Determination of the role of valencene in orange oil as a direct contributor to aroma quality

Valencene is the major sesquiterpene in orange peel oil and its concentration has been traditionally used to determine the oil's commercial value. Multidimensional GC-O/GC-MS was employed to determine the contribution of valencene to the aroma quality of a commercial orange oil. Thirty-seven aroma-active components were found in this orange oil. One of these components possessed a citrusy/woody aroma similar to that of valencene and eluted in the expected time region for valencene on a polar column. The volatiles in the valencene region were isolated by the heartcutting technique, directed to a second GC capillary column (DB-5) and split between a mass spectrometer and an olfactory port. Aroma activity was detected only from a peak identified as dodecanal, and not valencene. The identities of both compounds were confirmed from full scan mass spectra and reconfirmed with standards. Valencene concentrations in the original orange oil and three additional commercial orange oils were determined to be 54-68 mu g/g, using GC-FID with an internal standard. The results indicated that valencene produced no aroma activity at the levels found in orange oil. Its use as a causative indicator of good quality orange oil must be questioned. Valencene may simply be an easy to measure marker for increased fruit maturity, which is known to correlate positively with increased orange flavour quality. This study also demonstrates the need for careful chromatography involving multiple columns whenever assigning aroma activity to a particular compound in GC-O studies. Copyright (c) 2005 John Wiley & Sons, Ltd.