Comparative Profiling and Dynamic Evolution of Aroma Signatures in Xizang Qingke Baijiu Throughout the Multi-Round Brewing Process: A GC × GC-TOFMS Based Approach

To elucidate the flavor chemistry of Qingke (ighland barley) light-aroma baijiu under plateau conditions, this study analyzed three sequential fermentation and distillation rounds in Lhasa using comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry (GC × GC-TOFMS). Samples included first-round fermented Qingke baijiu (QXYC), second-round (QXEC), and third-round (QXSC) fermented Qingke baijiu. A total of 2245, 1437, and 1787 volatile compounds were tentatively identified in the first, second, and third rounds, respectively, revealing significant inter-round compositional dynamics. Metabolic pathway analysis demonstrated that terpene catabolism, protein digestion and absorption, and furfural degradation were the most significantly enriched pathways in the initial two rounds, driving the formation of key aroma precursors. Notably, the transition from the second to the third round was characterized by a metabolic shift wherein phenolic compounds became predominantly associated with bisphenol degradation, benzoate degradation, tyrosine metabolism, and protein digestion pathways, indicating substrate-dependent reprogramming of microbial metabolism in late-stage fermentation. These findings provide the first systematic molecular characterization of round-dependent flavor evolution in plateau-produced Qingke baijiu, establishing a foundational framework for understanding its unique sensory complexity and guiding precision quality control in high-altitude fermentation.