This study investigated the in vivo metabolic fate of rambutan peel polyphenols (RPPs) in rats. RPPs consisted primarily of ellagitannins, notably geraniin (341.24 mg/g dry weight). Following a single oral gavage of RPPs, 75 metabolites derived from ellagic acid, gallic acid, corilagin, and urolithins were identified. The potential metabolic pathways of RPPs included phase I metabolism (hydrolysis) and phase II metabolism (methylation, sulfation, and glucuronidation). Some prototype compounds (ellagic acid, ellagic acid hexuronide, and ellagic acid pentoside II) were detected, but with low systemic exposure and rapid elimination. Dimethyl ellagic acid glucuronide II showed high exposure and long residence. Gallic acid conjugates were rapidly excreted. The urolithin A glucuronide was identified as the primary microbially derived urolithin conjugate. Host-microbial co-metabolism critically enhances RPPs bioavailability, explaining their efficacy and supporting functional applications.
Liu et al. (Wed,) studied this question.