Several kinds of rose are used as perfumery materials, including damask rose and centifolia. If compounds are extracted from their flowers by the same method, are the resulting materials chemically alike?
In a study published in 2021, Ana Dobreva and colleagues extracted four rose species used in fragrance production with a liquefied-gas solvent and compared their chemical compositions. They investigated the composition of materials obtained by a method different from conventional distilled essential oils or absolutes.
- Comparing four species grown in the same experimental field
- Using instruments to examine the compounds and their proportions
- Phenylethanol stands out in damask rose
- Alba and centifolia had a different balance
- A composition closer to an absolute than an essential oil
- Not a universal ranking of the four species
- Summary
- References
Comparing four species grown in the same experimental field
The species were Rosa damascena, Rosa gallica, Rosa alba, and Rosa centifolia, referred to below as damask rose, gallica, alba, and centifolia. The flowers were grown in an institute’s experimental field in Kazanlak, Bulgaria.
Flowers were collected in the morning during 2019. Because the four species flower at different times, they were not harvested on the same day. They were stored frozen at −20°C until processing.
The researchers extracted them with R134a, chemically known as 1,1,1,2-tetrafluoroethane. The solvent is liquefied under pressure and brought into contact with the flowers to dissolve their constituents; the solvent is then separated to obtain the extract.
The paper calls this subcritical extraction. Here, it can be understood as extraction using a solvent in liquid form at a relatively low temperature, rather than heating it into a supercritical state. The range of compounds extracted differs from that in steam-distilled essential oil.
Using instruments to examine the compounds and their proportions
The extracts were separated by gas chromatography, with mass spectrometry used to identify candidate compounds. Signals were also measured with a flame ionization detector to compare the proportion each compound represented in the whole.
These proportions are relative values based on chromatographic peak areas. They are not fully corrected quantitative measurements accounting precisely for differences in detector response among compounds. The authors themselves describe them as values for comparison between samples. They are not concentrations relative to flower mass or contributions to odor intensity.
The paper organizes the many detected constituents into a list of 103 entries. These include compounds whose structures are not fully known and compounds that appear together in the analysis. It is not a list in which every constituent has been completely separated and structurally confirmed.
Phenylethanol stands out in damask rose
One major difference involved 2-phenylethanol, a compound with a rose-like odor. Its relative proportions in the table were about 59% for damask rose, 27% for gallica, 14% for alba, and 9% for centifolia.
Even with the same extraction method, the proportion of this representative aroma compound differed greatly. Its proportion alone cannot establish which extract smells most rose-like or is most preferred, however, because the study did not include human sensory testing.
In damask rose, the chemical group that includes 2-phenylethanol accounted for a large proportion. In gallica, that group and the hydrocarbons discussed below occurred in relatively similar proportions.
Alba and centifolia had a different balance
In alba and centifolia, aliphatic hydrocarbons, compounds made of carbon and hydrogen, accounted for about 40% of the relative area. These included nonadecane and heneicosane. The same group represented about 13% in damask rose, giving a different overall distribution.
These hydrocarbons are also associated with constituents on the flower surface. The authors describe roles in fragrance stability and fixation, but this study did not measure wear time on skin. A higher proportion cannot simply be interpreted as making perfume last longer.
The balance among odor-related alcohols also differed. Alba had about 14% geraniol and 6% nerol, high values among the four species. Citronellol, on the other hand, was highest in damask rose at about 5%.
Centifolia also showed characteristic esters derived from compounds such as nerol. Esters are a group of compounds containing linked parts derived from an alcohol and an acid. Thus, even alba and centifolia, whose major chemical groups were similar, differed in their detailed composition.
A composition closer to an absolute than an essential oil
Comparing their results with earlier composition studies, the researchers considered the R134a extracts closer to rose absolutes than to distilled essential oils. An absolute is a fragrance material made by removing waxes and other substances from a solvent extract of flowers.
Alongside 2-phenylethanol, these extracts contained fatty acids, relatively nonvolatile constituents, and compounds associated with waxes. Which compounds are recovered abundantly depends not only on the plant’s composition but also on the extraction solvent.
This similarity is a chemical comparison. The researchers did not produce essential oil and absolute in parallel from the same flowers and have people judge their odors equivalent. Even so, the authors see potential in obtaining candidate materials with characteristics close to existing ingredients through a different extraction method.
Not a universal ranking of the four species
The differences observed may reflect not only species-specific metabolism but also conditions during flowering and storage. The numbers of independent extraction or analytical replicates were not clearly reported, and statistical significance of differences among species was not tested.
The figures therefore cannot be fixed as proportions that always apply to damask rose or alba. Studies of other origins, years, and accessions would help reveal stable characteristics of the materials.
The authors presented the method as an environmentally promising alternative because of its low operating temperature and the ease of separating the solvent. However, the solvent was R134a, and the study did not measure environmental burdens covering its manufacture, recovery, leakage, or energy use. Low extraction temperature alone does not establish an environmental advantage for the entire process.
The study was funded by a Bulgarian National Science Fund project addressing the authenticity and quality control of rose materials.
Summary
When four rose species were extracted with the same solvent, they shared many constituents but differed in their distribution. Damask rose had a large proportion of the group centered on phenylethanol, while alba and centifolia had more hydrocarbons, revealing distinct chemical profiles.
The study’s value is in providing baseline data for considering plant species together with extraction method, rather than treating rose materials as chemically uniform. It offers a starting point for selecting ingredients or breeding for desired characteristics, followed by testing odor and actual formulation performance.
References
Dobreva, A., Nedeltcheva-Antonova, D., Nenov, N., Getchovska, K., & Antonov, L.(2021). Subcritical Extracts from Major Species of Oil-Bearing Roses—A Comparative Chemical Profiling. Molecules, 26(16), 4991. DOI: 10.3390/molecules26164991. Full text. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. CC BY 4.0.
