Pectin is a carbohydrate that is primarily used as a gelling agent for jams and jellies. These foods would be runny without the stabilizing effects of pectin, which bonds to molecules around it and gives fruit or jelly structure. In a similar fashion, pectin is also a good source of dietary fiber. Apples, with their rigid but juicy structure contain a high amount of pectin, constituting up to 1.5% pectin by weight.
Apples are long associated with health and vigor. Among their benefits rank: protection of brain health http://www.ncbi.nlm.nih.gov/pubmed/18298733, reduction of stroke risk http://www.ncbi.nlm.nih.gov/pubmed/23294925, reduction of diabetes risk http://www.bmj.com/content/347/bmj.f5001, and can help cancer prevention http://www.ncbi.nlm.nih.gov/pubmed/18855307.