Origin and yields of acetic acid in pentose-based Maillard reaction systems.

The formation of acetic acid from pentoses was studied in aqueous buffered systems (90-120 degrees C, pH 6.0-8.0) containing equimolar concentrations of 13C-labeled xylose and glycine. Acetic acid was quantified by gas chromatography-mass spectroscopy using an isotope dilution assay. Acetic acid was mainly formed from the C-1/C-2 carbon atoms of xylose (77-87%), while small amounts were also formed from the C-4/C-5 atoms of the pentose sugar (9-15%). Temperature and pH had only a small effect on the relative contribution of the sugar carbon atoms to acetic acid. These results support beta-dicarbonyl cleavage of 1-deoxypento-2,4-diulose as a major pathway leading to acetic acid in pentose-based Maillard reaction systems under food processing conditions. Acetic acid was confirmed as a major degradation product of pentoses at the early stage of the Maillard reaction, yielding 16 mol% and 28 mol% at pH 6.0 and pH 8.0, respectively.