Effects of Salt Concentration on Gel Quality and Stress Relaxation of Pig Skin Gelatin

To investigate the effect of different concentrations of sodium chloride (NaCl) on the gel properties of gelatin, the triple helix content, texture properties, water-holding capacity, water distribution, microstructure and stress relaxation characteristics of gels of 10% (m/m) pig skin gelatin solution containing different concentrations (0.0, 0.5 and 1.0 mol/L) of sodium chloride were analyzed. The results showed that with the increase in sodium chloride concentration, gumminess and chewiness was significantly reduced; the hardness of gelatin gel with 1.0 mol/L NaCl was 2.24 kg, lower than that (3.15 kg) of the control group. The increase in NaCl concentration limited the formation of triple helices in the gelatin solution; gelatine gels showed a looser network structure with increasing NaCl concentration, with reduced network density, increased pore size and a significant decrease in water-holding capacity. The stress relaxation behavior of gelatin gels with different salt concentrations was quite different. When the three-element Maxwell model was used to fit the stress relaxation test results, the equilibrium elastic modulus of gelatin gel with 1.0 mol/L NaCl was 53% lower than that of the control group. However, when the CONTIN model was used to fit the stress relaxation test results, the reproducibility of relaxation peak distribution of the gel was poor. In conclusion, the increase in NaCl reduced the formation of triple helix in gelatin gel, resulting in a loose network structure and ultimately weakening the mechanical properties and water retention capacity of gelatin gel. The decrease in mechanical properties of gelatin was consistent with the results of the stress relaxation test.