Key Aroma Compounds and Aroma Characteristics in Nongxiangxing Baijiu Characterized by GC-IMS, GC × GC-MS, and an Electronic Nose

Nongxiangxing (NXX) baijiu belongs to one of the major flavor categories of Chinese baijiu; however, the duration of storage is of vital importance in developing the distinctive flavor of baijiu, which may affect its aroma, taste, and body structure. In this research, the volatile compounds in five NXX baijiu (Y1, Y3, Y5, Y8, and Y11) from different storage years were qualitatively and quantitatively identified by gas chromatography-ion migration spectrometry (GC-IMS) and two-dimensional gas chromatography-combined mass spectrometry (GC × GC-MS). GC-IMS, orthogonal partial least-squares-discriminant analysis (OPLS-DA), and variable importance in projection (VIP) analysis identified 11 key aroma compounds; subsequently, relative odor activity value (ROAV ≥ 1) analysis was used to further determine 2 potential key aroma compounds. GC × GC-MS, OPLS-DA, and VIP analysis identified 16 key aroma compounds, and odor activity value (OAV ≥ 1) analysis was used to further determine 8 potential key aroma compounds. By integrating the electronic nose (E-nose) and key aroma compound analysis, the significant differences in aroma between samples were revealed, the aroma distribution between Y3 and Y5 was more similar, the aroma distribution between Y8 and Y11 was more similar, and the roasted aroma, nut aroma, fruit aroma, and ester aroma were more prominent in Y1. Moreover, the correlation analysis conducted between the response values of the E-nose sensors and the levels of some key aroma compounds detected by GC × GC-MS showed that the E-nose exhibited a strong discrimination ability for Y1.