Solvent effects on the molecular properties of pectins.

Measurements revealed that LiAc/HAc buffer, when compared with other solvents, gave relatively low values of turbidity for five commercial pectins with various apparent molar masses and degrees of methyl esterification (DE). Therefore, HPSEC with on-line light scattering and viscosity detection was employed to compare LiAc/HAc buffer against NaNO(3) solution, a commonly used mobile phase for measuring the molecular properties of these pectins and an additional pectin prepared by microwave extraction. Microwave-extracted pectin was included in the study for its higher molar mass and DE compared with commercial pectins. Most commercial samples were more soluble and had a higher molar mass when dissolved in NaNO(3) than in LiAc/HAc buffer, whereas the microwave-extracted pectin was more soluble in LiAc/HAc buffer and had about the same molar mass. Furthermore, association fragments of pectin contained in samples were more dissociated by LiAc/HAc buffer than by NaNO(3). For the samples studied, weight-average molar masses ranged from about 41000 to 307000, weight-average intrinsic viscosities from about 0.86 to 9.76 dL/g, z-average radii of gyration from about 13 to 45 nm, and Mark-Houwink constants from about 0.62 to 0.94.