Characterization of Odor-active Compounds in Moutai-flavor Daqu Using Aroma Extract Dilution Analysis

Daqu is the starter for baijiu saccharification and fermentation. The unique aroma of Moutai liquor is inseparable from the daqu used. Understanding of the flavor characteristics of Moutai-flavor Daqu and the flavor differences between various fermented-daqu is incomplete. The aroma characteristics of Moutai-flavor Daqu were investigated using sensory analysis and aroma extract dilution analysis. Differences between the aroma components of three different fermented-daqu were compared and analyzed using headspace solid-phase micro-extraction coupled with gas chromatography–mass spectrometry. Eighty–two odor active regions having a flavor dilution (FD) factor ≥5 were detected, of which 78 compounds (16 aromatics, 12 acids, 9 pyrazines, 8 pyrroles, 6 phenols, 4 furans, 4 pyridines, 4 ketones, 3 pyrones, 3 aldehydes, 3 pyrazoles, 2 sulfides, 2 lactones, 1 alcohol and 1 quinazoline) were specifically identified. The compounds 2-methoxyphenol, 4-ethylguaiacol, 2-methoxy-4-vinyl phenol and 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, of which the greatest FD factor was 3125, were identified as possible key contributors to the yellow rice cake-like, candy, smoky and caramel aroma of Moutai-flavor Daqu. The Maillard reaction products 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one and 2-methyl-3,5-dihydroxy-4H-pyran-4-one were identified in the daqu. Seventy-one aroma compounds were detected in fermented-daqu. The flavor contribution of each was calculated by statistical analysis, and the top 20 compounds were selected for further principal component analysis and content distribution analysis. The results show that there were significant differences between the three different fermented-daqu, which explains the differences in their sensory characteristics.