A light scattering study on the effects of pH on pectin aggregation in aqueous solution

Light-scattering measurements were carried out on pectins in aqueous solutions of pH ranging from about 4 to 2. The following pectin samples were used: three low methoxyl pectins which were demethylated by ammonia, acid and enzyme (all with a nearly similar methoxyl content from 6.1 to 6.2%), and pectin-NF with 12.04% methoxyl groups and sodium poly-galacturonic acid. When the pH of a 0.05% pectin solution containing 0.1 M NaCl was brought to pH 2 by adding HCl, the mol. wt and radius of gyration increased markedly, thus indicating that pectin molecules aggregate when the pH is lowered.