Heat-induced gelation of β-lactoglobulin at varying pH: Effect of tara gum on the rheological and structural properties of the gels

The effect of the non-gelling tara gum (TG) galactomannan on the thermal gelation of β-lactoglobulin, at 80 °C, and on the rheological behaviour and microstructure of the gels after quenching to 20 °C was studied at pH 7.0 and at pH 4.6, near the isoelectric point of the protein. Gels were analysed rheologically with dynamic mechanical analysis in shear and microstructurally by confocal scanning laser microscopy (CSLM). For all the concentrations studied, TG affected the gelation rate, the strength, and the strain sensitivity of the final gels but these effects depended on TG concentration and the pH. Gels obtained at pH 4.6 were stronger and showed higher sensitivity to strain than similar gels obtained at pH 7.0. The CSLM micrographs revealed that the mixed gels were two-phase and that the state of aggregation of β-lactoglobulin depended on TG concentration and pH. In general, the microstructures for pure and mixed β-lactoglobulin gels, obtained at pH 4.6, were more open and with larger clusters than the microstructures observed for gels obtained at pH 7.0.