this study, acid-soluble collagens were extracted from black and white skins of fresh flounder, and their physicochemical characteristics, emulsifying activity and emulsion stability were compared and analyzed. The structural characteristics were studied by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Additionally, solubility, rheological properties, isoelectric point, emulsifying activity index and emulsion stability were also investigated. FTIR analysis proved the existence of amide A, amide B, amide Ⅰ, amide Ⅱ, and amide Ⅲ, confirming that the triple helical chain conformation of the two collagens was completely maintained. The SEM results indicated that both collagens showed a porous, evenly distributed network structure, which proved that the original structure of collagen fibers was basically maintained during the extraction process. The emulsifying activity index (EAI) of the black skin collagen was significantly lower than that of the white skin collagen (P < 0.05), which were (2.60 ± 0.53) and (7.30 ± 0.41) m2/g, respectively, while the emulsion stability index (ESI) of the former was significantly higher than that of the latter (P < 0.05), which were (49.12 ± 5.18) and (27.56 ± 4.91) min, respectively. These results showed that certain differences exist in physicochemical characteristics and functional properties of acid-soluble collagens from different flounder skins.

Key words: Pleuronichthys cornutus, fish skin, acid-soluble collagen, extraction, physicochemical characterization