title: Allium Discoloration: Color Compounds Formed during Pinking of Onion and Leek.
abstract: Structures and formation pathways of compounds responsible for pink discoloration of onion and leek were studied. A procedure was developed for the isolation and purification of the color compounds from various model systems and their identification by HPLC-DAD-MS/MS. In total, structures of 15 major color compounds were tentatively determined. It was found that the pigment is a complex mixture of highly conjugated species composed of two N-substituted 3,4-dimethylpyrrole-derived rings linked by either a methine or a propenylidine bridge. These two-ring units are further modified by various C1- and C3-side chains. Experiments with isotope-labeled thiosulfinates revealed that the methine bridge and C1-side chains originate from the methyl group of methiin, whereas the C3 units are derived from the propenyl group of isoalliin.
authors.affiliation: Department of Applied Chemistry, University of South Bohemia , Branišovská 31, 370 05 České Budějovice, Czech Republic.
authors.forename: Roman
authors.initials: R
authors.lastname: Kubec
authors.affiliation: Department of Applied Chemistry, University of South Bohemia , Branišovská 31, 370 05 České Budějovice, Czech Republic.
authors.forename: Petra
authors.initials: P
authors.lastname: Urajová
authors.affiliation: Department of Food Analysis and Nutrition, Institute of Chemical Technology , Technická 5, 166 28 Prague 6, Czech Republic.
authors.forename: Ondřej
authors.initials: O
authors.lastname: Lacina
authors.affiliation: Department of Food Analysis and Nutrition, Institute of Chemical Technology , Technická 5, 166 28 Prague 6, Czech Republic.
authors.forename: Jana
authors.initials: J
authors.lastname: Hajšlová
authors.affiliation: Laboratory of Molecular Structure Characterization, Institute of Microbiology, v.v.i., Academy of Sciences of the Czech Republic , Vídeňská 1083, 142 20 Prague 4, Czech Republic.
authors.forename: Marek
authors.initials: M
authors.lastname: Kuzma
authors.affiliation: Laboratory of Molecular Structure Characterization, Institute of Microbiology, v.v.i., Academy of Sciences of the Czech Republic , Vídeňská 1083, 142 20 Prague 4, Czech Republic.
authors.forename: Jakub
authors.initials: J
authors.lastname: Zápal
mesh_terms: D002851:Chromatography, High Pressure Liquid; D003116:Color; D003545:Cysteine / Q000031:analogs & derivatives / Q000737:chemistry; D019697:Onions / Q000737:chemistry*; D010860:Pigments, Biological / Q000032:analysis* / Q000737:chemistry / Q000302:isolation & purification; D013441:Sulfinic Acids / Q000737:chemistry; D053719:Tandem Mass Spectrometry
chemical_list: D010860:Pigments, Biological; C495663:S-propyl cysteine sulfoxide; D013441:Sulfinic Acids; C100040:thiosulfinic acids; C008389:methiin; C006453:alliin; D003545:Cysteine
keywords: Allium; dipyrromethane; discoloration; isoalliin; leek; onion; pinking; plant pigment; pyrrole; thiosulfinate