Generation of 4-hydroxy-2,5-dimethyl-3(2H)-furanone from rhamnose as affected by reaction parameters: experimental design approach.

The formation of 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) was studied in aqueous model systems containing L-rhamnose and L-lysine. The approach consisted in systematically varying four reaction parameters (rhamnose concentration, rhamnose to lysine ratio, pH, and phosphate concentration) at 3 levels. A fractional factorial design was used to reduce the number of trials. The degradation of rhamnose was followed by high performance anion exchange chromatography and the formation of HDMF by solid phase extraction in combination with GC/MS. The study permitted the identification of critical reaction parameters that affect the formation of HDMF from rhamnose in aqueous systems. Although all studied parameters have some impact on the HDMF formation and rhamnose degradation kinetics, the effect of phosphate is by far the most important, followed by concentration of precursors and pH. The experimental design approach permitted us, with a limited number of experiments, to accurately model the effects of the four investigated reaction parameters on the kinetics of rhamnose degradation and HDMF formation (R(2)>0.93). Overall, the results indicate that rhamnose can be an excellent precursor of HDMF (yield >40 mol%), if the reaction conditions are well mastered.

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.