GC–MS characterisation and biological activity of essential oils from different vegetative organs ofPlectranthus barbatusandPlectranthus caninuscultivated in north Italy

Abstract

Essential oils (EOs) from the roots, stems and leaves of Plectranthus barbatus (A) and Plectranthus caninus (B), cultivated in north Italy, were obtained by steam distillation and chemically characterised by gas chromatography-mass spectrometry. The highest yields were obtained from roots (268.15 and 673.60 mg/kg from A and B), followed by leaves (64.34 and 26.65 mg/kg) and stems (19.76 and 18.63 mg/kg). A total of 128 structures were identified in A and 121 in B. Fe(++) chelating and antiradical activities (DPPH and ABTS) were evaluated: root and stem EOs showed the strongest activities, while EOs from leaves did not show relevant activities. All EOs were tested for their in vitro antimicrobial activity, showing optimal growth-inhibition in antibiogram (∅>35 mm) and MIC tests (32-64 μg/mL) against Candida albicans, while EOs from leaves of both species showed a good activity (25 < ∅ < 34 mm, MIC 64-128 μg/mL) against Escherichia coli.

Back to the Roots—An Overview of the Chemical Composition and Bioactivity of Selected Root-Essential Oils

“…However, although C. forskohlii is a highly aromatic herb, the chemistry and biological properties of its EO remain poorly known. Only a few phytochemical investigations have been conducted into the EO composition from C. forskohlii, indicating a tremendous variability in the chemical composition between different vegetative organs [166,167], as well as accordingly to different genotypes, plant origins, and grown altitudes [164,168]. Those variations may also be caused by pedoclimatic conditions and agricultural practices adopted [166].…”

“…Only a few phytochemical investigations have been conducted into the EO composition from C. forskohlii, indicating a tremendous variability in the chemical composition between different vegetative organs [166,167], as well as accordingly to different genotypes, plant origins, and grown altitudes [164,168]. Those variations may also be caused by pedoclimatic conditions and agricultural practices adopted [166]. However, the presence of 3-decanone Figure 1(19), bornyl acetate Figure 1(20), sesquiterpene hydrocarbons, and sesquiterpene alcohols in major concentrations gives the oil a unique combination of an attractive spicy and long-lasting odor [164].…”

“…However, the EO obtained by steam distillation from roots collected in north Italy revealed β-caryophyllene (15.1%) almost twice in concentration. Other main constituents were β-phellandrene (10.6%), β-gurjunene (10.6%), as well as humulene (6.3%) [ 166 ]. Analysis of another Indian C. forskohlii root sample led to the identification of 45 volatile compounds.…”

Anti-Candida Activity of Essential Oils from Lamiaceae Plants from the Mediterranean Area and the Middle East

“…and Esfand [ 56 ], Stachys spruneri Boiss. [ 71 ], Thymus willdenowii Boiss [ 84 ], Plectranthus barbatus Andrews, and Plectranthus caninus Roth [ 55 ]. When considering MIC values expressed as µL/mL, the two most active species were Nepeta cataria L. [ 108 ] and Zataria multiflora Boiss [ 82 ], with MIC values <0.3 ml/L.…”

“…Among these, terpinyl-acetate, α-terpineol, β-linalool, and γ-terpinene confer a strong anti- Candida activity to the EO when present as major components, as in the case of Salvia mirzayanii Rech.f. and Esfand [ 56 ], Plectranthus caninus Roth [ 55 ], and Thymus willdenowii Boiss. On the other hand, compounds making up a larger proportion of the EO are not necessarily responsible for the activity, and this makes it even more difficult to establish a correlation between chemical composition and biological efficacy.…”