Profiling of polar metabolites in fruits of Opuntia stricta var. dillenii by ion-pair high-performance countercurrent chromatography and off-line electrospray mass-spectrometry injection

Abstract

Electrospray mass spectrometry-profiling guided the metabolome investigation of a C18 reversed phase adsorbate of Opuntia stricta var. dillenii fruits following analytical, and semi-preparative high-performance countercurrent chromatography (HPCCC) fractionation, and visualization of molecular weight elution profiles based on selected single ion-traces. Experimental partition-ratio values K_D, and peak widths for detected metabolites were determined. Structural characterization of metabolites, and co-elution effects were monitored in the scan range m/z 150-2200. The polar ion-pair activated solvent system tert.-butylmethylether - n-butanol - acetonitrile - water (0.7% trifluoroacetic acid) [2:2:1:5]) was used for partition-ratio K_D improvement of ionic betalains. HPCCC operations were in the head-to-tail mode using the elution-extrusion approach. Selected ESI-MS ion traces visualized the elution of fourty-three metabolites, whereas twenty-one were identified as known betalain pigments, and their classic degradation products, and chlorinated betacyanin artefacts. Potentially, novel fruit metabolites of Opuntia were recognized by unknown molecular weights, and MS/MS fragmentations. Off-line ESI-MS fraction monitoring determined peak elution windows, and resulted in K_D-based chromatographic scales. Detectable metabolites were compared by separation- α, and resolution-factors R_S revealing a better performance of the analytical HPCCC experiment. Experimental metabolite K_D-values from analytical and semi-preparative HPCCC runs were widely consistent, and confirmed the reproducibility of the technique based on the used sample material.

Keywords: Analytical/semi-preparative ion-pair high-performance countercurrent chromatography; Betalains; Cactaceae; Electrospray mass-spectrometry based metabolite partition ratio K(D)-determination; Flavonoid glycosides; Off-line ESI–MS/MS injection metabolite profiling; Opuntia stricta var. dillenii.