Influence of measurement temperature on the rheological and microstructural properties of glucomannan gels with different thermal histories

Samples of 3% glucomannan gels made with 0.6 M KOH and preheated at Tht: 25 °C (A), 50 °C (B), 70 °C (C) and 90 °C (D) were studied at two measurement temperatures (Tm: 50 and 70 °C) and compared to Tm: 25 °C. Samples B and C were gels more thermo-stable at high measurement temperatures. This means that a preliminary heating at 50 and 70 °C would be needed to retain their structural integrity of these gels. When the preheated gels were subjected to high deformation (puncture test), rigidity increased with increasing Tm. Similarly, small deformation tests showed that at Tm: 50 °C and 70 °C, the C sample had better gel characteristics than the others: i.e. higher elasticity and lower frequency-dependence of viscoelastic moduli. This means that there was more particle aggregation, so that when gels C were heated they would maintain a high degree of internal cohesion and connectivity. Mechanical and rheological analyses were consistent with the structures shown in SEM photographs.

► Rheo-structural study of preheated KGM gels at several temperatures ► All preheated gels were thermostable. ► There was loss of structural integrity when the gels were not preheated. ► Increasing heat treatment temperature produced less elastic networks. ► Gel preheated at 70 °C showed the highest internal cohesion and connectivity.