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 T-ht: 25 degrees C (A), 50 degrees C (B), 70 degrees C (C) and 90 degrees C (D) were studied at two measurement temperatures (T-m: 50 and 70 degrees C) and compared to T-m: 25 degrees C. Samples B and C were gels more thermo-stable at high measurement temperatures. This means that a preliminary heating at 50 and 70 degrees 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 T-m. Similarly, small deformation tests showed that at T-m: 50 degrees C and 70 degrees 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. (C) 2012 Elsevier Ltd. All rights reserved.