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How do pectins contribute to the gel-like properties of plant cell walls?

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Cutaway illustration of a plant cell showing labeled internal structures including the nucleus, nucleolus, chloroplast, mitochondrion, vacuole, endoplasmic reticulum, ribosomes, Golgi apparatus, cell wall, and other key organelles. — Cell wall Cutaway drawing of a plant cell, showing the cell wall and internal organelles.

Pectins, or pectic polysaccharides, contribute to the gel-like properties of the plant cell wall matrix primarily through their chemical structure and their interaction with cations.12

These polysaccharides are characterized by a linear backbone containing galacturonic acid residues, which give the molecules a negative charge. Because of this charge, pectins bind tightly to positively charged ions, specifically calcium ions.12

The gel-like consistency is formed when these calcium ions cross-link the stretches of pure galacturonic acid residues within the pectin backbone. While these cross-links provide a semirigid structure, the segments of the backbone containing rhamnose remain in a more open, porous configuration. This combination of tight cross-linking and open, hydrated regions creates the characteristic semirigid gel properties of the cell wall matrix. This same chemical process is also utilized commercially in the production of jellies and preserves.123