Abstract: Gas chromatography-orbitrap-mass spectrometry (GC-Orbitrap-MS) combined with gas chromatography-quadruple-mass spectrometry-olfactometry (GC-Q-MS-O) was used to identify the ‘unknown’ aroma active compounds of soy sauce in this study. GC-Q-MS and GC-Orbitrap-MS identified 91 and 166 volatile compounds, respectively. The total peak area detected by Orbitrap-MS was 31 times as large as that detected by Q-MS. Four intense aroma-active areas with ‘fruity’, ‘fruity’, ‘grassy’ and ‘flowery and fruity’ notes were not identified in GC-Q-MS-O. In order to identify the 4 unknown compounds, the compound fragments and natural isotopic compositions were estimated by GC-Orbitrap-MS based on the high-precision mass spectral data. In addition, by comparing the mass spectra with the NIST mass spectral library as well as considering the retention index and aroma characteristics, they were identified as ethyl isobutyrate, ethyl butyrate, 3-hexen-2-one and 3,5,5-trimethyl-2-cyclohexenone (isophorone). This study showed that GC-Orbitrap-MS combined with GC-Q-MS-O could effectively reveal the ‘unknown’ aroma-active compounds whose contents were below the detection limit of quadrupole MS, or which could not be determined due to overlapping with other volatiles, which would be of important significance for the identification of aroma-active compounds in the field of flavor chemistry.

Key words: gas chromatography-mass spectrometry-olfactometry; gas chromatography-orbitrap-mass spectrometry; soy sauce; aroma-active compounds