Pectin is a naturally occurring polysaccharide found in the primary cell walls of fruits and vegetables, especially in apples, citrus fruits, and berries, as well as in the green parts of terrestrial plants. It acts as a gelling agent, thickener, and stabilizer in food production. Pectin is also utilized in pharmaceuticals and cosmetics for its functional properties. As a soluble fiber, it aids digestion and promotes gut health. Though widely studied, pectin's complex and heterogeneous structure makes it challenging to characterize, with industrial applications focusing on tailoring it to specific needs, particularly for high-sugar systems.

Pectins also carry nonsugar subsituents, essentially methanol, acetic acid, phenolic acids and occasionally amide groups. The esterification of galacturonic acid residues with methanol or acetic acid is a very important structural characteristic of pectic substances. The degree of methylation (DM) is defined as the percentage of carboxyl groups esterified with methanol. If more than 50% of the carboxyl groups are methylated the pectins are called high-methoxy pectins (HM), and less than that degree of methylation are called low methoxy (LM) pectins.