The study, published in the Journal of Agricultural and Food Chemistry, found three of the 12 compounds had not previously been described in the scientific literature.

"We found that several compounds have potent anti-proliferative activities against human liver, colon and breast cancer cells and may be partially responsible for the anti-cancer activities of whole apples," senior study author Rui Hai Liu of Cornell University's Institute of Comparative and Environmental Toxicology said in a statement.

"We believe that a recommendation that consumers eat five to 12 servings of a wide variety of fruits and vegetables daily is appropriate to reduce the risks of chronic diseases, including cancer, and to meet nutrient requirements for optimum health."

Liu and study co-author Xiangjiu He analyzed the peel from 230 pounds of Cornell Orchard red delicious apples, isolated their individual compounds, identified the structures of the promising compounds and tested the pure compounds against cancer cell growth in the laboratory.

They concluded triterpenoids, a type of naturally-occurring fat-soluble molecules, may be doing much of the anti-cancer work.