3-deoxyhexulose and 5-hydroxymethylfurfural

The degradation reaction of thermally treated 3-deoxy-d-erythro-hexos-2-ulose and methylglyoxal, both key intermediates in Maillard chemistry, was investigated. Different analytical strategies were accomplished to cover the broad range of formed products and their different chemical behavior. These involved HPLC-DAD and accordingly LC/MS analysis of the quinoxaline derivates, GC/MS analysis of the acetylated quinoxalines, and GC-FID analysis of the decyl ester of acetic acid. As a main degradation product of 3-deoxy-d-erythro-hexos-2-ulose, 5-(hydroxymethyl)furfural could be identified. At alkaline pH values, 3-deoxy-d-erythro-hexos-2-ulose generated various acids but no colored products. In contrast, thermal treatment of methylglyoxal yielded high molecular weight, brownish products. A dimer of methylglyoxal, first precursor for aldol-based polymerization of methylglyoxal, could be clearly identified by GC/MS.

Topics: Chromatography, High Pressure Liquid; Furaldehyde; Gas Chromatography-Mass Spectrometry; Hot Temperature; Hydrogen-Ion Concentration; Ketoses; Levulinic Acids; Maillard Reaction; Mass Spectrometry; Pyruvaldehyde

In this study, for the first time, the amount of 3-deoxy-D-erythro-hexos-2-ulose (3-DG) in fresh citrus and chestnut honeys was determined. 3-DG was measured as the corresponding quinoxalines after derivatization with orthophenylenediamine using reverse-phase high-performance liquid chromatography (RP-HPLC). Notwithstanding the freshness of the samples, high levels of 3-DG were detected in both honeys. The comparison of 3-DG and 5-hydroxymethylfurfural (HMF) concentrations, which was also quantified by RP-HPLC, showed that citrus honeys had the lowest amount of 3-DG (107 mg/kg) and the highest of HMF (16.7 mg/kg), while chestnut honeys had the opposite (398 and 1.2 mg/kg, respectively). During thermal treatment, different 3-DG and HMF trends were highlighted between the citrus and chestnut honeys; at the end, 3-DG formation was more favored with respect to HMF formation. Moreover, in citrus honeys, a good correlation between 3-DG and HMF levels was observed, which was not found in chestnut honeys, suggesting a role of the high pH values of these honeys on the degradation routes. The kinetic analysis showed the highest k value for 3-DG and HMF formation in chestnut and citrus honeys, respectively. The lowest Ea values related to 3-DG formation and the highest to HMF formation, indicating that the key intermediate 3-DG is easily formed at low temperatures, whilst the formation of HMF requires higher temperatures. For this reason, 3-DG seems to be an aging index rather than a thermal index and its use, at least for honeys at high pH values, together with HMF, could improve their quality assessment.

Topics: Chromatography, High Pressure Liquid; Citrus; Fagaceae; Flowers; Furaldehyde; Honey; Hot Temperature; Hydrogen-Ion Concentration; Ketoses; Kinetics; Time Factors