Degradation of glucose: reinvestigation of reactive alpha-Dicarbonyl compounds.

Maillard reactions influence the formation of flavor and color in processed foods in an important way. Reducing sugars and amino acids ultimately react to stable end products. To elucidate the complex formation pathways a vast number of experiments have been published. alpha-Dicarbonyl compounds are accepted as important key intermediates. In the present work the Maillard degradation of glucose in the presence of lysine was reinvestigated. alpha-Dicarbonyl compounds were trapped with o-phenylenediamine to give stable quinoxalines of d-arabino-hexos-2-ulose (glucosone), N(6)-(3,6-dideoxyhexos-2-ulos-6-yl)-l-lysine, 1-deoxy-d-erythro-2,3-hexodiulose (1-deoxyglucosone), 3-deoxy-d-erythro-hexos-2-ulose (3-deoxyglucosone), ethanedial (glyoxal), 2-oxopropanal (methylglyoxal), 3,4-dihydroxy-2-oxobutanal (threosone), 1-hydroxy-2,3-butanedione (1-deoxythreosone), 4-hydroxy-2-oxobutanal (3-deoxythreosone), 4,5-dihydroxy-2-oxopentanal (3-deoxypentosone) and 4,5-dihydroxy-2,3-pentanedione (1-deoxypentosone). Multilayer countercurrent chromatography (MLCCC) was used for the first time to separate quinoxalines from ethyl acetate and aqueous extracts of reaction mixtures. The purity and identity of isolated compounds was confirmed by NMR, HPLC-UV and HR-MS. Aerated and deaerated incubations of [(13)C]-labeled glucose in presence of lysine and degradations of glucosone and 3-deoxyglucosone allowed insights into the formation pathways. Within this context the formation of 1-deoxypentosone and the importance of N(6)-(3,6-dideoxyhexos-2-ulos-6-yl)-l-lysine (Lederer's glucosone) was established.