The Metabolic Fate of Apple Polyphenols in Humans
Apples (Malus spp., Rosaceae) and their products contain significant concentrations of polyphenols, which have diverse biological activities and may have important beneficial effects on human health. The main polyphenols in apples are hydroxycinnamic acids, dihydrochalcones, flavonols, catechins and oligomeric procyanidins, although triterpenoids are also present in apple peel and anthocyanins in red apples. Human intervention studies have provided clear evidence that dietary polyphenols are at least partially absorbed following ingestion. They undergo extensive metabolism during the absorption process and subsequent distribution in the body. Hence, plasma and tissues are not generally exposed to polyphenols in their ingested form in vivo, and knowledge about their bioavailability, metabolism and concentrations in target tissues is of great importance when evaluating their biological effects and for ensuring that in vitro studies have physiological relevance. Metabolites, such as glucuronides, sulfates and methylated derivatives have been investigated in vivo. In addition, activities of colonic microbiota have been shown to generate other metabolites, including phenolic and short chain fatty acids. It has also been shown that deconjugations catalyzed by intracellular enzymes can occur during gastrointestinal absorption, thereby releasing aglycones. The present review summarizes current knowledge of the bioavailability and metabolism of apple-derived polyphenols in humans.
Keywords: Apple polyphenols, metabolism, ADME, phloretin, phloridzin
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