Feasibility and Application of Liquid-liquid Extraction

19 In this study the feasibility of a LLE-GC-EI-MS method for the analysis of 43 phenolic acids 20 belonging to different chemical structure families which have been described in the literature as 21 microbial-derived metabolites after consumption of dietary polyphenols was proved. In addition, 22 the method was applied for the characterisation of phenolic metabolites resulting from the 23 incubation, in anaerobic conditions, of a commercial grape seed extract (GSE) and their 24 corresponding flavan-3-ol monomeric (GSE-M) and oligomeric (GSE-O) fractions with human 25 faeces from healthy volunteers (n=3). The method showed average values of repeatability and 26 reproducibility of 5.0 % and 6.3 %, respectively, adequate and low detection (1.8-30.8 μg L -1 ) 27 and quantification limits (6.0-102.8 μg L -1 ) and good recovery values (95 %, as average value). 28 A total of 27 phenolic acids were identified in the faecal solutions after incubation with the 29 grape seed extracts. In general, faecal samples incubated with GSE and GSE-M (monomeric 30 fraction) yield a higher formation of phenolic acids compared to the samples incubated with the 31 oligomer fraction (GSE-O). 32 33