Profile of plasma and urine metabolites after the intake of almond [Prunus dulcis (Mill.) D.A. Webb] polyphenols in humans.

Nut skins are considered to be a rich source of polyphenols and may be partially responsible for the numerous health effects associated with nut consumption. However, more bioavailability studies of nut skin polyphenols are needed to understand the health effects derived from nut consumption. The aim of the present study was to determine the profiles of both phase II and microbial-derived phenolic metabolites in plasma and urine samples before and after the intake of almond skin polyphenols by healthy human subjects (n = 2). Glucuronide, O-methyl glucuronide, sulfate, and O-methyl sulfate derivatives of (epi)catechin, as well as the glucuronide conjugates of naringenin and glucuronide and sulfate conjugates of isorhamnetin, were detected in plasma and urine samples after consumption of almond skin polyphenols. The main microbial-derived metabolites of flavanols, such as 5-(dihydroxyphenyl)-gamma-valerolactone and 5-(hydroxymethoxyphenyl)-gamma-valerolactone, were also detected in their glucuronide and sulfate forms. In addition, numerous metabolites derived from further microbial degradation of hydroxyphenylvalerolactones, including hydroxyphenylpropionic, hydroxyphenylacetic, hydroxycinnamic, hydroxybenzoic, and hydroxyhippuric acids, registered major changes in urine after the consumption of almond skin polyphenols. The urinary excretion of these microbial metabolites was estimated to account for a larger proportion of the total polyphenol ingested than phase II metabolites of (epi)catechin, indicating the important role of intestinal bacteria in the metabolism of highly polymerized almond skin polyphenols. To the authors' knowledge this study constitutes the most complete report of the absorption of almond skin polyphenols in humans.