Chemical Composition and Antimicrobial Activity of the Essential Oils of Three Closely Related Hypericum Species Growing Wild on the Island of Crete, Greece

Antibacterial, Antioxidant Potency, and Chemical Composition of Essential Oils from Dried Powdered Leaves and Flowers of Hypericum revolutum subsp. keniense (Schweinf.)

Hypericum revolutum subsp. keniense is a plant mainly used to treat diarrhoea, rheumatism, nervous disorders, and wounds in African traditional medicine. The objective of the current work was to establish antibacterial, antioxidant potency, and chemical composition of essential oil from the leaves and flowers of Hypericum revolutum subsp. keniense. The oils were isolated by steam distillation. Antibacterial activity against methicillin-resistant Staphylococcus aureus, Staphylococcus aureus (ATCC 12393), Escherichia coli (ATCC 25922), Acinetobacter baumannii (ATTC 19606), Salmonella enteritidis (NCTC12023), Salmonella typhimurium (ATCC 14028), Pseudomonas aeruginosa (ATCC 15442), and Haemophilus influenzae (ATCC 49766) was carried out by agar disk diffusion and microtiter broth dilution methods. Antioxidant activities of the essential oils were examined by different methods, DPPH, FRAP, and H₂O₂ assays. Chemical characterization was performed using gas chromatography interfaced with mass spectrometry, Fourier-transform infra-red (FTIR) spectroscopy, and quantification of phenolics and flavonoids by Folin-Ciocalteu reagent and aluminium nitrate, respectively. The oils showed potential antibacterial activity with mean zone of inhibition ranging from 20.67 ± 0.33 to 32.00 ± 1.00 mm at 100% oil concentration against the tested bacteria. Furthermore, the minimum inhibitory concentrations (MICs) in all the tested microorganisms were in the range from 250 to 15.6250 μg/ml. The essential oils derived from the leaves revealed varied antioxidant activity levels with the different methods of assay. The IC₅₀ of values obtained from the three methods, DPPH, FRAP, and H₂O₂ were ˃1000 μg/ml, 0.31 μg/ml, and 12.33 μg/ml, respectively. Caryophyllene (22.1%) and 2, 3, 4-trimethylhexane were the major chemical components of the essential oils derived from the leaves and flowers, respectively. FTIR spectroscopy of the essential oils from the leaves and flowers showed similarity at peaks for hydroxyl, unsaturated olefinic, and amine functional groups. Further findings indicated that the total phenolic and flavonoid contents essential oils derived from leaves were 130.4 6 ± 10.5 mg GAE/g dry weight and 0.911 ± 0.04 mg CE/g dry weight, respectively. It was therefore concluded that essential oils from the leaves and flowers of H. revolutum subsp. keniense have compounds that have antibacterial and antioxidant potency.

Hypericum Essential Oils—Composition and Bioactivities: An Update (2012–2022)

Hypericum genus, considered to comprise over 500 species that exhibit cosmopolitan distribution, has attracted human interest since ancient times. The present review aims to provide and summarize the recent literature (2012–2022) on the essential oils of the title genus. Research articles were collected from various scientific databases such as PubMed, ScienceDirect, Reaxys, and Google Scholar. Scientific reports related to the chemical composition, as well as the in vitro and in vivo pharmacological activities, are presented, also including a brief outlook of the potential relationship between traditional uses and Hypericum essential oils bioactivity.

Volatile and phenolic profiling of a traditional medicinal plant, Hypericum empetrifolium with in vitro biological activities

ETHNOPHARMACOLOGICAL RELEVANCE

Hypericum empetrifolium Willd is a member of the Hypericaceae family, mainly known in southern Greece, and western Turkey. Being a centuries-old medicinal plant, the aerial parts of the plant have been used for the treatment of herpes, kidney stones, gastric ulcer, and also for their anti-helminthic, and diuretic purposes traditionally.

AIM OF THE STUDY

The current study aimed to investigate the phytochemical profiles of the essential oil, and two ethanol extracts prepared from the aerial parts (H. empetrifolium aerial parts extract - HEA), and roots of the plant (H. empetrifolium roots extract - HER), and to provide data on antioxidant, anticholinesterase, antityrosinase, antiurease, cytotoxic, and antimicrobial activities of the extracts.

MATERIALS AND METHODS

In this study, volatile and phenolic compounds of the HEA and HER were analyzed by GC-MS and LC-MS/MS, respectively. Antioxidant potential of the extracts was clarified by using DPPH radical scavenging assay, ABTS cation radical assay, and the CUPRAC assay. Acetylcholinesterase, butyrylcholinesterase, urease, and tyrosinase inhibitory activity assays were used to determine enzyme inhibition capacity of the extracts. Cytotoxic activity of the extracts was established by using XTT assay. The antimicrobial activity of the extracts was determined by the microbroth dilution technique.

RESULTS

The major compounds of the essential oil were revealed as alloaromodendrene (24.7%), α-pinene (14.7%), β-pinene (10.7%), and α-terpineol (7.7%) by the GC-MS analysis. According to the LC-MS/MS analysis results, quinic acid was the most abundant constituent in both extracts with 20612.42 ± 169.02 μg/g extract in HEA extract, and with 2254.34 ± 18.49 μg/g extract in HER extract, respectively. The HEA extract was also found to be rich in terms of chlorogenic acid (5583.14 ± 38.52 μg/g extract), isoquercitrin (3076.77 ± 40.92 μg/g extract), and malic acid (2822.90 ± 31.90 μg/g extract). HEA extract exhibited a significant antioxidant effect with an IC₅₀ value of 11.98 ± 0.22 μg/mL according to the DPPH radical scavenging assay. Similar results were obtained with the ABTS cation radical assay, and the CUPRAC assay. HER extract showed a strong butyrylcholinesterase inhibitory effect with 88.69 ± 0.62% at 200 μg/mL concentration. Both extracts were considered to have moderate anti-tyrosinase activity compared to the standard at 200 μg/mL. The best antimicrobial activity was obtained for HEA against C. parapsilosis with an MIC value of 4.88 μg/mL. HEA also exhibited antifungal activity against C. tropicalis with 19.53 μg/mL. Only HER exhibited low cytotoxicity on A498 renal cell lines with 60.6% cell viability.

CONCLUSION

Unquestionably, H. empetrifolium Willd has ethnopharmacological importance according to these results, and further investigations are required to evaluate other therapeutic properties of the plant.

Evaluation of vapor-phase antifungal activities of selected plant essential oils against fungal strains growing on bread food model

The current study aimed to investigate antifungal activities of two commercially available essential oils (EOs), specifically Tea tree oil (Melaleuca alternifolia; TTEO) and St. John's wort oil (Hypericum perforatum; HPEO) against three Penicillium (P.) species: P. citrinum, P. expansum, and P. crustosum in in situ conditions. For this purpose, EOs were applied in the vapor phase to determine the growth inhibition of fungi artificially inoculated on sliced bread. Changes in colony growth rate were evaluated as markers for the mycelial growth inhibition (MGI) effect of the EOs. The antioxidant activities of the EOs were evaluated using the DPPH method. The moisture content (MC) and water activity (aw) of bread as a substrate for fungal growth were also measured. From the DPPH assay, we have found that both EOs (TTEO, HPEO) exhibited strong antioxidant activity (64.94 ±7.34%; 70.36 ±1.57%, respectively). The values for bread MC and aw were 43.01 ±0.341% and 0.947 ±0.006, respectively. Our results suggest that HPEO is the only weak inhibitor of P. citrinum and P. crustosum colony growths. Also, the highest concentrations of TTEO display only the weak capability of mycelial growth inhibition of P. citrinum and P. crustosum. By contrast, the colony growth of P. expansum was enhanced by both EOs at all levels used. In conclusion, the application of both EOs in the vapor phase against selected Penicillium species seems not to be a promising alternative to chemical inhibitors used for bread preservation.