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. 2026 Jun 26;11(27):39689–39699. doi: 10.1021/acsomega.5c12547

Chemical Analysis and Biological Activities of the Essential Oils of Beilschmiedia bidoupensis and Beilschmiedia tsangii Growing Wild in Vietnam

Dau Xuan Duc a, Hieu Tran-Trung a, Nguyen Dang Khoa b,c, Nguyen Minh Chanh b,c, Le Dang Quang d,e, Ho Le Thi f, Hoang Van Trung g, Vi Thi Thuan a, Le Duc Giang a,*
PMCID: PMC13382649  PMID: 42518439

Abstract

Our present work provides the first description of the chemical compositions of the essential oils extracted from the fresh leaves and stems of B. bidoupensis (BBLEO and BBSEO) and B. tsangii (BTLEO and BTSEO) growing wild in Vietnam. GC-MS and NMR results indicated overall similarities in the composition of BBLEO and BBSEO, both containing major compounds such as α-pinene, β-pinene, (6E)-nerolidol, and β-(E)-caryophyllene. In contrast, the analysis revealed marked differences in the chemical composition of B. tsangii essential oils. For example, BTLEO was characterized primarily by oxygenated sesquiterpenes, especially (6E)-nerolidol (24.30%), while BTSEO was dominated by monoterpene and sesquiterpene hydrocarbons, with α-phellandrene (21.45%) and β-(E)-caryophyllene (20.67%) as the major constituents. For in vitro bioactivity assays, B. tsangii essential oils exhibited measurable antioxidant activity in both DPPH and ABTS methods. Regarding enzyme inhibition, the Beilschmiedia oils displayed distinct selectivity. BBSEO was the only sample to exhibit moderate α-amylase inhibitory activity (IC50 = 0.230 ± 0.051 mg/mL). For α-glucosidase inhibition, both B. tsangii oils demonstrated inhibitory effects (IC50 values of 0.39 ± 0.06 mg/mL for BTLEO and 0.41 ± 0.08 mg/mL for BTSEO), whereas B. bidoupensis samples showed no activity. In addition, the essential oils inhibited the shoot and root growth of barnyardgrass (E. crus-galli) in a dose- and oil-dependent manner. Notably, BTLEO demonstrated promising allelopathic potential, achieving near-complete growth suppression at concentrations of 8 μL/mL or higher under the experimental conditions. In contrast, BBLEO showed a hormetic pattern with shoot stimulation at 0.5 μL/mL followed by inhibition at higher concentrations. In antifungal tests, the oils exhibited dose-dependent activity against Colletotrichum capsici and Fusarium oxysporum f.sp. cubense, with B. tsangii oils showing IC50 values ranging from 103.4 to 287.2 μg/mL. Overall, this study highlights the chemical diversity of these oils and their measurable in vitro antioxidant, enzyme–inhibitory, phytotoxic, and antifungal activities. While the results indicate potential for further exploration (e.g., as leads for crop-protection or bioactivity-guided studies), additional work, such as isolation of active constituents, mode-of-action validation, formulation, and in vivo/field evaluation, is required before inferring practical bioherbicidal, therapeutic, or antidiabetic applications.

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1. Introduction

Essential oils are complex liquid mixtures of volatile secondary metabolites that exhibit a wide array of biological activities, including antioxidant, antidiabetic, antimicrobial, herbicidal, and antifungal properties. − Due to their numerous biological activities relevant to human health, the environment, agriculture, and their characteristically low toxicity, essential oils have garnered substantial and increasing interest as natural alternatives across various fields. Consequently, current research has increasingly focused on essential oils as sustainable alternatives to synthetic agents in agriculture and medicine due to their multifaceted biological properties. ,,

The family Lauraceae, which is well-known for its essential oil-bearing plants, is one of the most widely distributed plant families in tropical regions, particularly in Southeast Asia and South America. This family comprises about 2850 known species in about 45 genera worldwide. Among these, Beilschmiedia Nees is one of the most widespread pantropical genera, comprising about 278 species of shrubs and medium trees. Several plants of this genus have been used in folk medicine to treat various diseases such as uterine tumors, rheumatism, pulmonary disorders, bacterial infections, malaria, and tuberculosis. − Previous phytochemical studies have demonstrated that the genus possesses a broad spectrum of bioactivities, such as anti-inflammatory, , cytotoxic, − antibacterial, ,, and other bioactivities. ,,− While recent investigations have identified unique constituents with diverse bioactivities in many Beilschmiedia species, the volatile profiles of several endemics remain uncharacterized. This data gap hinders a comprehensive understanding of the genus’s chemotaxonomic diversity and limits the discovery of novel bioactive scaffolds for pharmaceutical and bioherbicide development.

Beilschmiedia bidoupensis and Beilschmiedia tsangii are two such species underrepresented in current literature. While B. bidoupensis is a newly described species endemic to Vietnam, occurring solely within the Bidoup-Nui Ba National Park in the southern highlands, B. tsangii has long been recorded in Southeast China, Taiwan, and Vietnam. To date, no previous studies have reported the chemical compositions and bioactivities of the essential oils of B. bidoupensis and B. tsangii. Therefore, this study aims to bridge this knowledge gap by providing a comprehensive phytochemical characterization of the essential oils extracted from the leaves and stems of B. bidoupensis and B. tsangii. Beyond chemical profiling via GC-MS and NMR analysis, we evaluated their biological potential through a suite of assays targeting oxidative stress, enzyme inhibitory, antifungal, and herbicidal activities of these Beilschmiedia essential oils. The findings are expected to provide valuable insights into this plant’s essential oil profiling and bioactive potential.

2. Results and Discussion

2.1. Chemical Composition of the Essential Oils

2.1.1. GC-MS Analysis

The essential oils extracted from the leaves and stems of B. bidoupensis (coded as BBLEO and BBSEO, respectively), and the leaves and stems of B. tsangii (coded as BTLEO and BTSEO, respectively) via hydrodistillation were characterized as yellow liquids. The yields (v/w) were 0.20 ± 0.02%, 0.04 ± 0.00%, 0.04 ± 0.01%, and 0.05 ± 0.01%, respectively. The chemical composition of these essential oils was subsequently investigated using Gas Chromatography–Mass Spectrometry (GC-MS) techniques (Supporting Information, Figures S1 and S2). The relative percentages and Retention Indices (RIs) of the identified components are systematically listed in Tables S1 and S2, following their elution order on the HP-5MS UI column.

A total of 35 and 40 constituents were identified, accounting for 99.33% and 98.97% of the BBLEO and BBSEO, respectively (Table S1). These comprised mainly monoterpene hydrocarbons (79.08% for BBLEO and 66.61% for BBSEO), followed by oxygenated sesquiterpenes (7.49% for BBLEO and 22.09% for BBSEO) and sesquiterpene hydrocarbons (8.86% for BBLEO and 7.71% for BBSEO). In contrast, oxygenated monoterpenes are not abundant in these essential oils, representing only 2.49% for BBLEO and 1.28% for BBSEO. Accordingly, the major compounds of both oils were α-pinene (59.37% for BBLEO and 47.12% for BBSEO), (6E)-nerolidol (6.31% for BBLEO and 17.79% for BBSEO), β-pinene (9.83% for BBLEO and 7.45% for BBSEO), and β-(E)-caryophyllene (4.45% for BBLEO and 4.28% for BBSEO). Interestingly, β-(E)-ocimene was one of the main constituents in BBSEO (5.19%), but represented a small portion (1.24%) in BBLEO.

The GC-MS analysis revealed 66 constituents in the B. tsangii essential oils, which are shown in Table S2. Among these, a total of 50 and 59 components were identified in the BTLEO and BTSEO, respectively, accounting for 95.93% and 98.31% of the total oil composition. The B. tsangii essential oils were dominated by sesquiterpene hydrocarbons (40.10% for BTLEO and 37.09% for BTSEO), followed by oxygenated sesquiterpenes (44.88% for BTLEO and 11.76% for BTSEO), and monoterpene hydrocarbons (8.76% for BTLEO and 43.83% for BTSEO). The main components of these essential oils differ significantly. The most prevalent compounds in BTLEO were (6E)-nerolidol (24.30%), δ-cadinene (12.60%), γ-cadinene (10.08%), δ-cadinol (9.86%), α-eudesmol (6.32%), α-phellandrene (5.50%), and α-muurolene (3.10%). In contrast, six compounds, including α-phellandrene (21.45%), β-(E)-caryophyllene (20.67%), p-cymene (7.98%), β-phellandrene (4.91%), δ-cadinene (3.40%), and β-eudesmol (3.29%), were identified as main components in BTSEO. The MS fragmentation patterns of the major compounds identified in B. bidoupensis and B. tsangii essential oils are shown in Tables S3 and S4.

The PCA of essential oils from the fresh leaves and stems of B. bidoupensis and B. tsangii generated three Principal Components, of which the first two Principal Components (PC1 and PC2) showed 98.79% of the total variance. Specifically, PC1 reflected the large majority of the interspecies variation (78.69%), while PC2 accounted for 20.10% in differences between plant parts. Scores showed each sample in a different quadrant, as supported by the distribution of samples in the score plot (Figure ) and the corresponding loading values (Table S5).

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Principal Component Analyses (PCA) of the essential oil composition extracted from the fresh leaves and stems of B. bidoupensis (BBLEO and BBSEO) and B. tsangii (BTLEO and BTSEO) based on the principal compounds.

The analysis illustrates a clear separation among the four essential oils and highlights the main compounds associated with each sample, indicating their distinct chemical profiles. Notably, a compositional gradient was observed, with monoterpenes such as α- and β-pinene contributing positively to PC1, whereas sesquiterpenes including (6E)-nerolidol and δ- and γ-cadinene derivatives contributed negatively. Indeed, BBLEO and BBSEO were positioned on the right-hand side of the plot, whereas BTLEO and BTSEO were located on the opposite side, suggesting considerable differences in composition between these species. Specifically, BBLEO was greatly associated with α- and β-pinene, indicating that these monoterpenes contributed significantly to its separation. Similarly, BBSEO was located closer to α-pinene and β-(E)-ocimene, suggesting a higher relative abundance of these constituents. BTLEO was separated and strongly correlated with (6E)-nerolidol, as well as δ-cadinene and γ-cadinene, indicating that these sesquiterpenes played a major role in describing its chemical profile. In contrast, BTSEO was particularly positioned in the bottom left quadrant of the plot and associated with α-phellandrene and β (E)-caryophyllene. Overall, the PCA plot highlights clear chemical differentiation among the essential oils, with specific compounds contributing to the observed clustering patterns.

A comparison with existing literature highlights the significant chemical diversity of the Beilschmiedia essential oils. Phenylpropanoid was the most dominant group in the oil of B. pulverulenta aerial parts, with eugenol (45.3%) and eugenol acetate (5.6%) as the major constituents. The leaf essential oil of B. glabra was composed mainly of β-eudesmol (15.4%), β-selinene (12.2%), caryophyllene oxide (8.1%), and γ-gurjunene (5.2%), while the bark essential oil of this species contained high percentages of β-eudesmol (19.3%), β-selinene (16.9%), δ-cadinene (15.8%), germacrene D (9.8%), and β-caryophyllene (5.5%). The essential oils of B. kunstleri, B. maingayi, and B. penangiana gave β-caryophyllene (10.6–12.1%), β-eudesmol (17.5–24.1%), and δ-cadinene (17.5–28.7%) as the most abundant components, respectively. Additionally, the main compounds of the leaf essential oil of B. erythrophloia identified were β-caryophyllene (22.6%), α-humulene (21.9%), terpinen-4-ol (5.3%), cis-β-ocimene (5.1%), sabinene (5.0%), and limonene (4.5%). In summary, the chemical composition of the Beilschmiedia essential oils exhibits significant chemodiversity. The marked compositional differences observed between B. bidoupensis and B. tsangii likely reflect not only interspecific chemotaxonomic differentiation but also ecological modulation of terpene biosynthesis. Species-specific variation in terpene synthase activity and downstream oxidation pathways may contribute to the contrasting predominance of monoterpene hydrocarbons in B. bidoupensis oils and sesquiterpene/oxygenated sesquiterpene components in B. tsangii oils. In addition, the two species were collected from distinct habitats in Vietnam, which may differ in altitude, microclimate, and local ecological conditions. These factors are all known to influence volatile secondary metabolism. Organ-specific differences between leaves and stems may further reflect tissue-level regulation of terpene accumulation associated with different ecological functions. However, because plant age, developmental stage, season, and environmental variables were not independently controlled in the present study, these factors should be regarded as plausible contributors rather than demonstrated causes. Future studies incorporating replicated sampling across habitats, seasons, and ontogenetic stages will be necessary to disentangle chemotaxonomic versus ecological drivers of oil composition.

2.1.2. NMR Analysis

The 1H NMR spectrum of BBLEO showed all important signals of α-pinene, which was a main component of the oil (59.37%). The important signals appeared at δH 5.18 ppm (olefinic proton) and δH 1.66, 1.26, and 0.84 ppm (three methyl groups). A similar pattern was observed for BBSEO, as α-pinene was also characterized as the major compound (47.12%). In the 13C NMR spectrum of BBLEO, all signals of carbon of α-pinene were easily identified, including signals at δC 144.5, 116.0, 47.1, 40.8, 38.0, 31.5, 31.3, 26.4, 23.0, and 20.8 ppm. All these signals could be identified in BBSEO as well. In addition, several carbon signals of (6E)-nerolidol, the second major component of BBSEO, could be observed, such as olefinic carbons at δC 145.1 and 111.6 ppm (Supporting Information, Figures S3 and S4).

The 1H NMR spectrum of the B. tsangii essential oils is more complex than that of the B. bidoupensis essential oils. This difference is due to the lack of a single dominant component in the chemical profile of the B. tsangii oils; instead, their major compounds are present in quite similar concentrations and thus have overlapping NMR signals. However, several signals of (6E)-nerolidol as a main component in BTLEO are clear (olefinic protons at δH 5.86, 5.28, and 5.01 ppm; methyl protons at δH 1.63 and 1.38 ppm). Similarly, the 13C NMR spectrum of BTLEO shows important carbon signals such as olefinic carbon at δC 145.1, 133.7, 130.7, 124.3, 124.2, and 111.6 ppm; and oxygenated carbon at δC 73.5 ppm. In the 1H NMR spectrum of BTSEO, several peaks of α-phellandrene could be identified. Olefinic protons of α-phellandrene appear at δH 5.72–5.70, 5.65–5.63, and 5.63–5.60 ppm. Methyl protons of α-phellandrene appear at δH 1.64 ppm and 0.91–0.89 ppm. Additionally, in the 13C NMR spectrum of BTSEO, olefinic carbon signals appear at δC 130.1, 129.0, 126.3, and 120.5 ppm; three methyl carbons appear at δC 24.1, 19.9, and 19.8 ppm (Supporting Information, Figures S5 and S6).

2.2. Biological Activities of the Essential Oils

2.2.1. Antioxidant Activity

The antioxidant activities of essential oils from B. bidoupensis and B. tsangii were evaluated using DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-azino-bis­(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt) radical scavenging assays (Table ). IC50 values were used to quantify antioxidant potency, with lower values indicating stronger radical scavenging capacity. Across both assays, all essential oils exhibited higher IC50 values than Trolox (DPPH: 0.04 mg/mL; ABTS: 0.01 mg/mL).

1. Free Radical Scavenging Activity of B. bidoupensis and B. tsangii Essential Oils .
  IC50(mg/mL)
Samples DPPH ABTS
BBLEO 18.55 ± 0.12a n.d
BBSEO 3.58 ± 0.01b 0.18 ± 0.01a
BTLEO 1.09 ± 0.08c 0.08 ± 0.06b
BTSEO 0.42 ± 0.05d 0.03 ± 0.01c
Trolox 0.04 ± 0.00 0.01 ± 0.00
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a

Values are presented as mean ± SD (n = 3). Superscript letters indicate statistically significant differences within each column (p < 0.05). n.d: not detected.

For DPPH radical scavenging activity, BTSEO exhibited the highest DPPH scavenging activity (IC50 = 0.42 ± 0.05 mg/mL), followed by BTLEO (1.09 ± 0.08 mg/mL), BBSEO (3.58 ± 0.01 mg/mL), and BBLEO (18.55 ± 0.12 mg/mL). The superior performance of B. tsangii oils may be attributed to their rich content of sesquiterpenes and oxygenated compounds such as δ-cadine, β-(E)-caryophyllene, β-eudesmol, and α-eudesmol. In contrast, BBLEO, dominated by monoterpenes like α-pinene and β-pinene, showed the weakest activityconsistent with the generally lower antioxidant potential of monoterpenes. These findings aligned with previous research by Salleh et al., which showed that Beilschmiedia essential oils enriched in oxygenated sesquiterpenes exhibited markedly stronger antioxidant activity than oils dominated by monoterpenes. In particular, the oils of B. kunstleri, B. maingayi, and B. penangiana, which contain high levels of δ-cadinene, β-(E)-caryophyllene, β-eudesmol, and α-eudesmol, displayed the most potent radical-scavenging effects (DPPH IC50 = 84.7 μg/mL; ABTS IC50 = 108.3 μg/mL), whereas monoterpene-rich oils consistently showed weaker responses. This trend was attributed to the inherently greater radical-quenching efficiency of oxygenated sesquiterpenes compared with monoterpene hydrocarbons. For ABTS radical scavenging activity, a similar trend was observed in the ABTS assay. BTSEO again showed the strongest activity (IC50 = 0.03 ± 0.01 mg/mL), followed by BTLEO (0.08 ± 0.06 mg/mL) and BBSEO (0.18 ± 0.01 mg/mL). BBLEO showed no detectable activity in this assay. The enhanced ABTS scavenging capacity of BTSEO may be linked to the presence of p-cymene and β-phellandrene, which may act synergistically with cadinene-type sesquiterpenes and eudesmol derivatives.

Notably, all essential oils demonstrated stronger activity in the ABTS assay compared with that in DPPH, as reflected by consistently lower IC50 values. This discrepancy may be attributed to the distinct chemical nature of the radicals involved: ABTS•+ is soluble in both aqueous and organic media, allowing broader interaction with hydrophilic and lipophilic antioxidants, whereas DPPH• is limited to organic solvents and primarily reacts with lipophilic compounds. As a result, compounds such as eudesmol and nerolidol, which possess moderate polarity, may exhibit enhanced reactivity toward ABTS•+. This methodological difference underscores the importance of using multiple assays to comprehensively evaluate antioxidant potential.

Importantly, the DPPH and ABTS assays measure only direct radical-quenching reactions in simplified chemical systems and do not reflect antioxidant mechanisms involving metal chelation, enzyme regulation, ROS signaling, membrane interactions, or in vivo metabolism. Therefore, broader antioxidant claims require additional evaluations in future studies, including ORAC, FRAP, lipid peroxidation inhibition, or cell-based ROS assays.

2.2.2. Enzyme Inhibitory Activity

The essential oils of B. bidoupensis and B. tsangii were tested for their ability to inhibit α-amylase and α-glucosidase, enzymes that are fundamental to carbohydrate digestion and metabolism (Table ). IC50 values were used to quantify enzyme inhibition, with lower values indicating stronger inhibitory activity.

2. Enzyme Inhibitory Activities of B. bidoupensis and B. tsangii Essential Oils .
  IC50(mg/mL)
Essential oils α-amylase inhibition α-glucosidase inhibition
BBLEO n.d. n.d.
BBSEO 0.230 ± 0.051 n.d.
BTLEO n.d. 0.39 ± 0.06a
BTSEO n.d. 0.41 ± 0.08a
Acarbose 0.604 ± 0.150 1.19 ± 0.18
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a

Values are presented as mean ± SD (n = 3). Superscript letters indicate statistically significant differences within each column (p < 0.05). n.d: not detected.

For α-amylase inhibition, only BBSEO exhibited measurable α-amylase inhibitory activity (IC50 = 0.230 ± 0.051 mg/mL), while BBLEO, BTLEO, and BTSEO showed no detectable inhibition. The activity of BBSEO may be attributed to its balanced composition of monoterpenes (α-pinene, β-pinene) and sesquiterpene such as β-(E)-caryophyllene and (6E)-nerolidol. These compounds have been reported to interfere with carbohydrate-hydrolyzing enzymes by binding to their active sites or altering their conformation. Interestingly, BBLEO, despite sharing similar major constituents with BBSEO, did not show activity. This may be due to the lower diversity of active compounds or the absence of β-(E)-ocimene, which has been suggested to enhance enzyme inhibition through synergistic effects with other terpenes. , Regarding α-glucosidase inhibition, BTLEO and BTSEO demonstrated potent α-glucosidase inhibitory activity, with IC50 values of 0.39 ± 0.06 mg/mL and 0.41 ± 0.08 mg/mL, respectively. BBLEO and BBSEO showed no detectable inhibition. The comparable potency of BTLEO and BTSEO suggests that the sesquiterpene-rich profiles of B. tsangii oils, notably compounds such as δ-cadinene, β-(E)-caryophyllene, and oxygenated sesquiterpenes such as α-eudesmol, play a central role in enzyme inhibition. Previous studies have shown that oxygenated sesquiterpenes, especially eudesmol derivatives, exhibit effective affinity for α-glucosidase due to their ability to form hydrogen bonds with catalytic residues. The presence of α-phellandrene and p-cymene in BTSEO may also contribute to its inhibitory effect through hydrophobic interactions. The data suggest that BBSEO is the only essential oil with α-amylase inhibitory activity, while BTLEO and BTSEO selectively inhibit α-glucosidase. This highlights the functional diversity of essential oils based on their chemical compositions. BBSEO’s activity may be driven by monoterpenes and nerolidol derivatives, whereas BTSEO and BTLEO benefit from cadinene-type sesquiterpenes and eudesmol-related compounds. Although some samples exhibited lower IC50 values than acarbose under these assay conditions, these results should be interpreted only as preliminary screening, as essential oils are complex mixtures, and no kinetic or mechanistic analyses were performed. Accordingly, we refrain from making mechanistic interpretations or pharmacological implications.

2.2.3. Effect of Essential Oils on Shoot and Root Growth of Barnyardgrass (Echinochloa crus-galli)

The results clearly demonstrate that the shoot and root growth of barnyardgrass (E. crus-galli) were significantly affected by exposure to Beilschmiedia essential oils, with responses strongly dependent on concentration and oil type (Figure and Table S6). For shoot length, all oils displayed inhibitory effects relative to the control, but their inhibition dynamics varied. BTLEO exhibited the most rapid and pronounced suppression, achieving near-complete inhibition at 8 μL/mL and total suppression at 16 μL/mL. This highlights its strong allelopathic potency, potentially linked to specific bioactive terpenoid constituents. By contrast, BBLEO displayed a hormetic effect, stimulating shoot elongation at 0.5 μL/mL (23.03 mm vs 19.37 mm in the control) before rapidly switching to inhibition beyond 1 μL/mL, culminating in only 3.20 mm at 16 μL/mL. Such stimulation–inhibition thresholds are well documented in allelopathic interactions and underscore the complexity of dose-dependent phytotoxic responses. Meanwhile, BBSEO and BTSEO exerted consistent but less drastic reductions, reflecting stable inhibitory effects without the biphasic pattern observed in BBLEO.

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Effects of Beilschmiedia essential oils (concentration μL/mL) on shoot and root length development of Echinochloa crus-galli.

Root development was even more sensitive to essential oil exposure, as evidenced in Figure and Table S6. At 0.5 μL/mL, BTLEO reduced root length to 15.13 mm compared with 23.53 mm in the control, and complete suppression occurred at 16 μL/mL. BBSEO also induced a clear, linear inhibitory pattern, culminating in 1.17 mm root length at the highest concentration, while BTSEO displayed only moderate effects. Similar to the shoot response, BBLEO was weaker at low doses but became strongly suppressive at higher levels (0.83 mm at 16 μL/mL). The stronger root sensitivity suggests that essential oils likely interfere with root cell division and elongation, disrupting early resource acquisition and overall seedling establishment. Comparable findings were reported in garlic essential oil, which markedly inhibited root growth of E. crus-galli through phenolic and sulfur-containing volatiles.

The patterns observed in Table S6 were further clarified through radar plots (Figure A,B), which provide a visual synthesis of concentration-dependent inhibition patterns. Figure A highlights the rapid, linear suppression of shoot elongation by BTLEO, contrasted with the biphasic curve of BBLEO, which shifted from growth promotion to inhibition. This hormesis effect, clearly visible only in the radar visualization, illustrates the fine balance between stimulatory and inhibitory allelopathic thresholds. Figure B emphasizes the heightened vulnerability of roots, where both BTLEO and BBSEO achieved over 80% inhibition at 8 μL/mL, while BBLEO exhibited steep inhibition only at higher concentrations. Together, these figures add interpretive depth to the tabular data by enabling pattern recognition across oil types and dose ranges, revealing not just magnitudes but also ecological strategies of phytotoxic action.

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Radar chart showing the inhibition rate of shoot (A) and root (B) growth (%) of barnyardgrass (Echinochloa crus-galli) under the effects of BBLEO, BBSEO, BTLEO, and BTSEO at concentrations ranging from 0.5 to 16 μL/mL. Growth values used for inhibition-rate calculation were obtained from direct seedling-length measurements using a calibrated digital electronic caliper (0.01 mm resolution). Concentric circles represent inhibition levels from 0–100%, while point colors indicate concentration (light yellow = low, dark red = high). The chart was generated in RStudio using the fmsb package.

While E. crus-galli showed significant sensitivity to these essential oils, these results should be interpreted with caution regarding crop selectivity. Monocot weeds, such as Echinochloa spp., are often more susceptible than cereal crops due to differences in cuticle permeability and detoxification pathways. However, direct selectivity assays are still required to confirm the safety of these oils for rice or other crops. Soil interactions represent another critical factor influencing the bioherbicidal performance of essential oils. Volatile terpenoids are known to undergo rapid adsorption to soil organic matter, microbial degradation, and volatilization, processes that can markedly reduce their persistence and efficacy under field conditions. Consequently, the strong inhibitory effects observed in agar-based assays are best regarded as screening-level indicators of intrinsic phytotoxic potential, rather than predictors of field performance. Future work incorporating soil matrices and microbial activity will be necessary to assess the stability and bioavailability of Beilschmiedia essential oils in realistic agroecosystems.

To place the observed phytotoxicity in context, the inhibitory thresholds reported here are comparable to those documented for other essential oils evaluated against E. crus-galli. For example, garlic (Allium sativum) essential oil and clove (Syzygium aromaticum) oil have been reported to achieve 80–100% root inhibition at concentrations ranging from 5 to 20 μL/mL in laboratory assays, values that overlap with the effective range of BTLEO and BBSEO observed in this study. By contrast, commercial synthetic herbicides such as cyhalofop-butyl or bispyribac-sodium typically exert near-complete growth inhibition at substantially lower active ingredient concentrations under controlled conditions. This comparison underscores that essential oils are less potent on a mass basis, but act through multitarget and chemically diverse modes of action, which may reduce the risk of resistance development.

Overall, the pronounced inhibition by BTLEO and the dose-dependent, hormetic behavior of BBLEO highlight both the promise and the challenges of essential oil–based weed management. While the present findings establish a clear allelopathic signal against E. crus-galli, they also emphasize the necessity of subsequent studies addressing crop selectivity, soil interactions, formulation optimization, and direct comparisons with commercial herbicides under greenhouse and field conditions before practical application can be envisaged.

2.2.4. Antifungal Activity of the Essential Oils against Phytopathogenic Fungi

The antifungal activity of essential oils derived from plants has received abundant attention from scientists. However, the research on the antifungal activity of B. bidoupensis and B. tsangii has not been reported in the literature. In our study, C. capsici and F. oxysporum f.sp. cubense were used for evaluating the antifungal property of the oil samples. Colletotrichum capsici is a fungal pathogen responsible for anthracnose in chili peppers. While Fusarium oxysporum f.sp. cubense (FOC) is one of the most destructive soilborne fungal pathogens affecting bananas worldwide. Using essential oils as a green control strategy for these fungi has been important due to their safe properties. All essential oils of Beilschmiedia species were observed to exhibit the test fungi with a concentration–response gradient. However, the Minimum Inhibitory Concentration (MIC) values remained above 500 μg/mL (Figures , , and ). As expected, positive control completely inhibited all test fungi at 1000-fold dilution (equivalent to 250 μg/mL of the active ingredient; data not shown). Samples BBSEO and BBLEO moderately inhibited the test fungi (Figure ); however, both BTSEO and BTLEO were effectively active against all of the test fungi (Figures and ). BTSEO was most active against C. capsici, with an IC50 of 103.4 μg/mL (Table ). C. capsici was particularly sensitive to BTSEO, whereas F. oxysporum f.sp. cubense was more strongly inhibited by the leaf essential oils (IC50 of 173.3 μg/mL). Overall, the B. tsangii essential oils were more active against phytopathogenic fungi, compared to those of B. bidoupensis. According to the antifungal potency of B. tsangii, its essential oils could be a valuable resource for protecting food and plants from phytopathogenic fungi.

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Antifungal activity of the B. bidoupensis essential oils against Colletotrichum capsici. A: Mycelial growths of the test fungus in Petri dishes at 4 days after treatment. B: Inhibitory values (%) of two essential oils against mycelial growth of Colletotrichum capsici after 4 days. These essential oils were tested at concentrations ranging from 62.5 to 500 μg/mL (lanes 1 to 4). C: negative control.

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Antifungal activity of the B. tsangii essential oils against Colletotrichum capsici. A: Mycelial growths of the test fungus in Petri dishes at 4 days after treatment. B: Inhibitory values (%) of two essential oils against mycelial growth of Colletotrichum capsici after 4 days. These essential oils were tested at concentrations ranging from 62.5 to 500 μg/mL (lanes 1 to 4). C: negative control.

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Antifungal activity of the B. tsangii essential oils against Fusarium oxysporum f.sp. cubense (FOC). A: Mycelial growths of the test fungus in Petri dishes at 4 days after treatment. B: Inhibitory values (%) of two essential oils against the mycelial growth of Fusarium oxysporum f.sp. cubense after 4 days. These essential oils were tested at concentrations ranging from 62.5 to 500 μg/mL (lanes 1 to 4). C: negative control.

3. Half-Maximal Inhibitory Concentrations (IC50) of the B. tsangii Essential Oils against Phytopathogenic Fungi.
  Colletotrichum capsici Fusarium oxysporum f.sp. cubense
  IC 50 (CI 95%) μg/mL IC 50 (CI 95%) μg/mL
BTSEO 103.4 (78.6–136.1) 287.2 (222.0–371.7)
BTLEO 242.6 (204.7–287.7) 173.3 (143.3–209.4)
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The antimicrobial properties of compounds and essential oils isolated from Beilschmiedia species have been widely reported. Beilschmiedic acid P isolated from B. acuta was reported to possess antibacterial activity against K. pneumoniae, E. coli, P. aeruginosa, E. aerogenes, and P. stuartii, especially against E. coli with the MIC value of 16 μg/mL. Cryptobeilic acids A-B, beilschmins A-B, beilschmiedic acids B–C, suberosol B, erythrophloin C, and pipyahyine isolated from Beilschmiedia species were identified as potential antibacterial agents. The B. fordii leaf essential oil from Vietnam showed promising antibacterial activity (MIC value of 16.0 μg/mL) against S. aureus, B. cereus, and C. albicans. B. tonkinensis leaf oil strongly inhibited P. aeruginosa (MIC of 16 μg/mL) and A. niger (MIC of 32 μg/mL). B. madang bark essential oil showed antifungal activity against A. niger and A. fumigatus with an MIC of 62.5 μg/mL. In addition, B. miersii essential oil, which was primarily composed of sarisan (45.8%), eugenol methyl ether (27.7%), and safrole (5.8%) with a yield of 0.2%, exhibited antiphytopathogenic activity against the bacterium A. tumefaciens (IC50 = 5 μg/mL) and the oomycete P. cinnamomi (IC50 = 200 μg/mL). However, the antifungal activity of essential oils from Beilschmiedia species against phytopathogenic fungi such as C. capsici and F. oxysporum f.sp. cubense remains undescribed. Investigation of these antifungal activities is important because it may expand the potential applications of Beilschmiedia essential oils in food preservation and plant protection. Further studies should also investigate the oils against other phytopathogens, along with their phytotoxicity and safety concerns.

3. Conclusions

In conclusion, this study provides the first comprehensive analysis of the chemical composition and biological activities of essential oils distilled from two Vietnamese Beilschmiedia species. GC-MS analyses reveal that the oils have different chemical composition profiles. The oils of B. bidoupensis shared major compounds (α-pinene, β-pinene, (6E)-nerolidol, and β-(E)-caryophyllene), while B. tsangii oils were chemically unique (BTLEO dominated by (6E)-nerolidol; BTSEO by α-phellandrene and β-(E)-caryophyllene). The in vitro assays indicated that these oils possess varying degrees of biological activity. Notably, B. tsangii oils exhibited promising antioxidant and α-glucosidase inhibitory activities, while B. bidoupensis stem essential oil (BBSEO) showed specific inhibition against α-amylase. Additionally, the oils demonstrated antifungal properties and concentration-dependent phytotoxicity against E. crus-galli, with BTLEO showing the most marked growth suppression. Although these results highlight the bioactivity potential of Beilschmiedia essential oils, they remain preliminary. Further work is needed, including isolation of active constituents, mechanistic investigation, formulation optimization, and in vivo and/or field validation, before practical antifungal or bioherbicidal applications can be inferred.

4. Methods

4.1. Plant Material

Fresh leaves and stems of B. bidoupensis were collected in January 2024 from Bidoup-Nui Ba National Park, Lam Dong (12°09′28.10″N 108°32′07.02″E), Vietnam, and those of B. tsangii were collected in March 2024 from Son Tra, Da Nang (16°08′7.23″N 108°14′48.36″E), Vietnam. Botanical identification was achieved by Assoc. Prof. Dr. Nguyen Hoang Tuan (Faculty of Pharmacognosy and Traditional Medicine, Hanoi University of Pharmacy). Voucher specimens, HC029BB and HC060BT, were subsequently deposited at the Natural Products Laboratory, Department of Chemistry, Vinh University, Vietnam.

4.2. Chemicals

C7–C30 saturated alkanes standard, sodium sulfate, dichloromethane, starch (CAS 9005–84–9), and Tween 20 were obtained from Merck (Darmstadt, Germany). α-Amylase, α-glucosidase, acarbose, 4-nitrophenyl α-d-glucopyranoside, trolox (±6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and 2,2′-azino-bis­(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) were obtained from Sigma-Aldrich Inc. (St. Louis, MO, USA). 3,5-Dinitrosalicylic acid (DNS; CAS 609–99–4) was sourced from Macklin Biochemical Co., Ltd. (Shanghai, China). Dimethyl sulfoxide, ethanol, and methanol were supplied by Xilong Chemical Co., Ltd. (Guangdong, China). All chemicals were of analytical grade and used without further purification.

4.3. Distillation and Sample Preparation

The preparation of the essential oils involved three replicates of hydrodistillation from the leaves and stems of B. bidoupensis and B. tsangii. Five hundred grams of each fresh sample were thoroughly washed and fragmented before being placed in a Clevenger-style apparatus for distillation. The distillation process was carried out for approximately 5 h, beginning at the boiling point of water and continuing until a constant yield of essential oil was achieved. Following collection, the essential oils were treated with anhydrous sodium sulfate (Na2SO4) for desiccation and subsequently refrigerated at 4 °C pending further evaluation of their chemical profile and biological activity.

4.4. Chemical Composition Analysis

4.4.1. GC-MS and Principal Component Analysis (PCA)

The chemical constituents of the essential oils distilled from B. bidoupensis and B. tsangii were analyzed via the technique mentioned by Giang-An et al. through an Agilent 7890B GC system coupled to an Agilent 5977B MSD with an HP-5MS UI column (30 m × 0.25 mm ID × 0.25 μm, Agilent Technologies). Helium served as the carrier gas at a flow rate of 1.0 mL/min. A 1.0 μL sample of the essential oil, prediluted in dichloromethane (1/100, v/v), was manually injected in split mode (split ratio of 40:1). The heating procedure was as follows: the initial temperature was 60 °C (held for 3 min), then increased to 180 °C at a rate of 3 °C/min, and finally ramped to 240 °C at a rate of 5 °C/min (held for 5 min). The temperatures for Inlet-F, Aux-2, the MS Source, and the MS Quad were set at 300 °C, 250 °C, 230 °C, and 150 °C, respectively. The mass spectrometer utilized an Electron Impact (EI) ionization source, operating at an ionization energy of 70 eV. The acquisition parameters were full scan, with a scan range of 50–550 m/z at 2.0 scan/s. Data processing was performed using the MassHunter Workstation Software (Version B.08.00). The percentage of each oil constituent was determined by measuring its relative peak area in the GC chromatogram, without applying response factor correction. Component retention indices (RI) (experimental RI) were calculated relative to the retention times of a homologous series of C7–C30 (Merck). These experimental RIs were then compared to literature data. Constituent identification was achieved by comparing the mass spectra and retention indices of the components with those in published data (NIST 17 and Adams book). The Principal Components Analysis (PCA) was performed to evaluate the similarities among the essential oils based on their chemical composition using PAST 4.03 software.

4.4.2. NMR Analysis

Preparation for NMR analysis involved dissolving 50 mg of each Beilschmiedia essential oil sample in 0.5 mL of deuterated chloroform solvent, followed by transfer into 5 mm NMR tubes for data acquisition. The major constituents of four Beilschmiedia essential oils were evaluated using a Bruker 600 MHz instrument (Bruker, Massachusetts, United States). The 1H NMR data (recorded at 600 MHz) and 13C NMR data (recorded at 150 MHz) were obtained in deuterated chloroform solvent and confirmed by matching their NMR characteristics to previously reported literature data.

4.4.3. Assessing the Antioxidant Activity

The DPPH scavenging activities of the samples were performed based on the previous report, with minor modifications. The samples were dissolved in EtOH 70% to test concentrations and mixed with 0.3 mM DPPH solution at a ratio of 1/1 (v/v). The mixture was incubated in the dark for 30 min and then spectrophotometrically measured at 517 nm. Trolox (0–1000 μM) was used as a positive control, while ionized water replaced the sample in the negative control (NC). The DPPH scavenging activity (%) was calculated using the following equation:

RadicaScavengingRActivity(%)=[(ANC−AS)/ANC]×100 1

where ANC denoted the absorbance of the negative control, and AS represented the absorbance of the tested samples. The IC50 values were then estimated based on the fitted lines between concentrations and scavenging activity, using GraphPad Prism (8.4.2, GraphPad Software, San Diego, California, USA). A smaller value of IC50 means a higher scavenging activity of the samples.

The assay was conducted following a previously reported method with slight modifications. ABTS•+ radicals were freshly prepared by mixing ABTS (2.6 mM) with potassium persulfate (7.4 mM) in a 3/1 volume ratio and incubating the mixture at room temperature for 16 h. The resulting solution was diluted with phosphate-buffered saline (PBS; 0.1 M, pH 7.4) to an absorbance of 0.70 ± 0.02 at 734 nm. Sample solutions were mixed with the ABTS•+ solution at a 1/4 (v/v) ratio and incubated at room temperature for 10 min. Absorbance was measured at 734 nm to evaluate radical scavenging activity. Trolox (0–1000 μM) was used as the positive control, while ionized water served as the negative control. ABTS scavenging activity (%) was calculated using Equation . IC50 values were determined by fitting dose–response curves using GraphPad Prism (version 8.4.2; GraphPad Software, San Diego, CA, USA), where lower IC50 values indicated stronger antioxidant capacity.

4.4.4. Assessing the Enzyme Inhibitory Activity

The α-amylase inhibition assay was performed based on a previously reported method with slight modifications. α-Amylase solution (2.5 U/mL), test sample (2–20 mg/mL), and acarbose (0–2000 μg/mL) were prepared in PBS (0.1 M, pH 6.9). Each reaction consisted of 100 μL of sample or acarbose mixed with 100 μL of enzyme and incubated at room temperature for 5 min. Then, 250 μL of gelatinized potato starch (0.5%) and 250 μL of PBS were added, followed by a 20 min incubation. The reaction was stopped with 300 μL of DNS reagent and heated at 100 °C for 5 min. The final volume was adjusted to 1500 μL with distilled water, and absorbance was measured at 540 nm. The percentage of inhibition was calculated using the following equation:

Inhibition(%)=[(ANC−AS)/ANC]×100 2

where ANC is the absorbance of the negative control (PBS in place of the sample or acarbose), and AS is the absorbance of the test sample. A reagent blank was also prepared using the starch solution reacting directly with DNS. The IC50 values were determined by nonlinear regression analysis using GraphPad Prism software (version 8.4.2; GraphPad Software, San Diego, CA, USA), based on sigmoidal dose–response curves.

The α-glucosidase inhibition assay was performed based on a previously reported method with slight modifications. Briefly, 20 μL of α-glucosidase (0.1 U/mL) was mixed with 20 μL of test sample or acarbose and 140 μL of phosphate buffer (0.1 M, pH 6.9), followed by incubation at room temperature for 5 min. The reaction was initiated by adding 20 μL of p-nitrophenyl-α-d-glucopyranoside (pNPG, 2 mM) and incubating for an additional 20 min. The reaction was terminated with 100 μL of sodium carbonate (0.1 M), and absorbance was measured at 405 nm. Acarbose (0–2000 μg/mL) served as the positive control, while PBS was used in place of the sample or acarbose for the negative control. The percentage of inhibition was calculated using Equation , and IC50 values were determined using nonlinear regression analysis, as described for the α-amylase inhibition assay.

4.4.5. Assessing the Effect of Essential Oils on Shoot and Root Growth of Echinochloa crus-galli

The Beilschmiedia essential oils were diluted in a 0.1% (v/v) aqueous Tween 20 solution, which acted as a surfactant to enhance dispersion. The EO–Tween 20 mixtures were homogenized for 5 min in an ultrasonic bath to ensure complete emulsification. Seven concentrations of the essential oils were prepared: 0 (control: 0.1% Tween 20 without EO), 0.5, 1, 2, 4, 8, and 16 μL/mL. Each concentration was tested in triplicate. For each replicate, 10 seeds at the radicle emergence stage (approximately 1–2 mm radicle length) were selected to ensure physiological uniformity. The bioassays were conducted in sterile 55 mm diameter Petri dishes lined with autoclaved Whatman No.1 filter paper. A volume of 1 mL of the prepared oil solution was applied evenly to the filter paper using a sterile micropipette. Seeds were then placed equidistantly on the moist filter paper to prevent direct contact between seeds. The dishes were sealed with Parafilm to minimize evaporation and maintain internal humidity. All Petri dishes were arranged according to a completely randomized design (CRD) in a controlled laboratory environment under continuous darkness. The incubation temperature was maintained at 25–30 °C (±1 °C).

4.4.6. Assessing the Antifungal Activity of the Essential Oils against Phytopathogenic Fungi

The inhibitory bioassay evaluated the mycelial growth of the phytopathogenic fungi C. capsici and F. oxysporum f.sp. cubense based on the poisoned-food technique. The essential oil samples were dissolved in DMSO and incorporated into PDA media at concentrations from 62.5 to 500 μg/mL. Fungi were inoculated with 5 mm plugs and incubated at 25 °C for 4 days. Controls included a 2% DMSO negative control and the commercial fungicide Score 250 EC (250g/L of difenoconazole; Syngenta, Vietnam) at a dose of 1000-fold dilution as a positive control. All assays were conducted in duplicate and repeated to calculate the inhibition percentage and IC50 values. ,

Supplementary Material

ao5c12547_si_001.pdf (996.1KB, pdf)

Acknowledgments

This research is funded by the Vietnam Ministry of Education and Training under grant number B2025-TDV-02.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.5c12547.

  • GC chromatograms of Beilschmiedia bidoupensis and Beilschmiedia tsangii leaf and stem essential oils (Figures S1 and S2); 1H- and 13C NMR data of the essential oils recorded in CDCl3 (Figures S3–S6); results of the GC-MS analysis and MS fragmentation patterns of the major identified compounds (Tables S1–S4); loadings from the principal component analysis (Table S5); experimental data on the effect of Beilschmiedia essential oils on the shoot and root length development of barnyardgrass (Echinochloa crus-galli) (Table S6) (PDF)

The authors declare no competing financial interest.

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