Abstract: A series of edible composite films were prepared by blending tilapia skin gelatin with sodium alginate. The effects of sodium alginate on physicochemical properties of composite films were investigated. The results showed that tilapia skin gelatin had good film-forming property, but poor mechanical properties. The tensile strength and the elongation at break of composite films were improved compared with pure gelatin films. The maximum tensile strength of 6.6 MPa was obtained upon addition of 40% sodium alginate, an increase of 20% and 43%, respectively compared with pure gelatin film (5.5 MPa) and pure sodium alginate film (4.6 MPa); the maximum elongation at break of 120% was also achieved, an increase of 87.5% and 26.7% over pure gelatin film (64%) and pure sodium alginate film (88%), respectively. The water solubility and hygroscopicity of sodium alginate were as high as 100% and 48.7%, respectively. The water solubility of composite films was controlled below 55% and the hygroscopicity was in the range between 25% and 40%, which were greatly improved. The analysis of rheological properties and X-ray diffraction showed that sodium alginate and gelatin had good compatibility with each other, resulting in a stable composite film. Blended solutions of sodium alginate and gelatin were non-Newtonian fluid. The viscosity and thickening ability of composite films were higher than that of pure gelatin films.

Key words: tilapia skin, gelatin, sodium alginate, composite films, physicochemical properties