Polygalacturonic acid, calcium polygalacturonate, and samples of two cotton varieties are subjected to elevated temperatures for varying increments of time. The galacturonic acid residues of the heat-treated samples are quantified by digestion with pectinase along with EDTA, and the resultant solutions are analyzed by high performance anion exchange chromatography. Results indicate that galacturonic acid content decreases exponentially as a function of heating time, and that the rate constant for the degradation is temperaturedependent.
The energy of activation for degrading polygalacturonic acid is substantially lower than that for calcium polygalacturonate, and that for the cotton samples is essentially identical with that for calcium polygalacturonate. This phenomenon, along with supporting data, indicates that cotton fiber pectin is primarily non-esterified polygalacturonic acid with a large percentage of galacturonic acid residues crosslinked by calcium ions. The energy of activation for degrading cotton fiber pectin is substantially lower than that for cellulose, suggesting that heating cotton at normal ginning temperatures may degrade the pectin component.
