Acetylcholinesterase Inhibitors among Zingiber officinale Terpenes—Extraction Conditions and Thin Layer Chromatography-Based Bioautography Studies

Although numerous studies have been conducted on ginger extracts and fractions, the data on the pharmacological activity of single constituents of Zingiber officinale are still insufficient. To assess the antidementia properties of the plant, a thin layer chromatography (TLC)-based bioautography acetylcholinesterase inhibitory assay was performed on the Zingiber officinale diethyl ether extract. It led to the recognition of three active inhibitors among volatile constituents of the plant: ar-curcumene (A), α-sesquiphellandrene (B) and a-zingiberene (C). The identification of the components was possible thanks to the application of a TLC–HPLC-MS interface analysis of active zones and the GC-MS qualitative analysis of the tested samples. Based on the obtained results, the influence of several extraction techniques (hydrodistillation—HD, pressurized liquid extraction or accelerated solvent extraction—ASE, shaking maceration–SM, supercritical fluid extraction–SFE, and ultrasound-assisted extraction—UAE) on the recovery of the active metabolites from plant material was assessed to deliver enriched extracts. As a result, HD and SFE, were found to be the most efficient methods to recover the volatile components and the concentrations of A, B, and C reached 0.51 ± 0.025, 0.77 ± 0.045, and 1.67 ± 0.11 percent, respectively. Only HD and SFE were found to recover monoterpene hydrocarbons from the plant matrix. The remaining techniques provided extracts rich in more complex constituents, like sesquiterpenes.