Chemical constituents and biological activities of essential oils of Amomum genus(Zingiberaceae)

Hong Thien Van

Institute of Biotechnology and Food Technology, Industrial University of Ho Chi Minh City, No. 12 Nguyen Van Bao Street, Ward 4, Go Vap District,Ho Chi Minh City, Vietnam

ABSTRACT

Amomum Roxb. includes the aromatic and medicinal plants native to tropical and subtropical Asia belonging to the family Zingiberaceae.Members of Amomum genus have been used for a long time in traditional medicine for the treatment of throat trouble, congestion of lungs, inflammation of eyelids, and digestive disorders, etc.Amomum essential oils have been studied for their chemical profiles in which limonene, allo-aromadendrene, 1,8-cineole, camphor,farnesyl acetate, α-pinene, β-pinene, caryophyllene, camphene,D-camphor, santolina triene, methyl chavicol, bornyl acetate,β-elemene, δ-3-carene, etc. were the major compounds. Furthermore,the oils extracted from Amomum plants have been reported to possess antimicrobial, antioxidant, insecticidal, larvicidal, cytotoxic,anti-scabies, and anti-inflammatory activities. This review focuses on the chemical constituents and biological activities of the essential oils isolated from the different plant parts of Amomum plants. The objective of the present review is to highlight therapeutic potentials and provide evidence for future medicinal applications of these species of genus Amomum.

KEYWORDS: Amomum; Zingiberaceae; Essential oil; Bioactivity

1. Introduction

Essential oils are complex mixtures of volatile compounds that are produced by aromatic plants as secondary metabolites. They are produced by many plant parts such as leaves, seeds, flowers, peels,berries, rhizome, root, bark, wood, resin, petals[1]. Essential oils are characterized by the presence of bioactive compounds belonging to different functional groups, including alkanes, alcohols, aldehydes,ketones, esters, and acids[2]. Many valuable natural products used in some fields such as pharmaceutics, perfumes, cosmetics,aromatherapy, phytotherapy, spices, nutrition, and insecticides have been shown by previous reports[3].

The Zingiberaceae family comprises approximately 50 genera and more than 1 500 species distributed throughout tropical Africa, Asia,and tropical America[4,5]. The Ginger plants are well-known for their medicinal values[6]. For instance, some plant parts of Zingiberaceae species such as rhizomes, leaves, fruits, and seeds were used to treat cough, sore throat, improve digestion, reduce pain, and heal bruises and scars[6,7]. Members of Zingiberaceae provided many useful products for medicines, spices, cosmetics, and essential oil as important natural resources[8,9]. Furthermore, the essential oils isolated from Zingiberaceae plants contain several medicinal compounds, including terpenes, alcohols, ketones, flavonoids, and phytoestrogens[9].

Amomum Roxb. is a genus belonging to Zingiberaceae family and there are approximately 188 species distributed widely in tropical and subtropical Asia, especially in northeast India and the Indochinese floristic region[5,10]. Members of Amomum are extensively used for traditional medicine or food in many countries. For instance, Amomum subulatum (A. subulatum), one of the popular Amomum species, has been used for throat trouble,congestion of lungs, inflammation of eyelids, digestive disorders,and in the treatment of pulmonary tuberculosis[11]. Seeds and fruits of A. subulatum are used in spices and can play a preventive role in the occurrence of gastrointestinal disorders and respiratory problems[12,13]. Additionally, the chemical composition and bioactivities of the essential oils isolated from several Amomum species have been reported in the previous studies[14-17].

In spite of several reports about chemical profiles and biological activities attributed to the essential oils of Amomum species, there is still scarce information about these aspects. The present review,therefore, elaborates comprehensive information on the chemical composition and biological activities of the essential oils isolated from many different plant parts of Amomum species.

2. Chemical profiles of Amomum essential oils

Analysis of chemical profiles of the essential oils isolated from Amomum species showed that the oils consisted of some chemical groups, including monoterpene hydrocarbons, oxygenated monoterpenes, sesquiterpene hydrocarbons, oxygenated sesquiterpenes,and non-terpenes. Different plant parts such as leaves, flowers, fruits,stems, seeds, pods, rhizomes, and roots were investigated in the previous studies[14-18]. The major compounds of the Amomum essential oils isolated from various plant parts are stated in Table 1.

Table 1. Major components identified from Amomum essential oils.

Table 1. Major components identified from Amomum essential oils (continued).

Monoterpene hydrocarbons are the most abundant components found in the Amomum essential oils. β-Pinene was identified as the largest proportion of the essential oils isolated from six Amomum species, including Amomum glabrum (leaves)[14], Amomum maximum(leaves and stems)[15], Amomum repoense (leaves)[16], Amomum uliginosum (rhizomes)[17], Amomum villosum (A. villosum) (stems, roots,leaves, and rhizomes)[18-20], and Amomum xanthioides (A. xanthioides)(roots)[21,22]. α-Pinene was found as the most abundant component in the essential oils extracted from leaves, stems, roots, fruits, and flowers of Amomum muricarpum (A. muricarpum) in Vietnam[15].Two other monoterpene hydrocarbons, limonene, and santolina triene were the major compounds of the leaf and rhizome oils of Amomum aculeatum and Amomum newmanii collected from Vietnam and India, respectively[23,24]. The oils of Amomum longiligulare (A.longiligulare) roots collected from Vietnam contained camphene as a major compound[25]whereas β-phellandrene was the most abundant constituent of the oils of the Amomum rubidium rhizomes[26]. Furthermore, other monoterpene hydrocarbons,including, α-neocallitropsene, β-myrcene, (E)-β-ocimene, δ-3-carene, and p-cymene were also reported in the oils of Amomum agastyamalayanum (rhizomes)[24], and A. muricarpum (leaves, stems,roots) as the major compounds[15].

Oxygenated monoterpenes, another group of chemical continents,were also found in Amomum essential oils. In the fruit oils of some Amomum species collected from Vietnam, China, and India such as Amomum aromaticum (A. aromaticum), Amomum compactum,Amomum kravanh, A. subulatum, and Amomum tsao-ko (A. tsao-ko),1,8-cineole was found as the most abundant component[27-36]while this compound was also reported as the highest proportion in the oils of Amomum rubidum (A. rubidum) (leaves)[37], A. subulatum (pods,rinds, and seeds)[38-40], A. tsao-ko (pods and seeds)[38,41], Amomum uliginosum (rhizomes)[17]and Amomum verum (roots)[42]. Camphor was also found as the richest compound in the essential oils of Amomum biflorum (whole plants), A. longiligulare (fruits)[43], and Amomum villosum var. xanthioides whereas this compound in the oils of A. villosum fruits was the second highest percentage[44]. In the oils of the A. villosum fruits collected from China[45]and A. xanthioides fruits and seeds from Vietnam, bornyl acetate was the most abundant compound[22]while this compound was also present in the oils isolated from roots and fruits of A. longiligulare as one of the major component[25,43]. Terpinen-4-ol was the richest compound in the oils of A. subulatum leaves[46]while the other plant parts of this species contained the lower percentages[32,39,40]. Additionally, methyl chavicol, another compound belonging to oxygenated monoterpenes,had the highest percentage in the essential oils isolated from the rhizomes of Amomum pavieanum[47].

Another group of chemical continents which was found in Amomum oils was sesquiterpene hydrocarbons. β-Elemene presented in the essential oils extracted from leaves and stems of A. xanthioides collected from Vietnam as the richest component[22]. Caryophyllene was also found as the most abundant compound in the oils of the leaves and stems of A. longiligulare growing in Vietnam[25]. Alloaromadendrene was the most abundant compound in the essential oils of Amomum agastyamalayanum rhizomes from south India[24].Oxygenated sesquiterpenes were also reported in Amomum essential oils in which farnesyl acetate and spathulenol were identified as the highest percentage of chemical components in the essential oils of two species collected from Vietnam such as Amomum gagnepainii leaves[16]and A. xanthioides stems[21], respectively. The other oxygenated sesquiterpenes including α-bisabolol, zerumbone,humulene epoxide Ⅱ, and t-muurolol were also found as the major constituents in the oils of Amomum biflorum (whole plants)[48],Amomum gagnepainii (leaves)[16], A. longiligulare (leaves)[25], A.muricarpum (flowers)[15], respectively. On the other hand, decenal,the unique compound belonging to non-terpenes was found in the essential oils of the pods isolated from A. tsao-ko[38].

3. Biological activities of Amomum essential oils

3.1. Antimicrobial activity

Singtothong et al.[48]showed that the essential oils isolated from the whole plant of Amomum biflorum collected from Thailand could inhibit the growth of Staphylococcus aureus (S. aureus) with a minimum inhibitory concentration (MIC) value of 30 μg/mL.The essential oils of Amomum kravanh fruits from China showed significant activity against six bacterial pathogens, including three Gram-positive strains [S. aureus, Staphylococcus albus, Bacillus subtilis (B. subtilis)]and three Gram-negative bacteria [Salmonella enterica, Shigella dysenteriae, Escherichia coli (E. coli)]with MIC values of 5.0 mg/mL, 5.0 mg/mL, 2.5 mg/mL, 2.5 mg/mL, 1.25 mg/mL, and 2.5 mg/mL, respectively[29]. Recently, Nguyen et al.[14]demonstrated that the essential oils extracted from leaves and rhizomes of Amomum glabrum growing in Vietnam were able to resist against S. aureus with the MIC value of 5.67 μg/mL.Furthermore, the leaf oils of this species also had promising activity against Enterococcus faecalis, Bacillus cereus, and Candida albicans(C. albicans) with MIC values of 4.23 μg/mL, 67.98 μg/mL, and 1.56 μg/mL, respectively whereas MIC values of 18.67 μg/mL, 9.78 μg/mL and 10.23 μg/mL, respectively were shown by the rhizome oils towards the same microorganisms. Le et al.[52]demonstrated that the essential oils extracted from A. rubidum rhizomes collected from Bidoup Nui Ba National Park, Vietnam exhibited significant inhibitory activity on Aspergillus niger (A. niger) and Fusarium oxysporum with MIC values of 50 g/mL. In another study, Le et al.[37]also reported that the leaf and stem oils of this species showed antibacterial activity against Pseudomonas aeruginosa (P. aeruginosa)with MIC values of 25 μg/mL and 50 μg/mL, respectively while MIC value of 50 μg/mL was shown by both oils towards Fusarium oxysporum. Also, the oils of A. rubidum stems were able to resist C.albicans (MIC value of 50 μg/mL)[37].

Alam et al.[32]reported that the essential oils isolated from the fruits of A. subulatum collected from Delhi, India and Al-Mehran, Saudi Arabia were able to resist P. aeruginosa, E. coli, and Acinetobacter baumannii. Similarly, the oils extracted from the fruits of three different cultivars of A. subulatum such as varlangy, seremna and sawney could inhibit the growth of bacterial and fungal pathogens,including S. aureus (MIC values of 5 mg/mL, 2.5 mg/mL, 2.5 mg/mL, respectively), Klebsiella pneumonia (MIC values of 5 mg/mL,2.5 mg/mL, 5 mg/mL, respectively), E. coli (MIC values of 5 mg/mL only in seremna cultivar), C. albicans (MIC values of 2.5 mg/mL, 1.25 mg/mL, 1.25 mg/mL, respectively) and A. niger (MIC values of 5 mg/mL, 2.5 mg/mL, 5 mg/mL, respectively)[33]. Agnihotri et al.[53]reported that the fruit oils of A. subulatum collected from India exhibited significant inhibitory activity on 5 Gram-positive bacteria (Bacillus pumilus, B. subtilis, S. aureus, Staphylococcus epidermidis, and Micrococcus luteus), 2 Gram-negative bacteria (E.coli and P. aeruginosa), and 3 fungal strains (C. albicans, A. niger,and Saccharomyces cerevisiae).

Satyal et al.[39]demonstrated that the essential oils isolated from the seeds and rinds of A. subulatum showed significant activity against Bacillus cereus (MIC values of 625 μg/mL and 313 μg/mL),S. aureus (MIC values of 313 μg/mL and 625 μg/mL), E. coli (MIC values of 625 μg/mL and 1 250 μg/mL), P. aeruginosa (MIC values of 625 μg/mL and 1 250 μg/mL), A. niger (MIC values of 313 μg/mL and 19.5 μg/mL). In this study, Satyal et al.[39]also showed that the major components of the A. subulatum oils, including α-pinene,β-pinene, 1,8-cineole, and α-terpineol could inhibit the growth of 4 oral bacteria and one studied fungus. Rahman et al.[34]demonstrated that the fruit oils of A. subulatum growing in Pakistan showed good antifungal activity against 7 fungi, including Aspergillus flavus, A.niger, C. albicans, Fusarium oxysporum var. lycopersici, Microsporum canis, Pseudallescheria boydii, and Trichophyton simii. Meanwhile,the seed oils isolated from A. subulatum from Pakistan showed significant activity against 3 fungi (Aspergillus flavus, C. albicans,and Candida utilus) and 2 bacterial strains (E. coli and Lactobacillus acidophilus)[34]. Singh et al.[54]reported that the essential oils from A.subulatum leaves collected from India were found effective against two strains of Aspergillus flavus, Navjot 4NSt and Saktiman 3NSt,with 100% growth inhibition. Moreover, A. subulatum oils inhibited aflatoxin B1 production at 500 μg/mL[54].

Yang et al.[35]proved that the fruit essential oils of A. tsaoko collected from China were resistant to 5 bacterial and fungal pathogens, including B. subtilis, S. aureus, E. coli, Proteus vulgaris,Salmonella typhimurium, Candida sp. and Hansenula anomala with MIC values of 3.13 g/L, 0.2 g/L, 1.56 g/L, 6.25 g/L, 6.25 g/L,3.13 g/L, and 1.56 g/L, respectively. From another China sample,Cui et al.[50]showed the antibacterial activities of the whole plant oils of A. tsao-ko isolated by three efficient extraction methods including modified-solvent-free microwave extraction, solvent-free microwave extraction, and hydrodistillation. Consequently, the oils isolated through the modified-solvent free microwave extraction method showed the best antibacterial activity for 7 microorganisms,including S. aureus, Staphylococcus epidermidis, B. subtilis,Propionibacterium acnes, E. coli, P. aeruginosa, and C. albicans with MIC values of 5.86 mg/mL, 2.94 mg/mL, 5.86 mg/mL, 2.94 mg/mL, 5.86 mg/mL, 2.94 mg/mL, 5.86 mg/mL, respectively. On the other hand, the oil obtained via hydrodistillation and solvent-free microwave extraction methods could inhibit the growth of these microorganisms with MIC values of 5.94 mg/mL and 6.06 mg/mL,2.98 mg/mL and 3.03 mg/mL, 5.94 mg/mL and 6.06 mg/mL, 11.89 mg/mL and 3.03 mg/mL, 5.94 mg/mL and 12.11 mg/mL, 6.06 mg/mL and 3.03 mg/mL, 24.25 mg/mL and 12.11 mg/mL, respectively.Recently, Tangjitjaroenkun et al.[42]reported that the oils from the Amomum verum shoots growing in Thailand were able to resist against three Gram-positive bacteria, six Gram-negative bacteria and one pathogenic fungus, including B. subtilis (MIC value of 2.5 mg/mL), S. aureus (MIC value of 1.25 mg/mL), Staphylococcus saprophyticus (MIC value of ＞ 20 mg/mL), E. coli (MIC value of 1.25 mg/mL), P. aeruginosa (MIC value of ＞ 20 mg/mL), Salmonella typhimurium (MIC value of 2.5 mg/mL), Enterobacter cloacae (MIC value of 0.625 mg/mL), Klebsiella pneumonia (MIC value of 2.5 mg/mL), Proteus mirabilis (MIC value of ＞ 20 mg/mL), C. albicans (MIC value of 0.313 mg/mL).

3.2. Antioxidant capacity

Recent studies have shown the antioxidant activity of the essential oils isolated from several Amomum species[32,50,55]. For example,Alam et al.[32]demonstrated that the oils of A. subulatum fruits from India and Saudi Arabia were found effective against DPPH radical scavenger with the ICvalues of 219.38 mg/mL and 203.79 mg/mL, respectively. Additionally, Alam and Majumdar[55]showed that the fruit oils of three cultivars of A. subulatum collected from India,including seremna, varlangy and sawney were active on DPPH and ABTS radical cation. In the ABTS scavenging model, the ICvalues of the oils of the seremna, varlangy, and sawney were found to be 27.96, 31.34, and 32.49 μg/mL, respectively whereas these values in DPPH scavenging model were 172.3, 216.9, and 274.3 μg/mL,respectively. In another study, the antioxidant activity of the essential oils isolated from the whole plant of A. tsao-ko was also investigated using DPPH radical scavenging activity and β-carotene/linoleic acid bleaching assay. Accordingly, the ICvalue of the first assay was found to be 5.27 mg/mL while 0.63 mg/mL was the ICvalue of the later one[50].

3.3. Insecticidal, nematocidal and larvicidal activities

Wang et al.[36]reported that the essential oils and two major chemical components eucalyptol and limonene isolated from A.tsao-ko fruits showed insecticidal behaviour against the red flour beetle [Tribolium castaneum (T. castaneum)]and the cigarette beetle[Lasioderma serricorne (L. serricorne)]. Accordingly, limonene had the strong toxicity against T. castaneum and L. serricorne with LCvalues of 14.79 μg/adult and 13.66 μg/adult, respectively while another compound, eucalyptol, was able to resist against T. castaneum (LCvalue of 18.83 μg/adult) and L. serricorne (LCvalue of 15.58 μg/adult). Meanwhile, the essential oils of A. tsao-ko fruits possessed contact toxicity against T. castaneum and L. serricorne with LCvalues of 16.52 μg/adult and 6.14 μg/adult, respectively. Chen et al.[45]demonstrated that the essential oil of the A. villosum fruits and its major compounds, including camphor, camphene, limonene,and bornyl acetate had contact toxicity against T. castaneum and L.serricorne. This report showed that the toxicity against two beetles of the essential oils was found with LCvalues of 32.4 and 20.4 μg/adult, respectively. Furthermore, the toxicity against T. castaneum of four major compounds including limonene, camphene, camphor, and bornyl acetate was observed with LCvalues of 15.0, 21.6, 50.0, and 66.0 μg/adult, respectively. Meanwhile, these compounds exhibited stronger contact toxicity against L. serricorne than T. castaneum with LCvalues of 13.7, 19.9, 13.4, and 15.6 μg/adult, respectively[45].

Satyal et al.[39]showed that the essential oils of A. subulatum seeds were toxic to Caenorhabditis elegans (C. elegans), Drosophila melanogaster (D. melanogaster), and Solenopsis invicta × richteri (S.invicta × richteri) with LCvalues of 341, 441, and 1 500 μg/mL,respectively whereas the rind oils of this species also possessed the toxicity against D. melanogaster (LCvalue of 493 μg/mL) and S.invicta × richteri (LCvalue of 1 150 μg/mL). Additionally, four major chemical compounds of the essential oils from A. subulatum,including α-pinene, β-pinene, 1,8-cineole, and α-terpineol also had nematocidal and insecticidal activities. Among four components,α-pinene and β-pinene were only marginally toxic to C. elegans (LCvalue of ＞2 500 μg/mL) and S. invicta × richteri (LCvalue of ＞1 000 μg/mL) but strongly toxic to D. melanogaster (LCvalue of 161 μg/mL and 178 μg/mL, respectively). 1,8-Cineole was also highly toxic to C. elegans (LCvalue of 227 μg/mL), D. melanogaster (LCvalue of 234 μg/mL), and S. invicta × richteri (LCvalue of 294 μg/mL). Meanwhile, α-terpineol had the strong toxicity against D.melanogaster and S. invicta × richteri with the LCvalue of 188 μg/mL and 287 μg/mL, respectively, but this compound was weakly toxic to C. elegans with the LCvalue of 2 180 μg/mL[39]. Recently,Le et al.[26]showed that the essential oils isolated from the rhizomes of A. rubidum could display larvicidal activity against Aedes aegypti with the LCvalues of 22.85 and 22.62 μg/mL at 24 h and 48 h,respectively.

3.4. Cytotoxic activity

The cytotoxic activity of the essential oils and their major chemical compounds isolated from seeds and rinds of A. subulatum was assessed against the breast cancer (MCF-7) cell line using MTT assay[39]. The results showed that the seed and rind oils showed cytotoxic activity with 19.4% and 31.2% mortality on MCF-7 cell at 100 μg/mL, respectively. Meanwhile, four compounds, including α-pinene, β-pinene, 1,8-cineole and α-terpineol possessed the cytotoxic activity with 16.8%, 30.4%, 3.7% and 16.1% mortality on MCF-7 cell at 100 μg/mL, respectively[39]. By using MTT assay,Tangjitjaroenkun et al.[42]have recently demonstrated that the essential oils from Amomum verum shoots were able to kill human prostate adenocarcinoma cells (DU145) with the ICvalues of slightly more than 0.40 mg/mL, approximately 0.40 mg/mL and 0.185 mg/mL for 1, 4, and 7 d, respectively.

3.5. Anti-inflammatory activity

Nguyen et al.[27]showed the anti-inflammatory effects of the essential oils isolated from the fruits of A. aromaticum in RAW264.7 murine macrophage model. The oils strongly inhibited the production of nitric oxide in LPS-induced RAW264.7 cells (ICvalue of 0.45 μg/mL). Furthermore, this study also demonstrated the effects of the A. aromaticum oils on the two enzymes of inflammation process, inducible nitric oxide synthase, and cyclooxygenase-2. By using Western blot analysis, the inhibitory effects of A. aromaticum oils on both enzymes were still observed significantly although the concentration of the oils was low (0.3 μg/mL)[27]. Alam et al.[32]reported the anti-inflammatory activity of the essential oils of A. subulatum fruits collected from India and Saudi Arabia using a bovine soluble albumin denaturation method. As a result, the percent inhibition of protein denaturation by the oils of India and Saudi Arabia were 69.09% and 66.81% at 100 mg/mL, respectively.Moreover, the ICvalue for the Indian oils was 53.12 mg/mL while that of Saudi Arabian oils was 57.94 mg/mL[32].

3.6. Anti-scabies activity

Sarcoptes scabiei is the main itch mite that causes ectoparasitic infestation in humans[56]with pruritic lesions and papules on the surface of the skin[57]. Sharma et al.[46]showed the anti-scabies potential of the essential oils extracted from A. subulatum leaves against this itch mite using contact bioassay method. As a result, at 1% concentration, the A. subulatum oils with anti-scabies potentials of 33.3%, 45.6%, 56.6% and 80% could eliminate Sarcoptes scabiei within 20, 40, 60 and 80 minutes, respectively while these percentages were 42.4%, 63.3%, 83.3% and 100% at 5%concentration oils. Additionally, the anti-scabies activity increased at 10% concentration oils with 100% mortality within 60 minutes.

Biological activities of essential oil isolated from various plant parts of Amomum species are summarized in Table 2.

Table 2. Biological activity of essential oil isolated from various plant parts of Amomum species.

4. Conclusion

In this article, the relevant kinds of literature were used to summarize the chemical profiles and biological activities of the Amomum essential oils. Based on different geographic regions where these Amomum plants were collected, the present article showed the diversity of quantitative and qualitative compounds of the oils.Additionally, the bioactivities of the essential oils and the major chemical compounds of the oils isolated from many plant parts of Amomum species have shown therapeutic potentials, which provides evidence for future medicinal applications of these species of genus Amomum.

Conflict of interest statement

The author declares that there is no conflict of interest.

Author’s contributions

The present review was designed by HTV. HTV searched and handled the data, drafted the manuscript and resolved all the queries of editors and reviewers.