Study Evaluates Seven Helichrysum Species for Volatile Profile and Essential Oil Composition
The genus Helichrysum (Asteraceae) contains an estimated 600 species, many of which are aromatic herbs or dwarf perennial shrubs indigenous to South Africa. Sixteen species are native to Europe and the Mediterranean, where they are used in herbal medicine to treat a range of conditions, including respiratory infections, digestive disorders, fever, inflammation, and pain. These healing properties have been attributed to active compounds found in the aerial plant parts. Essential oil (EO) obtained from the helichrysum (curry plant; Helichrysum italicum) is commonly used for its health benefits, and its profile has been well researched. This study aimed to determine the volatile profile and EO composition of seven Helichrysum species for potential ornamental and medicinal use. Four are native to South Africa (gold carpet [H. cymosum ssp. cymosum], fragrant helichrysum [H. odoratissimum], silver bush everlasting [H. petiolare], and sticky everlasting [H. tenax]) and the remainder (strawflower [H. fontanesii], red everlasting [H. sanguineum], and H. saxatile) are from the Mediterranean Basin.
The plants used for analysis were grown in the botanical collection of CREA (Council for Agricultural Research and Economics), an Italian government research station in Liguria, Italy. All of the specimens were propagated and grown under the same conditions at CREA and collected in 2014.
The volatile compound analysis was conducted on fresh flower heads using the headspace solid-phase microextraction (HS-SPME) technique under identical conditions and testing procedures. For the EO analysis, dried aerial parts (flowers, leaves, branches) were hydrodistilled separately, and the EO for each was dehydrated then analyzed using gas chromatography–electron impact mass spectrometry (GC/EI-MS). Compounds were identified by comparing their retention time against a known standard. Data were analyzed using cluster analysis and nonmetric multidimensional scaling. An analysis was done using R 2.14.0 software.
The results of the HS-SPME volatile composition analysis found 80 compounds present among the seven species. Monoterpenes were the most prevalent class in all species, with H. tenax containing the most at 95.1%. Helichrysum sanguineum and H. fontanesii contained the highest percentage of sesquiterpenes at 68.0% and 66.3%, respectively. Cluster analysis divided the species into three groups, as follows: group I comprised of H. tenax, H. odoratissimum, H. saxatile, and H. petiolare; group II was solely H. fontanesii; and group III included H. sanguineum and H. cymosum. The predominant compounds found in group I were β-pinene and 1,8-cineole. Groups II and III contained more camphene, β-caryophyllene, and carvacrol.
There were 199 EO compounds identified through the GC/EI-MS analysis. Besides constituent differences found between species, the major class of terpenes present varied within species, depending on the source of the EO sample (i.e., flowers, leaves, or branches). Sesquiterpenes predominated in all parts of H. petiolare and H. fontanesii. Helichrysum odoratissimum had a high percentage of sesquiterpenes in the leaves, but equal amounts of sesquiterpenes and monoterpenes in the flowers. Helichrysum cymosum and H. tenax contained a high percentage of monoterpenes. Helichrysum saxatile was high in sesquiterpenes and non-terpenic compounds. Finally, H. sanguineum was high in sesquiterpene hydrocarbons in the flowers, monoterpene hydrocarbons in the leaves, and some non-terpenic compounds as well.
Cluster analysis of the EO results divided the species into four groups, as follows: group I with H. saxatile and H. petiolare; group II with H. fontanesii; group III with H. cymosum flowers and leaves; and group IV with H. tenax and H. odoratissimum flowers and leaves. The predominant compounds found in group I were β-hydroagarofuran, α-calacorene, and caryophyllene alcohol. Group II contained humulene epoxide II; group III contained the highest amounts of (Z)-β-ocimene and β-caryophyllene, and group IV was marked by α-pinene and β-caryophyllene.
The results of this evaluation indicate that the primary class of volatile compounds in the four South African species (H. cymosum, H. odoratissimum, H. petiolare, and H. tenax) was the monoterpenes. The Mediterranean species were characterized by higher sesquiterpene content. Helichrysum saxatile, an Italian species, was high in both monoterpenes and sesquiterpenes. The authors conclude that these species have both commercial EO and ornamental applications.
When comparing their results to those in published literature, the authors encountered some differences in the EO compositions between species in the CREA collection and species grown in their native habitats. This could be due to the difference in environmental and growing conditions in Liguria, Italy, as compared to the native habitats for each species. This study represents the first aromatic-compound and EO evaluation for H. fontanesii, H. sanguineum, and H. tenax, as well as the first complete EO evaluation of H. saxatile.
The authors did not provide any funding information or a conflict-of-interest statement.
Giovanelli S, De Leo M, Cervelli C, Ruffoni B, Ciccarelli D, Pistelli L. Essential oil composition and volatile profile of seven Helichrysum species grown in Italy. Chem Biodivers. March 6, 2018; [epub ahead of print]. doi: 10.1002/cbdv.201700545.