Improvement of gelatine extraction from tuna skin using a eutectic solvent

Abstract

The growing attention on sustainability in the food industry and waste management has increased interest in the valorisation of fish processing by-products, such as skin, which is rich in collagen and can be processed into gelatine. Traditional methods for gelatine extraction face significant challenges, particularly related to the use of harsh chemicals, environmental concerns, and inefficiencies in protein separation. This study proposes an improved method for gelatine extraction from tuna skin, using a eutectic solvent composed of urea and sodium acetate trihydrate, and also its 65 wt% aqueous solution, as maceration solvents. The method, applied to yellowfin and skipjack tuna skins, overcomes the limitations of previous approaches by reducing the extraction temperature and time, enhancing mass transfer, and improving the functional properties of the extracted gelatine. Compared to traditional extraction techniques and previous eutectic solvent-based methods, this approach avoids the use of aggressive solvents and the complex recovery of protein. The gelatine obtained exhibited improved characteristics, including higher hydroxyproline content, higher molecular weight of polypeptide chains, and better rheological properties (elastic modulus and melting and gelling temperatures). These improvements were more pronounced in the gelatine extracted from yellowfin tuna samples, particularly those pretreated with the aqueous solution of the eutectic mixture at 12 °C. The method also resulted in better thermal stability of the extracted gelatine, as confirmed by TGA analysis. This study highlights the potential of eutectic solvents, and their aqueous solutions, for efficient and sustainable gelatine extraction from fish skin, offering a promising alternative to traditional and less sustainable methods.