Impact of sodium ions on material properties, gelation and storage stability of citrus pectin
Material properties, gelation and storage stability of demethoxylated pectin samples strongly varied in dependence on the applied modification method. It was assumed that the content of sodium ions and their resulting electrostatic interactions with free carboxyl groups were crucial for these differences. Sodium ions were widely removed by acidic modification but added during alkaline and enzymatic modification using NaOH in a pH-stat method. It was the aim of the present study to investigate the individual impact of sodium ions on pectin properties using samples with similar molecular parameters but different sodium ion content. Sodium enrichment of pectin increased the pectin particle surface and, as a consequence, the pectin-water-interactions. Differences in molecular structure and material properties were reflected in simultaneous thermal analysis; an exothermic starting peak in DSC vanished and pectin pyrolysis was accelerated after sodium ion enrichment. Gel formation was affected by sodium ions. It was delayed in a sugar-acid system by reducing the number of hydrogen bonds and accelerated in a sugar-calcium system by reducing electrostatic repulsion. Sodium ions increased the storage stability of pectin. They were bound to free carboxyl groups (-COONa) and restricted degradation reactions during storage which required these groups, in particular depolymerisation by decarboxylation.
Published in: Food Hydrocolloids, 10.1016/j.foodhyd.2020.105750, Elsevier