Unsaturated fatty acid-associated lipid oxidation contributes to browning and flavor formation in high-temperature Daqu.

High-temperature Daqu (HTD) shows distinct browning intensities during fermentation, accompanied by differences in flavor quality. Unsaturated fatty acids (UFAs) as important precursors and reactive substrates in fermentation systems, may play a critical role in this process. In this study, UFAs profiles of HTD with different browning intensities were comparatively analyzed, alongside their physicochemical properties, enzyme activities, and microbiota. Our results revealed significant divergence in UFAs contents during fermentation, with linoleic acid and linolenic acid identified as key discriminatory factors. Microbiological analysis indicated that Kroppenstedtia and Thermomyces were potentially microbial contributors to modulate UFAs. Crucially, further investigations demonstrated that the oxidation of these UFAs facilitated browning and production of pyrazines in Daqu. Linoleic acid and linolenic acid increased pyrazine production by 1.7-fold and 2.6-fold. These findings indicate that lipid oxidation is closely associated with browning differentiation and quality variation in HTD, highlighting UFAs as promising novel targets for modulating Daqu quality.