Czech J. Food Sci., 2007, 25(3):119-130 | DOI: 10.17221/740-CJFS

Formation of α-hydroxycarbonyl and α-dicarbonyl compounds during degradation of monosaccharides

Ondřej Novotný, Karel Cejpek, Jan Velíšek

Department of Food Chemistry and Analysis, Faculty of Food and Biochemical Technology, Institute of Chemical Technology in Prague, Prague, Czech Republic

The formation of α-hydroxycarbonyl and α-dicarbonyl compounds from monosaccharides (glucose, fructose, arabinose, glyceraldehyde, and 1,3-dihydroxyacetone) was studied in three different model systems comprising an aqueous and alkaline solution of potassium peroxodisulfate (K₂S₂O₈), and a solution of sodium hydroxide, respectively. In total, six α-hydroxycarbonyl (in the form of O-ethyloximes) and six α-dicarbonyl compounds (as quinoxaline derivatives) were identified by GC/MS and quantified. Acetol, glycolaldehyde, 1,3-dihydroxyacetone, methylglyoxal, and glyoxal were the most abundant low molecular weight carbonyls. Within the model systems studied, the yield of α-hydroxycarbonyl and α-dicarbonyl compounds was 0.32-4.90% (n/n) and 0.35-9.81% (n/n), respectively. The yield of α-dicarbonyls was higher than that of α-hydroxycarbonyls only in aqueous solution of K₂S₂O₈ and in the other two model systems an inverse ratio of these two carbonyl types was found. For the first time, ethylglyoxal was identified as a sugar degradation product and several mechanisms explaining its formation were proposed. The achieved data indicated that low molecular weight α-hydroxycarbonyl and α-dicarbonyl compounds are predominantly formed by a direct retro-aldol reaction and α- and β-dicarbonyl cleavage. It was evident that some compounds were produced from the sugar fragmentation products. Thus, isomerisation, reduction of dicarbonyls by formaldehyde (cross-Cannizzaro reaction), and mutual disproportionation are possible reaction pathways participating in the formation of α-hydroxycarbonyl compounds. Oxidation and disproportionation of α-hydroxycarbonyl precursors as well as the aldol condensation of low molecular weight carbonyl species (followed by subsequent reactions) play an important role in the formation of several α-dicarbonyl compounds.

Keywords: monosaccharides; α-hydroxycarbonyl compounds; α-dicarbonyl compounds; retro-aldol reaction; peroxodisulfate; acetol; 1,3-dihydroxyacetone; glyceraldehyde; glycolaldehyde; acetoin; 1-hydroxybutan-2-one; lactaldehyde; glyoxal; methylglyoxal; ethylglyoxal; butane-2,3-dione; 1-hydroxybutane-2,3-dione; pentane-2,3-dione

Published: June 30, 2007  Show citation