Green pigment in crushed garlic (Allium sativum L.) cloves: Purification and partial characterization

Unknown green pigment, responsible for greening in crushed garlic cloves, was purified and characterized by using a series of column chromatography, liquid chromatography–electrospray ionization (LC–ESI), fast atom bombardment (FAB), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS), and nuclear magnetic resonance (NMR) spectroscopy. The purified green pigment was highly polar and slightly viscous, with a garlic flavor, and easily turned to a yellow or brown color with exposure to room temperature. The absorption spectrum in methanol showed a crude methanolic green pigment-like profile with two absorbance maxima at 440 and 590 nm.A compound based on MS spectra showing the ion peak at m/z 412 is responsible for greening. Although complete isolation of the molecular weight (MW) 411 compound for proper structure elucidation was not achieved in our experiments, the MS and NMR spectra of the MW 411 green pigment suggested the ambiguous structural assignment of one sulfur atom and odd numbers of nitrogen atoms, with 25–30 carbons including aromatic ring. Therefore, we suggest the possibility that the green pigment MW 411 observed in crushed garlic cloves is a new sulfur-containing nitrogenous water-soluble compound differing significantly from all previously reported green pigments in plants.