Enzymatically and chemically de-esterified lime pectins: characterisation,polyelectrolyte behaviour and calcium binding properties

A series of pectins with different levels and patterns of methyl esterifica tion was produced by treatment of a very highly methylated pectin with acid , alkali, plant pectin methyl esterase and fungus pectin methyl esterase. T he intrinsic pK values, as well as the free fractions of monovalent and cal cium counterions, were determined on pectin salt-free solutions. The variat ions of pK(a) versus the ionisation degree were found to depend on the de-e sterification process but a unique value of 2.90 +/- 0.15 was estimated for the intrinsic pK value. Calcium binding properties of chemically and enzym atically de-esterified pectins were investigated and experimental results w ere compared to Manning's theoretical values. A progressive dimerisation pr ocess for pectins with a blockwise distribution of carboxyl groups in the p resence of calcium ions is hypothesised. (C) 2001 Elsevier Science Ltd. All rights reserved.