Pectin is the major binding component of the cell walls of plants and fruits. It is chemically a polysaccharide, consisting of a linear chain of linked molecules of galacturonic acid; regions on the backbone with a lot of side chains are the so-called “hairy regions”, and regions with little side chains are referred to as “smooth regions”.

The structure of pectin

Pectin has the property to form a gel with sugar. For this reason, pectin is used in combination with sugar as a thickening agent in the food industry. A well-known usage of pectin is in jam making. Most fruits contain pectin, but not in sufficient amounts to form a thick gel when making jam; pectin is therefore added to improve the quality of jam. Pectin is added to a special sugar that can be used especially for making jam (jellifying sugar). Pectin and sugar form a network when heated, but not at room temperature. This is the reason why jam thickens while cooking.

The group of fruits containing enough pectin to form a gel is very small; an example is the quince. Commercially pectin is made from apple- and orange pulp and peel.