Aroma Constituents in Shanxi Aged Vinegar before and after Aging

Shanxi aged vinegar is one of the most famous Chinese traditional cereal vinegars produced by spontaneous solid-state fermentation. However, the aroma composition of Shanxi aged vinegar is still ambiguous. The Shanxi vinegars before and after aging were both analyzed by solvent-assisted flavor evaporation combined with gas chromatography-mass spectrometry (GC-MS) as well as gas chromatography-olfactometry (GC-O) in aroma extract dilution analysis. A total of 87 odor-active regions were found by GC-O, and 80 odor-active compounds were identified. By GC-MS/MS, in selected reaction monitoring mode, 30 important identifications were quantitated using authentic standards. In comparison, the aroma molecules for the vinegars before and after aging were almost the same; only their levels were altered, with mostly the esters and some compounds that produce pungent smells being lost and the levels of those from the Maillard reaction, especially the pyrazines (e.g., tetramethylpyrazine), being greatly increased. As for the aged vinegar, the compounds found to have high flavor dilution factors (>128) were 3-(methylthio)propanal, vanillin, 2,3-butanedione, tetramethylpyrazine, 3-methylbutanoic acid, γ-nonalactone, guaiacol, 3-(methylthio)propyl acetate, dimethyl trisulfide, phenylacetaldehyde, 2-ethyl-6-methylpyrazine, 2-acetylpyrazine, 2,3-dimethylpyrazine, furfural, and 3-hydroxy-2-butanone. However, the aroma compounds found at high concentrations (>25 μg/L) in the aged vinegar were acetic acid, followed by 2,3-butanedione, furfural, 3-hydroxy-2-butanone, tetramethylpyrazine, furfuryl alcohol, and 3-methylbutanoic acid.