Abiotic catalysis of the Maillard reaction and polyphenol-Maillard humification pathways by Al, Fe and Mn oxides

摘要

The Maillard reaction and integrated polyphenol-Maillard reaction are regarded as important pathways in natural humification. Little is known on the abiotic catalysis of these pathways by poorly crystalline Al and Fe(III) oxides. Therefore, the objective of this study was to compare catalysis of these humification pathways by poorly crystalline Al and Fe oxides and Mn oxide, which has been widely studied. Treatments containing an equimolar amount of glucose and glycine (Maillard reaction) or catechol, glucose and glycine (polyphenol-Maillard reaction) in the presence or absence of metal oxides, were conducted under environmentally relevant conditions, for 15 days under sterile conditions. The humification products were examined using C and Al K-edge, and Al, Fe and Mn L-edge NEXAFS spectroscopy. The redox-reactive Mn and Fe oxides enhanced humification in the Maillard and integrated catechol-Maillard systems to a greater extent than Al oxide. The Mn oxide sequestered substantially more C during humification than the other oxides, and the humic substances formed were more carboxylic in nature. Humification altered the surface chemistry of the oxides, especially the Mn oxide. The findings of this study are of fundamental importance in understandingthe role of metal oxides in abiotic humification pathways and C stabilization in soils and sediments.