Characterization of phytochemicals from twisted-leaf garlic (Allium obliquum L.) using liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry

Abstract

Introduction: Twisted-leaf garlic (Allium obliquum L.) is a wild Allium species, which is traditionally used as aroma plant for culinary purposes due to its unique, garlic-like flavor. It represents an interesting candidate for domestication, breeding and cultivation. Objectives: The objective of this work was to explore and comprehensively characterize polar and semi-polar phytochemicals accumulating in leaves and bulbs of A. obliquum. Method: Plant material obtained from a multiyear field trial was analyzed using a metabolite profiling workflow based on ultra-high performance liquid chromatography-coupled electrospray ionization quadrupole time-of-flight mass spectrometry (UHPLC/ESI-QTOFMS) and two chromatographic methods. For annotation of metabolites, tandem mass spectrometry experiments were carried out and the resulting accurate-mass collision-induced dissociation (CID) mass spectra interpreted. Onion and garlic bulb extracts were used as reference samples. Results: Important metabolite classes influencing nutritional, sensory and technological properties were detected and structurally characterized including fructooligosaccharides with a degree of polymerization of 3–5, S-alk(en)ylcysteine sulfoxides and other S-substituted cysteine conjugates, flavonoids including O- and C-glycosylated flavones as well as O-glycosylated flavonols, steroidal saponins, hydroxycinnamic acid conjugates, phenylethanoids and free sphingoid bases. In addition, quantitative data for non-structural carbohydrates, S-alk(en)ylcysteine sulfoxides and flavonoids are provided. Conclusion: The compiled analytical data including CID mass spectra of more than 160 annotated metabolites provide for the first time a phytochemical inventory of A. obliquum and lay the foundation for its further use as aroma plant in food industry.