Modeling alkylpyrazine formation in red jujube matrix under controlled conditions of pH and temperature

English. peer reviewed

English. Alkylpyrazines presented a pleasant "roasty" aroma and were considered as the key aroma compounds in freeze-dried red jujube. Their formation is significantly affected by temperature, pH and substrates. To understand the formation pathway of alkylpyrazines during the freeze-drying of red jujube, the solid-state models were first established. In these models, 35 mL of buffer solution (pH 5.5 and 7.8) containing glucose (5 g) and amino acids (5 g) was fully absorbed by an odorless red jujube matrix (8 g). Furthermore, the variation and correlations of volatile compounds during the heating (85 � C, 10 h) were detected and analyzed. The content of pyrazines at pH 7.8 was only 11.34% higher than that at pH 5.5 model. At pH 5.5 model, butane-2,3-dione, pentane-2,3-dione, pyruvic acid, isopropyl alcohol, acetone, and 2-hydroxypropionic acid were significantly correlated with 2-ethyl-3,5-dimethylpyrazine (3,5-EDMP). In the red jujube matrix, the dominant formation of 3,5-EDMP involved the generation of 2-aminopentane-3-one produced by the reaction of pentane-2,3-dione with ammonia, then condensed with aminoacetone (from Strecker degradation) to form dihydropyrazine, subsequently oxidized to 3,5-EDMP. A validation experiment was conducted under industrial freeze-dried conditions. The content of 3,5-EDMP with a "roasty" aroma was 15.3 times higher than that in the original red jujube when glucose (5 g) and L-lysine (5 g) were added. It was demonstrating that the aroma of red jujube products can be modulated by adding relevant aroma precursors.