## 2 Results and Discussion
### Terpenoids  
#### 2.2.1 Monoterpenes  
The monoterpene hydrocarbons total content is in a relatively narrow concentration range from 1.65 to 4.19%, with the main representative unsaturated bicyclic monoterpene (\(\alpha\)- and \(\beta\)-). Pinene isomers add pine- and turpentine-like notes to the fragrance profile. It is important to underline that \(\alpha\)-pinene was observed in whole _R. alba_ blossoms only and was not detected in rose petals, with a maximal concentration of 1.62% in white colored samples. Its isomer \(\beta\)-pinene was found in a maximal concentration of 2.01% in samples with pink colored petals. The high extraction temperature reduces the content of both pinene isomers--the lowest concentration (0.42% for \(\alpha\)- and 0.72% for \(\beta\)-pinene) was observed by extraction at 60 \({}^{\circ}\)C, while the SPME at room temperature increases pinene content. The acyclic monoterpene \(\beta\)-myrcene was found in trace amounts only.  
Oxygenated monoterpenes  
Monoterpene alcohols. The most abundant class of aroma compounds presented in the _R. alba_ VOCs profile is the monoterpene alcohols. Geraniol, nerol, and citronellol are the main compounds responsible for the fragrance and biological activity of the oil-bearing rose species and their aroma products (and are often being used for adulteration of the high-priced rose aroma products with synthetic compounds). Citronellol and nerol give the characteristic rosaceous essence. Geraniol is also basic for the scent and exerts the major pharmacological effects of the rose oil, such as antitumor, antibacterial, antifungal, antioxidant, and anti-inflammatory [36]. In this study, geraniol was the second most abundant single component, followed by citronellol and nerol. In general, their amounts in rose petals were found to be higher in comparison to the whole _R. alba_ blossom--geraniol shows a maximal concentration of 32.45% in white petals sample, while citronellol/nerol were observed in maximal concentration in mixed petals sample (26.5%). Linalool, known as one of the rose alcohols, adding rich floral and spicy notes to the rose aroma, was found in a maximal concentration of 0.81% in a whole blossom sample extracted at 30 \({}^{\circ}\)C.  
Ketones. It is generally accepted that rose ketones are very important for rose fragrance. \(\beta\)-damascone (1-(2,6,6-trimethyl-1-cyclohexenyl)]but-2-en-1-one), together with \(\beta\)-damascone (1-(2,6,6-trimethyl-1-cyclohex-1,3-dienyl)]but-2-en-1-one), plays an important organoleptic role as a trace component and as a quality marker of Bulgarian rose oil. In our study, \(\beta\)-damascone was found in a very low concentration <LOQ (0.005%) in fresh _R. alba_ flowers, while \(\beta\)-damascone was not detected.  
Oxides. Tetrahydro-4-methyl-2-(2-methylpropenyl)-2H-pyran (rose oxide), existing as _cis_- and _trans_-isomers, is a key minor component of the rose essential oil. In the current study, _cis_-rose oxide was observed in 0.03-0.12%, while the _trans_-isomer was found in a higher concentration (0.08-0.29%).  
These results are very important, because it has been previously reported and generally accepted that the isomeric rose oxides do not occur in the rose flowers, because these volatiles appear to be artefacts formed during the steam distillation process [6]. Our study undoubtedly confirms the presence of the rose ketones in fresh _R. alba_ flowers.