Aldehyde metabolism in Maotai-flavor Baijiu: insights from integrated metagenomic and metaproteomic analyses.
Acetaldehyde and acetal are crucial to the flavor of Maotai-flavor Baijiu, affecting aroma release and sauce-aroma traits. Targeted control of acetaldehyde metabolic flux is critical for stabilizing base liquor quality. However, the diversity of acetaldehyde-metabolizing enzymes and their microbial drivers remain uncharacterized, critically impeding precision control. This study selected the third production round to systematically investigate acetaldehyde accumulation dynamics and metabolic mechanisms. Time-resolved profiling showed that acetaldehyde and acetal concentrations display an initial rise, followed by a decline and stabilization. By integrated metagenomic and metaproteomic analyses, we confirmed that the metabolic network comprised two biosynthetic and three conversion pathways. The dominant biosynthetic pathway featured pyruvate decarboxylase (PDC)-catalyzed decarboxylation, while ethanolamine ammonia-lyase contributed minimally. Among conversion pathways, NADH-dependent alcohol dehydrogenase (NADH-ADH) reduction to ethanol predominated, with lower-flux oxidation to acetate and acetyl-CoA. Dynamic enzyme profiling revealed that PDC activity preceded the activation of NADH-ADH during stacking fermentation, resulting in a temporal mismatch between aldehyde production and consumption, which led to metabolic retention. During pit fermentation, acetaldehyde was more efficiently converted to ethanol through upregulation of NADH-ADH and NADH/NAD +  ratio. As main contributors of PDC and NADH-ADH, Schizosaccharomyces pombe and Saccharomyces cerevisiae exhibited dual regulatory roles in acetaldehyde metabolism, with their metabolic mode shifts governed by dissolved oxygen and the NADH/NAD +  ratio. Microbial interaction analysis and simulated fermentation confirmed that Pichia kudriavzevii synergized with Saccharomyces cerevisiae and Schizosaccharomyces pombe, driving rapid acetaldehyde accumulation during the stacking fermentation. These findings establish a theoretical framework for optimizing brewing processes and enhancing base liquor quality.
Li C, Yang F, Han Y, Yang C, Qin X, Zheng H, Chen L, Lu J, Zhang C, Lu F, Wang L