Effects of salt and sugar addition on the physicochemical properties and nanostructure of fish gelatin

Application of fish gelatin as a food component in replace of mammalian sources has attracted attentions recently. However, physicochemical properties of fish gelatin might be affected by other food components thus affecting its application. To determine whether and how sugar and salt components in food affect the physicochemical properties of fish gelatin, nanostructure of tilapia fish gelatin was studied by atomic force microscopy (AFM) with the secondary structure investigated by Fourier transform infrared (FTIR) spectroscopy. The results indicated that 1.5% NaCl addition led to a loss in molecular order in secondary structure which was accompanied with reducted gel strength; however, addition of 1.5% sucrose did not affect physicochemical and structural properties of fish gelatin. Fish gelatin possessed heterogeneous nanostructure including spherical aggregates, ring like structure, short and long rods as well as continuous fibre network. Incorporation of NaCl with fish gelatin increased diameter of spherical aggregates to more than two folds of control. These data suggest that addition of NaCl reduced gel strength through inducing large nano-aggregates, which could be at improper alignment that prevented the formation of a rigid gel. Interestingly, the fish skin gelatin studied here showed good storage stability over 30 days of storage at 4 °C. Sodium chloride affects fish gelatinʹs nanostructure and physicochemical properties more than sucrose at the same concentration.