Viscosity of galactomannans during high temperature processing: influence of degradation and solubilisation

The rheological properties of guar gum (GG) and locust bean gum (LBG), in r esponse to high temperature treatments, were measured using a rheometer equ ipped with a high pressure cell. This has allowed the viscosity to be asses sed at temperatures above 100 degrees C and as the polymer suspension is he ated from 20 to 121 degrees C and then cooled back to ambient temperature t o simulate a food sterilisation cycle. Activation energies for depolymerisa tion estimated from viscosity changes with time at a series of constant tem peratures were estimated as 63 kJ/mol for GG and 98, 104, 110 kJ/mol for th ree different samples of LEG. A model was developed to interpret the viscos ity change through the simulated sterilisation cycle. This took into accoun t the degradation of the polysaccharide and the change in viscosity due to thermal motion. Estimations of molecular weight changes during the heating process suggest that GG is more susceptible to thermal degradation than LEG . It is suggested that this is due to the greater ability of the latter to associate in solution. (C) 1999 Elsevier Science Ltd. All rights reserved.