Gas Chromatography/Olfactory Analysis of Lychee (Litchi chinesis Sonn.)

Volatile compounds from lychee ( Litchi chinesis Sonn.), a tropical fruit native to China, were extracted using both Freon 113 and ethyl acetate solvents. The odor-active compounds present in the fruit were isolated and characterized using gas chromatography/olfactory (GC/O), chromatography, and mass spectrometry. Authentic standards were used to determine mass spectral, retention index, and odor match. GC/O analysis detected at least 60 odor-active volatiles in the fruit extract. More odor-active volatiles were detected in the ethyl acetate extract than in the nonpolar Freon extract. Among the compounds that had significant odor activity, geraniol, guaiacol, vanillin, 2-acetyl-2-thiazoline, 2-phenylethanol, unknown ( 58 ), ( Z )-2-nonenal, β-damascenone, 1-octen-3-ol, Furaneol, and linalool were found to be the most odor-active. On the basis of their calculated odor activity values (OAV), isobutyl acetate, guaiacol, cis -rose oxide, 2-acetyl-2-thiazoline, β-damascenone, Furaneol, linalool, ( E )-2-nonenal, geraniol, and isovaleric acid were determined to significantly contribute to the aroma of this fruit. GC/O analysis confirmed that 2-phenylethanol was probably responsible for the floral character and that the citrus-fruity aroma is due to the presence of many odor-active terpenes, particularly geraniol. Although cis -rose oxide was only 30% as active in GC/O as the most potent odor, its high OAV indicates its importance to the character of lychee odor. An unknown sesquiterpene-like compound ( 58 ), with a lychee-like odor characteristic of the fresh fruit, was identified by GC/O as being a highly odor potent compound. Taken together, the aroma of lychee was determined to be due to the interaction between compounds with floral, nutty, citrus, and fruity aromas.