Structure–fracture relationships in gas-filled gelatin gels

Food aeration has become one of the fastest growing unit operations practiced in the food industry. Dispersed air (or other gases) provides an additional phase within the gel that may accommodate new textural and functional demands. This paper addresses the relationships between structural characteristics and fracture properties of gas-filled gelatin gels (GGG), and compare these properties with those of control gelatin gels (CGG). Three gases were used in the fabrication of GGG: air, nitrogen and helium. Experimental methods to determine density, gas hold-up, bubble sizes and bubble size distributions as well as fracture properties of GGG are presented. Increasing protein concentration produced higher density, lower gas hold-up and decreased polydispersity of bubbles due to its effect on increased solution viscosity. Type of gas affected density and gas hold-up due to the different diffusivities of gases and structures (bubble size, size distribution and number of bubbles per area) formed in GGG. Fracture values increased for both GGG and CGG with increasing protein concentration for the three gases used. GGG were weaker and less ductile than CGG, the decrease in stress and strain at fracture being between 70 and 80%, and 40 and 65%, respectively. A power law relationship (σf = 2.73 × 10−12ρG4.76) was found between the fracture stress and gel density for the three gases studied. This study shows that the presence of bubbles in gel-based food products results in unique textural properties conferred by the additional gaseous phase.