Pectin

Pectin is a complex, water-soluble polysaccharide that is found in almost all terrestrial plants, but mostly in fruits, especially the rind of cooking apples and citrus fruits. In a sense, pectin is part of the glue that holds the cells of the plant together and provides structure. The pectin content reaches its peak when the fruit is fully ripe. In unripe fruits, the pectin, called propectin, is not water soluble; and in overripe ones, it is broken down by enzymes.

The pectin content varies considerably from one type of plant to another. It is found in large quantities in apples (especially those growing wild), black currants (especially unripe ones), cranberries, quince, and prune plums, whereas there are only small amounts in other types of fruit, such as cherries, strawberries, and grapes.