Contribution of the side branches to rheological properties of pectins

Abstract

The rheological properties of apple pectins with different degrees of side branches were investigated in terms of the zero-shear viscosity ( η 0), the shear rate dependence of viscosity and the superposability of rheological data to a variety of generalization curves such as η sp versus c[ η], η sp versus cM w, η η 0 versus γ ̇ γ ̇ 0·8 and η η 0 versus γ ( η 0 − η s) M w/ cRT. Increase in branching of pectins resulted in higher η 0 and increasing shear rate dependence of viscosity. The gradients of η sp.0 versus c [η] in the concentrated region ( c [η] > c ∗ [η] ) were dependent upon the degree of branching, i.e. the higher the branching, the higher the gradients, whereas there was no significant difference in the dilute region ( c [η] < c ∗ [η] ) irrespective of the degree of branching. Pectins with a low degree of branching displayed better superposition in η η 0 versus γ ̇ γ ̇ 0·8 and η η 0 versus γ ( η 0 − η s) M w/ cRT curves when compared to the sample with more branches. Circular dichroism (CD) studies of pectins showed that the conformation of pectin molecules was not affected by the degree of branching. It is concluded that side branches of pectins can result in significant entanglements in concentrated solutions.