Authenticity assessment and detection of adulteration in Bulgarian rose (Rosa damascena Mill.) essential oils

Rose ( Rosa damascena Mill.) oil is one of the most expensive essential oils and therefore often subject to adulteration. Common cases of adulteration include the admixture of fatty oils or high-boiling glycols, the addition of specific compounds or of (fractions of) similar but cheaper essential oils [ 1 ]. Physicochemical properties like relative density, refractive index and optical rotation outside certain limits for rose oil specified in ISO 9842 indicate crude adulterations. Invisible under GC conditions usually applied for rose oil volatiles, the admixture of fatty oils or other non-volatiles is uncovered by GC/MS after transesterification, high-temperature GC using dimethyl polysiloxane as stationary phase and TLC on silica gel developed with isopropyl ether:acetic acid (94:6) and light petroleum:diethyl ether:acetic acid (90:10:1), respectively. Since enantiomeric ratios of chiral compounds are highly specific for an essential oil, chirality evaluation of linalool, β-citronellol, and cis/trans rose oxide is also used as a powerful tool in authenticity control of rose oil [ 2 ], and the ratio of R/S linalool in the present study was found to be 1.2, whereas β-citronellol is solely found in its S -configuration. Most significant, the ratios of major constituents in rose oil and typical minor compounds (not or hardly available as isolates or individual compounds) proved to be an appropriate authenticity criterion, and uncommon values were found to be diagnostic for adulteration with major constituents. Finally, NIR spectroscopy combined with chemometrics using cluster analysis covering data from in-house quality control of >100 batches provides an additional tool for genuineness and purity control purposes.