Location- and flowering-stage-dependent variation in the physicochemical profile of traditionally distilled Taif rose (Rosa damascena Mill. var. trigintipetala Dieck) oil

The essential oil of Rosa damascena Mill. var. trigintipetala Dieck cultivated in Taif, Saudi Arabia was investigated to assess the impact of harvest stage (early, mid, late flowering) and geographical origin (Al-Hada, Al-Shifa, Wadi Mahram) on its chemical composition and physicochemical properties, aiming to establish a scientific basis for national quality standards of Saudi rose oil. GC–MS profiling showed that citronellol declined from 30.5% (early) to 24.6% (late), while geraniol increased from 21.9% to 26.4% and nerol from 10.0% to 13.1%, with the (citronellol + nerol)/geraniol ratio decreasing from 1.72 to 1.51, closer to ISO 9842:2024 specifications. Saturated hydrocarbons rose from 12.4% to 13.9% across harvest stages, whereas unsaturated hydrocarbons declined from 4.3% to 2.7%. Physicochemical analysis confirmed compliance with ISO standards: refractive index (1.463–1.464), optical rotation (−4.39° to −3.25°), relative density (0.856–0.862), ester value (6.85–8.38), and flash point (83–87°C). Geographic differences were evident, with Al-Shifa oils richest in geraniol and nerol and lowest in methyl eugenol, Wadi Mahram oils highest in monoterpene alcohols and lowest in hydrocarbons, and Al-Hada oils distinguished by higher hydrocarbon fractions. Multivariate analyses, including PCA, heatmap visualization, and correlation analysis, further highlighted strong associations among monoterpene alcohols and hydrocarbons, reinforcing harvest stage and origin as critical determinants of oil quality. Late flowering is preferable when a geraniol- and nerol-rich profile is desired, whereas early flowering is advantageous for minimizing methyl eugenol and hydrocarbon content. Overall, Taif rose oils complied with ISO physicochemical requirements but exhibited distinct harvest- and location-dependent profiles. This work provides, to the best of our understanding, the first systematic evaluation of Saudi rose oil standardization and lays the foundation for region-specific quality specifications and national quality-control strategies.