Chemical Composition,Antioxidant, Anti-Bacterial,and Anti-Cancer Activities of Essential Oils Extracted from Citrus limetta Risso Peel Waste Remains after Commercial Use

Citrus plants are widely utilized for edible purposes and medicinal utility throughout the world. However, because of the higher abundance of the antimicrobial compound D-Limonene, the peel waste cannot be disposed of by biogas production. Therefore, after the extraction of D-Limonene from the peel wastes, it can be easily disposed of. The D-Limonene rich essential oil from the Citrus limetta risso (CLEO) was extracted and evaluated its radical quenching, bactericidal, and cytotoxic properties. The radical quenching properties were DPPH radical scavenging (11.35 ± 0.51 µg/mL) and ABTS scavenging (10.36 ± 0.55 µg/mL). There, we observed a dose-dependent antibacterial potential for the essential oil against pathogenic bacteria. Apart from that, the essential oil also inhibited the biofilm-forming properties of E. coli, P. aeruginosa, S. enterica, and S. aureus. Further, cytotoxicity was also exhibited against estrogen receptor-positive (MCF7) cells (IC₅₀: 47.31 ± 3.11 µg/mL) and a triple-negative (MDA-MB-237) cell (IC₅₀: 55.11 ± 4.62 µg/mL). Upon evaluation of the mechanism of action, the toxicity was mediated through an increased level of reactive radicals of oxygen and the subsequent release of cytochrome C, indicative of mitotoxicity. Hence, the D-Limonene rich essential oil of C. limetta is useful as a strong antibacterial and cytotoxic agent; the antioxidant properties exhibited also increase its utility value.     

The Chemical Composition and Antibacterial and Antioxidant Activities of Five Citrus Essential Oils

Increasing concerns over the use of antimicrobial growth promoters in animal production has prompted the need to explore the use of natural alternatives such as phytogenic compounds and probiotics. Citrus EOs have the potential to be used as an alternative to antibiotics in animals. The purpose of this research was to study the antibacterial and antioxidant activities of five citrus EOs, grapefruit essential oil (GEO), sweet orange EO (SEO), bergamot EO (BEO), lemon EO (LEO) and their active component d-limonene EO (DLEO). The chemical composition of EOs was analyzed by gas chromatography–mass spectrometry (GC-MS). The antibacterial activities of the EOs on three bacteria (Escherichia coli, Salmonella and Lactobacillus acidophilus) were tested by measuring the minimum inhibitory concentration (MIC), minimal bactericidal concentration (MBC) and inhibition zone diameter (IZD). The antioxidant activities of EOs were evaluated by measuring the free radical scavenging activities of DPPH and ABTS. We found that the active components of the five citrus EOs were mainly terpenes, and the content of d-limonene was the highest. The antibacterial test showed that citrus EOs had selective antibacterial activity, and the LEO had the best selective antibacterial activity. Similarly, the LEO had the best scavenging ability for DPPH radicals, and DLEO had the best scavenging ability for ABTS. Although the main compound of the five citrus EOs was d-limonene, the selective antibacterial and antioxidant activity of them might not be primarily attributed to the d-limonene, but some other compounds’ combined action.     

Chemical Composition,Insecticidal and Mosquito Larvicidal Activities of Allspice (Pimenta dioica) Essential Oil

Essential oils are biologically and environmentally safe pesticidal compounds yielded from aromatic plants. Spices are important sources of essential oils, and they are widely used in the medicine, food, and various other industries. Among the different spices, Allspice (Pimenta dioica) is underexplored in terms of its biological efficacy and a limited number of studies are available on the chemical composition of Allspice essential oil (AEO); thus, the present study evaluated the larvicidal property, the repellency, and the fumigant toxicity against common pests of stored products of AEO. AEO was found to inhibit the survival of larvae of such vectors as Aedis, Culex, and Armigeres species. Further, AEO was found to exert repellant effects against the pests of such stored products as Sitophilus, Callosobruchus, and Tribolium. Similarly, the fumigant toxicity was found to be high for AEO against these species. The contact toxicity of AEO was high against Sitophilus and Callosobruchus. Apart from that, the essential oil was found to be safe against a non-target organism (guppy fishes) and was found to be non-genotoxic in an Allium cepa model. Overall, the results of the present study indicate that the essential oil from Allspice could be used as an environmentally safe larvicidal and biopesticidal compound.     

Phytochemical Compositions and Antioxidant Activities of Essential Oils Extracted from the Flowers of Paeonia delavayi Using Supercritical Carbon Dioxide Fluid

Essential oils were extracted from dark-purple, red and yellow petals of Paeonia delavayi using Supercritical Carbon Dioxide method. The compositions of essential oils were analyzed using gas chromatography-mass spectrometry (GC-MS). Antioxidant activity assays were carried out using DPPH, ABTS- and FRAP methods. Total polyphenols and total flavonoids were measured to evaluate the in vitro antioxidant activity in addition to the volatile compounds contained in the essential oils extracted from the flower petals of P. delavayi with the three flower colors. A total of 194 compounds were detected from essential oils of P. delavayi flowers, including 83 in dark-purple petals, 90 in red petals and 80 in yellow petals. These compounds mainly include alcohols, aldehydes, ketones, alkenes, alkanes, esters and polyphenols. The results showed that the volatile compounds accumulated differentially among the essential oils from the different colors of flower petals. Principal component analysis (PCA) indicated that essential oils derived from dark-purple and red petals were more closely clustered while the yellow petal essential oil was very different with both the purple-red and red. Antioxidant assays suggested that the radical scavenging activity and the iron reduction antioxidant activity in the essential oils were highly correlated with the flower petal colors. These results suggest P. delavayi flower petals are potentially good resources for high quality essential oils and natural antioxidants.     

The Chemical Compositions,and Antibacterial and Antioxidant Activities of Four Types of Citrus Essential Oils

Nanfeng mandarins (Citrus reticulata Blanco cv. Kinokuni), Xunwu mandarins (Citrus reticulata Blanco), Yangshuo kumquats (Citrus japonica Thunb) and physiologically dropped navel oranges (Citrus sinensis Osbeck cv. Newhall) were used as materials to extract peel essential oils (EOs) via hydrodistillation. The chemical composition, and antibacterial and antioxidant activities of the EOs were investigated. GC-MS analysis showed that monoterpene hydrocarbons were the major components and limonene was the predominate compound for all citrus EOs. The antibacterial testing of EOs against five different bacteria (Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Salmonella typhimurium) was carried out using the filter paper method and the broth microdilution method. Kumquat EO had the best inhibitory effect on B. subtilis, E. coli and S. typhimurium with MIC (minimum inhibitory concentration) values of 1.56, 1.56 and 6.25 µL/mL, respectively. All citrus EOs showed the antioxidant activity of scavenging DPPH and ABTS free radicals in a dose-dependent manner. Nanfeng mandarin EO presented the best antioxidant activity, with IC₅₀ values of 15.20 mg/mL for the DPPH assay and 0.80 mg/mL for the ABTS assay. The results also showed that the antibacterial activities of EOs might not be related to their antioxidant activities.     

Chemical Composition and Antimicrobial Activity of the Essential Oils Extracted by Microwave-Assisted Hydrodistillation from the Flowers of Two Plumeria Species

Microwave-assisted hydrodistillation (MAHD) was applied to obtain essential oils from the fresh flowers of Plumeria rubra Linn (PRL) and Plumeria rubra Linn var. acutifolia (PRLA) cultivated in China, which were subsequently analyzed via gas chromatography with flame ionization detection and gas chromatography with mass spectrometry. The essential oils were assessed for their antimicrobial activity. A variation of the chemical composition attributed to varieties was revealed. The essential oil of PRLA was found to have a high content of carboxylic acids (59.7%) with n-hexadecanoic acid (35.8%) and n-tetradecanoic acid (11.2%) as main components. Whereas, the PRL oil was characterized by high hydrocarbon content (38.6%), in which 9-hexacosene (14.6%) was found to be the major constituent. All essential oils possessed antimicrobial activity especially against five bacteria with diameter of inhibition zone (DD) and minimum inhibitory concentrations (MIC) values in the range of 6.8 to 21.3 mm and 2.8 to 46.5 mg/mL, respectively.     

Effects of Supplemental Light Spectra on the Composition,Production and Antimicrobial Activity of Ocimum basilicum L. Essential Oil

This study was performed to investigate the effects of different supplemental light spectra and doses (duration and illuminance) on the essential oil of basil (Ocimum basilicum L.) cultivated in the net-house in Vietnam during four months. Ten samples of basil aerial parts were hydrodistilled to obtain essential oils which had the average yields from 0.88 to 1.30% (v/w, dry). The oils analyzed using GC-FID and GC-MS showed that the main component was methyl chavicol (87.4–90.6%) with the highest values found in the oils of basil under lighting conditions of 6 h/day and 150–200 µmol·m⁻²·s⁻¹. Additional lighting conditions caused the significant differences (p < 0.001) in basil biomass and oil production with the highest values found in the oils of basil under two conditions of (1) 71% Red: 20% Blue: 9.0% UVA in at 120 μmol·m⁻²·s⁻¹ in 6 h/day and (2) 43.5% Red: 43.5% Blue: 8.0% Green: 5.0% Far-Red at 100 μmol·m⁻²·s⁻¹ in 6 h/day. The oils of basil in some formulas showed weak inhibitory effects on only the Bacillus subtilis strain. Different light spectra affect the biomass and essential oil production of basil, as well as the concentrations of the major components in the oil.     

Combination of GC-MS Molecular Networking and Larvicidal Effect against Aedes aegypti for the Discovery of Bioactive Substances in Commercial Essential Oils

Dengue is a neglected disease, present mainly in tropical countries, with more than 5.2 million cases reported in 2019. Vector control remains the most effective protective measure against dengue and other arboviruses. Synthetic insecticides based on organophosphates, pyrethroids, carbamates, neonicotinoids and oxadiazines are unattractive due to their high degree of toxicity to humans, animals and the environment. Conversely, natural-product-based larvicides/insecticides, such as essential oils, present high efficiency, low environmental toxicity and can be easily scaled up for industrial processes. However, essential oils are highly complex and require modern analytical and computational approaches to streamline the identification of bioactive substances. This study combined the GC-MS spectral similarity network approach with larvicidal assays as a new strategy for the discovery of potential bioactive substances in complex biological samples, enabling the systematic and simultaneous annotation of substances in 20 essential oils through LC₅₀ larvicidal assays. This strategy allowed rapid intuitive discovery of distribution patterns between families and metabolic classes in clusters, and the prediction of larvicidal properties of acyclic monoterpene derivatives, including citral, neral, citronellal and citronellol, and their acetate forms (LC₅₀ < 50 µg/mL).     

Compositions and Biological Activities of Pomegranate Peel Polyphenols Extracted by Different Solvents

Pomegranate peel extract (PPE), which is abundant in polyphenols, holds immerse prospects for the treatment of airway infection. In this study, water and ethanol of 30%, 50%, and 80% were used to prepare PPE. A total of 18 phenols belonging to 8 categories of polyphenols were identified in PPE by HPLC-MS/MS. The PPE from the four extraction solvents possessed different antioxidant, antibacterial, and anti-inflammatory activities. Principal component analysis revealed that though total flavonoids (TFs), total polyphenols (TPs), and total tannins (TTs) were responsible for the reducing power of PPE, only TFs contributed to the effect of PPE in inhibiting lipid membrane peroxidation. TPs, TTs, and punicalagin were positively correlated with the antibacterial strength against S. aureus while TTs alone contributed to the inhibition of methicillin-resistant S. aureus, implying the crucial role of TT in suppressing bacteria. Meanwhile, TTs was associated with the prevention of IL-6 release. The PPE with higher contents of TPs, TTs, and punicalagin had a weaker capacity to decrease nitric oxide secretion. PPE of 30% ethanol gained the highest integrated score due to its stronger antioxidant, antibacterial, and anti-inflammatory activities. It is a suitable candidate for the therapy of respiratory tract infection.     

Chemical Composition and Antimicrobial and Antioxidant Activities of Essential Oil of Sunflower (Helianthus annuus L.) Receptacle

Sunflower (Helianthus annuus L.) contains active ingredients, such as flavonoids, alkaloids and tannins. Nevertheless, few studies have focused on essential oil from the receptacle of sunflower (SEO). In this work, we investigated the chemical composition and antimicrobial and antioxidant activities of SEO. The yield of SEO was about 0.42% (v/w) by hydrodistillation. A total of 68 volatile components of SEO were putatively identified by gas chromatography–mass spectrometry (GC-MS). The main constituents of SEO were α-pinene (26.00%), verbenone (7.40%), terpinolene (1.69%) and α-terpineol (1.27%). The minimum inhibitory concentration (MIC) of SEO against P. aeruginosa and S. aureus was 0.2 mg/mL. The MIC of SEO against S. cerevisiae was 3.2 mg/mL. The MIC of SEO against E. coli and Candida albicans was 6.4 mg/mL. The results showed that SEO had high antibacterial and antifungal activities. Three different analytical assays (DPPH, ABTS and iron ion reducing ability) were used to determine the antioxidant activities. The results showed that SEO had antioxidant activities. To summarize, the results in this study demonstrate the possibility for the development and application of SEO in potential natural preservatives and medicines due to its excellent antimicrobial and antioxidant activities.     

Anatomical and Phytochemical Characteristics of Different Parts of Hypericum scabrum L. Extracts,Essential Oils,and Their Antimicrobial Potential

Hypericum (Hypericaceae) is a genus that comprises a high number of species around the world. In this study, the roots, aerial parts, flowers, fruits, and aerial parts with flowers from Hypericum scabrum were macerated separately by methanol and water and then fractionated by different solvents of, such as ethyl acetate, n-hexane, butanol, dichloromethane, aqueous residue sub-extracts, and ethnobotanical use. All the extracts, sub-extracts and essential oils of H. scabrum were investigated for the first time in detail for their antimicrobial, total phenolics, and antioxidant activities. Anatomical structures of the root, stem, leaf, upper and lower leaf surface, stamen, sepal, and petal of H. scabrum were examined. The biochemical layout of essential oils was determined by GC and GC/MS. The antioxidant activity was determined by free radical scavenging activity (by DPPH). Antimicrobial activity was applied against Candida albicans ATCC 10231, Escherichia coli ATCC 8739, Staphylococcus aureus ATCC 6538, Bacillus subtilis ATCC 19659, and C. tropicalis ATCC 750 using microdilution methods. The essentials of the aerial parts, flower, and fruit are characterized by the presence of monoterpene hydrocarbons, whereas roots oil include alkanes. The GC-FID and GC-MS analysis showed that major components of roots, aerial parts, flowers, and fruits oils were undecane (66.1%); α-pinene (17.5%), γ-terpinene (17.4%), and α-thujene (16.9%); α-pinene (55.6%), α-thujene (10.9%), and γ-terpinene (7.7%); α-pinene (85.2%), respectively. The aerial part sub-extracts indicated a greater level of total phenolics and antioxidant potential. The n-hexane sub-extracts (from aerial part, flower, and aerial part with flower) showed the best activity against B. subtilis, with 39.06 µg/mL MIC value. The presented research work indicates that H. scabrum can be a novel promising resource of natural antioxidant and antimicrobial compounds.     

Antioxidant and Antimicrobial Activities of Chemically-Characterized Essential Oil from Artemisia aragonensis Lam. against Drug-Resistant Microbes

This study investigated the chemical composition, antioxidant and antimicrobial activity of essential oil extracted from Artemisia aragonensis Lam. (EOA). Hydrodistillation was employed to extract EOA. Gas chromatography with flame ionization detection (GC-FID) and gas chromatography-mass spectrometry analyses (GC-MS) were used to determine the phytochemical composition of EOA. Antioxidant potential was examined in vitro by use of three tests: 2.2-diphenyl-1-picrilhidrazil (DPPH), ferric reducing activity power (FRAP) and total antioxidant capacity assay (TAC). Agar diffusion and microdilution bioassays were used to assess antimicrobial activity. GC/MS and GC-FID detected 34 constituents in the studied EOA. The major component was Camphor (24.97%) followed by Borneol (13.20%), 1,8 Cineol (10.88%), and Artemisia alcohol (10.20%). EOA exhibited significant antioxidant activity as measured by DPPH and FRAP assays, with IC₅₀ and EC₅₀ values of 0.034 ± 0.004 and 0.118 ± 0.008 mg/mL, respectively. EOA exhibited total antioxidant capacity of 7.299 ± 1.774 mg EAA/g. EOA exhibited potent antibacterial activity as judged by the low minimum inhibitory concentration (MIC) values against selected clinically-important pathogenic bacteria. MIC values of 6.568 ± 1.033, 5.971 ± 1.033, 7.164 ± 0.0 and 5.375 ± 0.0 μg/mL were observed against S. aureus, B. subtills, E. coli 97 and E. coli 57, respectively. EOA displayed significant antifungal activity against four strains of fungi: F. oxysporum, C. albicans, A. flavus and A. niger with values of 21.50 ± 0.43, 5.31 ± 0.10, 21.50 ± 0.46 and 5.30 ± 0.036 μg/mL, respectively. The results of the current study highlight the importance of EOA as an alternative source of natural antioxidant and antibacterial drugs to combat antibiotic-resistant microbes and free radicals implicated in the inflammatory responses accompanying microbial infection.     

Chemical Profile,In Vitro Biological Activity and Comparison of Essential Oils from Fresh and Dried Flowers of Lavandula angustifolia L.

The chemical composition of essential oils (EOs) from dried and fresh flowers of Lavandula angustifolia L. (lavender), named LA 2019 and LA 2020, respectively, grown in central Italy was analyzed and compared by GC and GC-MS. For both samples, 61 compounds were identified, corresponding to 97.9% and 98.1% of the total essential oils. Explorative data analysis, performed to compare the statistical composition of the samples, resulted in a high level of global similarity (around 93%). The compositions of both samples were characterized by 10 major compounds, with a predominance of Linalool (35.3–36.0%), Borneol (15.6–19.4%) and 1,8-Cineole (11.0–9.0%). The in vitro antibacterial activity assay by disk diffusion tests against Bacillus subtilis PY79 and Escherichia coli DH5α showed inhibition of growth in both indicator strains. In addition, plate counts revealed a bactericidal effect on E. coli, which was particularly noticeable when using oil from the fresh lavender flowers at the highest concentrations. An in vitro antifungal assay showed that the EOs inhibited the growth of Sclerotium rolfsii, a phytopathogenic fungus that causes post-harvest diseases in many fruits and vegetables. The antioxidant activity was also assessed using the ABTS free radical scavenging assay, which showed a different antioxidant activity in both EOs. In addition, the potential application of EOs as a green method to control biodeterioration phenomena on an artistic wood painting (XIX century) was evaluated.     

Antimicrobial,Mosquito Larvicidal and Antioxidant Properties of the Leaf and Rhizome of Hedychium coronarium

The essential oil, methanolic and aqueous extracts of the leaves and rhizomes of Hedychium coronarium Koen. (Zingiberaceae) were assayed for their antimicrobial, mosquito larvicidal and antioxidant properties. The chemical composition of the essential oil of two organs was analyzed by GC/MS analysis. β‐Pinene (33.9%), α‐pinene (14.7%), 1,8‐cineole (13.3%), r‐elemene (11.0%) and carotol (9.1%) were the main components in the leaf oil, including 82.0% terpenoid compounds. The major constituents of the rhizome oil were 1,8‐cineole (37.3%), β‐pinene (23.0%), α‐terpineol (10.4%) and α‐pinene (9.9%), comprising 80.6% of the oil. The leaf and rhizome essential oil displayed significant antimicrobial activity, as determined by the disc‐diffusion method, inhibiting the growth of all five fungal and four bacterial strains tested. The antimicrobial nature of the essential oil is related to high terpenoid contents. The leaf oil exhibited the mosquito larvicidal activity with 2 h and 24 h LC₅₀ values of 111 and 90 ppm, respectively, while the rhizome oil showed the larvicidal activity with 2 h and 24 h LC₅₀ values of 86 and 47 ppm, respectively. β‐Pinene, α‐pinene and 1,8‐cineol in H. coronarium serve as the principal larvicidal components of both oils. The individual antioxidant assays such as DPPH scavenging activity, chelating effect of ferrous ions and reducing power have been used. The present study demonstrated that the polar extracts of H. coronarium possessed anti‐oxidant. Appreciable total phenolic content (18.5‐26.3 mg/g) was also detected by Folin‐Ciocalteu test.     

Phytochemical Profile,Antimicrobial, Cytotoxic,and Antioxidant Activities of Fresh and Air-Dried Satureja nabateorum Essential Oils

Satureja nabateorum (Danin and Hedge) Bräuchler is a perennial herb in the Lamiaceae family that was discovered and classified in 1998. This green herb is restricted to the mountains overlooking the Dead Sea, specifically in Jordan’s southwest, the Edom mountains, and the Tubas mountains in Palestine. Gas chromatography-mass spectrometry (GC-MS) analysis of essential oil (EO) of air-dried and fresh S. nabateorum resulted in the identification of 30 and 42 phytochemicals accounting for 99.56 and 98.64% of the EO, respectively. Thymol (46.07 ± 1.1 and 40.64 ± 1.21%) was the major compound, followed by its biosynthetic precursors γ-terpinene (21.15 ± 1.05% and 20.65 ± 1.12%), and p-cymene (15.02 ± 1.02% and 11.51 ± 0.97%), respectively. Microdilution assay was used to evaluate the antimicrobial property of EOs against Staphylococcus aureus (ATCC 25923), clinical isolate Methicillin-Resistant Staphylococcus aureus (MRSA), Enterococcus faecium (ATCC 700221) Klebsiella pneumoniae (ATCC 13883), Proteus vulgaris (ATCC 700221), Escherichia coli (ATCC 25922) and Pseudomonas aeruginosa (ATCC 27853) and Candida albicans (ATCC-90028). With a MIC of 0.135 μg/mL, the EOs has the most potent antibacterial action against K. pneumonia. Both EOs display good antifungal efficacy against C. albicans, with a MIC value of 0.75 μg/mL, which was better than that of Fluconazole’s (positive control, MIC = 1.56 μg/mL). The antioxidant capacity of EOs extracted from air-dried and fresh S. nabateorum was determined using the DPPH assay, with IC₅₀ values of 4.78 ± 0.41 and 5.37 ± 0.40 μg/mL, respectively. The tested EOs showed significant cytotoxicity against Hela, HepG2, and COLO-205 cells, with IC₅₀ values ranging from 82 ± 0.98 to 256 ± 1.95 μg/mL. The current work shows there is a possibility to use the S. nabateorum EOs for various applications.     

Oregano and Thyme Essential Oils Encapsulated in Chitosan Nanoparticles as Effective Antimicrobial Agents against Foodborne Pathogens

The use of natural compounds with biocidal activity to fight the growth of bacteria responsible for foodborne illness is one of the main research challenges in the food sector. This study reports the preparation and physicochemical characterization of chitosan nanoparticles loaded with Thymus capitatus (Th-CNPs) and Origanum vulgare (Or-CNPs) essential oils. The nanosystems were obtained by ionotropic gelation technique with high encapsulation efficiency (80–83%) and loading capacity (26–27%). Nanoparticles showed a spherical shape, bimodal particle size distribution, and good stability (zeta potential values > 40 mV). The treatment of the nanosuspensions at different temperatures (4 and 40 °C) and storage times (7, 15, 21, and 30 days) did not affect their physicochemical parameters and highlights their reservoir ability for essential oils also under stressful conditions. Both Or-CNPs and Th-CNPs exhibited an enhanced bactericidal activity against foodborne pathogens (S. aureus, E. coli, L. monocytogenes) than pure essential oils. These ecofriendly nanosystems could represent a valid alternative to synthetic preservatives and be of interest for health and food safety.     

Essential Oils from Vietnamese Asteraceae for Environmentally Friendly Control of Aedes Mosquitoes

Mosquitoes, in addition to being a biting nuisance, are vectors of several pathogenic viruses and parasites. As a continuation of our work identifying abundant and/or invasive plant species in Vietnam for use as ecologically friendly pesticidal agents, we obtained the essential oils of Blumea lacera, Blumea sinuata, Emilia sonchifolia, Parthenium hysterophorus, and Sphaeranthus africanus; analyzed the essential oils using gas chromatographic techniques; and screened the essential oils for mosquito larvicidal activity against Aedes aegypti and Aedes albopictus. The most active larvicidal essential oils were B. sinuata, which was rich in thymohydroquinone dimethyl ether (29.4%), (E)-β-caryophyllene (19.7%), α-pinene (8.8%), germacrene D (7.8%), and α-humulene (4.3%), (24-h LC₅₀ 23.4 and 29.1 μg/mL) on Ae. aegypti and Ae. albopictus, respectively, and Emilia sonchifolia, dominated by 1-undecene (41.9%) and germacrene D (11.0%), (24-h LC₅₀ 30.1 and 29.6 μg/mL) on the two mosquito species. The essential oils of P. hysterophorus and S. africanus were also active against mosquito larvae. Notably, B. sinuata, P. hysterophorus, and S. africanus essential oils were not toxic to the non-target water bug, Diplonychus rusticus. However, E. sonchifolia essential oil showed insecticidal activity (24-h LC₅₀ 48.1 μg/mL) on D. rusticus. Based on these results, B. sinuata, P. hysterophorus, and S. africanus essential oils appear promising for further investigations.     

The Antimicrobial Activity,Mosquito Larvicidal Activity,Antioxidant Property and Tyrosinase Inhibition of Piper Betle

The essential oil and methanolic and aqueous extracts of Piper betle L. were assayed for their antimicrobial activity, mosquito larvicidal activity, antioxidant property and mushroom tyrosinase inhibition. The methanolic and aquaous extracts showed strong activity against the yeasts: C. albicans, and M. pachydermatis. The crude essential oil exhibited a broad‐spectrum strong antimicrobial activity against all test organisms. The strongest activity was observed against C. albicans, followed by S. aureus and M. pachydermatis. The chemical composition of the essential oil and its fractions was analyzed by GC/MS analysis. Eugenol (36.2%), chavibetol acetate (16.9%), 4‐allylphenyl acetate (9.4%) and 4‐allylphenol (7.2%) were the main components, comprising 69.7% of the oil. The fractionation of the essential oil gave two fractions. Fraction I was rich in eugenol (71.3%) and fraction II in eugenol (46.4%), chavibetol acetate (19.4%) and 4‐allylphenyl acetate (11.8%). The essential oil exhibited the mosquito larvicidal activity with 2 h and 24 h LD₅₀ value of 86 and 48 ppm, respectively. The methanolic extract of P. betle showed larvicidal activity with 2 h and 24 h LD₅₀ value of 153 and 125 ppm, respectively, whereas the aqueous extract showed slight active. The individual antioxidant assays such as DPPH scavenging activity, chelating effect of ferrous ions and reducing power have been used. P. betle showed remarkable antioxidant activity in DPPH and reducing power assays. The activity observed can be attributed to the presence of the phenolic compounds. The essential oil exhibited concentration‐dependent inhibition of mushroom tyrosinase, giving an IC₅₀ value of 126 ppm. The fraction I showed a strong inhibition of tyrosinase activity, giving an IC₅₀ value of 115 ppm. The presence of 4‐allylphenolic components in the essential oil may play an important role in the inhibition of tyrosinase. In conclusion, the results presented here show that Piper betle essential oil could be considered as a natural antimicrobial, mosquito larvicidal, antioxidant and tyrosinase inhibition source.     

Chemical Composition,Antioxidant, Antibacterial,and Antibiofilm Activities of Backhousia citriodora Essential Oil

The essential oil of Backhousia citriodora, commonly known as lemon myrtle oil, possesses various beneficial properties due to its richness in bioactive compounds. This study aimed to characterize the chemical profile of the essential oil isolated from leaves of Backhousia citriodora (BCEO) and its biological properties, including antioxidant, antibacterial, and antibiofilm activities. Using gas chromatography–mass spectrometry, 21 compounds were identified in BCEO, representing 98.50% of the total oil content. The isomers of citral, geranial (52.13%), and neral (37.65%) were detected as the main constituents. The evaluation of DPPH radical scavenging activity and ferric reducing antioxidant power showed that BCEO exhibited strong antioxidant activity at IC₅₀ of 42.57 μg/mL and EC₅₀ of 20.03 μg/mL, respectively. The antibacterial activity results showed that BCEO exhibited stronger antibacterial activity against Gram-positive bacteria (Staphylococcus aureus and Staphylococcus epidermidis) than against Gram-negative bacteria (Escherichia coli and Klebsiella pneumoniae). For the agar disk diffusion method, S. epidermidis was the most sensitive to BCEO with an inhibition zone diameter of 50.17 mm, followed by S. aureus (31.13 mm), E. coli (20.33 mm), and K. pneumoniae (12.67 mm). The results from the microdilution method showed that BCEO exhibited the highest activity against S. epidermidis and S. aureus, with the minimal inhibitory concentration (MIC) value of 6.25 μL/mL. BCEO acts as a potent antibiofilm agent with dual actions, inhibiting (85.10% to 96.44%) and eradicating (70.92% to 90.73%) of the biofilms formed by the four tested bacteria strains, compared with streptomycin (biofilm inhibition, 67.65% to 94.29% and biofilm eradication, 49.97% to 89.73%). This study highlights that BCEO can potentially be a natural antioxidant agent, antibacterial agent, and antibiofilm agent that could be applied in the pharmaceutical and food industries. To the best of the authors’ knowledge, this is the first report, on the antibiofilm activity of BCEO against four common nosocomial pathogens.     

In Vitro Antimicrobial Activity of Lavender,Mint, and Rosemary Essential Oils and the Effect of Their Vapours on Growth of Penicillium spp. in a Bread Model System

The chemical composition, antioxidant activity, and antimicrobial properties of three commercially available essential oils: rosemary (REO), lavender (LEO), and mint (MEO), were determined in the current study. Our data revealed that the major components of REO, MEO, and LEO were 1,8-cineole (40.4%), menthol (40.1%), and linalool acetate (35.0%), respectively. The highest DPPH radical-scavenging activity was identified in MEO (36.85 ± 0.49%) among the investigated EOs. Regarding antimicrobial activities, we found that LEO had the strongest inhibitory efficiencies against the growth of Pseudomonas aeruginosa and Candida (C.) tropicalis, MEO against Salmonella (S.) enterica, and REO against Staphylococcus (S.) aureus. The strongest antifungal activity was displayed by mint EO, which totally inhibited the growth of Penicillium (P.) expansum and P. crustosum in all concentrations; the growth of P. citrinum was completely suppressed only by the lowest MEO concentration. The lowest minimal inhibitory concentrations (MICs) against S. enterica, S. aureus, and C. krusei were assessed for MEO. In situ analysis on the bread model showed that 125 µL/L of REO exhibited the lowest mycelial growth inhibition (MGI) of P. citrinum, and 500 µL/L of MEO caused the highest MGI of P. crustosum. Our results allow us to make conclusion that the analysed EOs have promising potential for use as innovative agents in the storage of bakery products in order to extend their shelf-life.