Reducing the Influence of the Thermally Induced Reactions on the Determination of Aroma-Active Compounds in Soy Sauce Using SDE and GC-MS/O

A method based on simultaneous distillation extraction (SDE) coupled with gas chromatography-mass spectrometry/olfactometry (GC-MS/O) was developed for the analysis of volatile profiles in soy sauce. Its optimum operating conditions were as follows: 100 mL soy sauce plus 100 mL saturated brine; 2 h extraction using 50 mL dichloromethane. Eighty-eight volatile compounds were identified. Of these, 26 aroma-active compounds were detected by GC-O including 3-(methylthio)propanal, 2-methoxy-4-vinylphenol, 2-methoxyphenol, 2-methylbutanoic acid, 2,3-butanedione, phenylacetaldehyde, 2-ethyl-6-methylpyrazine, 3-methylbutanal, 2-methylbutanal, 3-methyl-1-butanol, and 2-methyl-1-butanol (which occurred at a high odor intensity in both high-salt liquid-state fermentation soy sauce (HLFSS) and low-salt solid-state fermentation soy sauce (LSFSS). SDE analysis of the odorless soy sauce indicated 12 volatiles (mainly Strecker aldehydes and alpha-dicarbonyl compounds). Thus, the proportions of these compounds (1.94-54.07 %) shown in previous GC-MS results could result from thermal degradation of non-volatile compounds in soy sauce. Especially, the contribution of 3-methylbutanal, 2-methylbutanal, phenylacetaldehyde, 3-(methylthio)propanal, and 2,3-butanedione to the aroma of soy sauce could be overestimated by conventional SDE-GC-O. With a full consideration of such limitations, this study will improve the application of SDE on aroma analysis of complex food matrix.