Effect of temperature on the intrinsic viscosity and conformation of different pectins

Abstract

The effects of temperature on the intrinsic viscosity and on the conformation of pectin obtained from Citrus, Apple and Sunflower in a 0.17M NaCl solution were studied. Mark-Houwink plots for Orange, Apple and Sunflower pectin were obtained using HPSEC with online light scattering and viscosity detection. The intrinsic viscosity and flow activation energy Ea of pectin from the sources studied were measured over the temperature range 20–60°C. Ea values were 0.67, 0.69, 1.34, and 1.44 × 107 J/(kmol) for commercial Citrus, Orange, Sunflower and Apple pectin, respectively. Intrinsic viscosity decreased linearly with increasing temperature, for all pectins except Apple one. These results clearly indicated that Apple pectin underwent structural changes that were more drastic than those that occurred for pectin from the other sources. Ea increased with decreasing weight average molar mass Mw indicating that pectin with low Mw were more asymmetric than pectin with higher values of Mw. Changes in the Huggins coefficients Kh with temperature for pectin from the various sources were attributed to the ability of pectin to aggregate, disaggregate and re-aggregate according to the temperature at which it was stored.