SUPERCRITICAL CARBON-DIOXIDE EXTRACTION OF ONION FLAVORS AND THEIR ANALYSIS BY GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

Extraction with supercritical carbon dioxide (SC-CO2) produced fresh onion-like flavor components from onions. Combined gas chromatography-mass spectrometry analysis of SC-CO2 onion extract showed the presence of 28 sulfur-containing compounds, including diallyl thiosulfinate (or its isomer, di-1-propenyl thiosulfinate), propyl methanethiosulfonate, dithiin derivatives, diallyl sulfide, diallyl trisulfide, and 6 other tentatively identified compounds. A commercial steam-distilled onion oil analyzed under similar conditions did not contain detectable amounts of the compounds listed above but did have 13 other compounds in common with the SC-CO2 onion extract. The flavor compounds methyl propyl trisulfide, dipropyl trisulfide, and dipropyl tetrasulfide were detected only in the commercial steam-distilled onion oil and were present in high concentration.