Tsao et al. (2005) observed that the antioxidant activity of apple
polyphenols followed the following trend: cyanidin-3-O-galactoside
> procyanidins > quercetin > chlorogenic acid > phloridzin
and also reported a strong correlation between FRAP values and
flavan-3-ols. Previous literature has reported a direct correlation
between FRAP and total phenolic content (Huber & Rupasinghe,
2009). deGraft-Johnson et al. (2007) found that purified apple
quercetin glycosides in combination with other polyphenols exhibited
a strong ferric reducing ability compared to apple extract under
in vitro conditions, and also suggested the involvement of
catechol–OH group of the B-ring in ferric reduction.