The essential oil composition of selected Hemerocallis cultivars and their biological activity

Abstract The horticultural cultivars of Hemerocallis (daylily) have been used to treat diseases such as insomnia, inflammation and depression, and also as a vegetable in eastern Asia. Taking into consideration the fact, that the volatile compounds in Hemerocallis cultivars have not been investigated to date, we decided to study the composition of the essential oils (EOs) from the aerial parts of ten varieties collecting in Poland. EOs, obtained by hydrodistillation, were analyzed by GC/MS method that resulted in identification of 23-36 volatile compounds comprising 89.5%–96.3% of the total amount. The essential oils differed in their composition and they can be classified into three groups. The antibacterial and antioxidant activities of EOs were also evaluated. Gram-negative strains were most strongly inhibited by all tested oils. Two model systems have been used for the antioxidant efficacy, 2,2-diphenyl-1-picryl-hydrazyl (DPPH•) andβ-carotene bleaching assays. The essential oils with the high presence of oxygenated monoterpenes and monoterpene hydrocarbons showed higher antioxidant activity. The chemical composition of EOs of Hemerocallis cultivars and their biological activity is reported for the first time. Thus, the findings presented here suggest that the aerial parts of Hemerocallis cultivars may be candidates for the development of new phytomedicine. Graphical Abstract


Introduction
The essential oil-producing species are extensively arranged among the plant kingdom. The volatile compounds are not only important in plant physiology but also in pharmaceutical, food and cosmetics industries. Numerous studies showed that essential oils possess therapeutic properties and can prevent and cure many diseases [1].
To the best of our knowledge, there is only one report on chemical composition of the essential oils of Hemerocallis. Consequently, the purpose of the present research was carried out to investigate the chemical composition, and also antioxidant and antibacterial activities of the essential oils of the aerial parts of ten Hemerocallis cultivars.

Plant material and essential oils isolation
Flowers, leaves and stems of ten Hemerocallis cultivars, as shown in Table 1, were collected in the Maria Curie-Skłodowska University (UMCS) Botanical Garden in Lublin (Poland), at altitude of 181.2 m a.s.l. (coordinates 51°15'46" N; 22°30'51" E) in August 2017, in their full flowering phase. Taxonomical identification was confirmed by Dr. A. Dąbrowska.
The plants were dried in a drying chamber at 35°C, immediately after the harvest. The essential oils were obtained by 4-h hydrodistillation using the Clevenger apparatus. The ratio of dried material and distilled water was 1:7 (weight/volume). The weight of essential oils was measured after the process and according to the formula described in our previous study [28]. The oil yields are given in Table 2 and 3.

GC-MS analysis
The composition of essential oils of Hemerocallis cultivars was analyzed using GC-MS on a Trace GC Ultra apparatus (Thermo Electron Corporation, Milan, Italy) with FID and the MS DSQ II detector after dilution in diethyl ether (10 μL in 1 mL). More details of chromatographic conditions and quantitation methods can be found in the study of Szewczyk and co-authors [28]. The percentage data shown are mean values of three injections.

Antioxidant activity
Both assays were performed using 96-well microplates (Nunclon, Nunc, Roskilde, Denmark) and were measured in an Elisa Reader Infinite Pro 200F (Tecan Group Ltd., Männedorf, Switzerland). 2,2-diphenyl-1-picryl-hydrazyl (DPPH • ) free radical scavenging activity of the essential oils and BHT was tested using a previously described method [29]. 180 μL of methanolic DPPH • solution (0.07 mg/mL) was mixed with 20 μL of various concentrations of EOs. After shaking and incubation at 28°C for 30 min in the dark, absorbance was measured at 517 nm. To determine EC 50 values a dose response curves were plotted. β-carotene bleaching method was carried out according to previously described method [30] and modified by Deba and co-authors [31]. The absorbance was measured at 470 nm.

Antibacterial assay
Zones of bacterial growth inhibition caused by tested samples were evaluated for the reference microorganisms    The antibacterial activity of samples against bacteria was evaluated by measuring the zones of inhibition in the standard disk diffusion method (Kirby-Bauer Disk Diffusion Susceptibility Test Protocol). Antibacterial disc diffusion assays were carried out on Petri plates with solid medium (M-H agar). Suitable strain culture was separately spread over the agar surface using cotton swab. Next, 10 μL of the undiluted essential oils were brought using sterile disc (disc dispenser BioMaxima, Poland) on Petri plates with agar medium. After 18 h of incubation at 37°C zones of microbial growth produced around the tested samples were measured and recorded as the diameters of inhibition [mm]. All experiments were performed in fivefold.

Statistical analysis
All the results were expressed as means ± standard deviation (SD) of three independent experiments. One-way ANOVA with Tukey's post hoc test was used for the statistical analysis of significance of differences between means. P values below 0.05 were accepted as statistically significant. Calculations were done in Statistica 10.0 (StatSoft Poland, Cracow, Poland).
Ethical approval: The conducted research is not related to either human or animal use.

Results and discussion
From ancient time, Hemerocallis species have been cultivated in their native regions of Asia where these plants are still an important source of remedies and food.
In Chinese and Japanese medicine daylilies have been used to treat ailments such as insomnia, fever, diuretic, inflammation, depression, and anemia [8,23,32]. In Europe, Hemerocallis spp. appeared in the late sixteenth century where they were cultivated especially for ornamental purpose [8].
In the present study, the essential oils (EOs) of ten Hemerocallis cultivars were obtained by hydrodistillation from air-dried aerial parts (flowers, leaves and stems). All EOs were collected as a fragrant and pale-yellow liquids. The yield of EOs (expressed in percentage; % v/w relative to dry material weight) was comparable in all samples and ranged from 0.024% (H. 'Jaskółka') to 0.034% (H. 'Pink Solace'). The chemical composition was analyzed by the GC-MS method, that resulted in identification of 23-36 volatile compounds comprising from 89.5%-96.3% of the total volume in individual oils. All identified compounds in the aerial parts of Hemerocallis cultivars oils are given in Table 2 and 3.
The investigated essential oils differed in chemical composition. According to chemical profile they can be classified into three groups. The first group is composed of four EOs  (Table 3) had a lot of common constituents such as C13 ketones ((E)-β-damascenone, β-ionone, and geranylacetone), C18 ketones (farnesylacetone and hexahydrofarnesylacetone) as well as long chain aliphatic hydrocarbons, both saturated and unsaturated. All these constituents are present in EOs of the third group in significantly higher amounts than in the second group. To the contrary, the second group EOs were characterized by pronounced amounts of very volatile C5 aliphatic aldehydes with the same skeleton, 2-and 3-methylbutanal, 2-methylenebutanal (2-ethylacrolein), and trans-2-methylbut-2-enal (tiglic aldehyde) as well as furfural and furfuryl alcohol. EO 3 contained elemicin (13.0%) and methyleugenol (2.6%).  In all EOs the same unidentified constituent was found (RI 1336), its mass spectrum is presented in Figure  2. This compound was the main constituent of EOs from the second (34.2-55.9%) and third group (21.6-39.8%) and minor component of the first group EOs (traces to 1.8%).
Only one report on essential oil composition of daylily Hemerocallis flava from China was found. The essential oil obtained by simultaneous distillation-extraction (SDE) contained 3-furfuryl alcohol (47.9%) and 2-furfural (10.4%) as main out of 51 constituents [36]. Considering the fact that composition of volatile oils depends on many factors, such as botanical traits, cultivation and climatic factors, as well as plant materials storage and/or treatments applied during the processing of raw material [37], it is hard to make a reliable comparison with only one published work on the essential oils in Hemerocallis species. Further investigation of composition and bioactivity of EOs in relation to other populations of Hemerocallis cultivars are needed.   It is known, as a result of bacterial resistance, that the efficacy of antibiotic therapy decreases, which needs new and safe drug strategies [38,39]. There it was favourable to examine safe therapies based on plants materials, which can prevent bacterial resistance.
Importantly, this significant activity was directed against the Gram-negative strains of both reference and troublesome clinical pathogens derived from patients' urine or infected wounds (Figure 3).
None of the tested strains, in tested concentration, showed significant activity against Gram-positive bacteria. This means that Hemerocallis oils have a narrow spectrum of action directed against Gram-negative pathogens ( Figure 4).
Recently, attention is focused on the protective function of naturally occurring antioxidants [40]. The present research was also undertaken to investigate the antioxidant activities of essential oils from ten Hemerocallis cultivars using two protocols with 2,2-diphenyl-1-picrylhydrazyl (DPPH • ) radicals and β-carotene/linoleic acid. The results are summarized in Table 4 showed higher scavenging ability and they had IC 50 values from 4.49±0.28 μg/mL to 19.62±0.11 μg/mL, whereas those of the synthetic antioxidant (BHT) activity was 18.32±0.92 μg/mL. Our results are in agreement with those obtained by Ruberto and Baratta [41], who showed that some monoterpene hydrocarbons and oxygenated compounds like allylic alcohols have an appreciable antioxidant activity. The essential oils of H. fulva (4) and H. 'Rebel Cause' (1) were found to be less efficient in the DPPH • assay with IC 50 values of 60.72±1.10 and 51.59±1.13 μg/mL, respectively.
In the second method that measures the ability to inhibit lipid peroxidation, the essential oils of 8 (H. 'Bożena'), 4 (H. fulva), 2 (H. citrina), 5 (H. 'Chicago Apache'), and also 1 (H. 'Rebel Cause') had a great activity with IC 50 values even twenty one times lower than BHT used as lipophilic antioxidant reference.
From the obtained results, it can be concluded that the essential oil of Hemerocallis 'Bożena' (8) and H. citrina (2) had the best antioxidant activity in both performed assays.

Conclusions
The present study reported the composition, antibacterial and antioxidant activity of essential oils from Hemerocallis cultivars. The examined essential oils contained mainly oxygenated monoterpenes with 1,8-cineole being the major constituent. In all EOs the same unidentified constituent (RI 1336) was found in a great quantity. The obtained EOs, especially from H. 'Bożena', H. 'Danuta', and also H. 'Catherine Woodbuery', and H. citrina demonstrated strong antimicrobial activity against Gramnegative bacteria. Moreover, our observations suggest that essential oils from the aerial parts of Hemerocallis 'Bożena' and H. citrina possess strong antioxidative activity and they might be a good potential source of preservatives used in cosmetics, food and pharmaceutical industries.

Conflicts of Interest:
The authors declare no conflict of interest.