THE EFFECT OF THE DEGREE OF ESTERIFICATION ON THE THERMAL-STABILITY AND CHAIN CONFORMATION OF PECTINS

The degradation of pectins in aqueous (NaCl 0.1 mol/dm3, initial pH 7) non-buffered solutions increases with temperature and methyl content when evaluated from the evolution of the specific viscosity versus time. Approximating the initial phase of the degradation by a first order kinetics, the activation energies for the beta elimination are respectively estimated as 93 and 68 kJ mol-1 for pectins with a degree of esterification of 72 and 28%. The intrinsic viscosity of pectins with different degrees of esterification, in 0.1 mol/dm3 NaCl aqueous solutions, is found to decrease as temperature increases. Assuming that the effect of excluded volume is predominant over the intrinsic conformational change of the backbone with temperature, the Huggins coefficient is found to be a decreasing function of the expansion factor alpha3.