pectic

Pectic substances are a family of complex polysaccharides that are major components of plant primary cell walls and the middle lamella. They include protopectin (insoluble), pectin (soluble), and pectic acid, and are rich in galacturonic acid. The main structural motifs are homogalacturonan and rhamnogalacturonan I and II, with various side chains of sugars such as rhamnose, arabinose, and galactose. The degree of esterification of galacturonic acid residues (DE) governs their gelling behavior: high-methoxyl pectin requires sugar and acidic conditions to gel, while low-methoxyl pectin gels in the presence of divalent cations like calcium, often with less sugar.

In plants, pectic substances contribute to cell adhesion in the middle lamella, influence cell wall porosity, and play a role in growth and ripening. Enzymes such as pectin methylesterase and polygalacturonase modify them during development, leading to tissue softening in fruits.

Industrial and culinary relevance: Pectin is commercially extracted from citrus peels and apple pomace by hot dilute acid, then purified and dried. It is used as a gelling agent, thickener, and stabilizer in jams, jellies, yogurts, and beverages, as well as in pharmaceutical and cosmetic formulations.

Because of its diverse structure and properties, pectic substances are a central topic in plant biology and food science.