Dilute pectin solutions are Newtonian but at a moderate
concentration, they exhibit the non-Newtonian, pseudoplastic
behaviour characteristics. As with solubility, the viscosity of a pectin
solution is related to the molecular weight, DE, concentration of the
preparation, and the pH and presence of counterions in the
solution. Viscosity, solubility, and gelation are generally related. For
example, factors that increase gel strength will increase the tendency
to gel, decrease solubility, and increase viscosity, and vice versa.
These properties of pectins are a function of their structure, which is
that of a linear polyanion (polycarboxylate). As such, monovalent
cation salts of pectins are highly ionised in solution, and the
distribution of ionic charges along the molecule tends to keep it in an
extended form by reason of coulombic repulsion (Paoletti, 1986).
Furthermore, this same coulombic repulsion between the
carboxylate anions prevents aggregation of the polymer chains. (The
number of negative charges is, of course, determined by the DE.) In
addition, each polysaccharide chain, and especially each
carboxylate group, will be highly hydrated. Solutions of monovalent
salts of pectins exhibit stable viscosity because each polymer chain
is hydrated, extended, and independent