Optimization of Headspace Solid-Phase Micro-extraction (HS-SPME) for Analyzing Soy Sauce Aroma Compounds via Coupling with Direct GC-Olfactometry (D-GC-O) and Gas Chromatography-Mass Spectrometry (GC-MS)

The aim of this study was to develop an effective analytical procedure to analyse the aroma-active compounds of soy sauce using headspace solid-phase micro-extraction (HS-SPME) coupled to gas chromatography-mass spectrometry/olfactometry (GC-MS/O). Optimization of SPME focusing on type of fibre, exposure time, extraction temperature and ionic strength was supported by gas chromatography-mass spectrometry (GC-MS). The optimized HS-SPME conditions were as follows: carboxen/polydimethylsiloxane (CAR/PDMS) fibre, NaCl concentration of 270 g/L, extraction temperature of 45 °C and 30-min exposure time. Under these conditions, 25 aroma-active compounds were detected in soy sauce by HS-SPME-GC-O. 2-Methylbutanal (malty), 3-(methylthio)propanal (cooked potato-like), dimethyl trisufide (sulfury, cooked onion), 2-methoxyphenol (smoky) and 2-phenylethanol (flowery) were the most intense. The overall odour impression of the CAR/PDMS-fibre-derived SPME extract detected via human sniffing resembled that of original soy sauce. The intensity of aromas detected by D-GC-O correlated well with the total peak area of GC-MS analysis. Thus, SPME coupled with D-GC-O offers an automated facile method to allow in situ optimization of SPME performance and ultimately effective analysis of aromas.