Dual microelectromembrane extraction as a tunable platform for the determination of antioxidant compounds with varied hydrophobicity in oral bioaccessibility assays of food commodities: a proof of concept

An automatic millifluidic dual microelectromembrane extraction (D-µEME) method as a front-end to HPLC-UV-Vis is herein proposed for the first time to facilitate the matrix clean-up of relatively polar polyphenolic acidic (PPA) antioxidants with a relatively broad range of lipophilicity (logP from -0.27 to 2.14) from simulated gastric extracts of oral bioaccessibility tests. The flow setup is amenable to handle microliter volumes of two distinct organic phases along with donor and acceptor phases unsupervised, conduct in-tube D-µEME in parallel without supporting membranes, and mix the two acceptor phases automatically prior to online HPLC-UV-Vis. The target antioxidants involve gallic acid, chlorogenic acid, 4-hydroxybenzoic acid, caffeic acid, and trans-cinnamic acid. Various solvents are explored to investigate their compatibility for simultaneous D-µEME, including 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, and 1-nonanol, as well as deep eutectic solvents, e.g., thymol/6-methyl coumarin, and ionic liquids as additives to alcohols. Notably, 1-pentanol and 1-octanol exhibit the best performances in extracting the most polar (gallic acid and chlorogenic acid) and the least polar analytes (trans-cinnamic acid), respectively, notwithstanding both solvents are amenable to retrieve analytes with medium hydrophobicity (4-hydroxybenzoic acid and caffeic acid). The effects of the voltage, the extraction time, and the sample ionic strength on the extraction recoveries are also investigated in detail. Under the selected D-µEME conditions, the overall linear ranges span from 1.25 to 80 mg/L, with limits of detection ranging from 0.2 to 3.3 mg/L. The flow-based D-µEME is resorted to oral bioaccessibility assays in the gastric phase of the target compounds from eggplant, blueberry, and coffee bean extracts, with relative extraction recoveries ranging from 71.5 to 133.5%.