title: Studies on nonenzymatic oxidation mechanisms in neobetanin, betanin, and decarboxylated betanins.
abstract: A comprehensive nonenzymatic oxidation mechanism in betanin plant pigment as well as its derivatives, 2-decarboxybetanin, 17-decarboxybetanin, 2,17-bidecarboxybetanin, and neobetanin, in the presence of ABTS cation radicals was investigated by LC-DAD-ESI-MS/MS. The main compounds formed during the first step of betanin and 2-decarboxybetanin oxidation are 2-decarboxy-2,3-dehydrobetanin and 2-decarboxyneobetanin, respectively. In contrast to betanin, the reaction mechanism for 2-decarboxybetanin includes more oxidation pathways. Parallel transformation of 2-decarboxybetanin quinone methide produces neoderivatives according to an alternative reaction that omits the presumably more stabile intermediate 2-decarboxy-2,3-dehydrobetanin. The main oxidation product after the first reaction step for both 17-decarboxybetanin and 2,17-bidecarboxybetanin is 2,17-decarboxy-2,3-dehydrobetanin. This product is formed through irreversible decarboxylation of the 17-decarboxybetanin quinone methide or by oxidation of 2,17-bidecarboxybetanin. Oxidation of neobetanin results primarily in a formation of 2-decarboxy-2,3-dehydroneobetanin by a decarboxylative transformation of the formed neobetanin quinone methide. The elucidated reaction scheme will be useful in interpretation of redox activities of betalains in biological tissues and food preparations.
authors.affiliation: Department of Analytical Chemistry, Institute C-1, Faculty of Chemical Engineering and Technology, Cracow University of Technology, ul. Warszawska 24, Cracow 31-155, Poland. swybran@chemia.pk.edu.pl
authors.forename: Sławomir
authors.initials: S
authors.lastname: Wybraniec
authors.forename: Karolina
authors.initials: K
authors.lastname: Starzak
authors.forename: Anna
authors.initials: A
authors.lastname: Skopińska
authors.forename: Boris
authors.initials: B
authors.lastname: Nemzer
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Pietrzkowski
authors.forename: Tadeusz
authors.initials: T
authors.lastname: Michałowski
mesh_terms: D050859:Betacyanins / Q000737:chemistry*; D002384:Catalysis; D003653:Decarboxylation; D005505:Food Coloring Agents / Q000737:chemistry*; D006865:Hydrogenation; D010084:Oxidation-Reduction; D010860:Pigments, Biological / Q000737:chemistry*
chemical_list: D050859:Betacyanins; D005505:Food Coloring Agents; D010860:Pigments, Biological