The Contribution of Oxidation Reactions to Non-Enzymatic Browning

Dear Colleagues,

Due to its heterogenous and non-selective nature, color formation in non-enzymatic browning reactions is not comprehensively understood. In this regard, oxidation in the presence of molecular oxygen, which is catalyzed in the presence of transition metals or under alkaline conditions, plays a vital role in the formation of precursor molecules, most prominently sugar- and lipid-derived 1,2-dicarbonyl compounds, but also ortho-quinones of phenolic compounds. Although addition reactions of C-H-acidic carbonyl compounds, amines, or even thiols are considered to contribute to the formation of complex colorants, known as melanoidins (the ‘Maillard reaction’) and melanins, such simple addition reactions do not result in the formation of chromophore systems. Apart from simple condensation, the oxidation of these products is a widely accepted reaction pathway, occurring during polymerization, which enables the formation of sufficiently large conjugated π-electron systems that are required for these compounds to exhibit a meaningful brown color intensity.

This Special Issue of Oxygen aims at bringing together the latest knowledge, ideas, considerations, and overviews on non-enzymatically induced oxidation reactions of compounds that contribute to the formation of colored products. We highly appreciate contributions of original research and review articles related to the non-enzymatic browning of primarily carbohydrates, lipids, and phenolic compounds that might be induced or accelerated by redox-active species or even molecular oxygen.

Prof. Dr. Sascha Rohn
Dr. Clemens Kanzler
Guest Editors

Leon Valentin Bork
Guest Editor Assistant

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• color formation
• non-enzymatic browning
• oxidation
• quinones
• carbonyl compounds
• phenolic compounds
• melanoidins
• melanins