Difference Analysis of Volatile Nitrogen-Containing Compounds in Different Rounds of Base Distillates of Soy Sauce Aroma Type Baijiu

Volatile nitrogen-containing compounds account for a small proportion in soy sauce aroma type Baijiu, but they have the characteristics of strong aroma and low odor threshold, which have an important impact on the flavor of the Baijiu. In this study, the 1st~7th rounds of distillates of soy sauce aroma type Baijiu were selected as the research targets. The liquid-liquid extraction method combined with comprehensive two-dimensional gas chromatography-nitrogen chemiluminescence detector technology was employed to conduct both qualitative and quantitative analyses of volatile nitrogen-containing compounds. A total of 37 kinds of volatile nitrogen-containing compounds were successfully identified, including 16 pyrazine compounds, 4 pyrrole compounds, 4 nitrogen-containing ester compounds, 3 thiazole compounds, 3 pyridine compounds, and 7 other compounds. The quantitative analysis results indicated that the mass concentrations ranked from high to low were pyrazines, thiazoles, nitrogen-containing esters, pyrroles, and pyridines. Based on these quantitative findings, orthogonal partial least-squares discriminant analysis was implemented to screen out 13 volatile nitrogen-containing compounds with variable projection values exceeding 1. The results further revealed that the compositions of the base distillates from the 3rd, 4th, and 5th rounds were relatively analogous and could be distinctly differentiated from those of the other rounds. By integrating the odor activity value (OAV) method, the OAVs of the 13 compounds were calculated. Notably, the OAVs of 2-ethyl-6-methylpyrazine and 2, 3, 5-trimethylpyrazine were greater than 1 in the 5th to 7th rounds, while the OAVs of 2-ethyl-3, 5-dimethylpyrazine and 2, 3-diethyl-5-methylpyrazine were greater than 1 across the 1st to 7th rounds. These four volatile nitrogen-containing compounds exhibited flavor contributions with statistical significance in different distillation rounds. The research aimed to elucidate the contribution of volatile nitrogen-containing compounds to the flavor of base Baijiu across different distillation rounds, addressing the research gap on thiazoles, pyrroles, and pyridines. By identifying key flavor compounds and quantifying their contributions, this study provided a theoretical foundation for the precise regulation and optimization of flavor quality in soy sauce aroma type Baijiu.