Influence of pH on formation and properties of gellan gels

Abstract

The effect of pH (3.5, 5.3 and 7.0) on the formation of deacylated gellan gels was studied using oscillatory shear measurements and microcalorimetric trials in heating–cooling cycles at 1°Cmin−1. In addition, the mechanical properties and structure of the gels formed at the different pH values were evaluated by uniaxial compression and scanning electron microscopy, respectively. An increase in pH led to an increase in temperature and decrease in enthalpy of the coil–helix transition. These results were attributed to a decreased formation of junction zones at higher pH values due to greater electrostatic repulsion between the gellan molecules. As a consequence, gels formed at neutral pH were more fragile and deformable than acid gels. All the samples showed thermo-reversible rheological behavior, presenting the same rheological properties at 20°C, before and after heating to 90°C.