a chemical substance that is found in some fruits and is sometimes added to jam and jelly to make it less liquid.——朗文当代大辞典

Any of a class of neutral colloidal carbohydrates formed naturally in plant tissues, esp. fruits and fleshy roots, by the enzymatic breakdown of protopectin, consisting mainly of partially methoxylated polymers of galacturonic acid, and having the property of forming gels with sugars and acids (as in jams and jellies), as a result of which they are extracted or synthesized for use as emulsifying or gelling agents.——牛津当代大辞典  @en