Rheology, texture and microstructure of gelatin gels with and without milk proteins

The effects of gelatin concentration, pH and addition of milk proteins on the physical and microstructural properties of type B gelatin gels were studied by small deformation rheology, texture analysis and scanning electron microscopy. Whey protein isolate (WPI), milk protein concentrate (MPC) and skim milk powder (SMP) were used as sources of milk proteins. The elasticity of gelatin gels was significantly affected by the concentration of gelatin. Higher gelatin concentrations led to a stronger gel, and higher gelling and melting temperatures. However, all the gelatin gels at concentrations from 1.0 to 5.0% melted below human body temperature. Rheological properties of gelatin gels were independent of pH in the range pH 4.6–8.0. At pH 3.0 gelation of gelatin was significantly inhibited. Addition of SMP and MPC significantly enhanced the rheological properties of gelatin gels, while addition of WPI had a negative effect on them. However, the effect of addition of milk proteins was dependent on the gelatin concentration. Textural results showed that addition of all milk powders increased the hardness of gelatin gels at high gelatin concentration (5.0%). The fracturability of the gels was greatly influenced by pH. Addition of milk proteins and high gelatin concentration (5.0%) both caused loss of gel fracturability. Microstructural results showed that gelatin concentration and pH had a marked influence on the gel structure, and the addition of MPC and SMP changed the structure of the gelatin gels; a structure similar to pure gelatin gel was observed after addition of WPI.