pectin, any of a group of white, amorphous, complex carbohydrates that occur in ripe fruits and certain vegetables. Fruits rich in pectin are the peach, apple, currant, and plum. Protopectin, present in unripe fruits, is converted to pectin as the fruit ripens. Pectin forms a colloidal solution in water and gels on cooling. When fruits are cooked with the correct amount of sugar, and when the acidity is optimum and the amount of pectin present is sufficient, jams and jellies can be made. In overripe fruits, the pectin becomes pectic acid, which does not form jelly with sugar solutions. Commercial preparations of pectin are available for jelly making. An indigestible, soluble fiber, pectin is a general intestinal regulator that is used in many medicinal preparations, especially as an antidiarrhea agent.

Any of a class of carbohydrates found in certain plant cell walls and tissues. They are principally composed of a galactose derivative, galacturonic acid. In fruits, pectin keeps the walls of adjacent cells joined together, helping them remain firm and hold their shape. As fruits become overripe, the pectin breaks down to simple sugars that dissolve more readily, so the fruits become soft and lose their shape. Because it forms a thick, gel-like solution when added in small amounts to fruit acids, sugar, and water, pectin is used to make jellies, jams, and marmalades. Its thickening properties also make it useful in the confectionery, pharmaceutical, and textile industries.

Learn more about pectin with a free trial on Britannica.com.