Acid gelation of gellan: Effect of final pH and heat treatment conditions

The influence of polysaccharide concentration, final pH (2.0–4.0) and heat treatment temperature (70 or 90 °C/30 min) on the rheological properties, water-holding capacity (WHC), turbidity and microstructure of gellan gels formed by acidification with glucono-δ-lactone (GDL) was evaluated. In addition the gelation kinetics was monitored by oscillatory rheological measurements. Heating the solutions, raising the polymer concentration and lowering the final pH decreased the time taken to reach gel point. Failure stress increased at lower pH values, higher polysaccharide concentration and with the application of heating before acidification. However, gels heated after acidification showed decreased failure stress. All the gels were transparent and the WHC improved at higher concentrations and pH values or at lower pH values and gellan concentrations. The microstructure and turbidity showed good correlation with the mechanical properties, which could explain the influence of the process conditions on the gel properties.