Aroma impact compounds in Liuyang douchi, a Chinese traditional fermented soya bean product

Two procedures for the isolation of volatiles from Liuyang douchi, the typical representative of Aspergillus-type douchi, were compared: solid-phase microextraction (SPME) and simultaneous steam distillation extraction (SDE). Compared with SDE, the SPME extract was judged to be more similar to the aroma of the starting materials. The aroma impact compounds of the SPME extract were then determined using GC-MS and gas chromatography-olfactometry (GC-O). From the detection frequencies and the intensities of the peaks, twenty-eight volatile compounds were detected in the sniffing port of GC-O. Identification of twenty-two aroma impact compounds was based on the combination of sensory descriptors, linear retention index values, GC-MS data and co-injection of authentic standards. Compounds with the greatest aroma intensities include 2-methyl-butanal, ethyl 2-methylbutyrate, isoamyl acetate, 2,6-dimethylpyrazine, 1-octen-3-ol, 2-pentyl furan, benzeneacetaldehyde, phenylethyl alcohol, phenethyl acetate and phenethyl butyrate. These compounds might have an impact on the overall aroma of Liuyang douchi.