However, it is not quite as simple as that. Fructose in the skin of an apple ( which begins absorption in the stomach ) is less cariogenic than fructose in apple juice which is classified as an extrinsic sugars. Therefore, although fruit juice can be labeled as having no added sugar it is rendered cariogenic , as fructose is removed from the plant cell wall and is broken down by salivary amylase in the mouth.