Thermostability analyses of glucomannan gels. Concentration influence

Abstract

This paper examines the thermostability of glucomannan gels (3 and 5 %) deacetylated with 0.6 N KOH (A3, A5) and 1 N NaOH (B3, B5) at both concentrations. Gels were heated at heat treatment temperature (Tht): 25, 50, 70 and 90 °C for 20 min. Different analyses: puncture, small amplitude oscillatory shear (SAOS) and scanning electron microscopy (SEM) were made at 25 °C. All gels (irrespective of alkali and glucomannan concentration) behaved as thermo-irreversible with permanently bonded networks. Some structural differences were found depending on the alkali and glucomannan concentration and Tht range: increased Tht produced stronger networks in A3 and B3, which were more orderly in A3. At high Tht, A3 had a more elastic network, with higher water binding capacity (WBC) than B3. At 5% glucomannan, gel networks (A5–B5) were tighter and were less reinforced by temperature. Mechanical and rheological analyses were consistent with the structures shown in SEM photographs.