Analysis of Helichrysum (Immortelle) Chemistry, Antioxidant Activity, and Chemotaxonomy
Traditionally, helichrysum (immortelle; Helichrysum italicum, Asteraceae) has been used for the treatment of scars and cuts, as well as used as a liver stimulant and diuretic. The essential oil of helichrysum has been found to have anti-inflammatory, antioxidant, fungicidal, and astringent effects. As an emollient and fragrance in the cosmetic and perfume industry, the chemical composition of helichrysum essential oil has been somewhat characterized. The aim of this study was to further characterize the chemical content and antioxidant activity of helichrysum aerial parts and to assess the chemotaxonomy of the H. italicum taxa.
The flowering aerial parts of helichrysum (H. italicum ssp. italicum) were collected in May 2011, near Valdanos, Montenegro. The air-dried aerial parts of the plant were extracted with 45% ethanol and dried. The air-dried flowering upper parts of helichrysum were submitted to hydrodistillation to produce the essential oil.
The essential oil was characterized by using chromatography and mass spectrometry techniques. Principal component analysis (PCA) and cluster analysis (CA) was used to compare the main chemical constituents identified in this study with 16 different H. italicum taxa. The dried ethanol extract was dissolved in an aqueous solution for analysis of total phenolics and flavonoids. Both the essential oil and the ethanol extract were assessed for antioxidant activity using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The ethanol extract was also evaluated for inhibition of hydroxyl radical (•OH) generation.
The essential oil yield was found to be 0.15 ± 0.02%. A total of 27 compounds were identified, which represented 96.1% of the total oil composition. Most of the compounds were oxygenated monoterpenes (43.9%) and sesquiterpene hydrocarbons (41.2%). [Note: There are discrepancies between the article text and the data in Table 1, which lists these as 43.1% and 42.2%, respectively.] The major compounds found in the oil were neryl acetate (28.2%), neryl propionate (9.1%), γ-curcumene (17.8%), and ar-curcumene (8.3%). [Note: There are discrepancies for three of these compounds among the abstract, article text, and data in Table 1, which lists these as neryl acetate (29.2%), neryl propionate (10.1%), and γ-curcumene (18.8%).] Other compounds found included α-selinene (3.9%), isoitalicene (3.2%), thymol (2.8%), and α-cedrene (2.4%). These concentrations are consistent with previous reports for this plant subspecies.
PCA indicated that H. italicum ssp. italicum from Greece, H. italicum ssp. serotinum from the Iberian Peninsula, and plant material collected from the region of former Yugoslavia could all be clearly differentiated from one another based on different dominant chemical components. Helichrysum italicum ssp. italicum and H. italicumssp. microphyllum were phylogenetically similar and had similar dominant chemical components. These and other taxa consisting of the main chemical components (e.g., neryl acetate) were found to represent four chemotypes. Two of these chemotypes had subchemotypes. CA indicated similar results in terms of the differentiation of H. italicum ssp. italicum from Greece and H. italicum ssp. serotinum from the Iberian Peninsula. The other taxa were classified in a similar way as that found by PCA, but with some differences, especially for the italicum subspecies.
The yield of the aqueous ethanol extract was 19.77%. The total phenolics and total flavonoids of this extract were found to be 31.97 ± 1.42 mg gallic acid equivalents (GAE)/g of dry extract and 20.68 ± 0.66 mg quercetin equivalents (QE)/g of dry extract, respectively. The radical scavenging capacity (RSC) of the ethanol extract and the essential oil was dose-dependent. In terms of DPPH RSC, the half maximal inhibitory concentration (IC50) was significantly lower (more effective) for the ethanol extract (0.99 µg/ml) compared to the essential oil (1.76 mg/ml) (P value not given). [Note: Table 3 lists the essential oil IC50 as 1.37 mg/ml.] The extract had results that were similar to propyl gallate and quercetin dihydrate. Only the ethanol extract was evaluated for •OH scavenging capacity (IC50 = 26.47 µg/ml), but the RSC was significantly less effective compared to its DPPH RSC (P value not given).
The chemical constituents identified from the essential oil of helichrysum aerial parts in this study are consistent with reports assessing the main chemical components of this plant subspecies. A chemotaxonomic analysis suggests that different regions of the world can affect the chemistry of the essential oil. The authors recommend classifying the species further based on these chemical differences. The authors also indicate that helichrysum extracts and essential oils may be effective natural antioxidants for foodstuff and pharmaceuticals. Further studies should be conducted on how differences in chemical composition may affect biological activity, fragrance, and other qualities of the helichrysum extracts and essential oils.
Kladar NV, Anačkov GT, Rat MM, et al. Biochemical characterization of Helichrysum italicum (Roth) G.Don subsp. italicum (Asteraceae) from Montenegro: phytochemical screening, chemotaxonomy, and antioxidant properties. Chem Biodivers. 2015;12(3):419-431.