Humification reaction pathway

There has been some recent criticism of the Maillard reaction as a possible humification pathway (Burdon, 2001 Sutton and Sposito, 2005 von Liitzow et al., 2006). First, the critics argue that the Maillard reaction results in the formation of heterocyclic N, whereas soil N consists primarily of amide N based on 15N CPMAS NMR (Knicker and Liidemann, 1995 Knicker, 2004) studies. However, Jokic et al. (2004a) clearly showed, using N K-edge XANES, that the Maillard reaction catalyzed by bimessite under ambient temperature conditions and environmentally relevant pH not only produces heterocyclic N but also a significant amount of amide N (Figure 2.8). 

Environmental organic matter is a composite of humic and nonhumic substances, which is formed through operation and interactions of various biotic and abiotic processes. Humic substances are formed through both selected preservation (residue) and catalytic synthesis mechanisms. Both enzymatic and mineral catalyses contribute to the formation of humic substances in the environment. The relative importance of these catalytic reactions would depend on vegetation, microbial population and activity, enzymatic activity, mineralogical composition and surface chemistry of environmental particles, management practices, and environmental conditions. Selective preservation pathways would play a more important role in humification processes in poorly drained soils and lake sediments, compared with more aerated environmental conditions. 

Hardie, A. G., Dynes, J. I, Kozak, L. M., and R M. Huang. (2007). Influence of polyphenols on the integrated polyphenol-Maillard reaction humification pathway as catalyzed by birnessite. Annals Environ. Sci. 1, 91-110. 

Jokic, A., Wang, M. C., Liu, C. Frenkel, A. I., and Huang, P. M. (2004b). Integration of the polyphenol and Maillard reactions into a unified abiotic pathway for humification in nature the role of 8-Mn02. Org. Geochem. 35, 747-762. 

Figure 1.6. Formation of the Amadori compound from D-glucopyranose (D-glucose) and glycine. Note that a molecule of water is split off. Tlie Amadori compound is an intermediate product in the Maillard reaction, which is perceived as one of the pathways in humification. (From Mossine et al., 1994.)...

---