High-intensity ultrasound promoted the aldol-type condensation as an alternative mean of synthesizing pyrazines in a Maillard reaction model system of D-glucose-(13)C(6) and L-glycine

This study evaluated how the generation of pyrazines was promoted by high-intensity ultrasound (HIU) in a Maillard reaction (MR) model system of glucose-glycine. Carbohydrate module labeling (CAMOLA) technique was adopted using D-glucose-(13)C(6) to elucidate the carbon skeleton of both intermediate and final MR products (MRPs). In the D-glucose-(13)C(6)-glycine HIU-MR model system, the concentration of 11 types of pyrazines was significantly higher than their counterparts in the thermal MR. Results of CAMOLA analysis showed that a significantly lower proportion of [M](+) in pyrazines with long-length side chains was observed when compared with the pyrazines generated in thermal MR. This phenomenon may suggest the aldol-type condensation was promoted by the HIU, which is a conversion from pyrazines with short-length side chains to those with long-length side chains involving carbonyl compounds. Furthermore, the analysis of isotopomers distribution in 2,3-dimethyl-quinoxaline as the o-phenylenediamine-derivatized 2,3-butanedione indicated that the increased proportion of [M + 4](+) in 2,3-dimethyl-quinoxaline (15.74% ± 0.11%) was attributed to a cleavage of D-glucose-(13)C(6) promoted by the HIU. The above-mentioned findings elucidate that the aldol-type condensation and cleavage of D-glucose contribute to the promoted synthesis of pyrazines. The HIU would generate an extremely high temperature and pressure environment that is favored by the aldol-type condensation as a high-pressure favored reaction. The HIU, therefore, can be further developed as a promising technique to promote flavor generation through the MR.