Determination of volatiles and indicators during aging of soy sauces

Abstract

In this study, volatile compounds of soy sauces were investigated according to aging of 12 months. Both solid phase micro-extraction (SPME) and stir bar sorptive-extraction (SBSE) methods were employed for qualitative and quantitative analysis of volatile components. A total of 144 and 129 compounds were identified in aged soy sauces by SPME and SBSE, respectively. In SPME analysis, the contents of most compounds, such as acids, aldehydes, benzene and benzene derivatives, esters, lactones, pyrazines, pyrones, and pyrroles, were increased, while those of alcohols and ketones were decreased according to aging. In the case of SBSE method, most acids, aldehydes, benzene and benzene derivatives, esters, and sulfur-containing compounds were enhanced, whereas some alcohols and aldehydes were decreased. In addition, principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were conducted to discriminate soy sauce samples depending on aging. Commonly, most alcohols and ketones were detected as main contributors in SPME (0-5 months) and SBSE (0-4 months). On the other hand, esters, aldehydes, furan-2-ylmethanol, benzene and benzene derivatives, methanethiol and maltol were closely related to SPME (6-9 months) and SBSE (5-9 months). Benzene and benzene derivatives, esters, 2-methylpropanoicacid, 3-methylbutanoic acid and 2-acetylpyrrole were identified in 12 month. Moreover, the major volatiles, which were related to the differentiation of aging period in soy sauce samples, were determined as aging indicators, including ethyl 3-methylbutanoate (ethyl isovalerate), ethyl pentanoate (ethyl valerate), 1-octen-3-yl acetate, 3-(methylthio)-1-propanol (methionol), ethyl benzoate, ethyl 2-phenylacetate, 1-(1H-pyrrol-2-yl)ethanone (2-acetylpyrrole), and 5-pentyl-2-oxolanone (γ-nonalactone).