| The Maillard reaction, a carbonyl-amino condensation reaction, is a ubiquitous chemical reaction in nature and a well-documented critical food (flavor, color, nutritional value, toxicity) and biological reaction that involves aging, inflammation, cardiovascular disease, etc. Polyphenolic components (of plant origin) have not been considered as reactants in the thermally catalyzed reactions involved in flavor generation. This study primarily focuses on understanding the mechanisms of how epicatechin (a polyphenolics compound) functions as a reactant in Maillard model systems and in particular with Maillard reaction transient intermediates using GC, GC-MS, LC/MS and NMR analysis for structural confirmation.; Preliminary experiments conducted on aqueous Maillard model systems consisting of 4 amino acids plus 2 hexose sugars indicated that the addition of epicatechin or epigallocatechin gallate dramatically altered (reduced) the generation of Maillard-type flavor compounds. The mechanisms of how EC behaves as a reactants in Maillard chemistry were subsequently investigated by labeling studies ( 13C, 15N) in an aqueous glucose-glycine model system. Analysis of the non-volatiles by LC/MS indicated that epicatechin combined with C2, C3, and C4 sugar fragments to form adduct reaction products which were otherwise absent in control a sample with no epicatechin added. Glycine was not required under these reaction conditions to catalyze glucose fragmentation, as similar adduct reaction products were obtained when glucose was directly combined with EC.; The identity of the individual sugar fragments that were being trapped by epicatechin in aqueous Maillard systems was established by direct comparison of LC/MS peak retention times and ion abundances. The LC/MS chromatograms of epicatechin-sugar fragment adducts generated in the glucose/glycine system were compared with adducts generated via direct combination of epicatechin and well-known sugar carbonyls---glyoxal, acetol, glyceraldehyde, methylglyoxal etc.; In conclusion, the reduction of flavor generation due to addition of epicatechin in Maillard model systems was ascribed to direct trapping of C 2, C3 and C4 carbonyl compounds in aqueous model systems. Further the identification that EC formed covalent bonds with reactive carbonyl such as glyoxal, methylglyoxal provides a new mechanism for elucidating the epidemiological evidence supporting a positive health link between dietary intake of polyphenolic flavonoids and the reduction of several age-related chronic diseases. (Abstract shortened by UMI.)... |
