Characterization of association and gelation of pectin in methanol-water mixtures.

Turbidity, swelling, and rheological features of semidilute systems of pectin in methanol-water media of different composition have been investigated. By increasing the percentage of methanol in the mixture, the thermodynamic properties of the pectin/methanol/water system become poorer, as shown by increasing turbidity and decreasing swelling. Effects of oscillatory and steady shear flows on intermolecular associations and gelation of pectin in methanol/water mixtures are reported. The effects of methanol concentration on the growth and structure of shear-induced gels, stabilized through hydrogen bonds, are analyzed. Steady shear measurements on these systems reveal shear thickening at low shear rates and disruption of intermolecular associative junctions at high shear rates.