African catfish (Clarias gariepinus) skin gelatin: Extraction optimization and physical–chemical properties

• Use of fish by-products.
• Variables that can influence the viscosity of the African catfish skin gelatin.
• High temperatures and prolonged extraction times resulted in reduced viscosity.
• Increasing the H2SO4 concentration promotes high viscosity.

Large amounts of by-products are generated in fish processing. It is estimated that the residues from filleting can represent up to 75% of the total weight, and that approximately 30% of such residues consist of skin and bones. There is currently an increased interest in fish gelatin. This work investigated the variables of the extraction process that can potentially influence the gelatin properties of catfish skin and its physicochemical characteristics. The screening step determined the extraction temperature °C, extraction time h, and H2SO4% p/v concentration, which were selected to assemble a central composite rotational design (CCRD) in order to elucidate its effect on gelatin viscosity (p < 0.05). The viscosities of the African catfish skin gelatin were between 2.05 and 2.85 mPa·s. The extraction process exhibited a yield of 11.4% and gelatin gel strength and melting point was of 234 g and 25.7 °C, respectively.