Influence of the substituents of the carboxyl groups and of the rhamnose content on the solution properties and flexibility of pectins

Viscometric measurements were carried out on well-characterized apple, citrus, sugar-beet pectins in order to analyse the effect of the nature and the amount of substituents (methyl, amide, acetyl groups) and of the rhamnose content on the flexibility of the polymeric backbone. Through the dependence of the intrinsic viscosity with the ionic strength the flexibility parameter B was determined. B values between 0.072 and 0.017 indicate that pectins are relatively stiff molecules. However, an increase in flexibility is noticeable with the rise of the rhamnose content and of the amount of amide groups of the pectic acids. The flexibility is also sensitive to the degree of methylation.