A study of the effect of locust bean gum on the rheological behaviour and microstructure of a β-lactoglobulin gel at pH 7

Abstract

The effect of locust bean gum (LBG), a non-gelling polysaccharide, on the thermal gelation of β-lactoglobulin, at 80 °C, and on the gel properties after quenching to 20 °C was studied by small deformation rheology and by confocal laser scanning microscopy (CLSM). The concentration of β-lactoglobulin was kept constant at 10 wt% and that of LBG varied from 0 to 0.78 wt%. For all the concentrations studied, the presence of LBG enhanced the aggregation rate and the strength of the protein gel, but the magnitude of these effects depended on the β-lactoglobulin/LBG ratio: 0.35 wt% LBG resulted only in a very slight increase of G′, whereas 0.45 wt% LBG caused a ~fivefold jump; for higher LBG concentrations, the differences between the systems were quite small. The linear viscoelastic behaviour, at 20 °C, was characterized over the 10−5 to 100 rad/s frequency range by combining the dynamic and retardation tests. Compliance data were converted from the time to the frequency domain. The viscoelastic plateau was seen to extend down in the 0.001–0.0001 rad/s range and its lower limit seemed not to vary much with LBG concentration. Its upper limit was visibly beyond 100 rad/s. The observed microstructure of the gels showed that they were two-phase and that the state of aggregation of β-lactoglobulin was influenced by the β-lactoglobulin/LBG ratio.