Effects of Urea on the Formation of Perfume Compounds by Ascorbic Acid-Methionine Model Reaction

Abstract

By the headspace-solid phase micro-extraction – gas chromatography – mass spectrometry (Headspace-SPME–GC–MS) technology, this article identifies products from the model reaction between ascorbic acid and methionine (ASA-Met), and studies the impacts of urea on the formation of perfume compounds from the model reaction. 17 perfume compounds have been identified, including pyrazine, sulfur compounds ,thiophene, pyrrole and compounds containing benzene rings, of which sulfur compounds, such as alicyclic sulfides, thioether and pyrazine, are the main flavor components. For urea being added to the model system, one the one hand, the yields of some sulfur compounds will be significantly reduced; on the other hand, it promotes the production of several nitrogen compounds such as methyl pyrazine, ethyl pyrazine and 2,6-dimethyl pyrazine, and other alkyl pyrazine. This indicates that urea inhibits the thermal degradation of Met in the model reaction, and also implies that as the nitrogen source during the thermal degradation of urea NH3 may be generated. After a competing reaction occurs between NH3 and the degradation products of H2S and ASA, nitrogen compounds are formed, such as alkyl pyrazine, so as to cause the lower production of sulfur compounds.