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Evaluation of SPE as Preparative Technique for the Analysis of Phenolic Metabolites in Human Feces

Muñoz-González, Irene, Sánchez-Patán, Fernando, Jiménez-Girón, Ana, Cueva, Carolina, Monagas, María, Martín-Álvarez, Pedro J., Moreno-Arribas, M. Victoria, Bartolomé, Begoña
Food analytical methods 2014 v.7 no.4 pp. 844-853
benzoic acid, caffeic acid, cinnamic acid, feces, gallic acid, humans, hydrochloric acid, intestinal microorganisms, metabolites, phenols, protocatechuic acid, solid phase extraction, syringic acid, volunteers
Solid phase extraction (SPE) methodology has been evaluated as a cleanup strategy prior to the analysis of phenolic metabolites in fecal samples by UPLC–DAD–ESI–TQ MS. Among the sorbents tested, Oasis® HLB led to the higher phenolic standard recoveries. Sample acidification (0.4 M HCl, final concentration) before SPE considerably improved standard recoveries. Values of the process efficiency (CSPE/CWᵢₜₕₒᵤₜ SPE) for a standard solution containing gallic acid, protocatechuic acid, caffeic acid, benzoic acid, 3-phenylpropionic acid, (+)-catechin, (−)-epicatechin, procyanidin B2, and 4-hydroxybenzoic 2,3,5,6 d₄acid were acceptable (>90 %) for all compounds, except for procyanidin B2 (26 %). The developed SPE methodology was applied to fecal samples of individuals subjected to a wine intervention study. Phenolic metabolites, including intermediate metabolites (phenyl-γ-valerolactones and phenylvaleric acid derivatives) and end products (simple phenols, hydroxyphenylpropionic, hydroxyphenylacetic, hydroxycinnamic, and hydroxybenzoic acids) were identified. Most of the compounds (n = 14) exhibited values of process efficiency between 85 and 115 %. Although some compounds (n = 4) showed process efficiency>115 %, there was a group of metabolites (4-O-methylgallic acid, syringic acid, and 4-hydroxy-5-(3′,4′-dihydroxyphenyl)-valeric acid) whose process efficiency was <85 %, which represented a serious limitation and made us to discard SPE as a preparative technique for the analysis of these phenolic metabolites. Finally, the paper reports the concentrations of phenolic metabolites in a randomized set of human fecal samples from healthy volunteers (n = 15) without any previous SPE application. Large inter-individual variability was observed, which was attributed to differences in human gut microbiota composition.