Among the most important constituents of apple juice are phenolic compounds, such as: hydroxycinnamic acids, dihydrochalcones, flavonols (quercetin glycosides), catechins and oligomeric procyanidins.
Apples have the highest proportion of free polyphenols compared to other fruits. Polyphenols are usually divided into several different groups (simple phenols, benzoic acids, phenyl propanoids, and flavonoids) on the basis of the number of carbon atoms in conjunction with the structure of the basic phenolic skeleton.
The polyphenols content in apples can range widely from 10 mg to 500 mg/ 100g of raw material. The amount of polyphenols in juices is much smaller. This is mainly due to clarification processes or thermal juice preservation (pasteurization).
The concentration of polyphenols is influenced by the plant variety as well as environmental factors, including geographic region, growing season, and storage.
Apples without skin contain less than half the amount of quercetin, the most abundant apple flavonoid, harbored by whole apples.
Quercetin is a member of the class of flavonoids called flavonoles and forms the backbone for many other flavonoids including the citrus flavonoids like rutin, hesperidins, Naringenin and tangeritin.
Quercetin is a flavonoid derived from flavone, a natural polyphenolic antioxidant. Quercetin occurs in nature as easily hydrolysable glycoside (quercetin3-galactoside, quercetin-3-glucoside, and quercetin3-rhamnoside).
Apple juice rich with polyphenol
