Purity and yield of collagen extracted from southern catfish ( Silurus meridionalis Chen) skin through improved pretreatment methods

The economic and sustainable use of fish-processing by-products has received considerable attention. Large amounts of fish skin discarded by industry processes can be a source of collagen extraction. This study developed a method to extract collagen with high purity and yield from Southern catfish skins through improved pretreatment methods. Multiple degreasing methods effectively removed fat from fish skins and obtained a maximum degreasing rate (90.24%). The results of electrophoretic, hydroxyproline-content, and extraction-rate analyses revealed that the collagen extracted from defatted skin, which decoloured in 0.5% hydrogen peroxide solution (pH 10), exhibited higher purity and the highest yield (23.14% wet weight and 78.57% dry weight, respectively) as compared with other decolouration conditions. The histological appearance of pretreated fish skin indicated that the non-collagenous substances were removed effectively and the fibres loosened. Amino acid analysis, ultraviolet spectra, Fourier transform infrared (FTIR) spectroscopy, and thermal-stability analysis indicated that the collagen isolated from fish skin under optimal pretreated conditions was classified as type I. Our method for the optimal pretreatment of collagen extracted from fish skin following degreasing and decolouring procedures resulted in improved collagen purity and yield.