The Effect of Concentration on the Cross-Linking and Gelling of Sodium Carbonate-Soluble Apple Pectins.

The cross-linking and gelation of low-methoxy pectins are basic processes commonly used in different industries. The aim of this research was to evaluate the cross-linking process of the sodium carbonate-soluble pectins (named DASP) extracted from apples, characterized by a low degree of methylesterification as a function of its concentration in water (CDASP). The cross-linking process was studied with a dynamic light scattering method, atomic force microscope (AFM), viscosity and pH measurements. An increase in CDASP above 0.01% resulted in a decrease in the aggregation index (AI) and the change of its sign from positive to negative. The value of AI = 0 occurred at CDASP = 0.33 ± 0.04% and indicated the formation of a pectin network. An increase in CDASP caused the changes in viscosity of pectin solutions and the nanostructure of pectins spin-coated on mica observed with AFM, which confirmed results obtained. The hydrogen bonds were involved in the cross-linking process.

Structure-Related Gelling of Pectins and Linking with Other Natural Compounds: A Review.

Pectins are polysaccharides present commonly in dicotyledonous and non-grass monocotyledonous plants. Depending on the source, pectins may vary in molecular size, degrees of acetylation and methylation and contents of galacturonic acid and neutral sugar residues. Therefore, pectins demonstrate versatile gelling properties and are capable of forming complexes with other natural compounds, and as a result, they are useful for designing food products. This review focuses on the structure-related mechanisms of pectin gelling and linking with other natural compounds such as cellulose, hemicellulose, ferulic acid, proteins, starch, and chitosan. For each system, optimal conditions for obtaining useful functionality for food design are described. This review strongly recommends that pectins, as a natural biocomponent, should be the focus for both the food industry and the bioeconomy since pectins are abundant in fruits and may also be extracted from cell walls in a similar way to cellulose and hemicellulose. However, due to the complexity of the pectin family and the dynamic structural changes during plant organ development, a more intensive study of their structure-related properties is necessary. Fractioning using different solvents at well-defined development stages and an in-depth study of the molecular structure and properties within each fraction and stage, is one possible way to proceed with the investigation.

Cross-linking of sodium carbonate-soluble pectins from apple by zinc ions.

Sodium carbonate-soluble pectin fraction forms a self-organized network on mica and may have the potential ability to bind zinc ions. The aim of this research was to characterize the interaction of zinc ions with this fraction extracted from apples using rheological measurements and FT-IR study. The addition of zinc ions (10 and 20 mM of ZnSO4·7H2O) to 5% pectin water solution caused a significant increase in viscosity, which may be connected with the formation of a pectin network. Moreover, the addition of zinc ions resulted in an almost 1.5-fold decrease in the flow behaviour index and a 5-fold increase in the consistency index. FT-IR studies showed a decrease in the intensity of the bands connected with νas and νs(COO-) and γ(COH)ring as a result of the presence of zinc ions. Therefore, it may be supposed that these ions interact with the carboxylate and hydroxyl groups of galacturonic acid units.